NSIS Working Group Attila Bader
INTERNET-DRAFT Lars Westberg
Intended status: Experimental Ericsson
Expires: 06 November 2010 Georgios Karagiannis
University of Twente
Cornelia Kappler
DeZem GmbH
Tom Phelan
Sonus
06 May 2010
RMD-QOSM - The NSIS Resource Management in Diffserv QOS Model
<draft-ietf-nsis-rmd-20.txt>
Abstract
This document describes an NSIS QoS Model for networks that use the
Resource Management in Diffserv (RMD) concept. RMD is a technique
for adding admission control and pre-emption function to
Differentiated Services (Diffserv) networks. The RMD QoS Model
allows devices external to the RMD network to signal reservation
requests to edge nodes in the RMD network. The RMD Ingress edge nodes
classify the incoming flows into traffic classes and signals resource
requests for the corresponding traffic class along the data path to
the Egress edge nodes for each flow. Egress nodes reconstitute the
original requests and continue forwarding them along the data path
towards the final destination. In addition, RMD defines notification
functions to indicate overload situations within the domain to the
edge nodes.
Status of this Memo
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Bader, et al. [Page 1]
INTERNET-DRAFT RMD-QOSM
This Internet-Draft will expire on November 06, 2010.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . .5
3. Overview of RMD and RMD-QOSM . . . . . . . . . . . . . .. . .6
3.1 RMD . . . . . . . . . . . . . . . . . . . . . . . . . . .6
3.2 Basic features of RMD-QOSM . . . . . . . . . . . . . . . 9
3.2.1 Role of the QNEs . . . . . . . .. . . . . . . . . .9
3.2.2 RMD-QOSM/QoS-NSLP signaling . . . . . . . . . . . 10
3.2.3 RMD-QOSM Applicability and considerations. . . . .12
4. RMD-QOSM, Detailed Description . . . . . . . . . . . .. . . 14
4.1 RMD-QSpec Definition . . . . . . . . . . . . . . . . . .14
4.1.1 RMD-QOSM QoS Desired and QoS Available . . . . . .15
4.1.2 PHR Container . . . . . . . . . . . . . . . . . . 16
4.1.3 PDR Container . . . . . . . . . . . . . . . . . .18
4.2 Message format . . . . . . . . . . . . . . . . . . . . .21
4.3 RMD node state management . . . . . . . . . . . . . . . 21
4.3.1 Aggregated versus per flow reservations at the
QNE edges . . . . . . . . . . . . . . . . . . . . 21
4.3.2 Measurement-based method . . . . . . . . . . . . .23
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4.3.3 Reservation-based method . .. . . . . . . . . . . 25
4.4 Transport of RMD-QOSM messages . . . . . . . . . . . . .26
4.5 Edge discovery and addressing of messages . . . . . . . 29
4.6 Operation and sequence of events . . . . . . . . . . . .30
4.6.1 Basic unidirectional operation . . . . . . . . . .30
4.6.1.1 Successful reservation. . . . . . . . . . . .31
4.6.1.2 Unsuccessful reservation . . . . . . . . . . 42
4.6.1.3 RMD refresh reservation. . . . . . . . . . . 45
4.6.1.4 RMD modification of aggregated reservation . 49
4.6.1.5 RMD release procedure. . . . . . . . . . . . 50
4.6.1.6 Severe congestion handling . . . . . . . . .57
4.6.1.7 Admission control using congestion
notification based on probing . . . . . . . 63
4.6.2 Bidirectional operation . . . . . . . . . . . . . 66
4.6.2.1 Successful and unsuccessful reservation . . .69
4.6.2.2 Refresh reservation . . . . . . . . . . . . .73
4.6.2.3 Modification of aggregated reservation . . . 74
4.6.2.4 Release procedure . . . . . . . . . . . . . .74
4.6.2.5 Severe congestion handling . . . . . . . . . 75
4.6.2.6 Admission control using congestion
notification based on probing . . . . . . . .77
4.7 Handling of additional errors . . . . . . . . . . . . . 79
5. Security Consideration. . . . . . . . . . . . . . . . . . . 79
6. IANA Considerations. . . . . . . . . . . . . . . . . . . . .85
7. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . .86
8. Authors` Addresses. . . . . . . . . . . . . . . . . . . . . 87
9. Normative References . . . . . . . . . . . . . . . . . . . .88
10. Informative References . . . . . . . . . . . . . . . . . . 88
1. Introduction
This document describes a Next Steps In Signaling (NSIS) QoS model
for networks that use the Resource Management in Diffserv (RMD)
framework ([RMD1], [RMD2], [RMD3], [RMD4]). RMD adds admission
control to Diffserv networks and allows nodes external to the
networks to dynamically reserve resources within the Diffserv
domains.
The Quality of Service NSIS Signaling Layer Protocol (QoS-NSLP)
[QoS-NSLP] specifies a generic protocol for carrying Quality of
Service(QoS) signaling information end-to-end in an IP network.
Each network along the end-to-end path is expected to implement a
specific QoS Model (QOSM) specified by the QSpec template [QSP-T]
that interprets the requests and installs the necessary mechanisms,
in a manner that is appropriate to the technology in use in the
network, to ensure the delivery of the requested QoS.
This document specifies an NSIS QoS Model for RMD networks (RMD-
QOSM), and an RMD-specific QSpec (RMD-QSPec) for expressing
reservations in a suitable form for simple processing by internal
nodes.
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They are used in combination with the QoS-NSLP to provide
QoS signaling service in an RMD network. Figure 1 shows an RMD
network with the respective entities.
Stateless or reduced state Egress
Ingress RMD nodes Node
Node (Interior Nodes; I-Nodes) (Stateful
(Stateful | | | RMD QoS
RMD QoS NLSP | | | NSLP Node)
Node) V V V
+-------+ Data +------+ +------+ +------+ +------+
|-------|--------|------|------|------|-------|------|---->|------|
| | Flow | | | | | | | |
|Ingress| |I-Node| |I-Node| |I-Node| |Egress|
| | | | | | | | | |
+-------+ +------+ +------+ +------+ +------+
=================================================>
<=================================================
Signaling Flow
Figure 1: Actors in the RMD-QOSM
Many network scenarios, such as the "Wired Part of Wireless Network"
scenario, which is described in section 8.4 of [RFC3726] require that
the impact of the used QoS signaling protocol on the network
performance should be minimised. In such network scenarios, the
performance of each network node that is used in a communication path
has an impact on the end-to-end performance. As such, the end-to-end
performance of the communication path can be improved by optimizing
the performance of the interior nodes. One of the factors that can
contribute to this optimization is the minimization of the QoS
signalling protocol processing load and the minimization of the
number of states on each interior node.
Another requirement that is imposed by such network scenarios is that
whenever a severe congestion situation occurs in the network, the
used QoS signaling protocol shoud be able to solve them. In case of a
route change or link failure a severe congestion situation may occur
in the network. Typically, routing algorithms are able to adapt and
change their routing decisions to reflect changes in the topology and
traffic volume. In such situations the re-routed traffic will have to
follow a new path. Interior nodes located on this new path may become
overloaded, since they suddenly might need to support more traffic
than they have capacity for. These severe congestion situations will
severely affect the overall performance of the traffic passing
through such nodes.
RMD-QoSM is an edge-to-edge (intra-domain) QoS Model that in
combination with the QoS-NSLP and QSPEC specifications is designed to
support the requirements mentioned above:
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o Minimal Impact on Interior Node Performance;
o Increase of scalability;
o Ability to deal with severe congestion
Internally to the RMD network, RMD-QOSM together with QoS-NSLP
[QoS-NSLP] defines a scalable QoS signaling model in which per-flow
QoS-NSLP and NTLP states are not stored in Interior nodes but
per-flow signaling is performed (see [QoS-NSLP]) at the edges.
In the RMD-QOSM, only routers at the edges of a Diffserv domain
(Ingress and Egress nodes) support the (QoS-NSLP) stateful
operation, see Section 4.7 of [QoS-NSLP]. Interior nodes support
either the(QoS-NSLP) stateless operation, or a reduced-state
operation with coarser granularity than the edge nodes.
After the terminology in Section 2, we give an overview of RMD and
the RMD-QOSM in Section 3. This document specifies several RMD-
QOSM/QoS-NSLP signaling schemes. In particular, Section 3.2.3
identifies which combination of sections are used for the
specification of each RMD-QOSM/QoS-NSLP signaling scheme. In Section
4 we give a detailed description of the RMD-QOSM, including the role
of QNEs, the definition of the QSpec, mapping of QSpec generic
parameters onto RMD-QOSM parameters, state management in QNEs, and
operation and sequence of events. Section 5 discusses security
issues.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC2119].
The terminology defined by GIST [GIST] and QoS-NSLP [QoS-NSLP]
applies to this draft.
In addition, the following terms are used:
NSIS domain: a NSIS signalling capable domain.
RMD domain: a NSIS domain that is capable of supporting the RMD-QOSM
signalling and operations.
Edge node: a QoS-NSLP node on the boundary of some
administrative domain that connects one NSIS domain to a node
either in another NSIS domain or in a non NSIS domain.
NSIS aware node: a node that is aware of NSIS signalling and RMD-
QOSM operations, such as severe congestion detection and DSCP
marking.
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NSIS unaware: a node that is unware of NSIS signalling, but is
aware of RMD-QOSM operations such as severe congestion detection
and DSCP marking.
Ingress node: An edge node in its role in handling the traffic
as it enters the NSIS domain.
Egress node: An edge node in its role in handling the traffic
as it leaves the NSIS domain.
Interior node: a node in a NSIS domain that is not an edge node.
Congestion: is a temporal network state that occurs when the traffic
(or when traffic associated with a particular PHB) passing through a
link is slightly higher than the capacity allocated for the link (or
allocated for the particular PHB). If no measures are taken than the
traffic passing through this link may temporarily slightly degrade in
QoS. This type of congestion is usually solved using admission
control mechanisms.
Severe congestion: Is the congestion situation on a particular link
within the RMD domain where a significant increase in its real packet
queue situation occurs, such as when due to a link failure re-routed
traffic has to be supported by this particular link.
3. Overview of RMD and RMD-QOSM
3.1. RMD
The Differentiated Services (Diffserv) architecture ([RFC2475],
[RFC2638]) was introduced as a result of efforts to avoid the
scalability and complexity problems of Intserv [RFC1633].
Scalability is achieved by offering services on an aggregate
rather than per-flow basis and by forcing as much of the per-flow
state as possible to the edges of the network. The service
differentiation is achieved using the Differentiated Services (DS)
field in the IP header and the Per-Hop Behavior (PHB) as the main
building blocks. Packets are handled at each node according to the
PHB indicated by the DS field in the message header.
The Diffserv architecture does not specify any means for devices
outside the domain to dynamically reserve resources or receive
indications of network resource availability. In practice, service
providers rely on short active time Service Level Agreements (SLAs)
that statically define the parameters of the traffic that will be
accepted from a customer.
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INTERNET-DRAFT RMD-QOSM
RMD was introduced as a method for dynamic reservation of resources
within a Diffserv domain. It describes a method that is able to
provide admission control for flows entering the domain and a
congestion handling algorithm that is able to terminate flows in
case of congestion due to a sudden failure (e.g., link, router)
within the domain.
In RMD, scalability is achieved by separating a fine-grained
reservation mechanism used in the edge nodes of a Diffserv domain
from a much simpler reservation mechanism needed in the Interior
nodes. Typically it is assumed that edge nodes support per-
flow QoS states in order to provide QoS guarantees for each flow.
Interior nodes use only one aggregated reservation state per traffic
class or no states at all. In this way it is possible to handle
large numbers of flows in the Interior nodes. Furthermore, due to
the limited functionality supported by the Interior nodes, this
solution allows fast processing of signaling messages.
The possible RMD-QOSM applicabilities are described in Section
3.2.3. Two main basic admission control modes are supported:
reservation-based and measurement-based admission control that can
be used in combination with a severe congestion handling solution.
The severe congestion handling solution is used in the situation
that a link/node becomes severely congested due to the fact that the
traffic supported by a failed link/node is rerouted and has to be
processed by this link/node. Furthermore, RMD-QOSM supports both
uni-directional and bi-directional reservations.
Another important feature of RMD-QOSM is that the intra-domain
sessions supported by the edges can be either per flow sessions or
per aggregate sessions. In case of the per flow intra-domain
sessions, the maintained per flow intra-domain states have a one-to-
one dependency to the per flow end-to-end states supported by the
same edge. In case of the per-aggregate sessions the maintained per-
aggregate states have a one-to-many relationship to the per flow
end-to-end states supported by the same edge.
In the reservation-based method, each Interior node maintains
only one reservation state per traffic class. The Ingress edge
nodes aggregate individual flow requests into PHB traffic classes,
and signal changes in the class reservations as necessary. The
reservation is quantified in terms of resource units (or bandwidth).
These resources are requested dynamically per PHB and reserved on
demand in all nodes in the communication path from an Ingress node
to an Egress node.
The measurement-based algorithm continuously measures traffic levels
and the actual available resources, and admits flows whose resource
needs are within what is available at the time of the request. The
measurement based algorithm is used to support a predictive service
where the service commitment is somewhat less reliable than the
service that can be supported by the reservation based method.
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A main assumption that is taken by such measurement based admission
control mechanisms is that the aggregated PHB traffic passing through
an RMD interior node is high and therefore, current measurement
characteristics are considered to be an indicator of future load.
Once an admission decision is made, no record of the decision need be
kept at the interior nodes. The advantage of measurement-based
resource management protocols is that they do not require pre-
reservation state nor explicit release of the reservations at the
interior nodes. Moreover, when the user traffic is variable,
measurement based admission control could provide higher network
utilization than, e.g., peak-rate reservation. However, this can
introduce an uncertainty in the availability of the resources.
It is important to emphasize that the RMD measurement based schemes
described in this document do not use any refresh procedures, since
these approaches are used in stateless nodes, see Section 4.6.1.3.
Two types of measurement based admission control schemes are
possible:
* Congestion notification function based on probing:
This method can be used to implement a simple measurement-based
admission control within a Diffserv domain. In this scenario the
interior nodes are not NSIS aware nodes. In these interior nodes
thresholds are set for the traffic belonging to different PHBs in
the measurement based admission control function. In this scenario
an end-to-end NSIS message is used as a probe packet, meaning that
the DSCP field in the header of the IP packet that carries the NSIS
message is re-marked when the predefined congestion threshold is
exceeded. Note that when the predefined congestion threshold is
exceeded all packets are remarked by a node, including NSIS
messages. In this way the edges can admit or reject flows that are
requesting resources. The frequency and durations that the congestion
level is above the threshold resulting in remarking, is tracked and
used to influence the admission control decisions.
* NSIS measurement-based admission control:
In this case the measurement-based admission control functionality
is implemented in NSIS aware stateless routers. The main difference
between this type of admission control and the congestion
notification based on probing is related to the fact that this type
of admission control is applied mainly on NSIS aware nodes.
With the measurement based scheme the requested peak bandwidth of a
flow is carried by the admission control request. The admission
decision is considered as positive if the currently carried traffic,
as characterized by the measured statistics, plus the requested
resources for the new flow exceeds the system capacity with a
probability smaller than a value alpha. Otherwise, the admission
decision is negative. It is important to emphasize that due to the
fact that the RMD interior nodes are stateless, they do not store
information of previous admission control requests.
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This could lead to a situation where the admission control accuracy
is decreased when multiple simultaneous flows (sharing a common
interior node) are requesting admission control simultaneously. By
applying measuring techniques, see e.g., [JaSh97], [GrTs03], which
are using current and past information on NSIS sessions that
requested resources from an NSIS aware interior node, the decrease in
admission control accuracy can be limited.
RMD describes the following procedures:
* Classification of an individual resource reservation or a resource
query into Per Hop Behavior (PHB) groups at the Ingress node of
the domain,
* Hop-by-hop admission control based on a PHB within the
domain. There are two possible modes of operation for internal
nodes to admit requests. One mode is the stateless or
measurement-based mode, where the resources within the domain are
queried. Another mode of operation is the reduced-state
reservation or reservation based mode, where the resources within
the domain are reserved.
* a method to forward the original requests across the domain up to
the Egress node and beyond.
* a congestion control algorithm that notifies the egress edge nodes
about congestion. It is able to terminate the appropriate number
of flows in case a of congestion due to a sudden failure (e.g.,
link or router failure) within the domain.
3.2. Basic features of RMD-QOSM
3.2.1 Role of the QNEs
The protocol model of the RMD-QOSM is shown in Figure 2. The figure
shows QNI and QNR nodes, not part of the RMD network, that are the
ultimate initiator and receiver of the QoS reservation requests. It
also shows QNE nodes that are the Ingress and Egress nodes in the
RMD domain (QNE Ingress and QNE Egress), and QNE nodes that are
Interior nodes (QNE Interior).
All nodes of the RMD domain are usually QoS-NSLP aware nodes.
However, in the scenarios where the congestion notification function
based on probing is used, then the interior nodes are not NSIS
aware. Edge nodes store and maintain QoS-NSLP and NTLP states and
therefore are stateful nodes. The NSIS aware Interior nodes are
NTLP stateless. Furthermore they are either QoS-NSLP stateless (for
NSIS measurement-based operation), or are reduced state nodes
storing per PHB aggregated QoS-NSLP states (for reservation-based
operation).
Note that the RMD domain MAY contain Interior nodes that are
not NSIS aware nodes (not shown in the figure).
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INTERNET-DRAFT RMD-QOSM
These nodes are assumed to have sufficient capacity for flows that
might be admitted. Furthermore, some of these NSIS unaware nodes MAY
be used for measuring the traffic congestion level on the data path.
These measurements can be used by RMD-QOSM in the congestion control
based on probing operation and/or severe congestion operation
(see Section 4.6.1.6).
|------| |-------| |------| |------|
| e2e |<->| e2e |<------------------------->| e2e |<->| e2e |
| QoS | | QoS | | QoS | | QoS |
| | |-------| |------| |------|
| | |-------| |-------| |-------| |------| | |
| | | local |<->| local |<->| local |<->| local| | |
| | | QoS | | QoS | | QoS | | QoS | | |
| | | | | | | | | | | |
| NSLP | | NSLP | | NSLP | | NSLP | | NSLP | | NSLP |
|st.ful| |st.ful | |st.less/ |st.less/ |st.ful| |st.ful|
| | | | |red.st.| |red.st.| | | | |
| | |-------| |-------| |-------| |------| | |
|------| |-------| |-------| |-------| |------| |------|
------------------------------------------------------------------
|------| |-------| |-------| |-------| |------| |------|
| NTLP |<->| NTLP |<->| NTLP |<->| NTLP |<->| NTLP |<->|NTLP |
|st.ful| |st.ful | |st.less| |st.less| |st.ful| |st.ful|
|------| |-------| |-------| |-------| |------| |------|
QNI QNE QNE QNE QNE QNR
(End) (Ingress) (Interior) (Interior) (Egress) (End)
st.ful: stateful, st.less: stateless
st.less red.st.: stateless or reduced state
Figure 2: Protocol model of stateless/reduced state operation
3.2.2 RMD-QOSM/QoS-NSLP Signaling
The basic RMD-QOSM/QoS-NSLP signaling is shown in Figure 3. The
signalling scenarios are accomplished using the QoS-NSLP processing
rules defined in [QoS-NSLP], in combination with the RMF triggers
sent via the QoS-NSLP-RMF API described in [QoS-NSLP].
Due to the fact that within the RMD domain a different QoS model can
be supported than the end-to-end QoS model applied at the edges of
the RMD domain, the RMD interior node reduced state reservations can
be updated independently of the per-flow end-to-end reservations, see
Section 4.7 of [QoS-NSLP]. Therefore, two different RESERVE messages
are used within the RMD domain. One RESERVE message that is
associated with the per flow end-to-end reservations and is used by
the edges of the RMD domain and one that is associated with the
reduced state reservations within the RMD domain.
A RESERVE message is created by a QNI with an Initiator QSpec
describing the reservation and forwarded along the path towards the
QNR.
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INTERNET-DRAFT RMD-QOSM
When the original RESERVE message arrives at the Ingress node,
an RMD-QSpec is constructed based on the initial QSpec in the message
(usually the Initiator QSpec). The RMD-QSpec is sent in a intra-
domain, independent RESERVE message through the Interior nodes
towards the QNR. This intra-domain RESERVE message uses the GIST
datagram signaling mechanism. Note that the RMD-QOSM cannot directly
specify that the GIST datagram mode SHOULD be used. This can however
be notified by using the GIST API Transfer-Attributes, such as
unreliable, low level of security and use of local policy.
Meanwhile, the original RESERVE message is sent to the Egress node
on the path to the QNR using the reliable transport mode of NTLP.
Each QoS-NSLP node on the data path processes the intra-domain
RESERVE message and checks the availability of resources with either
the reservation-based or the measurement-based method.
QNE Ingress QNE Interior QNE Interior QNE Egress
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
RESERVE | | | |
-------->| RESERVE | | |
+--------------------------------------------->|
| RESERVE` | | |
+-------------->| | |
| | RESERVE` | |
| +-------------->| |
| | | RESERVE` |
| | +------------->|
| | | RESPONSE`|
|<---------------------------------------------+
| | | | RESERVE
| | | +------->
| | | |RESPONSE
| | | |<-------
| | | RESPONSE |
|<---------------------------------------------+
RESPONSE| | | |
<--------| | | |
Figure 3: Sender-initiated reservation with Reduced State Interior
Nodes
When the message reaches the Egress node, and the reservation is
successful in each Interior node, an intra-domain (local) RESPONSE`
is sent towards the ingress node and the original (end-to-end)
RESERVE message is forwarded to the next domain. When the Egress
node receives a RESPONSE message from the downstream end, it is
forwarded directly to the Ingress node.
If an intermediate node cannot accommodate the new request, it
indicates this by marking a single bit in the message, and continues
forwarding the message until the Egress node is reached. From the
Egress node an intra-domain RESPONSE` and an original RESPONSE
message are sent directly to the Ingress node.
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INTERNET-DRAFT RMD-QOSM
As a consequence in the stateless/reduced state domain only sender-
initiated reservation can be performed and functions requiring per
flow NTLP or QoS-NSLP states, like summary and reduced refreshes,
cannot be used. If per flow identification, is needed, i.e.,
associating the flow IDs for the reserved resources, Edge nodes act
on behalf of Interior nodes.
3.2.3 RMD-QOSM Applicability and considerations
The RMD-QOSM is a Diffserv-based bandwidth management methodology
that is not able to provide a full Diffserv support.
The reason of this is that the RMD-QOSM concept can only support the
(Expedited Forwarding) EF-like functionality behavior, but is not
able to support the full set of (Assured Forwarding) AF-like
functionality. The bandwidth information REQUIRED by the EF-like
functionality behaviour can be supported by RMD-QOSM carrying the
bandwidth information in the <QoS Desired> parameter, see [QSP-T].
The full set of (Assured Forwarding) AF-like functionality requires
information that is specified in two token buckets. The RMD-QOSM is
not supporting the use of two token buckets and therefore, it is not
able to support the full set of AF-functionality. Note however,
that RMD-QOSM could also support a single AF PHB, when the traffic
or the upper limit of the traffic can be characterized by a single
bandwidth parameter. Moreover, it is considered that in case of
tunnelling, the RMD-QOSM supports only the uniform tunnelling mode
for Differentiated services, see [RFC2983].
The RMD domain MUST be engineered in such a way that each QNE Ingress
maintains information about the smallest MTU that is supported on the
links within the RMD domain.
A very important consideration on using RMD-QOSM is that within one
RMD domain only one of the following RMD-QOSM schemes can be used at
a time. Thus a RMD router can never process and use two different
RMD-QOSM signaling schemes at the same time.
However, all RMD QNEs supporting this specification MUST support the
combination the "per flow RMD reservation based" in combination with
"severe congestion handling by proportional data packet marking"
scheme. If the RMD QNEs support more RMD-QOSM schemes then the
operator of that RMD domain MUST pre-configure all the QNE edge nodes
within one domain such that the <SCH> field included in the "PHR
container", see Section 4.1.2 and the "PDR Container", see Section
4.1.3, will use always the same value, such that within one RMD
domain only one of the below described RMD-QOSM schemes is used at a
time.
The congestion situations, see Section 2, are solved using admission
control mechanism, e.g., "per flow congestion notification based on
probing", while the severe congestion situations, see Section 2, are
solved using the severe congestion handling mechanisms, e.g., "Severe
congestion handling by proportional data packet marking".
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The RMD domain MUST be engineered in such a way that RMD-QOSM
messages could be transported using the GIST Query and
Data messages in Q-mode, see [GIST]. This means that the Path MTU
MUST be engineered in such a way that the RMD-QOSM message are
transported without fragmentation. Furthermore, the RMD domain MUST
be engineered in such a way to guarantee capacity for the GIST
Query and Data messages in Q-mode, within the rate control limits
imposed by GIST, see [GIST].
The RMD domain has to be configured such that the GIST context-free
flag (C-flag) MUST be set (C=1) for Query messages and Data
messages sent in Q-mode, see [GIST].
Moreover, the same deployment issues and extensibility considerations
described in [GIST] and [Extens-NSIS] apply to this document.
It is important to note that the concepts described in Sections
4.6.1.6.2, 4.6.2.5.2, 4.6.1.6.2 and 4.6.2.5.2 contributed to
the PCN WG standardisation.
The available RMD-QOSM/QoS-NSLP signaling schemes are:
* "per flow congestion notification based on probing" (see
Sections 4.3.2, 4.6.1.7., 4.6.2.6.). Note that this scheme uses for
severe congestion handling the "Severe congestion handling by
proportional data packet marking", see Section 4.6.1.6.2,
4.6.2.5.2). Furthermore, the interior nodes are considered to be
Diffserv aware, but NSIS unaware nodes, see Section 4.3.2.
* "per flow RMD NSIS measurement based admission control" (see
Sections 4.3.2, 4.6.1, 4.6.2). Note that this scheme uses for
severe congestion handling the "Severe congestion handling by
proportional data packet marking", see Section 4.6.1.6.2,
4.6.2.5.2). Furthermore, the interior nodes are considered to be
NSIS aware nodes, see Section 4.3.2.
* "per flow RMD reservation based" in combination with "severe
congestion handling by the RMD-QOSM refresh procedure" (see
Sections 4.3.3, 4.6.1, 4.6.1.6.1, 4.6.2.5.1). Note that this
scheme uses for severe congestion handling the "Severe congestion
handling by the RMD-QOSM refresh" procedure, see Section 4.6.1.6.1,
4.6.2.5.1). Furthermore, the intra-domain sessions supported by the
edge nodes are per flow sessions, see Section 4.3.3.
* "per flow RMD reservation based" in combination with "severe
congestion handling by proportional data packet marking" procedure
(see Sections 4.3.3, 4.6.1, 4.6.1.6.2, 4.6.2.5.2). Note that
this scheme uses for severe congestion handling the "Severe
congestion handling by proportional data packet marking" procedure,
see Section 4.6.1.6.2, 4.6.2.5.2). Furthermore, the intra-domain
sessions supported by the edge nodes are per flow sessions, see
Section 4.3.3.
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* "per aggregate RMD reservation based" in combination with
"severe congestion handling by the RMD-QOSM refresh procedure" (see
Sections 4.3.1, 4.6.1, 4.6.1.6.1, 4.6.2.5.1). Note that this
scheme uses for severe congestion handling the "Severe congestion
handling by the RMD-QOSM refresh" procedure, see Section 4.6.1.6.1,
4.6.2.5.1). Furthermore, the intra-domain sessions supported by the
edge nodes are per aggregate sessions, see Section 4.3.1. Moreover,
this scheme can be considered to be a reservation-based scheme,
since the RMD interior nodes are reduced-state nodes, i.e., they do
not store NTLP/GIST states but they do store per PHB-aggregated
QoS-NSLP reservation states.
* "per aggregate RMD reservation based" in combination with
"severe congestion handling by proportional data packet marking"
procedure (see Sections 4.3.1, 4.6.1, 4.6.1.6.2, 4.6.2.5.2).
Note that this scheme uses for severe congestion handling the
"Severe congestion handling by proportional data packet marking"
procedure, see Section 4.6.1.6.2, 4.6.2.5.2). Furthermore, the
intra-domain sessions supported by the edge nodes are per aggregate
sessions, see Section 4.3.1. Moreover, this scheme can be
considered to be a reservation-based scheme, since the RMD interior
nodes are reduced-state nodes, i.e., they do not store NTLP/GIST
states but they do store per PHB-aggregated QoS-NSLP reservation
states.
4. RMD-QOSM, Detailed Description
This section describes the RMD-QOSM in more detail. In particular,
it defines the role of stateless and reduced-state QNEs, the
RMD-QOSM QSpec Object, the format of the RMD-QOSM QoS-NSLP messages
and how QSpecs are processed and used in different protocol
operations.
4.1. RMD-QSpec Definition
The RMD-QOSM uses the QSpec format specified in [QSP-T].
The Initiator/Local QSPEC bit, i.e., <I> is set to "Local" (i.e.,
"1") and the <Qspec Proc> is set as follows:
* Message Sequence = 0: Sender initiated
* Object combination = 0: <QoS Desired> for RESERVE and
<QoS Reserved> for RESPONSE
The <QSPEC Version> used by RMD-QOSM is the default version, i.e.,
"0", see [QSP-T]. The <QSPEC Type> value used by the RMD-QOSM is
specified in [QSP-T] and is equal to: "2".
The <Traffic Handling Directives> contains the following fields:
<Traffic Handling Directives> = <PHR container> <PDR container>
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The Per Hop Reservation container (PHR container) and
the Per Domain Reservation container (PDR container) are specified
in Section 4.1.2 and 4.1.3, respectively. The <PHR container>
contains the traffic handling directives for intra-domain
communication and reservation. The <PDR container> contains
additional traffic handling directives that is needed for
edge-to-edge communication. The parameter IDs used by the <PHR
container> and <PDR container> are assigned by IANA, see Section 6.
The RMD-QOSM <QoS Desired> and <QoS Reserved>, are specified in
Section 4.1.1. The RMD-QOSM <QoS Desired> and <QoS Reserved> and the
<PHR container> are used and processed by the Edge and Interior
nodes. The <PDR container> field is only processed by Edge nodes.
4.1.1. RMD-QOSM QoS Desired and QoS Reserved
The RESERVE message contains only the QoS Desired object [QSP-T]. The
QoS Reserved object is carried by the RESPONSE message.
In RMD-QOSM the <QoS Desired> and <QoS Reserved> objects contain the
following parameters:
<QoS Desired> = <TMOD-1> <PHB Class> <Admission Priority>
<QoS Reserved> = <TMOD-1> <PHB Class> <Admission Priority>
The bit format of the <PHB Class> (see [QSP-T] and Figure 4 and
Figure 5) and <Admission Priority> complies to the bit format
specified in [QSP-T].
Note that for the RMD-QOSM a reservation established without an
<Admission Priority> parameter is equivalent to a reservation
established with an <Admission Priority> whose value is 1.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DSCP |0 0 0 0 0 0 0 0 X 0|
+---+---+---+---+---+---+---+---+
Figure 4: DSCP parameter
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PHB ID code |0 0 X X|
+---+---+---+---+---+---+---+---+
Figure 5: PHB ID Code parameter
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4.1.2. PHR Container
This section describes the parameters used by the PHR container,
which are used by the RMD-QOSM functionality available at the
Interior nodes.
<PHR container> = <O>, <K>, <S>,<M>,
<Admitted Hops>, <B>, <Hop_U>, <Time Lag>, <Max Admitted Hops>
The bit format of the PHR container can be seen in Figure 6. Note
that in Figure 6 <Hop U> is represented as <U>. Furthermore, in
Figure 6 <Max Admitted Hops> is represented as <Max Adm Hops>.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|E|N|r| Container ID |r|r|r|r| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|M| Admitted Hops|B|U| Time Lag |O|K| SCH | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max Adm Hops | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: PHR container
Container ID: 12 bit field, indicating the PHR type:
PHR_Resource_Request, PHR_Release_Request, PHR_Refresh_Update.
"PHR_Resource_Request" (Container ID = 17): initiate or update
the traffic class reservation state on all nodes located on the
communication path between the QNE(Ingress) and QNE(Egress) nodes.
"PHR_Release_Request" (Container ID = 18): explicitly release, by
subtraction, the reserved resources for a particular flow
from a traffic class reservation state.
"PHR_Refresh_Update" (Container ID = 19): refresh the
traffic class reservation soft state on all nodes located on the
communication path between the QNE(Ingress) and QNE(Egress)
nodes according to a resource reservation request that was
successfully processed during a previous refresh period.
<S> (Severe Congestion):
1 bit. In case of a route change refreshing RESERVE messages
follow the new data path, and hence resources are requested
there. If the resources are not sufficient to accommodate the new
traffic severe congestion occurs. Severe congested Interior nodes
SHOULD notify Edge QNEs about the congestion by setting the S bit.
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<O> (Overload):
1 bit. This field is used during the severe congestion handling
scheme that is using the RMD-QOSM refresh procedure. This bit is set
when an overload on a QNE interior node is detected and when this
field is carried by the "PHR_Refresh_Update" container. <O>
SHOULD be set to"1" if the <S> bit is set. For more details see
Section 4.6.1.6.1.
<M>:
1 bit. In case of unsuccessful resource reservation or resource
query in an Interior QNE, this QNE sets the M bit in order to
notify the Egress QNE.
<Admitted Hops>:
8 bit field. The <Admitted Hops> counts the number of hops in the
RMD domain where the reservation was successful. The <Admitted
Hops> is set to "0" when a RESERVE message enters a domain and it
MUST be incremented by each Interior QNE, provided that the Hop_U bit
is not set. However when a QNE that does
not have sufficient resources to admit the reservation is reached,
the M Bit is set, and the <Admitted Hops> value is frozen, by setting
the Hop_U bit to "1". Note that the <Admitted Hops> parameter in
combinations with the <Max Admitted Hops> and <K> parameters are used
during the RMD partial release procedures, see Section 4.6.1.5.2.
<Hop_U> (NSLP_Hops unset):
1-bit. The QNE(Ingress) node MUST set the <Hop_U> parameter to
0. This parameter SHOULD be set to "1" by a node when the node does
not increase the <Admitted Hops> value. This is the case when an
RMD-QOSM reservation-based node is not admitting the reservation
request. When <Hop_U> is set "1" the <Admitted Hops> SHOULD NOT be
changed. Note that this flag in combination with the <Admitted Hops>
flag are used to locate the last node that successfully processed a
reservation request, see Section 4.6.1.2.
<B>: 1 bit. When set to "1" it indicates bi-directional reservation.
<Time Lag>: It represents the ratio between the "T_Lag" parameter,
which is the time difference between the departure time of
the last sent "PHR_Refresh_Update" control information container and
the departure time of the "PHR_Release_Request" control information
container,and the length of the refresh period, "T_period", see
Section 4.6.1.5.
<K>: 1 bit. When set to "1" it indicates that the resources/bandwidth
carried by a tearing RESERVE MUST NOT be released and the
resources/bandwidth carried by a non tearing RESERVE MUST NOT be
reserved/refreshed. For more details see Section 4.6.1.5.2.
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<Max Admitted Hops>:
8-bit. The <Admitted Hops> value that has been carried by the
PHR container field used to identify the RMD reservation based node
that admitted or process a "PHR_Resource_Request"
<SCH>: 3-bit. The <SCH> value that is used to specify which of the 6
RMD-QOSM scenarios, see Section 3.2.3, MUST be used within the RMD
domain. The operator of an RMD domain MUST pre-configure all the QNE
edge nodes within one domain such that the <SCH> field included in
the "PHR container", will use always the same value, such that within
one RMD domain only one of the below described RMD-QOSM schemes can
be used at a time. All the QNE interior nodes MUST interpret this
field before processing any other PHR container payload fields. The
currently defined <SCH> values are:
o 0: RMD-QOSM scheme MUST be: "per flow congestion notification
based on probing";
o 1: RMD-QOSM scheme MUST be: "per flow RMD NSIS measurement
based admission control",
o 2: RMD-QOSM scheme MUST be: "per flow RMD reservation based"
in combination with "severe congestion handling by the RMD-
QOSM refresh procedure";
o 3 : RMD-QOSM scheme MUST be: "per flow RMD reservation based"
in combination with "severe congestion handling by
proportional data packet marking"
o 4: RMD-QOSM scheme MUST be: "per aggregate RMD reservation
based" in combination with "severe congestion handling by
the RMD-QOSM refresh procedure"
o 5: RMD-QOSM scheme MUST be: "per aggregate RMD reservation
based" in combination with "severe congestion handling by
proportional data packet marking"
o 6 - 7: reserved
The default value of the <SCH> field MUST be set to the value equal
to 3.
4.1.3. PDR container
This section describes the parameters of the PDR container, which are
used by the RMD-QOSM functionality available at the
Edge nodes.
The bit format of the PDR container can be seen in Figure 7.
<PDR container> = <O> <S> <M> <Max
Admitted Hops> <B> [<PDR Bandwidth>]
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Note that in Figure 7 <Max Admitted Hops> is represented as
<Max Adm Hops>.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|E|N|r| Container ID |r|r|r|r| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|M| Max Adm Hops |B|O| SCH | EMPTY |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PDR Bandwidth(32-bit IEEE floating point.number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: PDR container
Container ID: 12-bit field identifying the type of PDR container
field.
"PDR_Reservation_Request" (Container ID = 20):
Generated by the QNE(Ingress) node in order to initiate or update
the QoS-NSLP per domain reservation state in the QNE(Egress) node
"PDR_Refresh_Request" (Container ID = 21): generated by
the QNE(Ingress) node and sent to the QNE(Egress) node to refresh,
in case needed, the QoS-NSLP per domain reservation states
located in the QNE(Egress) node
"PDR_Release_Request" (Container ID = 22): generated
and sent by the QNE(Ingress) node to the QNE(Egress) node to release
the per domain reservation states explicitly
"PDR_Reservation_Report" (Container ID = 23): generated
and sent by the QNE(Egress) node to the QNE(Ingress) node to
report that a "PHR_Resource_Request" and a
"PDR_Reservation_Request" traffic handling directive fields have been
received and that the request has been admitted or rejected
"PDR_Refresh_Report" (Container ID = 24) generated and
sent by the QNE(Egress) node in case needed, to the QNE(Ingress)
node to report that a "PHR_Refresh_Update" traffic handling directive
field has been received and has been processed
"PDR_Release_Report" (Container ID = 25) generated and
sent by the QNE(Egress) node in case needed, to the QNE(Ingress)
node to report that a "PHR_Release_Request" and a
"PDR_Release_Request" traffic handling directive fields have been
received and have been processed.
"PDR_Congestion_Report" (Container ID = 26): generated
and sent by the QNE(Egress) node to the QNE(Ingress) node and used
for congestion notification.
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<S> (PDR Severe Congestion):
1-bit. Specifies if a severe congestion situation occurred.
It can also carry the <S> parameter of the
"PHR_Resource_Request" or "PHR_Refresh_Update" fields.
<O> (Overload):
1 bit. This field is used during the severe congestion handling
scheme that is using the RMD-QOSM refresh procedure. This bit is set
when an overload on a QNE interior node is detected and when this
field is carried by the ""PDR_Congestion_Report" container.
<O> SHOULD be set to"1" if the <S> bit is set. For more details see
Section 4.6.1.6.1.
<M> (PDR Marked):
1-bit. Carries the <M> value of the "PHR_Resource_Request" or
"PHR_Refresh_Update" traffic handling directive fields.
<B>: 1 bit Indicates bi-directional reservation.
<Max Admitted Hops>:
8-bit. The <Admitted Hops> value that has been carried by the
PHR container field used to identify the RMD reservation based node
that admitted or process a "PHR_Resource_Request"
<PDR Bandwidth>:
32 bits. This field specifies the bandwidth that either applies
when the "B" flag is set to "1" and when this parameter is carried
by a RESPONSE message, or when a severe congestion occurs and the
QNE edges maintain an aggregated intra-domain QoS-NSLP operational
state and it is carried by a NOTIFY message. In the situation that
the "B" flag is set to "1" this parameter specifies the requested
bandwidth that have to be reserved by a node in the reverse
direction and when the intra-domain signaling procedures require a
bi-directional reservation procedure. In the severe congestion
situation this parameter specifies the bandwidth that has to be
released.
<SCH>: 3-bit. The <SCH> value that is used to specify which of the 6
RMD scenarios, see Section 3.2.3, MUST be used within the RMD domain.
The operator of an RMD domain MUST pre-configure all the QNE edge
nodes within one domain such that the <SCH> field included in the
"PDR container", will use always the same value, such that within one
RMD domain only one of the below described RMD-QOSM schemes can be
used at a time. All the QNE interior nodes MUST interpret this field
before processing any other "PDR container" payload fields. The
currently defined <SCH> values are:
o 0: RMD-QOSM scheme MUST be: "per flow congestion notification
based on probing";
o 1: RMD-QOSM scheme MUST be: "per flow RMD NSIS measurement
based admission control",
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o 2: RMD-QOSM scheme MUST be: "per flow RMD reservation based"
in combination with "severe congestion handling by the RMD-
QOSM refresh procedure";
o 3 : RMD-QOSM scheme MUST be: "per flow RMD reservation based"
in combination with "severe congestion handling by
proportional data packet marking"
o 4: RMD-QOSM scheme MUST be: "per aggregate RMD reservation
based" in combination with "severe congestion handling by
the RMD-QOSM refresh procedure"
o 5: RMD-QOSM scheme MUST be: "per aggregate RMD reservation
based" in combination with "severe congestion handling by
proportional data packet marking"
o 6 - 7: reserved
The default value of the <SCH> field MUST be set to the value equal
to 3.
4.2. Message Format
The format of the messages used by the RMD-QOSM complies with the
QoS-NSLP and QSpec template specifications. The QSpec used by RMD-
QOSM is denoted in this document as RMD-QSpec and is described in
Section 4.1.
4.3. RMD node state management
The QoS-NSLP state creation and management is specified in
[QoS-NSLP]. This section describes the state creation and
management functions of the Resource Management Function (RMF) in
the RMD nodes.
4.3.1 Aggregated operational and reservation states at the QNE Edges
The QNE Edges maintain both the intra-domain QoS-NSLP operational
and reservation states, while the QNE Interior nodes maintain only
reservation states. The structure of the intra-domain QoS-NSLP
operational state used by the QNE edges is specified in [QoS-NSLP].
In this case the intra-domain sessions supported by the edges are per
aggregate sessions that have a one-to-many relationship to the per
flow end-to-end states supported by the same edge.
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Note that the method of selecting the end-to-end sessions that form
an aggregate is not specified in this document. An example how this
can be accomplished is by monitoring the GIST routing states used by
the end-to-end sessions and group the ones that use the same <PHB
class>, QNE Ingress and QNE Egress addresses and the value of the
priority level. Note that this priority level should be deduced from
the priority parameters carried by the initial QSpec object.
The operational state of this aggregated intra-domain session MUST
contain a list with BOUND_SESSION_IDs.
The structure of the list depends on whether a unidirectional
reservation or a bidirectional reservation is supported.
When the operational state (at QNE ingress and QNE egress) supports
unidirectional reservations then this state MUST contain a list with
BOUND_SESSION_IDs maintaining the SESSION_ID values of its bound
end-to-end sessions. The BINDING_CODE associated with this
BOUND_SESSION_ID is set to code (Aggregated sessions). Thus the
operational state maintains a list of BOUND_SESSION_IDs entries.
Each entry is created when an end-to-end session joins the
aggregated intra-domain session and is removed when an end-to-end
session leaves the aggregate.
It is important to emphasize that in this case, the operational
state (at QNE ingress and QNE egress) that is maintained by each
end-to-end session bound to the aggregated intra-domain session it
MUST contain in the BOUND_SESSION_ID, the SESSION_ID value of the
bound tunnelled intra-domain (aggregate) session. The BINDING_CODE
associated with this BOUND_SESSION_ID is set to code (Aggregated
sessions).
When the operational state (at QNE ingress and QNE egress) supports
bidirectional reservations then the operational state MUST contain a
list of BOUND_SESSION_ID sets. Each set contain two
BOUND_SESSION_IDs. One of the BOUND_SESSION_IDs maintains the
SESSION_ID value of one of bound end-to-end session. The
BINDING_CODE associated with this BOUND_SESSION_ID is set to code
(Aggregated sessions). Another BOUND_SESSION_ID, within the same set
entry, maintains the SESSION_ID of the bidirectional bound end-to-
end session. The BINDING_CODE associated with this BOUND_SESSION_ID
is set to code (Bi-directional sessions).
Note that in each set, a one to one relation exists between each
BOUND_SESSION_ID with BINDING_CODE set to (Aggregate sessions) and
each BOUND_SESSION_ID with BINDING_CODE set to (Bi-directional
sessions). Each set is created when an end-to-end session joins the
aggregated operational state and is removed when an end-to-end
session leaves the aggregated operational state.
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It is important to emphasize that in this case, the operational
state (at QNE ingress and QNE egress) that is maintained by each
end-to-end session bound to the aggregated intra-domain session it
MUST contain two types of BOUND_SESSION_IDs. One is the
BOUND_SESSION_ID that MUST contain the SESSION_ID value of the bound
tunelled aggregated intra-domain session that is using the
BINDING_CODE set to (Aggregated sessions). The other
BOUND_SESSION_ID maintains the SESSION_ID of the bound bidirectional
end-to-end session. The BINDING_CODE associated with this
BOUND_SESSION_ID is set to code (Bi-directional sessions).
When the QNE Edges use aggregated QoS-NSLP reservation states, then
the PHB class value and the size of the aggregated
reservation, e.g., reserved bandwidth have to be maintained.
Note that this type of aggregation is an edge to edge aggregation
and is similar to the aggregation type specified in [RFC3175].
The size of the aggregated reservations needs to be
greater or equal to the sum of bandwidth of the inter domain
(end-to-end) reservations/sessions it aggregates, see e.g., Section
1.4.4 of [RFC3175].
A policy can be used to maintain the amount of REQUIRED bandwidth on
a given aggregated reservation by taking into account the sum of the
underlying inter domain (end-to-end) reservations, while endeavouring
to change reservation less frequently. This MAY require a trend
analysis. If there is a significant probability that in the next
interval of time the current aggregated reservation is exhausted, the
Ingress router MUST predict the necessary bandwidth and request it.
If the Ingress router has a significant amount of bandwidth reserved
but has very little probability of using it, the policy MAY predict
the amount of bandwidth REQUIRED and release the excess. To increase
or decrease the aggregate, the RMD modification procedures SHOULD be
used (see Section 4.6.1.4).
The QNE interior node are reduced state nodes, i.e., they do not
store NTLP/GIST states but they do store per PHB-aggregated QoS-NSLP
reservation states. These reservation states are maintained and
refreshed in the same way as described in Section 4.3.3.
4.3.2 Measurement-based method
The QNE Edges maintain per flow intra-domain QoS-NSLP operational
and reservation states that are containing similar data structures
as described in Section 4.3.1. The main difference is associated
with the different types of the used MRI and the bound end-to-end
sessions. The structure of the maintained BOUND_SESSION_IDs depends
on whether a unidirectional reservation or a bidirectional
reservation is supported.
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When unidirectional reservations are supported then the operational
state associated with this per flow intra-domain session MUST
contain in the BOUND_SESSION_ID the SESSION_ID value of its bound
end-to-end session. The BINDING_CODE associated with this
BOUND_SESSION_ID is set to code (Tunnelled and end-to-end sessions).
When bidirectional reservations are supported then the operational
state (at QNE ingress and QNE egress) MUST contain two types of
BOUND_SESSION_IDs. One is the BOUND_SESSION_ID that maintains the
SESSION_ID value of the bound tunnelled per-flow intra-domain
session. The BINDING_CODE associated with this BOUND_SESSION_ID is
set to code (Tunnelled and end-to-end sessions).
The other BOUND_SESSION_ID maintains the SESSION_ID of the bound
bidirectional end-to-end session. The BINDING_CODE associated with
this BOUND_SESSION_ID is set to code (Bi-directional sessions).
Furthermore, the QoS-NSLP reservation state maintains the PHB class
value, the value of the bandwidth requested by the end-to-end
session bound to the intra-domain session and the value of the
priority level.
The measurement-based method can be classified in two schemes:
* Congestion notification based on probing:
In this scheme the interior nodes are Diffserv aware but not NSIS
aware nodes. Each interior node counts the bandwidth that is used
by each PHB traffic class. This counter value is stored in an
RMD_QOSM state. For each PHB traffic class a predefined congestion
notification threshold is set. The predefined congestion
notification threshold is set according to, an engineered bandwidth
limitation based on e.g. agreed Service Level Agreement or a
capacity limitation of specific links. The threshold is usually less
than the capacity limit, i.e., admission threshold, in order to
avoid congestion due to the error of estimating the actual traffic
load. The value of this threshold SHOULD be stored in another
RMD_QOSM state.
In this scenario end-to-end NSIS message is used as a probe packet.
In this case the DSCP field of the GIST message is re-marked when the
predefined congestion notification threshold is exceeded in an
interior node. It is required that the remarking happens to all
packets that are belonging to the congested PHB traffic class so that
the probe can't pass the congested router without being remarked. In
this way it is ensured that the end-to-end NSIS message passed
through the node that it is congested. This feature is very useful
when flow-based ECMP (Equal Cost Multiple Path) routing is used to
detect only flows that are passing through the congested node.
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* NSIS measurement-based admission control:
The measurement based admission control is implemented in NSIS aware
stateless routers. Thus the main difference between this type of the
measurement-based admission control and the congestion notification-
based admission control is the fact that the interior nodes are NSIS
aware nodes. In particular, the QNE Interior nodes operating
in NSIS measurement-based mode are QoS-NSLP stateless nodes, i.e.,
they do not support any QoS-NSLP or NTLP/GIST states. These
measurement-based nodes store two RMD-QOSM states per PHR group.
These states reflect the traffic conditions at the node and are not
affected by QoS-NSLP signaling. One state stores the measured user
traffic load associated with the PHR group and another state stores
the maximum traffic load threshold that can be admitted per PHR
group. When a measurement-based node receives a intra-domain RESERVE
message, it compares the requested resources to the available
resources (maximum allowed minus current load) for the requested PHR
group. If there are insufficient resources, it sets the <M> bit in
the RMD-QSpec. No change to the RMD-QSpec is made when there are
sufficient resources.
4.3.3 Reservation-based method
The QNE Edges maintain intra-domain QoS-NSLP operational and
reservation states that are containing similar data structures as
described in Section 4.3.1.
In this case the intra-domain sessions supported by the edges are per
flow sessions that have a one-to-one relationship to the per
flow end-to-end states supported by the same edge.
The QNE Interior nodes operating in reservation-based mode are QoS-
NSLP reduced state nodes, i.e., they do not store NTLP/GIST states
but they do store per PHB-aggregated QoS-NSLP states.
The reservation-based PHR installs and maintains one reservation
state per PHB, in all the nodes located in the communication path.
This state is identified by the PHB class value and it maintains the
number of currently reserved resource units (or bandwidth). Thus,
the QNE Ingress node signals only the resource units requested by
each flow. These resource units, if admitted, are added to the
currently reserved resources per PHB.
For each PHB a threshold is maintained that specifies the maximum
number of resource units that can be reserved. This threshold
could, for example, be statically configured.
An example of how the admission control and its maintenance process
occurs in the interior nodes is described in Section 3 of [CsTa05].
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The simplified concept that is used by the per traffic class
admission control process in the interior nodes, is based on the
following equation:
last + p <= T,
where p: requested bandwidth rate, T: admission threshold, which
reflects the maximum traffic volume that can be admitted in the
traffic class, last: a counter that records the aggregated sum of
the signaled bandwidth rates of previous admitted flows.
The per-PHB group reservation states maintained in the interior
nodes are soft states, which are refreshed by sending periodic
refresh intra-domain RESERVE messages, which are initiated by the
Ingress QNEs. If a refresh message corresponding to a number of
reserved resource units (i.e., bandwidth) is not received, the
aggregated reservation state is decreased in the next refresh period
by the corresponding amount of resources that were not refreshed.
The refresh period can be refined using a sliding window algorithm
described in [RMD3].
The reserved resources for a particular flow can also be
explicitly released from a PHB reservation state by means of a
intra-domain RESERVE release/tear message, which is generated by the
Ingress QNEs.
The usage of explicit release enables the instantaneous release of
the resources regardless of the length of the refresh period. This
allows a longer refresh period, which also reduces the number of
periodic refresh messages.
Note that both in case of measurement- and (per-flow and aggregated)
RMD reservation-based methods,the way of how the maximum bandwidth
thresholds are maintained is out of the specification of this
document. However, when admission priorities are supported, the
Maximum Allocation [RFC4125] or the Russian Dolls [RFC4127] bandwidth
allocation model MAY be used. In this case three types of priority
traffic classes within the same PHB, e.g., Expedited Forwarding, can
be differentiated. These three different priority traffic classes,
which are associated to the same PHB, are denoted in this document as
PHB_low_priority, PHB_normal_priority and PHB_high_priority, and are
identified by the PHB class value and the priority value, which is
carried in the <Admission Priority> RMD-QSpec parameter.
4.4. Transport of RMD-QOSM messages
As mentioned in Section 1, The RMD-QOSM aims to support a number of
additional requirements, e.g., Minimal Impact on Interior Node
Performance. Therefore, RMD-QOSM is designed be very lightweight
signaling with regard to the number of signaling message roundtrips
and the amount of state established at involved signaling nodes with
and without reduced state on QNEs. The actions allowed by a QNE
Interior node are minimal (i.e., only those specified by the RMD-
QOSM).
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For example, only the QNE Ingress and the QNE Egress nodes are
allowed to initiate certain signaling messages. QNE Interior nodes
are, for example, allowed to modify certain signaling message
payloads. Moroever, RMD signaling is targeted towards intra-domain
signaling only. Therefore, RMD-QOSM relies on the security and
reliability support that is provided by the bound end-to-end session,
which is running between the boundaries of the RMD domain (i.e., the
RMD-QOSM QNE edges), and the security provided by the D-mode. This
implies the usage of the Datagram Mode.
Therefore, the intra-domain messages used by the RMD-QOSM are
intended to operate in the NTLP/GIST Datagram mode (see [GIST]). The
NSLP functionality available in all RMD-QOSM aware QoS NSLP nodes
requires from the intra-domain GIST, via the QoS-NSLP RMF API, see
[QoS-NSLP], to:
* operate in unreliable mode. This can be satisfied by passing this
requirement from the QoS-NSLP layer to the GIST layer via the API
Transfer-Attributes.
* do not create a message association state. This requirement can be
satisfied by a local policy, e.g., the QNE is configured to do not
create a message association state
* the interior nodes do not create any NTLP routing state.
This can be satisfied by passing this requirement from the QoS-NSLP
layer to the GIST layer via the API. However, between the QNE
Egress and QNE Ingress routing states that are associated with
intra-domain sessions SHOULD be created that can be used for the
communication of GIST Data messages sent by a QNE Egress directly
to a QNE Ingress. This type of routing state associated with an
intra-domain session can be generated and used in the following
way:
* When the QNE Ingress has to send an initial intra-domain RESERVE
message, the QoS-NSLP sends this message by including in the GIST
API SendMessage primitive, the Unreliable and No security
attributes. In order to optimise this procedure, the RMD domain
MUST be engineered in such a way that GIST will piggyback this NSLP
message on a GIST QUERY message. Furthermore, GIST sets the C-flag
(C=1), see [GIST] and uses the Q-mode. The GIST functionality
in each QNE Interior node will receive the GIST QUERY message and
by using the RecvMessage GIST API primitive it will pass the intra-
domain RESERVE message to the QoS-NSLP functionality. At the same
time the GIST functionality uses the Routing-State-Check boolean
to find out if the QoS-NSLP needs to create a routing state. The
QoS-NSLP sets this Boolean to inform GIST to not create a routing
state and to forward the GIST QUERY further downstream with the
modified QoS-NSLP payload, which will include the modified intra-
domain RESERVE message. The intra-domain RESERVE is sent in the
same way up to the QNE Egress. The QNE Egress needs to create a
routing state.
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Therefore at the moment that the GIST functionality
passes the intra-domain RESERVE message, via the GIST RecvMessage
primitive, to the QoS-NSLP, then at the same time the QoS-NSLP
sets the Routing-State-Check boolean such that a routing state is
created. The GIST creates the routing state using normal GIST
procedures. After this phase the QNE Ingress and QNE Egress have,
for the particular session, routing states that can route traffic
directly from QNE Ingress to QNE Egress and from QNE Egress to
QNE Ingress. The routing state at the QNE Egress can be used by
the QoS-NSLP and GIST to send an intra-domain RESPONSE or intra-
domain NOTIFY directly to the QNE Ingress using GIST Data
messages. Note that this routing state is refreshed using normal
GIST procedures. Note that in the above description it is
considered that the QNE Ingress can piggyback the initial RESERVE
(NSLP) message on the GIST QUERY message. If the piggybacking of
this NSLP (initial RESERVE) message would not be possible on the
GIST QUERY message, then the GIST QUERY message sent by the QNE
Ingress node would not contain any NSLP data. This GIST QUERY
message would only be processed by the QNE Egress to generate a
routing state.
After the QNE Ingress is informed that the routing state at the QNE
Egress is initiated, it would have to send the initial RESERVE
message using similar procedures as for the situation that it would
send an intra-domain RESERVE message that is not an initial
RESERVE, see next bullet. This procedure is not efficient and
therefore it is RECOMMENDED that the RMD domain MUST be engineered
in such a way that the GIST protocol layer, which is processed on a
QNE Ingress, will piggyback an initial RESERVE (NSLP) message on a
GIST QUERY message that uses the Q-mode.
* When the QNE Ingress needs to send an intra-domain RESERVE
message that is not an initial RESERVE, then the QoS-NSLP sends
this message by including in the GIST API SendMessage primitive
such attributes that the usage of the Datagram Mode is implied,
e.g., Unreliable attribute. Furthermore the Local policy attribute
is set such that GIST sends the intra-domain RESERVE message in a
Q-mode even if there is a routing state at the QNE Ingress. In this
way the GIST functionality uses its local policy to send the intra-
domain RESERVE message by piggybacking it on a GIST DATA message
and sending it in Q- mode even if there is a routing state for this
session. The intra-domain RESERVE message is piggybacked on the
GIST DATA message that is forwarded and processed by the QNE
Interior nodes up to the QNE Egress.
The transport of the original (end-to-end) RESERVE message is
accomplished in the following way:
At the QNE ingress the original (end-to-end) RESERVE message is
forwarded but ignored by the stateless or reduced-state nodes, see
Figure 3.
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The intermediate (interior) nodes are bypassed using
multiple levels of NSLP-ID values (see [QoS-NSLP]). This is
accomplished by marking the end-to-end RESERVE message, i.e.,
modifying the QoS-NSLP default NSLP-ID value to another NSLP-ID
predefined value.
The marking MUST be accomplished by the ingress by modifying the
QoS_NSLP default NSLP-ID value to a NSLP-ID predefined value. In
This way the egress MUST stop this marking process by reassigning
the QoS-NSLP default NSLP-ID value to the original (end-to-end)
RESERVE message. Note that the assignment of these NSLP-ID values is
a QOS-NSLP issue, which SHOULD be accomplished via IANA [QoS-NSLP].
4.5 Edge discovery and message addressing
Mainly, the Egress node discovery can be performed either by using
the GIST discovery mechanism [GIST], manual configuration or any
other discovery technique. The addressing of signaling messages
depends on the used GIST transport mode. The RMD-QOSM/QoS-NSLP
signaling messages that are processed only by the Edge nodes use the
peer-peer addressing of the GIST connection (C) mode.
RMD-QOSM/QoS-NSLP signaling messages that are processed by all nodes
of the Diffserv domain, i.e., Edges and Interior nodes, use the end-
end addressing of the GIST datagram (D) mode. Note that the RMD-QOSM
cannot directly specify that the GIST connection or the GIST datagram
mode SHOULD be used. This can only be specified by using, via the
QoS-NSLP-RMF API, the GIST API Transfer-Attributes, such as
reliable or unreliable, high or low level of security and by the use
of local policies. RMD QoS signaling messages that are addressed to
the data path end nodes are intercepted by the Egress nodes. In
particular, at the ingress and for downstream intra-domain messages,
the RMD-QOSM instructs the GIST functionality, via the GIST API to
use among others:
* unreliable and low level security Transfer-Attributes
* do not create a GIST routing state
* uses the D-mode MRI
The intra-domain RESERVE messages can then be transported by using
the Query D-mode, see Section 4.4..
At the QNE Egress and for upstream intra-domain messages, the RMD-
QOSM instructs the GIST functionality, via the GIST API to use among
others:
* unreliable and low level of security Transfer-Attributes
* The GIST functionality uses the routing state associated with the
intra-domain session to send an upstream intra-domain message
directly to the QNE Ingress, see Section 4.4.
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4.6. Operation and sequence of events
4.6.1. Basic unidirectional operation
This section describes the basic unidirectional operation and
sequence of events/triggers of the RMD-QOSM. The following basic
operation cases are distinguished:
* Successful reservation (Section 4.6.1.1),
* Unsuccessful reservation (Section 4.6.1.2),
* RMD refresh reservation (Section 4.6.1.3),
* RMD modification of aggregated reservation (4.6.1.4)
* RMD release procedure (Section 4.6.1.5.)
* Severe congestion handling (Section 4.6.1.6.)
* Admission control using congestion notification based on probing
(Section 4.6.1.7.).
The QNEs at the Edges of the RMD domain support the RMD QoS Model and
end-to-end QoS models, which process the RESERVE message differently.
Note that the term end-to-end QoS model applies to any QoS model that
is initiated and terminated outside the RMD-QOSM aware domain.
However, there might be situations where a QoS model is initiated
and/or terminated by the QNE Edges and is considered to be an end-to-
end QoS model. This can occur when the QNE Edges can also operate as
either QNI or as QNR and at the same time they can operate as either
sender or receiver of the data path.
It is important to emphasize that the content of this section is used
for the specification of the following RMD-QOSM/QoS-NSLP signaling
schemes, when basic unidirectional operation is assumed:
* "per flow congestion notification based on probing";
* "per flow RMD NSIS measurement based admission control",
* "per flow RMD reservation based" in combination with "severe
congestion handling by the RMD-QOSM refresh procedure"
* "per flow RMD reservation based" in combination with "severe
congestion handling by proportional data packet marking"
* "per aggregate RMD reservation based" in combination with
"severe congestion handling by the RMD-QOSM refresh procedure"
* "per aggregate RMD reservation based" in combination with
"severe congestion handling by proportional data packet marking"
For more details, please see Section 3.2.3.
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In particular, the described functionality described in Sections
4.6.1.1, 4.6.1.2, 4.6.1.3, 4.6.1.5, 4.6.1.4 and 4.6.1.6 applies to
the RMD reservation-based and to the NSIS measurement-based admission
control methods. The described functionality in Section 4.6.1.7
applies to the admission control procedure that uses the congestion
notification based on probing. The QNE Edge nodes maintain either per
flow QoS-NSLP operational and reservation states or aggregated QoS-
NSLP operational and reservation states.
When the QNE Edges maintain aggregated QoS-NSLP operational and
reservation states, the RMD-QOSM functionality MAY accomplish a RMD
modification procedure (see Section 4.6.1.4), instead of the
reservation initiation procedure that is described in this
subsection. Note that it is RECOMMENDED that the QNE implementations
of RMD-QOSM process the QoS-NSLP signaling messages with a higher
priority than data packets. This can be accomplished as described in
Section 3.3.4 of [QoS-NSLP] and it can be requested via the QoS-NSLP-
RMF API described in [QoS-NSLP]. The signalling scenarios described
in this section are accomplished using the QoS-NSLP processing rules
defined in [QoS-NSLP], in combination with the RMF triggers sent via
the QoS-NSLP-RMF API described in [QoS-NSLP].
According to Section 3.2.3 it is specified that only the "per flow
RMD reservation based" in combination with "severe congestion
handling by proportional data packet marking" scheme MUST be
implemented within one RMD domain. However, all RMD QNEs supporting
this specification MUST support the combination the "per flow RMD
reservation based" in combination with "severe congestion handling by
proportional data packet marking" scheme. If the RMD QNEs support
more RMD-QOSM schemes then the operator of that RMD domain MUST pre-
configure all the QNE edge nodes within one domain such that the
<SCH> field included in the "PHR container", see Section 4.1.2 and
the "PDR Container", see Section 4.1.3, will use always the same
value, such that within one RMD domain only one of the below
described RMD-QOSM schemes is used at a time.
All QNE nodes located within the RMD domain, MUST read and
interpret the <SCH> field included in the "PHR container" before
processing all the other "PHR container" payload fields.
Moreover, all QNE edge nodes located at the boarder of the RMD
domain, MUST read and interpret the <SCH> field included in the "PDR
container" before processing all the other "PDR container" payload
fields.
4.6.1.1. Successful reservation
This section describes the operation of the RMD-QOSM where a
reservation is successfully accomplished.
The QNI generates the initial RESERVE message, and it is forwarded
by the NTLP as usual [GIST].
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4.6.1.1.1. Operation in Ingress node
When an end-to-end reservation request (RESERVE) arrives at the
Ingress node (QNE), see Figure 8, it is processed based on the end-
to-end QoS model. Subsequently, the combination:
<TMOD-1>, <PHB Class>, <Admission Priority> are derived from the
<QoS Desired> object of the initial QSpec.
The QNE Ingress MUST maintain information about the smallest MTU that
is supported on the links within the RMD domain.
The value of the "Maximum Packet Size-1 (MPS)" value included in the
end-to-end QoS Model <TMOD-1> parameter is compared with the smallest
MTU value that is supported by the links within the RMD domain. If
the "Maximum Packet Size-1 (MPS)" is larger than this smallest MTU
value within the RMD domain, then the end-to-end reservation request
is rejected, see Section 4.6.1.1.2. Otherwise, the admission process
continues.
The <TMOD-1> parameter contained in the original initiator QSPEC are
mapped into the equivalent RMD-Qspec <TMOD-1> parameter representing
only the peak bandwidth in the local RMD-QSpec. This can be
accomplished by setting the RMD-QSpec <TMOD-1> fields as follows:
token rate (r) = peak traffic rate (p), the bucket depth (b) = large,
and the minimum policed unit (m) = large.
Note that the bucket size, (b], is measured in bytes. Values of this
Parameter may range from 1 byte to 250 gigabytes, see [RFC2215]. Thus
the maximum value that (b) could get is in order of 250 gigabytes.
The minimum policed unit, [m], is an integer measured in bytes and
must be less than or equal to Maximum Packet Size (MPS). Thus the
maximum value that (m) can get is (MPS). [Part94] and [TaCh99]
describe a method of calculating the values of some Token Bucket
parameters, e.g., calculation of large values of (m) and (b), when
the token rate (r), peak rate (p) and MPS are known.
The "Peak Data Rate-1 (p)" value of the end-to-end QoS Model <TMOD-1>
parameter is copied into the Peak Data Rate-1 (p) value of the Peak
Data Rate-1 (p)" value of the local RMD-Qspec <TMOD-1>.
The MPS value of the end-to-end QoS Model <TMOD-1> parameter is
copied into the MPS value of the local RMD-Qspec <TMOD-1>.
If the initial QSpec does not contain the <PHB Class> parameter,
then the selection of the <PHB class> that is carried by the intra-
domain RMD-QSpec is defined by a local policy similar to the
procedures discussed in [RFC2998] and [RFC3175].
For example, in the situation that the initial QSpec is used by
the IntServ Controlled Load QOSM then the Expedited Forwarding (EF)
PHB is appropriate to set the <PHB class> parameter carried by the
intra-domain RMD-QSpec, see [RFC3175].
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If the initial QSpec does not carry the <Admission Priority>
parameter then the <Admission Priority> parameter in the RMD-QSpec
will not be populated. If the initial QSpec does not carry the
<Admission Priority> parameter, but it carries other priority
parameters, then it is considered that edges as being stateful nodes,
are able to control the priority of the sessions that are
entering or leaving the RMD domain in accordance to the priority
parameters.
Note that the RMF reservation states, see Section 4.3, in
the QNE edges store the value of the <Admission Priority> parameter
that is used within the RMD domain in case of pre-emption and severe
congestion situations, see Section 4.6.1.6.
If the RMD domain supports pre-emption during the admission control
process, then the QNE Ingress node can support the building
blocks specified in the [QoS-NSLP] and during the admission
control process use the example pre-emption handling algorithm
described in Appendix 4.
Note that in the above described case, the QNE egress uses, if
available, the tunnelled initial priority parameters, which can
be interpreted by the QNE egress.
If the initial QSpec carries the <Excess Treatment> parameter,
then the QNE ingress and QNE egress nodes MUST control the excess
traffic that is entering or leaving the RMD domain in accordance to
the <Excess Treatment> parameter. Note that the RMD-QSpec does not
carry the <Excess Treatment> parameter.
If the requested <TMOD-1> parameter carried by the initial QSpec,
cannot be satisfied, then an end to end RESPONSE message has to be
generated. However, in order to decide whether the end-to-end
reservation request was locally (at the QNE Ingress) satisfied, also
a local(at the QNE_Ingress) RMD-QoSM admission control procedure has
to be performed. In other words, the RMD-QOSM functionality has to
verify whether the value included in the "Peak Data Rate-1 (p)"
field of RMD-QOSM <TMOD-1> can be reserved and stored in the
RMD-QOSM reservation states, see Sections 4.6.1.1.2 and 4.3.
An initial QSpec object MUST be included in the end-to-end
RESPONSE message. The parameters included in the QSpec <QoS
Reserved> object are copied from the original <QoS Desired> values.
The "E" flag associated with the QSPEC <QoS Reserved> object and the
"E" flag associated with the local RMD-QSpec <TMOD-1> parameter are
set. In addition, the INFO-SPEC object is included in the end to end
RESPONSE message. The error code used by this INFO-SPEC is:
Error severity class: Transient Failure
Error code value: Reservation failure
Furthermore, all the other RESPONSE parameters are set according to
the end-to-end QoS model or according to [QoS-NSLP] and [QSP-T].
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If the request was satisfied locally (see Section 4.3), the Ingress
QNE node generates two RESERVE messages: one intra-domain and
one end-to-end RESERVE message. Note however, that when the
aggregated QOS-NSLP operational and reservation states are used by
the QNE Ingress, then the generation of the intra-domain RESERVE
message depends on the availability of the aggregated QoS-NSLP
operational state. If this aggregated QoS-NSLP operational state is
available, then the RMD modification of aggregated reservations
described in section 4.6.1.4. is used.
It is important to note that when "per flow RMD reservation based"
scenario is used within the RMD domain, the retransmission within the
RMD domain SHOULD be disallowed. The reason of this is related to the
fact that the QNI Interior nodes are not able to differentiate
between a retransmitted RESERVE message associated with a certain
session and an initial RESERVE message belonging to another session.
However, the QNE Ingress have to report a failure situation upstream.
When the QNE Ingress transmits the (intra-domain or end-to-end)
RESERVE with RII object set, it waits for a RESPONSE from the QNE
Egress for a QOSNSLP_REQUEST_RETRY period.
If the QNE Ingress transmitted an intra-domain or end-to-end RESERVE
message with the RII object set and it fails to receive the
associated intra-domain or end-to-end RESPONSE, respectively, after
the QOSNSLP_REQUEST_RETRY period expires, it considers that the
reservation failed. In this case the QNE Ingress SHOULD generate an
end-to-end RESPONSE message that will include among others an
INFO-SPEC object. The error code used by this INFO-SPEC is:
Error severity class: Transient Failure
Error code value: Reservation failure
Furthermore, all the other RESPONSE parameters are set according to
the end-to-end QoS model or according to [QoS-NSLP] and [QSP-T].
Note however, that if the retransmission within the RMD domain is not
disallowed then the procedure described in Appendix
A.5 SHOULD be used on QNE Interior nodes, see also [Chan07]. In this
case the stateful QNE Ingress uses the retransmission procedure
described in [QoS-NSLP].
If a rerouting takes place then the stateful QNE ingress is following
the procedures specified in [QoS-NSLP].
At this point the intra-domain and end-to-end operational states MUST
be initiated or modified according to the REQUIRED binding
procedures. The way of how the BOUND_SESSION_IDs are initiated and
maintained in the intra-domain and end-to-end QoS-NSLP operational
states is described in Section 4.3.1 and 4.3.2.
These two messages are bound together in the following way. The end-
to-end RESERVE SHOULD contain in the BOUND_SESSION_ID the SESSION_ID
of its bound intra-domain session.
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Furthermore, if the QNE Edge nodes maintain intra-domain per flow
QoS-NSLP reservation states then the value of Binding_Code MUST be
set to code "Tunnel and end-to-end sessions", see Section 4.3.2.
In addition to this then the intra-domain and end-to-end RESERVE
messages are bound using the Message binding procedure described
in [QoS-NSLP].
In particular the <MSG_ID> object is included in the intra-domain
RESERVE message and its bound <BOUND_MSG_ID> object is carried by the
end-to-end RESERVE message. Furthermore, the Message_Binding_Type
flag is SET (value is 1), such that the message dependency is bi-
directional.
If the QOS-NSLP edges maintain aggregated intra-domain QoS-NSLP
operational states then the value of Binding_Code MUST be set to code
"Aggregated sessions".
Furthermore, in this case the retransmission within the RMD domain
is allowed and the procedures described in Appendix A.5 SHOULD be
used on QNE Interior nodes. This is necessary due to the fact that
when retransmissions are disallowed then the associated with (micro)
flows belonging to the aggregate will loose their reservations. Note
that in this case the stateful QNE Ingress uses the retransmission
procedure described in [QoS-NSLP].
The intra-domain RESERVE message is associated with the (local NTLP)
SESSION_ID mentioned above. The selection of the IP source and IP
destination address of this message depends on how the different
inter-domain (end-to-end) flows are aggregated by the QNE Ingress
node (see Section 4.3.1). As described in Section 4.3.1, the QNE
Edges maintain either per flow, or aggregated QoS-NSLP reservation
states for the RMD QoS model, which are identified by (local NTLP)
SESSION_IDs (see [GIST]). Note that this NTLP SESSION ID is a
different one than the SESSION_ID associated with the end-to-end
RESERVE message.
If no QOS-NSLP aggregation procedure at the QNE Edges is supported
then the IP source and IP destination address of this message MUST be
equal to the IP Source and IP destination addresses of the data flow.
The intra-domain RESERVE message is sent using the NTLP datagram
mode (see Sections 4.4, 4.5). Note that the GIST datagram mode can be
selected using the unreliable GIST API Transfer-Attributes. In
addition, the intra-domain RESERVE (RMD-QSpec) message MUST include a
PHR container (PHR_Resource_Request) and the RMD QOSM <QoS Desired>
object.
The end-to-end RESERVE message includes the initial QSpec and it
is sent towards the Egress QNE.
Note that after completing the initial discovery phase, the GIST
connection mode can be used between the QNE Ingress and QNE Egress.
Note that the GIST connection mode can be selected using the reliable
GIST API Transfer-Attributes.
Bader, et al. [Page 35]
INTERNET-DRAFT RMD-QOSM
The end-to-end RESERVE message is forwarded using the GIST
forwarding procedure to bypass the Interior stateless or reduced-
state QNE nodes, see Figure 8. The bypassing procedure is
described in Section 4.4.
At the QNE Ingress the end-to-end RESERVE message is marked, i.e.,
modifying the QoS-NSLP default NSLP-ID value to another NSLP-ID
predefined value that will be used by the GIST message carrying the
end-to-end RESPONSE message to bypass the QNE Interior nodes. Note
that the QNE Interior nodes, see [GIST], are configured to handle
only certain NSLP-Ids, see [QoS-NSLP].
Furthermore, note that the initial discovery phase and the process of
sending the end-to-end RESERVE message towards the QNE Egress MAY be
done simultaneously. This can be accomplished only if the GIST
implementation is configured to perform that, via e.g., a local
policy. However, the selection of the discovery procedure cannot be
selected by the RMD-QOSM.
The (initial) intra-domain RESERVE message MUST be sent by the QNE
Ingress and it MUST contain the following values (see QoS-NSLP-RMF
API described in [QoS-NSLP]):
* the value of the <RSN> object is generated and processed as
described in [QoS-NSLP];
* the SCOPING flag MUST NOT be set, meaning that a default
scoping of the message is used. Therefore, the QNE Edges MUST
be configured as RMD boundary nodes and the QNE Interior nodes
MUST be configured as Interior (intermediary) nodes;
* the <RII> MUST be included in this message, see [QoS-NSLP].
* The flag REPLACE MUST be set to FALSE = 0;
* The value of the Message ID value carried by the <MSG_ID> object
is set according to [QoS-NSLP]. The value of the
Message_binding_Type is set to "1".
* the value of the <REFRESH_PERIOD> object MUST be calculated
and set by the QNE Ingress node as described in Section 4.6.1.3;
* the value of the <PACKET_CLASSIFIER> object is associated with
the path-coupled routing MRM, since RMD-QOSM is used with the
path-coupled MRM. The flag that has to be set is the flag T (traffic
class) meaning that the packet classification of packets is based on
the DSCP value included in the IP header of the packets. Note that
the DSCP value used in the MRI can be derived by the value of <PHB
class> parameter, which MUST be carried by the intra-domain RESERVE
message. Note that the QNE Ingress being a QNI for the intra-domain
session it can pass this value to GIST, via the GIST API.
* the PHR resource units MUST be included into the
"Peak Data Rate-1 (p)" field of the local RMD-QSpec <TMOD-1>
parameter of the "<QoS Desired> object.
Bader, et al. [Page 36]
INTERNET-DRAFT RMD-QOSM
When the QNE edges use per flow intra-domain QoS-NSLP states, then
the "Peak Data Rate-1 (p)" value included in the initial QSpec
<TMOD-1> parameter is copied into the "Peak Data Rate-1 (p)" value of
the local RMD-QSpec <TMOD-1> parameter.
When the QNE edges use aggregated intra-domain QoS-NSLP operational
states, then the "Peak Data Rate-1 (p)" value of the the local RMD-
QSpec <TMOD-1> parameter can be obtained by using the bandwidth
aggregation method described in Section 4.3.1;
* the value of the <PHB class> parameter can be defined by using the
method of copying the <PHB Class> parameter carried by
the initial QSpec into the <PHB class> carried by the RMD-QSpec,
which is described above in this subsection.
* the value of the Container ID field of the PHR container
MUST be set to 17, (i.e., PHR_Resource_Request;)
* the value of the <Admitted Hops> parameter in the PHR container
MUST be set to "1". Note that during a successful reservation each
time a RMD-QOSM aware node processes the RMD-QSpec, the <Admitted
Hops> parameter is increased by one.
* the value of the <Hop_U> parameter in the PHR container MUST be
set to "0";
* the value of the <Max Admitted Hops> is set to "0".
* If the initial QSpec carried an <Admission Priority>
parameter, then this parameter SHOULD be copied into the RMD-QSpec
and carried by the (initiating) intra-domain RESERVE.
Note that for the RMD-QOSM a reservation established without an
<Admission Priority> parameter is equivalent to a reservation with
<Admission Priority> value 1.
Note that in this case each admission priority is associated with
a priority traffic class. The three priority traffic classes
(PHB_low_priority, PHB_normal_priority, PHB_high_priority) MAY be
associated with the same PHB, see Section 4.3.3.
* In a single RMD domain case the PDR container MAY not be included
into the message.
Note that the intra-domain RESERVE message does not carry the
BOUND_SESSION_ID object. The reason of this is that the end-to-end
RESERVE carries in the BOUND_SESSION_ID object the SESSION_ID value
of the intra-domain session.
When an end-to-end RESPONSE message is received by the QNE
Ingress node, which was sent by a QNE Egress node see Section
4.6.1.1.3, then it is processed according to [QoS-NSLP]
and end-to-end QoS model rules.
Bader, et al. [Page 37]
INTERNET-DRAFT RMD-QOSM
When an intra-domain RESPONSE message is received by the QNE Ingress
node, which was sent by a QNE Egress see Section 4.6.1.1.3, it uses
the QoS-NSLP procedures to match it to the earlier sent intra-domain
RESERVE message. After this phase, the RMD-QSpec has to be identified
and processed.
The RMD QoSM reservation has been successful if the <M> bit carried
by the "PDR Container" is equal to "0" (i.e., not set).
Furthermore, the INFO_SPEC object is processed as defined in the
QoS-NSLP specification. In case of successful reservation the
INFO_SPEC object MUST have the following values:
* Error Severity Class: Success
* Error Code value: Reservation successful
If the end-to-end RESPONSE message has to be forwarded to a
node outside the RMD-QOSM aware domain then the values of
the objects contained in this message (i.e., <RII/RSN>, <INFO_SPEC>,
[QSPEC ]) MUST be set by the QOS-NSLP protocol functions of the QNE.
If an end-to-end QUERY is received by the QNE Ingress then the same
bypassing procedure has to be used as the one applied for an end-to-
end RESERVE message. In particular, it is forwarded using the GIST
forwarding procedure to bypass the Interior stateless or reduced-
state QNE nodes.
4.6.1.1.2 Operation in the Interior nodes
Each QNE Interior node MUST use the QoS-NSLP and RMD-QOSM parameters
of the intra-domain RESERVE (RMD-QSpec) message as follows (see
QoS-NSLP-RMF API described in [QoS-NSLP]):
* the values of the <RSN>, <RII>, <PACKET_CLASSIFIER>,
<REFRESH_PERIOD>, objects MUST NOT be changed.
The interior node is informed by the <PACKET_CLASSIFIER> object
that the packet classification SHOULD be done on the DSCP value.
The flag that has to be set in this case is the flag T (traffic
class). The value of the DSCP value MUST be obtained via the MRI
parameters that the QoS-NSLP receives from GIST. A QNE Interior
MUST be able to associate the value carried by the RMD-QSpec <PHB
class> parameter and the DSCP value obtained via GIST. This is
REQUIRED, because there are situations that the <PHB class>
parameter is not carrying a DSCP value, but a "PHB ID code", see
Section 4.1.1.
* The flag REPLACE MUST be set to FALSE = 0;
* when the RMD reservation based methods described in Section 4.3.1
and 4.3.3 are used, the "Peak Data Rate-1 (p)" value of the
local RMD-QSpec <TMOD-1> parameter is used by the QNE Interior
node for admission control. Furthermore, if the
<Admission Priority> parameter is carried by the RMD-QOSM
<QoS Desired> object, then this parameter is processed as
described in the following bullets.
Bader, et al. [Page 38]
INTERNET-DRAFT RMD-QOSM
* in case of the RMD reservation-based procedure, and if these
resources are admitted (see Section 4.3.1, 4.3.3), they are added
to the currently reserved resources. Furthermore, the value of the
<Admitted Hops> parameter in the PHR container has to be increased
by one.
* If the bandwidth allocated for the PHB_high_priority traffic is
fully utilized, and a high priority request arrives, other
policies on allocating bandwidth can be used, which are beyond the
scope of this document.
* If the RMD domain supports pre-emption during the admission
control process, then the QNE Interior node can support the
building blocks specified in the [QoS-NSLP] and during the
admission control process use the pre-emption handling algorithm
specified in Appendix 4.
* in case of the RMD measurement based method (see Section 4.3.2),
and if the requested into the "Peak Data Rate-1 (p)" value of the
local RMD-QSpec <TMOD-1> parameter is admitted, using a MBAC
algorithm, then the number of this resources will be used to
update the MBAC algorithm according to the operation described in
Section 4.3.2.
4.6.1.1.3 Operation in the Egress node
When the end-to-end RESERVE message is received by the egress node,
it is only forwarded further, towards QNR, if the processing of the
intra-domain RESERVE(RMD-QSpec) message was successful at all nodes
in the RMD domain. In this case, the QNE Egress MUST stop the marking
process that was used to bypass the QNE Interior nodes by reassigning
the QoS-NSLP default NSLP-ID value to the end-to-end RESERVE message,
see Section 4.4. Furthermore, the carried BOUND_SESSION_ID object
associated with the intra-domain session MUST be removed after
processing. Note that the received end to end RESERVE was tunneled
within the RMD domain. Therefore, the tunnelled initial QSpec
carried by the end-to-end RESERVE message has to be processed/set
according to the [QSP-T] specification.
If a rerouting takes place, then the stateful QNE egress is following
the procedures specified in [QoS-NSLP].
At this point the intra-domain and end-to-end operational states MUST
be initiated or modified according to the REQUIRED binding
procedures.
The way of how the BOUND_SESSION_IDs are initiated and maintained in
the intra-domain and end-to-end QoS-NSLP operational states is
described in Section 4.3.1 and 4.3.2.
If the processing of the intra-domain RESERVE(RMD-QSpec) was not
successful at all nodes in the RMD domain then the inter-domain (end-
to-end) reservation is considered as being failed.
Bader, et al. [Page 39]
INTERNET-DRAFT RMD-QOSM
Furthermore, if the initial QSpec object used an object combination
of type 1 or, 2, where the <QoS Available> is populated, and the
intra-domain RESERVE(RMD-QSpec) was not successful at all nodes in
the RMD domain it MUST be considered that the QoS Available is not
satisfied and that the the inter-domain (end-to-end) reservation is
considered as being failed.
Furthermore, note that when the QNE Egress uses per flow intra-domain
QoS-NSLP operational states, see Sections 4.3.2 and 4.3.3, the QNE
Egress SHOULD support the message binding procedure described in
[QoS-NSLP], which can be used to synchronize the arrival of the end
to end RESERVE and the intra-domain RESERVE (RMD-QSpec) messages, see
Section 5.7 and QoS-NSLP-RMF API described in [QoS-NSLP]. Note that
the intra-domain RESERVE message carries the <MSG_ID> object and its
bound end-to-end RESERVE message carries the <BOUND_MSG_ID> object.
Both these objects carry the Message_Binding_Type flag set to the
value of 1. If these two messages do not arrive during the time
defined by the MsgIDWait timer, then the reservation is considered as
being failed. Note that the timer has to be pre-configured and it has
to have the same value in the RMD domain. In this case an end-to-end
RESPONSE message, see QoS-NSLP-RMF API described in [QoS-NSLP], is
sent towards the QNE ingress with the following INFO_SPEC values:
Error Class: Transient Failure
Error Code: Mismatch synchronization between end-to-end RESERVE
and intra-domain RESERVE
When the intra-domain RESERVE(RMD-QSpec) is received by the QNE
Egress node of the session associated with the intra-domain
RESERVE(RMD-QSpec) (the PHB session) with the session included in
its <BOUND_SESSION_ID> object MUST be bound according to the
specification given in [QoS-NSLP]. The SESSION_ID included
in the BOUND_SESSION_ID parameter stored in the intra-domain QoS-NSLP
operational state object is the SESSION_ID of the session associated
with the end-to-end RESERVE message(s). Note that if the QNE Edge
nodes maintain per flow intra-domain QoS NSLP operational states then
the value of Binding_Code = (Tunnel and end-to-end sessions) is used
If the QNE Edge nodes maintain per aggregated QoS-NSLP intra-domain
reservation states then the value of Binding_Code = (Aggregated
sessions), see Sections 4.3.1, 4.3.2.
If the RMD domain supports pre-emption during the admission control
process, then the QNE Egress node can support the building
blocks specified in the [QoS-NSLP] and during the admission
control process use the example pre-emption handling algorithm
described in Appendix 4.
The end-to-end RESERVE message is generated/forwarded further
upstream according to the [QoS-NSLP] and [QSP-T] specifications.
Furthermore, the "B" (BREAK) QoS-NSLP flag in the end to end
RESERVE message MUST NOT be set, see QoS-NSLP-RMF API described in
QoS-NSLP.
Bader, et al. [Page 40]
INTERNET-DRAFT RMD-QOSM
QNE (Ingress) QNE (Interior) QNE (Interior) QNE (Egress)
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
RESERVE | | |
--->| | | RESERVE |
|------------------------------------------------------------>|
|RESERVE(RMD-QSpec) | | |
|------------------->| | |
| |RESERVE(RMD-QSpec) | |
| |------------------>| |
| | | RESERVE(RMD-QSpec) |
| | |------------------->|
| |RESPONSE(RMD-QSpec)| |
|<------------------------------------------------------------|
| | | RESERVE
| | | |-->
| | | RESPONSE
| | | |<--
| |RESPONSE | |
|<------------------------------------------------------------|
RESPONSE | | |
<---| | | |
Figure 8: Basic operation of successful reservation procedure used by
the RMD-QOSM
The QNE Egress MUST generate an intra-domain RESPONSE (RMD-Qspec)
message. The intra-domain RESPONSE (RMD-QSpec) message MUST
be sent to the QNE Ingress node, i.e., the previous stateful hop by
using the procedures described in Sections 4.4 and 4.5.
The values of the RMD-QSpec that is carried by the intra-domain
RESPONSE message MUST be used and/or set in the following way
(see QoS-NSLP-RMF API described in [QoS-NSLP]):
* the RII object carried by the intra-domain RESERVE message, see
Section 4.6.1.1.1, has to be copied and carried by the
intra-domain RESPONSE message.
* the value of the Container ID field of the PDR container
MUST be set "23" (i.e., PDR_Reservation_Report);
* the value of the <M> field of the PDR container MUST be equal to
the value of the <M> parameter of the PHR container that was
carried by its associated intra-domain RESERVE(RMD-QSpec)
message. This is REQUIRED since the value of the <M> parameter is
used to indicate the status if the RMD reservation request to the
Ingress edge.
If the binding between the intra-domain session and the end-to-end
session uses a Binding_Code is (Aggregated sessions), and there is no
aggregated QoS-NSLP operational state associated with the intra-
domain session available, then the RMD modification of aggregated
reservation procedure described in Section 4.6.1.4. can be used.
Bader, et al. [Page 41]
INTERNET-DRAFT RMD-QOSM
If the QNE Egress receives an end-to-end RESPONSE message, it is
processed and forwarded towards the QNE Ingress. In particular, the
non-default values of the objects contained in the end-to-end
RESPONSE message MUST be used and/or set by the QNE Egress as
follows (see QoS-NSLP-RMF API described in [QoS-NSLP]):
* the values of the <RII/RSN>, <INFO_SPEC>, [ QSPEC ] objects are
set according to [QoS-NSLP] and/or [QSP-T]. The INFO_SPEC object
SHOULD be set by the QoS-NSLP functionality. In case of successful
reservation the INFO_SPEC object SHOULD have the following values:
Error Severity Class: Success,
Error Code value: Reservation successful,
* Furthermore, an initial QSpec object MUST be included in the
end-to-end RESPONSE message. The parameters included in the QSPEC
<QoS Reserved> object are copied from the original <QoS Desired>
values.
The end-to-end RESPONSE message are delivered as normal, i.e.,
is addressed and sent to its upstream QoS-NSLP neighbor, i.e., QNE
Ingress node.
Note that if a QNE Egress receives an end-to-end QUERY that was
bypassed through the RMD domain, it MUST stop the marking
process that was used to bypass the QNE Interior nodes. This can be
done by reassigning the QoS-NSLP default NSLP-ID value to the end-to-
end QUERY message, see Section 4.4.
4.6.1.2. Unsuccessful reservation
This section describes the operation where a request for reservation
cannot be satisfied by the RMD-QOSM.
The QNE Ingress, the QNE Interior and QNE Egress nodes process and
forward the end-to-end RESERVE message and the intra-domain
RESERVE(RMD-QSpec) message in a similar way as specified in Section
4.6.1.1. The main difference between the unsuccessful operation and
successful operation is that one of the QNE nodes does not admit the
request due to e.g., lack of resources. This also means that the QNE
edge node MUST NOT forward the end-to-end RESERVE message towards the
QNR node.
Note that the described functionality applies to the RMD reservation-
based methods, see Sections 4.3.1, 4.3.2, and to the NSIS
measurement-based admission control method, see Section 4.3.2.
The QNE Edge nodes maintain either per flow QoS-NSLP reservation
states or aggregated QoS-NSLP reservation states. When the QNE edges
maintain aggregated QoS-NSLP reservation states, the RMD-QOSM
functionality MAY accomplish a RMD modification procedure (see
Section 4.6.1.4.), instead of the reservation initiation procedure
that is described in this subsection.
Bader, et al. [Page 42]
INTERNET-DRAFT RMD-QOSM
4.6.1.2.1 Operation in the Ingress nodes
When an end-to-end RESERVE message arrives at the QNE Ingress and
if: (1) the "Maximum Packet Size-1 (MPS)" included in the end-to-end
QoS Model <TMOD-1> is larger than this smallest MTU value within the
RMD domain, or (2) there are no resources available, the QNE Ingress
MUST reject this end-to-end RESERVE message and send an end-to-end
RESPONSE message back to the sender, as described in the QoS-NSLP
specification, see [QoS-NSLP] and [QSP-T].
When an end-to-end RESPONSE message is received by an Ingress
node, see Section 4.6.1.2.3, the values of the <RII/RSN>,
[<INFO_SPEC> ], [<QSPEC>] objects are processed according to the QoS-
NSLP procedures.
If the end-to-end RESPONSE message has to be forwarded upstream to a
node outside the RMD-QOSM aware domain then the values of
the objects contained in this message (i.e., <RII/RSN>, <INFO_SPEC>,
[ QSPEC ]) MUST be set by the QOS-NSLP protocol functions of the QNE.
When an intra-domain RESPONSE message is received by the QNE Ingress
node, which was sent by a QNE Egress, see Section 4.6.1.2.3, it uses
the QoS-NSLP procedures to match it to the earlier sent intra-domain
RESERVE message. After this phase, the RMD-QSpec has to be identified
and processed. Note that in this case the RMD Resource Management
Function (RMF) is notified that the reservation has been
unsuccessful, by reading the <M> parameter of the PDR container.
Note that when the QNE edges maintain a per flow QoS-NSLP reservation
state the RMD-QOSM functionality, has to start an RMD release
procedure (see Section 4.6.1.5). When the QNE edges maintain
aggregated QoS-NSLP reservation states the RMD-QOSM functionality MAY
start a RMD modification procedures (see Section 4.6.1.4.).
4.6.1.2.2 Operation in the Interior nodes
In case of the RMD reservation based scenario, and if the
intra-domain reservation request is not admitted by the QNE Interior
node then the <Hop_U> and <M> parameters of the PHR container MUST be
set to "1". The <Admitted Hops> counter MUST NOT be increased.
Moreover, the value of the <Max Admitted Hops> MUST be set equal to
the <Admitted Hops> value.
Furthermore, the "E" flag associated with the QSpec <QoS Desired>
object and the "E" flag associated with the local RMD-QSpec <TMOD-1>
parameter SHOULD be set. In case of the RMD measurement based
scenario, the <M> parameter of the PHR container MUST be set to "1".
Furthermore, the "E" flag associated with the QSpec <QoS Desired>
object and the "E" flag associated with the local RMD-QSpec <TMOD-1>
parameter SHOULD be set. Note that the <M> flag seems to be set in a
similar way as the "E" flag used by the local RMD-QSpec <TMOD-1>
parameter. However, the ways of how the two flags are processed by a
QNE are different.
Bader, et al. [Page 43]
INTERNET-DRAFT RMD-QOSM
In general, if a QNE Interior node receives a RMD-QSpec <TMOD-1>
parameter with the "E" flag set and a PHR container type
"PHR_Resource_Request", with the <M> parameter set to "1" , then this
"PHR Container" and the RMD-QOSM <QoS Desired> object) MUST NOT be
processed. Furthermore, when the <K> parameter that is included in
the "PHR Container" and carried by a RESERVE message is set to "1",
then this "PHR Container" and the RMD-QOSM <QoS Desired> object) MUST
NOT be processed.
4.6.1.2.3 Operation in the Egress nodes
In the RMD reservation based, see Sections 4.3.3, and the RMD NSIS
measurement based scenario, see Section 4.3.2, when the <M> marked
intra-domain RESERVE(RMD-QSpec) is received by the QNE Egress node
(see Figure 9) the session associated with the intra-domain
RESERVE(RMD-QSpec) (the PHB session) and the end-to-end session MUST
be bound.
Moreover, if the initial QSpec object (used by the end-to-end QoS
model) used an object combination of type 1 or, 2, where the <QoS
Available> is populated, and the intra-domain RESERVE(RMD-QSpec) was
not successful at all nodes in the RMD domain, i.e., the intra-domain
RESERVE(RMD-QSpec) message is marked, it MUST be considered that the
QoS Available is not satisfied and that the inter-domain (end-to-
end) reservation is considered as being failed.
When the QNE Egress uses per flow intra-domain QoS-NSLP operational
states, see Section 4.3.2 and 4.3.3, then the QNE Egress node MUST
generate an end-to-end RESPONSE message that has to be sent to its
previous stateful QoS-NSLP hop (see QoS-NSLP-RMF API described in
[QoS-NSLP]).
* the values of the <RII/RSN>, <INFO_SPEC> objects are set
by the standard QoS-NSLP protocol functions. In case of the
unsuccessful reservation the INFO_SPEC object SHOULD have the
following values:
Error Severity Class: Transient Failure
Error Code value: Reservation failure
The QSpec that was carried by the end to end RESERVE belonging to the
same session as this end-to-end RESPONSE is included in this message.
In particular, the parameters included in the QSpec <QoS Reserved>
object of the end-to-end RESPONSE message are copied
from the initial <QoS Desired> values included in its associated
end-to-end RESERVE message. The "E" flag associated with
the QSpec <QoS Reserved> object and the "E" flag associated with the
<TMOD-1> parameter included in the end-to-end RESPONSE are set.
In addition to the above, similarly to the successful operation,
see Section 4.6.1.1.3, the QNE Egress MUST generate an intra-domain
RESPONSE message that has to be sent to its previous stateful QoS-
NSLP hop.
Bader, et al. [Page 44]
INTERNET-DRAFT RMD-QOSM
The values of the <RII/RSN>, <INFO_SPEC> objects are set by
the standard QoS-NSLP protocol functions. In case of the unsuccessful
reservation the INFO_SPEC object SHOULD have the following values
(see QoS-NSLP-RMF API described in [QoS-NSLP]):
Error Severity Class: Transient Failure
Error Code value: Reservation failure
QNE (Ingress) QNE (Interior) QNE (Interior) QNE (Egress)
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
RESERVE | | |
--->| | | RESERVE |
|------------------------------------------------------------>|
|RESERVE(RMD-QSpec:M=0) | |
|------------------->| | |
| |RESERVE(RMD-QSpec:M =1) |
| |------------------>| |
| | | RESERVE(RMD-QSpec:M=1)
| | |------------------->|
| |RESPONSE(RMD-QOSM) | |
|<------------------------------------------------------------|
| |RESPONSE | |
|<------------------------------------------------------------|
RESPONSE | | |
<---| | | |
RESERVE(RMD-QSpec: Tear=1, M=1, <Admitted Hops>=<Max Admitted Hops>
|------------------->| | |
|RESERVE(RMD-QSpec: Tear=1, M=1, K=1) |
| |------------------>| |
| RESERVE(RMD-QSpec: Tear=1, M=1, K=1)|
| | |------------------->|
Figure 9: Basic operation during unsuccessful reservation
initiation used by the RMD-QOSM
The values of the RMD-QSpec MUST be used and/or set
in the following way (see QoS-NSLP-RMF API described in [QoS-NSLP]):
* the value of the <PDR Control Type> of the PDR container MUST be
set to "23" (PDR_Reservation_Report);
* the value of the <Max Admitted Hops> parameter of the PHR
container included in the received <M> marked intra-domain
RESERVE (RMD-QSpec) MUST be included
in the <Max Admitted Hops> parameter of the PDR container;
* the value of the <M> parameter of the PDR container MUST be "1".
4.6.1.3 RMD refresh reservation
In case of RMD measurement-based method, see Section 4.3.2, QoS-NSLP
reservation states in the RMD domain are typically not maintained,
therefore, this method typically does not use an intra-domain refresh
procedure.
Bader, et al. [Page 45]
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However, there are measurement based optimization schemes,
see [GrTs03], which MAY use the refresh procedures described in
Sections 4.6.1.3.1, and 4.6.1.3.3. However, this measurement based
optimization schemes can only be applied in the RMD domain if the QNE
edges are configured to perform intra-domain refresh procedures and
if all the QNE interior nodes are configured to perform the
measurement based optimization schemes.
In the description given in this subsection it is assumed that the
RMD measurement based scheme does not use the refresh procedures.
When the QNE edges maintain aggregated or per flow QoS-NSLP
operational and reservation states, see Sections 4.3.1 and 4.3.3,
then the refresh procedures are very similar. If the RESERVE messages
arrive within the soft state time-out period, the corresponding
number of resource units are not removed. However, the transmission
of the intra-domain and end-to-end (refresh) RESERVE message are not
necessarily synchronized. Furthermore, the generation of the end-to-
end RESERVE message, by the QNE edges, depends on the locally
maintained refreshed interval (see [QoS-NSLP]).
4.6.1.3.1 Operation in the Ingress node
The Ingress node MUST be able to generate an intra-domain (refresh)
RESERVE(RMD-QSpec) at any time defined by the refresh period/timer.
Before generating this message, the RMD QoS signaling model
functionality is using the RMD traffic class (PHR) resource units for
refreshing the RMD traffic class state.
Note that the RMD traffic class refresh periods MUST be equal in
all QNE edge and QNE Interior nodes and SHOULD be smaller (default:
more than two times smaller) than the refresh period at the QNE
Ingress node used by the end-to-end RESERVE message. The intra-domain
RESERVE (RMD-QSpec) message MUST include a RMD-QOSM <QoS Desired> and
a PHR container (i.e., PHR_Refresh_Update).
An example of this refresh operation can be seen in Figure 10.
QNE (Ingress) QNE (Interior) QNE (Interior) QNE (Egress)
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
|RESERVE(RMD-QSpec) | | |
|------------------->| | |
| |RESERVE(RMD-QSpec) | |
| |------------------>| |
| | | RESERVE(RMD-QSpec) |
| | |------------------->|
| | | |
| |RESPONSE(RMD-QSpec)| |
|<------------------------------------------------------------|
| | | |
Figure 10: Basic operation of RMD specific refresh procedure
Bader, et al. [Page 46]
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Most of the non-default values of the objects contained in this
message MUST be used and set by the QNE Ingress in the same
way as described in Section 4.6.1.1. The following objects are
used and/or set differently:
* the PHR resource units MUST be included into the
"Peak Data Rate-1 (p)" field of the local RMD-QSpec <TMOD-1>
parameter. The "Peak Data Rate-1 (p)" field value of the local RMD-
QSpec <TMOD-1> parameter depends on how the different inter domain
(end-to-end) flows are aggregated by the QNE Ingress node (e.g.,
the sum of all the PHR requested resources of the aggregated
flows), see Section 4.3.1. If no QOS-NSLP aggregation is
accomplished by the QNE Ingress node, the "Peak Data Rate-1 (p)"
value of the local RMD-QSpec <TMOD-1> parameter SHOULD be equal to
the "Peak Data Rate-1 (p)" value of the local RMD-QSpec <TMOD-1>
parameter of its associated new (initial) intra-domain RESERVE
(RMD-QSpec) message, see Section 4.3.3.;
* the value of the Container field of the "PHR Container"
MUST be set to "19", i.e., "PHR_Refresh_Update";
When the intra-domain RESPONSE (RMD-QSpec) message, see Section
4.6.1.3.3., is received by the QNE Ingress node, then:
* the values of the <RII/RSN>, <INFO_SPEC>, [QSP-T] objects are
processed by the standard QoS-NSLP protocol functions (see Section
4.6.1.1.);
* the "PDR Container" has to be processed by the RMD-QOSM
functionality in the QNE Ingress node. The RMD-QOSM functionality
is notified by the <PDR M> parameter of the PDR container
that the refresh procedure has been successful or unsuccessful.
All session(s) (when aggregated QoS-NSLP operational and
reservation states are used, see Section 4.3.1, there will be more
than one sessions) associated with this RMD specific refresh
session MUST be informed about the success or failure of the
refresh procedure. In case of failure, the QNE Ingress node has
to generate (in a standard QoS-NSLP way) an error end-to-end
RESPONSE message that will be sent towards QNI.
4.6.1.3.2 Operation in the Interior node
The intra-domain RESERVE (RMD-QSpec) message is received and
processed by the QNE Interior nodes. Any QNE edge or QNE Interior
node that receives a "PHR_Refresh_Update" field
MUST identify the traffic class state (PHB) (using the
<PHB Class> parameter). Most of the parameters in this refresh
intra-domain RESERVE (RMD-QSpec) message MUST be used and/or set by
a QNE Interior node in the same way as described in Section 4.6.1.1.
The following objects are used and/or set differently:
Bader, et al. [Page 47]
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* the "Peak Data Rate-1 (p)" value of the local RMD-QSpec <TMOD-1>
parameter of the RMD-QOSM <QoS Desired> is used by the QNE Interior
node for refreshing the RMD traffic class state. These resources
(included in the "Peak Data Rate-1 (p)" value of local RMD-QSpec
<TMOD-1>), if reserved, are added to the currently reserved
resources per PHB and therefore they will become a part of
the per traffic class (per-PHB) reservation state, see Sections
4.3.1 and 4.3.3. If the refresh procedure cannot be fulfilled then
the <M> and <S> fields carried by the PHR container MUST be set to
"1".
* Furthermore, the "E" flag associated with <QoS Desired> object and
the "E" flag associated with the local RMD-QSpec <TMOD-1>
parameter SHOULD be set.
Any PHR container of type "PHR_Refresh_Update", and its associated
local RMD-QSpec <TMOD-1>, whether it is marked or not and independent
of the "E" flag value of the local RMD-QSpec <TMOD-1> parameter, is
always processed, but marked bits are not changed.
4.6.1.3.3 Operation in the Egress node
The intra-domain RESERVE(RMD-QSpec) message is received and
processed by the QNE Egress node. A new intra-domain RESPONSE
(RMD-QSpec) message is generated by the QNE Egress node and MUST
include a PDR (type PDR_Refresh_Report).
The (refresh) intra-domain RESPONSE (RMD-QSpec) message MUST be sent
to the QNE Ingress node, i.e., the previous stateful hop. The
(refresh) intra-domain RESPONSE (RMD-QSpec) message MUST be
explicitly routed to the QNE Ingress node, i.e., the previous
stateful hop, using the procedures described in Section 4.5.
* the values of the <RII/RSN>, <INFO_SPEC> objects are set
by the standard QoS-NSLP protocol functions, see [QoS-NSLP].
* The value of the <PDR Control Type> parameter of the PDR container
MUST be set "24" (i.e. PDR_Refresh_Report).
In case of successful reservation the INFO_SPEC object SHOULD
have the following values:
Error Severity Class: Success
Error Code value: Reservation successful
* In case of unsuccessful reservation the INFO_SPEC object SHOULD
have the following values:
Error Severity Class: Transient Failure
Error Code value: Reservation failure
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The RMD-QSpec that was carried by the intra-domain RESERVE
belonging to the same session as this intra-domain RESPONSE is
included in the intra-domain RESPONSE message. The parameters
included in the QSPec <QoS Reserved> object are copied from the
original <QoS Desired> values. If the reservation is unsuccessful
then "E" flag associated with the QSpec <QoS Reserved> object and the
"E" flag associated with the local RMD-QSpec <TMOD-1> parameter are
set. Furthermore, the <M> and <S> PDR Container bits are set to "1".
4.6.1.4. RMD modification of aggregated reservations
In the case when the QNE edges maintain QoS-NSLP aggregated
operational and reservation states and the aggregated reservation has
to be modified (see Section 4.3.1) the following procedure is
applied:
* When the modification request requires an increase of the reserved
resources, the QNE Ingress node MUST include the corresponding
value into the "Peak Data Rate-1 (p)" value of the local RMD-QSpec
<TMOD-1> parameter of the RMD-QOSM <QoS Desired> which is sent
together with a "PHR_Resource_Request" control information. If a
QNE edge or QNE Interior node is not able to reserve the number of
requested resources, the "PHR_Resource_Request" that is associated
with the local RMD-QSpec <TMOD-1> parameter MUST be <M> marked,
i.e., the <M> bit is set to the value of "1". In this situation
the RMD specific operation for unsuccessful reservation will be
applied (see Section 4.6.1.2).
* When the modification request requires a decrease of the
reserved resources, the QNE Ingress node MUST include this value
into the "Peak Data Rate-1 (p)" value of the local RMD-QSpec
<TMOD-1> parameter of the RMD-QOSM <QoS Desired>. Subsequently an
RMD release procedure SHOULD be accomplished (see Section 4.6.1.5).
Note that if the complete bandwidth associated with the aggregated
reservation maintained at the QNE ingress does not have to be
released then the TEAR flag MUST be set to OFF. This is because the
NSLP operational states associated with the aggregated reservation
states at the edge QNEs MUST NOT be turned off. However, if the
complete bandwidth associated with the aggregated reservation
maintained at the QNE ingress has to be released, then the TEAR
flag MUST be set to ON.
It is important to be emphasized that this RMD modification scheme
applies only to the following two RMD-QOSM schemes:
* "per aggregate RMD reservation based" in combination with
"severe congestion handling by the RMD-QOSM refresh procedure";
* "per aggregate RMD reservation based" in combination with
"severe congestion handling by proportional data packet marking.
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4.6.1.5 RMD release procedure
This procedure is applied to all RMD mechanisms that maintain
reservation states. If a refresh RESERVE message does not arrive at a
QNE Interior node within the refresh time-out period then the
bandwidth requested by this refresh RESERVE message is not updated.
This will mean that the reserved bandwidth associated with the
reduced state is decreased in the next refresh period by the amount
of the corresponding bandwidth that has not been refreshed, see
section 4.3.3.
This soft state behavior provides certain robustness for the system
ensuring that unused resources are not reserved for long time.
Resources can be removed by an explicit release at any time. However,
in the situation that an end-to-end (tear) RESERVE is retransmitted,
see Section 5.2.4 in [QoS-NSLP], then this message MUST NOT initiate
an intra-domain (tear) RESERVE message. This is because the amount
bandwidth within the RMD domain associated with the (tear) end-to-end
RESERVE has already been released and therefore, this amount of
bandwidth within the RMD domain MUST NOT once again be released.
When the RMD-RMF of a QNE edge or QNE Interior node processes a
"PHR_Release_Request" PHR container it MUST identify the
<PHB Class> parameter and estimate the time period that elapsed
after the previous refresh, see also Section 3 of [CsTa05].
This MAY be done by indicating the time lag, say "T_lag", between the
last sent "PHR_Refresh_Update" and the "PHR_Release_Request" control
information container by the QNE Ingress node, see [RMD1] and
[CsTa05] for more details. The value of "T_Lag"
is first normalized to the length of the refresh period, say
"T_period". The ratio between the "T_Lag" and the length of the
refresh period, "T_period", is calculated. This ratio is then
introduced into the <Time Lag> field of the "PHR_Release_Request".
When the above mentioned procedure of indicating the "T_lag" is used
and when a node (QNE Egress or QNE Interior) receives the
"PHR_Release_Request" PHR container, it MUST store the arrival
time. Then it MUST calculate the time difference, "Tdiff", between
the arrival time and the start of the current refresh period,
"T_period". Furthermore, this node MUST derive the value of the
"T_Lag", from the <Time Lag> parameter. "T_Lag" can be found by
multiplying the value included in the <Time Lag> parameter with the
length of the refresh period, "T_period". If the derived time lag,
"T_lag", is smaller than the calculated time difference, "T_diff",
then this node MUST decrease the PHB reservation state with the
number of resource units indicated in the "Peak Data Rate-1 (p)"
field of the local RMD-QSpec <TMOD-1> parameter of the RMD-QOSM <QoS
Desired> that has been sent together with the "PHR_Release_Request"
"PHR Container", but not below zero.
Bader, et al. [Page 50]
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An RMD specific release procedure can be triggered by an end-to-end
RESERVE with a TEAR flag set ON (see Section 4.6.1.5.1) or it can be
triggered by either an intra-domain RESPONSE, an end-to-end RESPONSE
or an end-to-end NOTIFY message that includes a marked (i.e., PDR
<M> and/or PDR <S> parameters are set ON) "PDR_Reservation_Report" or
"PDR_Congestion_Report" and/or an INFO_SPEC object.
4.6.1.5.1. Triggered by a RESERVE message
This RMD explicit release procedure can be triggered by a tear (TEAR
flag set ON) end-to-end RESERVE message. When a tear (TEAR flag
set ON) end-to-end RESERVE message arrives to the QNE Ingress
then the QNE Ingress node SHOULD process the message in a standard
QoS-NSLP way (see [QoS-NSLP]). In addition to this, the RMD RMF
is notified, as specified in [QoS-NSLP].
Same as for the scenario described in Section 4.6.1.1., a bypassing
procedure has to be initiated by the QNE Ingress node. The bypassing
procedure is performed according to the description given in Section
4.4. At the QNE Ingress the end-to-end RESERVE message is marked,
i.e., modifying the QoS-NSLP default NSLP-ID value to another NSLP-ID
predefined value that will be used by the GIST message that carries
the end-to-end RESERVE message to bypass the QNE Interior nodes.
Before generating an intra-domain tear RESERVE, the RMD-QOSM has to
release the requested RMD-QOSM bandwidth from the RMD traffic class
state maintained at the QNE Ingress.
This can be achieved by identifying the traffic class (PHB) and then
subtracting the amount of RMD traffic class requested resources,
included in the "Peak Data Rate-1 (p)" field of the local RMD-QSpec
<TMOD-1> parameter, from the total reserved amount of resources
stored in the RMD traffic class state. The <Time Lag> is used as
explained in the introductory part of Section 4.6.1.5.
QNE (Ingress) QNE (Interior) QNE (Interior) QNE (Egress)
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
RESERVE | | |
--->| | | RESERVE |
|------------------------------------------------------------>|
|RESERVE(RMD-QSpec:Tear=1) | |
|------------------->| | |
| |RESERVE(RMD-QSpec:Tear=1) |
| |------------------->| |
| | RESERVE(RMD-QSpec:Tear=1)
| | |------------------->|
| | | RESERVE
| | | |-->
Figure 11: Explicit release triggered by RESERVE used by the RMD-QOSM
Bader, et al. [Page 51]
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After that the REQUIRED bandwidth is released from the RMD-QOSM
traffic class state at the QNE Ingress, an intra-domain RESERVE (RMD-
QOSM) message has to be generated. The intra-domain RESERVE (RMD-
QSpec) message MUST include a "RMD QoS object combination" field and
a PHR container, (i.e., "PHR_Release_Request") and it MAY include a
PDR container, (i.e., PDR_Release_Request). An example of this
operation can be seen in Figure 11.
Most of the non default values of the objects contained in the
tear intra-domain RESERVE message are set by the QNE Ingress node in
the same way as described in Section 4.6.1.1. The following objects
are set differently (see QoS-NSLP-RMF API described in [QoS-NSLP]):
* The <RII> object MUST NOT be included in this message. This is
because the QNE Ingress node does not need to receive a
response from the QNE Egress node;
* If the release procedure is not applied for the RMD modification
of aggregated reservation procedure, see Section 4.6.1.4, then
the TEAR flag MUST be set to ON;
* the PHR resource units MUST be included into the "Peak Data Rate-1
(p)" value of the local RMD-QSpec <TMOD-1> parameter of the RMD-
QOSM <QoS Desired>;
* the value of the <Admitted Hops> parameter MUST be set to "1";
* the value of the <Time Lag> parameter of the PHR container is
calculated by the RMD-QOSM functionality (see 4.6.1.5) the value
of the <Control Type> parameter of PHR container is set to "18"
(i.e., PHR_Release_Request).
Any QNE Interior node that receives the combination of the RMD-
QOSM <Qos Desired> object and the "PHR_Release_Request" control
information container MUST identify the traffic class (PHB)
and release the requested resources included in the "Peak Data Rate-1
(p)" value of the local RMD-QSpec <TMOD-1> parameter. This can be
achieved by subtracting the amount of RMD traffic class requested
resources, included in the "Peak Data Rate-1 (p)" field of the local
RMD-QSpec <TMOD-1> parameter, from the total reserved amount of
resources stored in the RMD traffic class state. The value of the
<Time Lag> parameter of the "PHR_Release_Request" container is used
during the release procedure as explained in the introductory part of
Section 4.6.1.5.
The intra-domain tear RESERVE (RMD-QSpec) message is received and
processed by the QNE Egress node. The RMD-QOSM <QoS Desired>) and
the "PHR RMD-QOSM control" container (and if available the "PDR
Container") are read and processed by the RMD QoS node.
The value of the "Peak Data Rate-1 (p)" field of the local RMD-QSpec
<TMOD-1> parameter of the RMD-QOSM <QoS Desired> and the value of the
<Time Lag> field of the PHR container MUST be used by the RMD release
procedure.
Bader, et al. [Page 52]
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This can be achieved by subtracting the amount of RMD
traffic class requested resources, included in the "Peak Data Rate-1
(p)" field value of the local RMD-QSpec <TMOD-1> parameter, from the
total reserved amount of resources stored in the RMD traffic class
state.
The end-to-end RESERVE message is forwarded by the next hop (i.e.,
the QNE Egress) only if the intra-domain tear RESERVE (RMD-QSpec)
message arrives at the QNE Egress node. Furthermore, the QNE Egress
MUST stop the marking process that was used to bypass the QNE
Interior nodes by reassigning the QoS-NSLP default NSLP-ID value to
the end-to-end RESERVE message, see Section 4.4.
Note that when the QNE edges maintain aggregated QoS-NSLP reservation
states the RMD-QOSM functionality MAY start a RMD modification
procedures (see Section 4.6.1.4.) that uses the explicit release
procedure described above, in this subsection. Note that if the
complete bandwidth associated with the aggregated reservation
maintained at the QNE ingress has to be released then the TEAR flag
MUST be set to ON. Otherwise, the TEAR flag MUST be set to OFF, see
Section 4.6.1.4.
4.6.1.5.2 Triggered by a marked RESPONSE or NOTIFY message
This RMD explicit release procedure can be triggered by either an
intra-domain RESPONSE message with a PDR container carrying among
others the <M> and <S> parameters with values <M>=1 and <S>=0 (see
Section 4.6.1.2) an intra-domain (refresh) RESPONSE message carrying
a PDR Container with <M>=1 and <S>=1 (see Section 4.6.1.6.1) or an
end to end NOTIFY message (see Section 4.6.1.6.) with an INFO_SPEC
object with the following values:
Error Severity Class: Informational
Error Code value: Congestion situation
When the aggregated intra-domain QoS-NSLP operational states are used
then an end-to-end NOTIFY message used to trigger an RMD release
procedure MAY contain a PDR container that carries a <M> and a <S>
with values <M>=1 and <S>=1, and a bandwidth value in the <PDR
Bandwidth> parameter included in a "PDR_Refresh_Report" or
"PDR_Congestion_Report" container.
Note that in all explicit release procedures, before generating an
intra-domain tear RESERVE, the RMD-QOSM has to release the requested
RMD-QOSM bandwidth from the RMD traffic class state maintained at the
QNE Ingress. This can be achieved by identifying the traffic class
(PHB) and then subtracting the amount of RMD traffic class requested
resources, included in the "Peak Data Rate-1 (p)" field of the
local RMD-QSpec <TMOD-1> parameter, from the total reserved amount of
resources stored in the RMD traffic class state.
Bader, et al. [Page 53]
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Figure 12 shows the situation that the intra-domain tear RESERVE is
generated after being triggered by either an intra-domain (refresh)
RESPONSE message that carries a PDR Container with <M>=1 and <S>=1,
or by an end-to-end NOTIFY message that do not carry a PDR container,
but an INFO_SPEC object. The error code values carried by this NOTIFY
message are:
Error Severity Class: Informational
Error Code value: Congestion situation
Most of the non-default values of the objects contained in the
tear intra-domain RESERVE(RMD-QSpec) message are set by the QNE
Ingress node in the same way as described in Section 4.6.1.1.
The following objects MUST be used and/or set differently (see
QoS-NSLP-RMF described in [QoS-NSLP]):
* The value of the <M> parameter of the PHR container MUST be set
to "1".
* the value of the <S> parameter of the
"PHR container" MUST be set to "1".
* The RESERVE message MAY include a PDR container. Note that this
is needed if bi-directional scenario is used, see Section 4.6.2.
QNE (Ingress) QNE (Interior) QNE (Interior) QNE (Egress)
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
| NOTIFY | | |
|<-------------------------------------------------------|
|RESERVE(RMD-QSpec:Tear=1,M=1,S=1) | |
| ---------------->|RESERVE(RMD-QSpec:Tear=1, M=1,S=1) |
| | | |
| |----------------->| |
| | RESERVE(RMD-QSpec:Tear=1, M=1,S=1)
| | |----------------->|
Figure 12: Basic operation during RMD explicit release procedure
triggered by NOTIFY used by the RMD-QOSM.
Note that if the values of the <M> and <S> parameters included in the
PHR container carried by a intra-domain tear RESERVE(RMD-QOSM) are
set as ((<M>=0 and <S>=1) or (<M>=0 and <S>=0) or (<M>=1 and <S>=1))
then the <Max Admitted Hops> value SHOULD NOT be compared to the
<Admitted Hops> value and the value of the <K> field MUST NOT be set.
Any QNE edge or QNE Interior node that receives the intra-domain tear
RESERVE it MUST check the <K> field included in the PHR Container. If
the <K> fied is "0" then the traffic class state (PHB) has to be
identified, using the <PHB Class> parameter, and the the requested
resources included in the "Peak Data Rate-1 (p)" field of the
local RMD-QSpec <TMOD-1> parameter have to be released.
Bader, et al. [Page 54]
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This can be achieved by subtracting the amount of RMD traffic class
requested resources, included in the "Peak Data Rate-1 (p)" field of
the local RMD-QSpec <TMOD-1> parameter, from the total reserved
amount of resources stored in the RMD traffic class state. The value
of the <Time Lag> parameter of the PHR field is used during the
release procedure as explained in the introductory part of Section
4.6.1.5. Afterwards, the QNE Egress node MUST terminate the tear
intra-domain RESERVE(RMD-QSpec) message.
The RMD specific release procedure that is triggered by an
intra-domain RESPONSE message with <M>=1 and <S>=0 PDR container (see
Section 4.6.1.2) generates an intra-domain tear RESERVE message
that uses the combination of <Max Admitted Hops> and <Admitted_Hops>
fields to calculate and specify when the <K> value carried by the
"PHR Container" can be set. When the <K> field is set, then the "PHR
Container" and the RMD-QOSM <QoS Desired> carried by an intra-domain
tear RESERVE MUST NOT be processed.
The RMD specific explicit release procedure that uses the combination
of <Max Admitted Hops>, <Admitted_Hops> and <K> fields to release
resources/bandwidth in only a part of the RMD domain, is denoted as
RMD partial release procedure.
This explicit release procedure can be used, for example, during
unsuccessful reservation (see Section 4.6.1.2). When the RMD-
QoSM/QoS-NSLP signaling model functionality of a QNE Ingress node
receives a PDR container with values <M>=1 and <S>=0, of type
"PDR_Reservation_Report", it MUST start an RMD partial release
procedure.
In this situation, after that the REQUIRED bandwidth is released from
the RMD-QOSM traffic class state at the QNE Ingress, an intra-domain
RESERVE (RMD-QOSM) message has to be generated. An example of this
operation can be seen in Figure 13.
Most of the non-default values of the objects contained in the
tear intra-domain RESERVE(RMD-QSpec) message are set by the QNE
Ingress node in the same way as described in Section 4.6.1.1.
The following objects MUST be used and/or set differently:
* The value of the <M> parameter of the PHR container MUST be set
to "1".
* The RESERVE message MAY include a PDR container.
* the value of the <Max Admitted Hops> carried by the "PHR
Container" MUST be set equal to the <Max Admitted Hops> value
carried by the "PDR Container" (with <M>=1 and <S.=0) carried by
the received intra-domain RESPONSE message that triggers the
release procedure.
Any QNE edge or QNE Interior node that receives the intra-domain tear
RESERVE has to check the value of the <K> field in the "PHR
Container" before releasing the requested resources.
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If the value of the <K> field is "1", then all the QNEs located
downstream, including the QNE Egress, MUST NOT process the carried
"PHR Container" and the RMD-QOSM <QoS Desired> object by the intra-
domain tearing RESERVE.
QNE (Ingress) QNE (Interior) QNE (Interior) QNE (Egress)
Node that marked
PHR_Resource_Request
<PHR> object
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
| | | |
| RESPONSE (RMD-QSpec: M=1) | |
|<------------------------------------------------------------|
RESERVE(RMD-QSpec: Tear=1, M=1, <Admit Hops>=<Max Admitted Hops>, K=0)
|------------------->| | |
| |RESERVE(RMD-QSpec: Tear=1, M=1, K=1) |
| |------------------>| |
| | RESERVE(RMD-QSpec: Tear=1, M=1, K=1)|
| | |------------------->|
| | | |
Figure 13: Basic operation during RMD explicit release procedure
Triggered by RESPONSE used by the RMD-QOSM
If the <K> field value is "0", any QNE edge or QNE Interior node that
receives the intra-domain tear RESERVE can release the resources by
subtracting the amount of RMD traffic class requested resources,
included in the "Peak Data Rate-1 (p)" field of the local RMD-QSpec
<TMOD-1> parameter, from the total reserved amount of resources
stored in the RMD traffic class state. The value of the <Time Lag>
parameter of the PHR field is used during the release procedure as
explained in the introductory part of Section 4.6.1.5.
Furthermore, the QNE MUST perform the following procedures.
If the values of the <M> and <S> parameters included in the
"PHR_Release_Request" PHR container are (<M=1> and <S>=0) then the
<Max Admitted Hops> value MUST be compared with the calculated
<Admitted Hops> value. Note that each time that the intra-domain
tear RESERVE is processed and before being forwarded by a QNE, the
<Admitted Hops> value included in the PHR container is increased by
one.
When these two values are equal then the intra-domain
RESERVE(RMD-QSpec) that is forwarded further towards the QNE Egress
MUST set the <K> value of the carried "PHR Container" to "1".
The reason of doing this is that the QNE node that is currently
processing this message was the last QNE node that successfully
processed the RMD-QOSM <QoS Desired>) and PHR container of its
associated initial reservation request (i.e., initial intra-domain
RESERVE(RMD-QSpec) message). Its next QNE downstream node was unable
to successfully process the initial reservation request, therefore,
this QNE node marked the <M> and <Hop_U> parameters of the
"PHR_Resource_Request".
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Note that finally the QNE Egress node MUST terminate the intra-domain
RESERVE(RMD-QSpec) message.
Morover, note that the above described RMD partial release procedure
applies to the situation that the QNE edges maintain a per flow QoS-
NSLP reservation state.
When the QNE edges maintain aggregated intra-domain QoS-NSLP
operational states and a severe congestion occurs, then the QNE
Ingress MAY receive an end to end NOTIFY message (see Section
4.6.1.6.) with a PDR container that carries the <M>=0 and <S>=1
fields and a bandwidth value in the <PDR Bandwidth> parameter
included in a "PDR_Congestion_Report" container. Furthermore the
same end-to-end NOTIFY message carries an INFO_SPEC object with the
following values:
Error Severity Class: Informational
Error Code value: Congestion situation
The end-to-end session associated with this NOTIFY message maintains
the BOUND_SESSION_ID of the bound aggregated session, see Sections
4.3.1. The RMD-QOSM at QNE Ingress MUST start a RMD modification
procedures (see Section 4.6.1.4) that uses the RMD explicit release
procedure described above in this section. In particular, the RMD
explicit release procedure releases the bandwidth value included in
the <PDR Bandwidth> parameter, within the "PDR_Congestion_Report"
container, from the reserved bandwidth associated with the aggregated
intra-domain QoS-NSLP operational state.
4.6.1.6. Severe congestion handling
This section describes the operation of the RMD-QOSM when a severe
congestion occurs within the Diffserv domain.
When a failure in a communication path, e.g., a router or a link
failure occurs, the routing algorithms will adapt to failures by
changing the routing decisions to reflect changes in the topology and
traffic volume. As a result, the re-routed traffic will follow a new
path, which MAY result in overloaded nodes as they need to support
more traffic. This MAY cause severe congestion in the communication
path. In this situation the available resources, are not enough to
meet the REQUIRED QoS for all the flows along the new path.
Therefore, one or more flows SHOULD be terminated, or forwarded in a
lower priority queue.
Interior nodes notify edge nodes by data marking or marking the
refresh messages.
4.6.1.6.1 Severe congestion handling by the RMD-QOSM refresh procedure
This procedure applies to all RMD scenarios that use a RMD refresh
procedure. The QoS-NSLP and RMD are able to cope with congested
situations using the refresh procedure, see Section 4.6.1.3.
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If the refresh is not successful in an QNE Interior node, edge nodes
are notified by setting <S>=1 (<M>=1) marking the refresh messages
and by setting the <O> field in the "PHR_Refresh_Update" container,
carried by the intra-domain RESERVE message.
Note that the overload situation can be detected by using the example
given in appendix A.1.1. In this situation, when the given
signaled_overload_rate parameter given in appendix A.1.1 is higher
than 0 then the value of the <Overload> field is set to "1".
The calculation of this is given in appendix A.1.1 and denoted
as the signaled_overload_rate parameter. The flows can be terminated
by the RMD release procedure described in Section 4.6.1.5.
The intra-domain RESPONSE message that is sent by the QNE Egress
towards QNE Ingress will contain a PDR container with a Container ID
=26, i.e., "PDR_Congestion_Report". The values of the <M>, <S> and
<O> fields of this container SHOULD be set equal to the values of the
<M>, <S> and <O> fields, respectively, carried by the
"PHR_Refresh_Update" container. Part of the flows, corresponding to
the <O>, are terminated, or forwarded in a lower priority queue.
The flows can be terminated by the RMD release procedure described in
Section 4.6.1.5.
Furthermore, note that the above functionalities apply also for the
scenario where the QNE Edge nodes maintain either per flow QoS-NSLP
reservation states or aggregated QoS-NSLP reservation states.
In general, relying on the soft state refresh mechanism solves the
congestion within the time frame of the refresh period. If this
mechanism is not fast enough additional functions SHOULD be used,
which are described in Section 4.6.1.6.2.
4.6.1.6.2 Severe congestion handling by proportional data packet marking
This severe congestion handling method requires the following
functionalities.
4.6.1.6.2.1 Operation in the Interior nodes
The detection and marking/remarking functionality described in this
section applies to NSIS aware, but also to NSIS unaware nodes. This
means however, that the "not NSIS aware" nodes MUST be configured
such that they can detect the congestion/severe congestion situations
and remark packets in the same way as the "NSIS aware" nodes do.
The Interior node detecting severe congestion remarks data packets
passing the node. For this remarking, two additional DSCPs can be
allocated for each traffic class. One DSCP MAY be used to indicate
that the packet passed a congested node. This type of DSCP is denoted
in this document as "affected DSCP" and is used to indicate that a
packet passed through a severe congested node.
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The use of this DSCP type eliminates the possibility that, due to
e.g. flow-based ECMP (Equal Cost Multiple Paths) enabled routing, the
egress node either does not detect packets passed a severe congested
node or erroneously detects packets that actually did not pass the
severe congested node. Note that this type of DSCP MUST only be used
if all the nodes within the RMD domain are configured to use it.
Otherwise, this type of DSCP MUST NOT be applied. The other DSCP MUST
be used to indicate the degree of congestion by marking the bytes
proportionally to the degree of congestion. This type of DSCP is
denoted in this document as "encoded DSCP".
Note that in this document the terms marked packets or marked bytes
refer to the "encoded DSCP". The terms unmarked packets or unmarked
bytes are representing the packets or the bytes belonging to these
packets that their DSCP is either the "affected DSCP" or the original
DSCP. Furthermore, in the algorithm described below it is considered
that the router MAY drop received packets. The counting/measuring of
marked or unmarked bytes described in this section is accomplished
within measurement periods. All nodes within a RMD domain use the
same, fixed measurement interval, say T seconds, which MUST be
pre-configured.
It is RECOMMENDED that the total number of additional (local and
experimental) DSCPs needed for severe congestion handling within an
RMD domain SHOULD be as low as possible and it SHOULD NOT exceed the
limit of 8. One possibility to reduce the number of used DSCPs is to
use only the "encoded DSCP" and not to use "affected DSCP" marking.
Another possible solution is for example, to allocate one DSCP for
severe congestion indication for each of the AF classes that can be
supported by RMD-QOSM.
An example of a remarking procedure can be found in Appendix A.1.1.
4.6.1.6.2.2 Operation in the Egress nodes
When the QNE edges maintain a per flow intra-domain QoS-NSLP
operational state, see sections 4.3.2, 4.3.3, then the following
procedure is followed. The QNE Egress node applies a predefined
policy to solve the severe congestion situation, by selecting a
number of inter-domain (end-to-end) flows that SHOULD be terminated,
or forwarded in a lower priority queue.
When the RMD domain does not use the "affected DSCP"
marking then the egress MUST generate an ingress/egress pair
aggregated state, for each ingress and for each supported PHB. This
is because the edges MUST be able to detect in which ingress/egress
pair a severe congestion occurs. This is because otherwise the QNE
Egress will not have any information on which flows or groups of
flows were affected by the severe congestion.
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When the RMD domain supports the "affected DSCP" marking then the
egress is able to detect all flows that are affected by the severe
congestion situation. Therefore, when the RMD domain supports the
"affected DSCP" marking, then the Egress MAY not generate and
maintain the ingress/egress pair aggregated reservation States. Note
that these aggregated reservation states MAY not be associated with
aggregated intra-domain QoS-NSLP operational states.
The ingress/egress pair aggregated reservation state can be derived
by detecting, which flows are using the same PHB and are sent by the
same Ingress (via the per flow end-to-end QoS-NSLP states).
Some flows, belonging to the same PHB traffic class might get
other priority than other flows belonging to the same PHB traffic
class. This difference in priority can be notified to the egress and
ingress nodes either by the RESERVE message that carries the QSpec
associated with the end-to-end QoS model, e.g.,, <Preemption
Priority> & <Defending Priority> parameter, or by using a local
defined policy. The priority value is kept in the reservation states,
see Section 4.3, which might be used during admission control and/or
severe congestion handling procedures. The terminated flows are
selected from the flows having the same PHB traffic class as the PHB
of the marked (as "encoded DSCP") and "affected DSCP" (when applied
in the complete RMD domain) packets and (when the ingress/egress pair
aggregated states are available) that are belonging to the same
ingress/egress pair aggregate.
For flows associated with the same PHB traffic class the priority of
the flow plays a significant role. An example of calculating the
number of flows associated with each priority class that have to be
terminated is explained in Appendix A.1.2.
For the flows (sessions) that have to be terminated, the QNE Egress
node generates and sends an end-to-end NOTIFY message to the QNE
Ingress node (its upstream stateful QoS-NSLP peer) to indicate the
severe congestion in the communication path.
The non-default values of the objects contained in the NOTIFY
message MUST be set by the QNE Egress node as follows
(see QoS-NSLP-RMF API described in [QoS-NSLP]):
* the values of the <INFO_SPEC> object is set by the standard
QoS-NSLP protocol functions.
* the INFO_SPEC object MUST include information that notifies that
the end-to-end flow MUST be terminated. This information is as
follows:
Error Severity Class: Informational
Error Code value: Congestion situation
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When the QNE edges maintain a per aggregate intra-domain QoS-NSLP
operational state, see sections 4.3.1 then the QNE Edge has to
calculate, per each aggregate intra-domain QoS-NSLP operational
state, the total bandwidth that has to be terminated in order to
solve the severe congestion. The total to be released bandwidth is
calculated in the same way as in the situation that the QNE edges
maintain per flow intra-domain QoS-NSLP operational states.
Note that for the aggregated sessions that are affected, the QNE
Egress node generates and sends one end-to-end NOTIFY message to the
QNE Ingress node(its upstream stateful QoS-NSLP peer) to indicate the
severe congestion in the communication path. Note that this end-to-
end NOTIFY message is associated with one of the end-to-end sessions
that is bound to the aggregated intra-domain QoS-NSLP operational
state.
The non-default values of the objects contained in the NOTIFY
message MUST be set by the QNE Egress node in the same way as the
ones used by the end-to-end NOTIFY message described above for the
situation that the QNE Egress maintains a per flow intra-domain
operational state. In addition to this the end-to-end NOTIFY MUST
carry the RMD-Qspec, which contains a PDR container with a
Container ID =26, i.e., "PDR_Congestion_Report". The
value of the <S> SHOULD be set. Furthermore, the value of the <PDR
Bandwidth> parameter MUST contain the bandwidth, associated with the
aggregated QoS-NSLP operational state, which has to be released.
Furthermore, the number of end-to-end sessions that have to be
terminated will be calculated as in the situation that the QNE edges
maintain per flow intra-domain QoS-NSLP operational states. Similarly
for each, to be terminated, ongoing flow the egress will notify the
ingress in the same way as in the situation that the QNE edges
maintain per flow intra-domain QoS-NSLP operational states.
Note that QNE egress SHOULD restore the original DSCP
values of the remarked packets, otherwise multiple actions for the
same event might occur. However, this value MAY be left in its
remarking form if there is an SLA agreement between domains that a
downstream domain handles the remarking problem.
An example of a detailed severe congestion operation in the Egress
Nodes can be found in Appendix A.1.2.
4.6.1.6.2.3 Operation in the Ingress nodes
Upon receiving the (end-to-end) NOTIFY message, the QNE Ingress node
resolves the severe congestion by a predefined policy, e.g., by
refusing new incoming flows (sessions), terminating the affected and
notified flows (sessions), and blocking their packets or shifting
them to an alternative RMD traffic class (PHB).
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This operation is depicted in Figure 14, where the QNE Ingress, for
each flow (session) to be terminated, receives a NOTIFY message that
carries the "Congestion situation" error code.
When the QNE Ingress node receives the end-to-end NOTIFY message, it
associates this NOTIFY message with its bound intra-domain session,
see Sections 4.3.2, 4.3.3. via the BOUND_SESSION_ID information
included in the end-to-end per-flow QoS-NSLP state. The QNE Ingress
uses the operation described in Section 4.6.1.5.2 to terminate the
intra-domain session.
QNE (Ingress) QNE (Interior) QNE (Interior) QNE (Egress)
user | | | |
data | user data | | |
------>|----------------->| user data | user data |
| |---------------->S(# marked bytes) |
| | S----------------->|
| | S(# unmarked bytes)|
| | S----------------->|Term.
| NOTIFY S |flow?
|<-----------------|-----------------S------------------|YES
|RESERVE(RMD-QSpec:Tear=1,M=1,S=1) S |
| ---------------->|RESERVE(RMD-QSpec:T=1, M=1,S=1) |
| | S |
| |---------------->S |
| | RESERVE(RMD-QSpec:Tear=1, M=1,S=1)
| | S----------------->|
Figure 14: RMD severe congestion handling
Note that the above functionality applies to the RMD reservation-
Based, see Section 4.3.3 and to both measurement-based admission
control methods (i.e., congestion notification based on probing and
the NSIS measurement-based admission control), see Section 4.3.2.
In the case that the QNE edges support aggregated intra-domain QoS-
NSLP operational states the following actions take place. The QNE
Ingress MAY receive an end to end NOTIFY message with a PDR container
that carries a <S> marked and a bandwidth value in the <PDR
Bandwidth> parameter included in a "PDR_Congestion_Report" container.
Furthermore the same end-to-end NOTIFY message carries an INFO_SPEC
object with the "Congestion situation" error code.
When the QNE Ingress node receives this end-to-end NOTIFY message,
it associates the NOTIFY message with the aggregated intra-domain
QoS-NSLP operational state via the BOUND_SESSION_ID information
included in the end-to-end per-flow QoS-NSLP operational state, see
Section 4.3.1.
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The RMD-QOSM at the QNE Ingress node by using the
total to be released bandwidth value included in the <PDR Bandwidth>
parameter MUST reduce the bandwidth associated and reserved by the
RMD aggregated session. This is accomplished by triggering the RMD
modification for Aggregated reservations procedure described in
Section 4.6.1.4.
In addition to the above, the QNE Ingress MUST select a number of
inter-domain (end-to-end) flows (sessions) that MUST be terminated.
This is accomplished in the same way as in the situation that the QNE
edges maintain per flow intra-domain QoS-NSLP operational states.
The terminated end-to-end sessions are selected from the end-to-end
sessions bound to the aggregated intra-domain QoS-NSLP operational
state. Note that the end-to-end session associated with the received
end-to-end NOTIFY message that notified the severe congestion MUST
also be selected for termination.
For the flows (sessions) that have to be terminated, the QNE Ingress
node generates and sends an end-to-end NOTIFY message upstream
towards the sender (QNI). The values carried by this message are:
* the values of the <INFO_SPEC> object is set by the standard
QoS-NSLP protocol functions.
* the INFO_SPEC object MUST include information that notifies that
the end-to-end flow MUST be terminated. This information is as
follows:
Error Severity Class: Informational
Error Code value: Congestion situation
4.6.1.7 Admission control using congestion notification based on probing
The congestion notification function based on probing can be used to
implement a simple measurement-based admission control within a
Diffserv domain. At interior nodes along the data path congestion
notification thresholds are set in the measurement based admission
control function for the traffic belonging to different PHBs. These
interior nodes are not NSIS aware nodes.
4.6.1.7.1 Operation in Ingress nodes
When an end-to-end reservation request (RESERVE) arrives at the
Ingress node (QNE), see Figure 15, it is processed based on the
procedures defined by the end-to-end QoS model.
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The DSCP field of the GIST datagram message that is used to transport
this probe RESERVE message, SHOULD be marked with the same value of
DSCP as the data path packets associated with the same session. In
this way it is ensured that the end-to-end RESERVE (probe) packet
passed through the node that it is congested. This feature is very
useful when ECMP based routing is used to detect only flows that are
passing through the congested router.
When (end-to-end) RESPONSE message is received by the Ingress node,it
will be processed based on the procedures defined by the end-to-end
QoS model.
4.6.1.7.2 Operation in Interior nodes
These Interior nodes are not needed to be NSIS aware nodes and they
do not need to process NSIS functionality of NSIS messages. Note that
the "not NSIS aware" nodes MUST be configured such that they can
detect the congestion/severe congestion situations and remark packets
in the same way as the "NSIS aware" nodes do.
Using standard functionalities congestion notification thresholds are
set for the traffic belonging to different PHBs, see Section 4.3.2.
The end-to-end RESERVE message, see Figure 15, is used as a probe
packet.
The DSCP field of all data packets and of the GIST message carrying
the RESERVE message will be re-marked when the corresponding
"congestion notification" threshold is exceeded, see Section 4.3.2.
Note that when the data rate is higher than the congestion
notification threshold then also the data packets are remarked. An
example of the detailed operation of this procedure is given in
Appendix A.2.1.
4.6.1.7.3 Operation in Egress nodes
As emphasised in Section 4.6.1.6.2.2, the egress node, by using the
per flow end-to-end QoS-NSLP states, can derive which flows are using
the same PHB and are sent by the same ingress.
For each ingress, the egress SHOULD generate an ingress/egress pair
aggregated (RMF) reservation state for each supported PHB. Note that
this aggregated reservation state does not require that also an
aggregated intra-domain QoS-NSLP operational state is needed.
In Appendix A.2.2 an example is described how and when a (probe)
RESERVE message that arrives at the egress, is admitted or rejected.
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If the request is rejected then the Egress node SHOULD
generate an (end-to-end) RESPONSE message to notify that the
reservation is unsuccesfull. In particular it will generate an
INFO_SPEC object of:
Error Severity Class: Transient Failure
Error Code value: Reservation failure
The QSpec that was carried by the end to end RESERVE belonging to
the same session as this end to end RESPONSE is included in this
message. The parameters included in the QSpec <QoS Reserved> object
are copied from the original <QoS Desired> values. The "E" flag
associated with the <QoS Reserved> object and the "E" flag associated
with local RMD-QSpec <TMOD-1> parameter are also set. This RESPONSE
message will be sent to the Ingress node and it will be processed
based on the end-to-end QoS model.
Note that QNE egress SHOULD restore the original DSCP values of the
remarked packets, otherwise multiple actions for the same event might
occur. However, this value MAY be left in its remarking form if there
is an SLA agreement between domains that a downstream domain handles
the remarking problem. Note that the break "B" flag carried by the
end-to-end RESERVE message MUST NOT be set.
QNE (Ingress) Interior Interior QNE (Egress)
(not NSIS aware) (not NSIS aware)
user | | | |
data | user data | | |
------>|----------------->| user data | |
| |---------------->| user data |
| | |----------------->|
user | | | |
data | user data | | |
------>|----------------->| user data | user data |
| |---------------->S(# marked bytes) |
| | S----------------->|
| | S(# unmarked bytes)|
| | S----------------->|
| | S |
RESERVE | | S |
------->| | S |
|----------------------------------->S |
| | RESERVE(re-marked DSCP in GIST)
| | S----------------->|
| |RESPONSE(unsuccessful INFO-SPEC) |
|<------------------------------------------------------|
RESPONSE(unsuccessful INFO-SPEC) | |
<------| | | |
Figure 15: Using RMD congestion notification function for admission
control based on probing
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4.6.2 Bi-directional operation
This section describes the basic bidirectional operation and
sequence of events/triggers of the RMD-QOSM. The following basic
operation cases are distinguished:
* Successful and unsuccessful reservation (Section 4.6.2.1);
* Refresh reservation (Section 4.6.2.2);
* Modification of aggregated reservation (Section 4.6.2.3);
* Release procedure (Section 4.6.2.4);
* Severe congestion handling (Section 4.6.2.5);
* Admission control using congestion notification based on probing
(Section 4.6.2.6).
It is important to emphasize that the content of this section is used
for the specification of the following RMD-QOSM/QoS-NSLP signaling
schemes, when basic unidirectional operation is assumed:
* "per flow congestion notification based on probing";
* "per flow RMD NSIS measurement based admission control",
* "per flow RMD reservation based" in combination with "severe
congestion handling by the RMD-QOSM refresh procedure"
* "per flow RMD reservation based" in combination with "severe
congestion handling by proportional data packet marking"
* "per aggregate RMD reservation based" in combination with
"severe congestion handling by the RMD-QOSM refresh procedure"
* "per aggregate RMD reservation based" in combination with
"severe congestion handling by proportional data packet marking"
For more details, please see Section 3.2.3.
In particular, the described functionality described in Sections
4.6.2.1, 4.6.2.2, 4.6.2.3, 4.6.2.4, 4.6.2.5 applies to the RMD
reservation-based and to the NSIS measurement-based admission control
methods. The described functionality in Section 4.6.2.6 applies to
the admission control procedure that uses the congestion notification
based on probing. The QNE Edge nodes maintain either per flow QoS-
NSLP operational and reservation states or aggregated QoS-NSLP
operational and reservation states.
RMD-QOSM assumes that asymmetric routing MAY be applied in the RMD
domain. Combined sender-receiver initiated reservation cannot be
efficiently done in the RMD domain because upstream NTLP states are
not stored in Interior routers.
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Therefore, the bi-directional operation SHOULD be performed by two
sender-initiated reservations (sender&sender). We assume that the
QNE edge nodes are common for both upstream and downstream
directions, therefore, the two reservations/sessions can be bound at
the QNE edge nodes. Note that if this is not the case then the bi-
directional procedure could be managed and maintained by nodes
located outside the RMD domain, by using other procedures than the
ones defined in RMD-QOSM.
This (intra-domain) bi-directional sender&sender procedure can then
be applied between the QNE edges (QNE Ingress and QNE Egress) nodes
of the RMD QoS signaling model. In the situation a security
association exists between the QNE Ingress and QNE Egress nodes (see
Figure 15), and the QNE Ingress node has the REQUIRED "Peak Data
Rate-1 (p)" values of the local RMD-QSpec <TMOD-1> parameters for
both directions, i.e., QNE Ingress towards QNE Egress and QNE Egress
towards QNE Ingress, then the QNE Ingress MAY include both "Peak Data
Rate-1 (p)" values of the local RMD-QSpec <TMOD-1> parameters (needed
for both directions) into the RMD-QSpec within a RESERVE message. In
this way the QNE Egress node is able to use the QoS parameters needed
for the "Egress towards Ingress" direction (QoS-2). The QNE Egress
is then able to create a RESERVE with the right QoS parameters
included in the QSpec, i.e., RESERVE (QoS-2). Both directions of the
flows are bound by inserting <BOUND_SESSION_ID> objects at the QNE
Ingress and QNE Egress, which will be carried by bound end-to-end
RESERVE messages.
|------ RESERVE (QoS-1, QoS-2)----|
| V
| Interior/stateless QNEs
+---+ +---+
|------->|QNE|-----|QNE|------
| +---+ +---+ |
| V
+---+ +---+
|QNE| |QNE|
+---+ +---+
^ |
| | +---+ +---+ V
| |-------|QNE|-----|QNE|-----|
| +---+ +---+
Ingress/ Egress/
statefull QNE statefull QNE
|
<--------- RESERVE (QoS-2) -------|
Figure 16: The intra-domain bi-directional reservation scenario in
the RMD domain
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Note that it is RECOMMENDED that the QNE implementations of RMD-QOSM
process the QoS-NSLP signaling messages with a higher priority than
data packets. This can be accomplished as described in Section 3.3.4
in [QoS-NSLP] and the QoS-NSLP-RMF API [QoS-NSLP].
A bidirectional reservation, within the RMD domain, is indicated by
the PHR <B> and PDR <B> flags, which are set in all messages. In this
case two BOUND_SESSION_ID objects SHOULD be used.
When the QNE edges maintain per-flow intra-domain QoS-NSLP
operational states then the end-to-end RESERVE message carries two
BOUND_SESSION_IDs. One BOUND_SESSION_ID carries the SESSION_ID of the
tunneled intra-domain (per-flow) session that is using a BINDING_CODE
with value set to code (Tunneled and end-to-end sessions). Another
BOUND_SESSION_ID carries the SESSION_ID of the bound bidirectional
end-to-end session. The BINDING_CODE associated with this
BOUND_SESSION_ID is set to code (Bi-directional sessions).
When the QNE edges maintain aggregated intra-domain QoS-NSLP
operational states then the end-to-end RESERVE message carries two
BOUND_SESSION_IDs. One BOUND_SESSION_ID carries the SESSION_ID of the
tunneled aggregated intra-domain session that is using a BINDING_CODE
with value set to code (Aggregated sessions). Another
BOUND_SESSION_ID carries the SESSION_ID of the bound bidirectional
end-to-end session. The BINDING_CODE associated with this
BOUND_SESSION_ID is set to code (Bi-directional sessions).
The intra-domain and end-to-end QoS-NSLP operational states are
initiated/modified depending on the binding type, see Section 4.3.1,
4.3.2, 4.3.3.
If no security association exists between the QNE Ingress and QNE
Egress nodes the bi-directional reservation for the sender&sender
scenario in the RMD domain SHOULD use the scenario specified in
[QoS-NSLP] as "Bi-directional reservation for sender&sender
scenario". This is because in this scenario the RESERVE message sent
from QNE Ingress to QNE Egress does not have to carry the QoS
parameters needed for the "Egress towards Ingress" direction (QoS-2).
In the following sections it is considered that the QNE
edge nodes are common for both upstream and downstream directions
and therefore, the two reservations/sessions can be bound at the
QNE edge nodes. Furthermore, it is considered that a security
association exists between the QNE Ingress and QNE Egress nodes,
and the QNE Ingress node has the REQUIRED "Peak Data Rate-1 (p)"
value of the local RMD-QSpec <TMOD-1> parameters for both directions,
i.e., QNE Ingress towards QNE Egress and QNE Egress towards QNE
Ingress.
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According to Section 3.2.3 it is specified that only the "per flow
RMD reservation based" in combination with "severe congestion
handling by proportional data packet marking" scheme MUST be
implemented within one RMD domain. However, all RMD QNEs supporting
this specification MUST support the combination the "per flow RMD
reservation based" in combination with "severe congestion handling by
proportional data packet marking" scheme. If the RMD QNEs support
more RMD-QOSM schemes then the operator of that RMD domain MUST pre-
configure all the QNE edge nodes within one domain such that the
<SCH> field included in the "PHR container", see Section 4.1.2 and
the "PDR Container", see Section 4.1.3, will use always the same
value, such that within one RMD domain only one of the below
described RMD-QOSM schemes is used at a time.
All QNE nodes located within the RMD domain, MUST read and
interpret the <SCH> field included in the "PHR container" before
processing all the other "PHR container" payload fields.
Moreover, all QNE edge nodes located at the boarder of the RMD
domain, MUST read and interpret the <SCH> field included in the "PDR
container" before processing all the other "PDR container" payload
fields.
4.6.2.1 Successful and unsuccessful reservations
This section describes the operation of the RMD-QOSM where a RMD
Intra-domain bi-directional reservation operation, see Figure 16 and
Section 4.6.2, is either successfully or unsuccessfully accomplished.
The bi-directional successful reservation is similar to a
combination of two unidirectional successful reservations that are
accomplished in opposite directions, see Figure 17. The main
differences of the bi-directional successful reservation procedure
with the combination of two unidirectional successful reservations
accomplished in opposite directions are as follows. Note also that
the intra-domain and end-to-end QoS-NSLP operational states generated
and maintained by the end-to-end RESERVE messages contain, compared
to the unidirectional reservation scenario, a different
BOUND_SESSION_ID data structure, see Section 4.3.1, 4.3.2, 4.3.3.
In this scenario the intra-domain RESERVE message sent by the QNE
Ingress node towards the QNE Egress node, is denoted in Figure 17 as
RESERVE (RMD-QSpec): "forward". The main differences between the
intra-domain RESERVE (RMD-QSpec):"forward" message used for the bi-
directional successful reservation procedure and a RESERVE (RMD-
QSpec) message used for the unidirectional successful reservation are
as follows (see QoS-NSLP-RMF API described in [QoS-NSLP]):
* the RII object MUST NOT be included in the message. This is
because no RESPONSE message is REQUIRED.
* the <B> bit of the PHR container indicates a bi-directional
reservation and it MUST be set to "1".
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* the PDR container is also included into the RESERVE(RMD-QSpec):
"forward" message. The value of the Container ID is
"20", i.e., "PDR_Reservation_Request". Note that the response
PDR container sent by a QNE Egress to a QNE Ingress node is not
carried by an end-to-end RESPONSE message, but it is carried by an
intra-domain RESERVE message that is sent by the QNE Egress node
towards the QNE Ingress node (denoted in Figure 16 as
RESERVE(RMD-QSpec):"reverse").
* the <B> PDR bit indicates a bi-directional reservation and is set
to "1".
* the <PDR Bandwidth> field specifies the
requested bandwidth that has to be used by the QNE Egress node to
initiate another intra-domain RESERVE message in the reverse
direction.
The RESERVE(RMD-QSpec):"reverse" message is initiated by the QNE
Egress node at the moment that the RESERVE(RMD-QSpec):"forward"
message is successfully processed by the QNE Egress node.
The main differences between the RESERVE(RMD-QSpec):"reverse"
message used for the bi-directional successful reservation procedure
and a RESERVE(RMD-QSpec) message used for the unidirectional
successful reservation are as follows:
QNE (Ingress) QNE (int.) QNE (int.) QNE (int.) QNE (Egress)
NTLP stateful NTLP st.less NTLP st.less NTLP st.less NTLP stateful
| | | | |
| | | | |
|RESERVE(RMD-QSpec) | | |
|"forward" | | | |
| | RESERVE(RMD-QSpec): | |
|--------------->| "forward" | | |
| |------------------------------>| |
| | | |------------->|
| | | | |
| | |RESERVE(RMD-QSpec) |
| RESERVE(RMD-QSpec) | "reverse" |<-------------|
| "reverse" | |<--------------| |
|<-------------------------------| | |
Figure 17: Intra-domain signaling operation for successful
bi-directional reservation
* the RII object is not included in the message. This is because no
RESPONSE message is REQUIRED;
* the value of the "Peak Data Rate-1 (p)" field of the local RMD-
QSpec <TMOD-1> parameter is set equal to the value of the
<PDR Bandwidth> field included in the RESERVE(RMD-QSpec):"forward"
message that triggered the generation of this RESERVE(RMD-QSpec):
"reverse" message;
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* the <B> bit of the PHR container indicates a bi-directional
reservation and is set to "1";
* the PDR container is included into the
RESERVE(RMD-QSpec):"reverse" message. The value of the
Container ID is "23", i.e., "PDR_Reservation_Report";
* the <B> PDR bit indicates a bi-directional reservation and is
set to "1".
Figure 18 and Figure 19 show the flow diagrams used in case of a
unsuccessful bi-directional reservation. In Figure 18 it
is considered that the QNE that is not able to support the
requested "Peak Data Rate-1 (p)" value of local RMD-QSpec <TMOD-1>
is located in the direction QNE Ingress towards QNE Egress. In
Figure 19 it is considered that the QNE that is not able to support
the requested "Peak Data Rate-1 (p)" value of local RMD-QSpec
<TMOD-1> is located in the direction QNE Egress towards QNE Ingress.
The main differences between the bi-directional unsuccessful
procedure shown in Figure 18 and the bi-directional successful
procedure are as follows:
* the QNE node that is not able to reserve resources for a
certain request is located in the "forward" path, i.e., path
from QNE Ingress towards the QNE Egress.
* the QNE node that is not able to support the requested "Peak Data
Rate-1 (p)" value of local RMD-QSpec <TMOD-1> it MUST mark the <M>
bit, i.e., set to value "1", of the RESERVE(RMD-QSpec): "forward".
QNE(Ingress) QNE (int.) QNE (int.) QNE (int.) QNE (Egress)
NTLP stateful NTLP st.less NTLP st.less NTLP st.less NTLP stateful
| | | | |
|RESERVE(RMD-QSpec): | | |
| "forward" | RESERVE(RMD-QSpec): | |
|--------------->| "forward" | M RESERVE(RMD-QSpec):
| |--------------------------->M "forward-M marked"
| | | M-------------->|
| | RESPONSE(PDR) M |
| | "forward - M marked"M |
|<------------------------------------------------------------|
|RESERVE(RMD-QSpec, K=0) | M |
|"forward - T tear" | M |
|--------------->| | M |
| RESERVE(RMD-QSpec, K=1) M |
| | "forward - T tear" M |
| |--------------------------->M |
| | RESERVE(RMD-QSpec, K=1) |
| | "forward - T tear" |
| | M-------------->|
Figure 18: Intra-domain signaling operation for unsuccessful
bi-directional reservation (rejection on path QNE(Ingress)
towards QNE(Egress))
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The operation for this type of unsuccessful bi-directional
reservation is similar to the operation for unsuccessful uni-
directional reservation shown in Figure 9.
The main differences between the bi-directional unsuccessful
procedure shown in Figure 19 and the in bi-directional successful
procedure are as follows:
* the QNE node that is not able to reserve resources for a
certain request is located in the "reverse" path, i.e., path
from QNE Egress towards the QNE Ingress.
* the QNE node that is not able to support the requested
"Peak Data Rate-1 (p)" value of local RMD-QSpec <TMOD-1> it MUST
mark the <M> bit, i.e., set to value "1", the
RESERVE(RMD-QSpec):"reverse".
QNE (Ingress) QNE (int.) QNE (int.) QNE (int.) QNE (Egress)
NTLP stateful NTLP st.less NTLP st.less NTLP st.less NTLP stateful
| | | | |
|RESERVE(RMD-QSpec) | | |
|"forward" | RESERVE(RMD-QSpec): | |
|--------------->| "forward" | RESERVE(RMD-QSpec): |
| |-------------------------------->|"forward" |
| | RESERVE(RMD-QSpec): |------------->|
| | "reverse" | | |
| | RESERVE(RMD-QSpec) | |
| RESERVE(RMD-QSpec): M "reverse" |<-------------|
| "reverse - M marked" M<---------------| |
|<--------------------------------M | |
| | M | |
|RESERVE(RMD-QSpec, K=0): M | |
|"forward - T tear" M | |
|--------------->| RESERVE(RMD-QSpec, K=0): | |
| | "forward - T tear" | |
| |-------------------------------->| |
| | M |------------->|
| | M RESERVE(RMD-QSpec, K=0):
| | M reverse - T tear" |
| | M |<-------------|
| M RESERVE(RMD-QSpec, K=1) |
| | M "forward - T tear" |
| | M<---------------| |
| RESERVE(RMD-QSpec, K=1)M | |
| "forward - T tear" M | |
|<--------------------------------M | |
Figure 19: Intra-domain signaling normal operation for unsuccessful
bi-directional reservation (rejection on path QNE(Egress)
towards QNE(Ingress)
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* the QNE Ingress uses the information contained in the received
PHR and PDR containers of the RESERVE(RMD-QSpec): "reverse" and
generates a tear intra-domain RESERVE(RMD-QSpec):
"forward - T tear" message. This message carries a
"PHR_Release_Request" and a "PDR_Release_Request" control
information. This message is sent to QNE Egress node.
The QNE Egress node uses the information contained in the
"PHR_Release_Request" and the "PDR_Release_Request" control
info containers to generate a RESERVE(RMD-QSpec):"reverse - T
tear" message that is sent towards the QNE Ingress node.
4.6.2.2 Refresh reservations
This section describes the operation of the RMD-QOSM where a RMD
intra-domain bi-directional refresh reservation operation is
accomplished.
The refresh procedure in case of RMD reservation-based method
follows a similar scheme as the successful reservation procedure,
described in Section 4.6.2.1, and depicted in Figure 17 and the
way of how the refresh process of the reserved resources is
maintained, is similar to the refresh process used for the intra-
domain uni-directional reservations (see Section 4.6.1.3).
Note that the RMD traffic class refresh periods used by the bound bi-
directional sessions MUST be equal in all QNE edge and QNE Interior
nodes.
The main differences between the RESERVE(RMD-QSpec):"forward"
message used for the bi-directional refresh procedure
and a RESERVE(RMD-QSpec):"forward" message used for the bi-
directional successful reservation procedure are as follows:
* the value of the Container ID of the PHR container is
"19", i.e., "PHR_Refresh_Update".
* the value of the Container ID of the PDR container is
"21", i.e., "PDR_Refresh_Request".
The main differences between the RESERVE(RMD-QSpec):"reverse"
message used for the bi-directional refresh procedure and the RESERVE
(RMD-QSpec): "reverse" message used for the bi-directional successful
reservation procedure are as follows:
* the value of the Container ID of the PHR container is
"19", i.e., "PHR_Refresh_Update".
* the value of the Container ID of the PDR container is
"24", i.e., "PDR_Refresh_Report".
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4.6.2.3 Modification of aggregated intra-domain QoS-NSLP operational
reservation states
This section describes the operation of the RMD-QOSM where RMD
intra-domain bi-directional QoS-NSLP aggregated reservation states
have to be modified.
In the case when the QNE edges maintain, for the RMD QoS model,
QoS-NSLP aggregated reservation states and if such an aggregated
reservation has to be modified (see Section 4.3.1) then similar
procedures to Section 4.6.1.4. are applied. In particular:
* When the modification request requires an increase of the reserved
resources, the QNE Ingress node MUST include the corresponding value
into the "Peak Data Rate-1 (p)" field local RMD-QSpec <TMOD-1>
parameter of the RMD-QOSM <QoS Desired>), which is sent together with
a "PHR_Resource_Request" control information. If a QNE edge or QNE
Interior node is not able to reserve the number of requested
resources, then the "PHR_Resource_Request" associated with the
local RMD-QSpec <TMOD-1> parameter MUST be marked. In this situation
the RMD specific operation for unsuccessful reservation will be
applied (see Section 4.6.2.1). Note that the value of the
<PDR Bandwidth> parameter, which is sent within a
"PDR_Reservation_Request" container, represents the increase of the
reserved resources in the "reverse" direction.
* When the modification request requires a decrease of the
reserved resources, the QNE Ingress node MUST include this value
into the "Peak Data Rate-1 (p)" field of the local RMD-QSpec <TMOD-1>
parameter of the RMD-QOSM <QoS Desired>). Subsequently an RMD release
procedure SHOULD be accomplished (see Section 4.6.2.4). Note that the
value of the <PDR Bandwidth> parameter, which is sent within a
"PDR_Release_Request" container, represents the decrease of the
reserved resources in the "reverse" direction.
4.6.2.4 Release procedure
This section describes the operation of the RMD-QOSM where a RMD
intra-domain bi-directional reservation release operation is
accomplished. The message sequence diagram used in this procedure is
similar to the one used by the successful reservation procedures,
described in Section 4.6.2.1, and depicted in Figure 17. However, the
way of how the release of the reservation is accomplished, is similar
to the RMD release procedure used for the intra-domain uni-
directional reservations (see Section 4.6.1.5 and Figure 18 and
Figure 19).
The main differences between the RESERVE (RMD-QSpec):
"forward" message used for the bi-directional release procedure
and a RESERVE (RMD-QSpec): "forward" message used for the bi-
directional successful reservation procedure are as follows:
* the value of the Container ID of the PHR container is
"18", i.e."PHR_Release_Request";
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INTERNET-DRAFT RMD-QOSM
* the value of the Container ID of the PDR container is
"22", i.e., "PDR_Release_Request";
The main differences between the RESERVE (RMD-QSpec): "reverse"
message used for the bi-directional release procedure and the RESERVE
(RMD-QSpec): "reverse" message used for the bi-directional successful
reservation procedure are as follows:
* the value of the Container ID of the PHR container is
"18", i.e., "PHR_Release_Request";
* the PDR container is not included in the RESERVE (RMD-QSpec):
"reverse" message.
4.6.2.5 Severe congestion handling
This section describes the severe congestion handling operation used
in combination with RMD intra-domain bi-directional reservation
procedures. This severe congestion handling operation is similar to
the one described in Section 4.6.1.6.
4.6.2.5.1 Severe congestion handling by the RMD-QOSM bi-directional
refresh procedure
This procedure is similar to the severe congestion handling procedure
described in Section 4.6.1.6.1. The difference is related to how the
refresh procedure is accomplished, see Section 4.6.2.2 and to how the
flows are terminated, see Section 4.6.2.4.
4.6.2.5.2 Severe congestion handling by proportional data packet marking
This section describes the severe congestion handling by proportional
data packet marking when this is combined with a RMD intra-domain
bi-directional reservation procedure. Note that the detection and
marking/remarking functionality described in this section and used by
Interior nodes, applies to NSIS aware, but also to NSIS unaware
nodes. This means however, that the "not NSIS aware" Interior nodes
MUST be configured such that they can detect the congestion
situations and remark packets in the same way as the Interior "NSIS
aware" nodes do.
This procedure is similar to the severe congestion handling procedure
described in Section 4.6.1.6.2. The main difference is related to the
location of the severe congested node, i.e. "forward" or "reverse"
path. Note that when a severe congestion situation occurs on
e.g. on a forward path, and flows are terminated to solve the severe
congestion in forward path, then the reserved bandwidth associated
with the terminated bidirectional flows will also be released.
Therefore, a careful selection of the flows that have to be
terminated SHOULD take place. An example of such a selection is
given in Appendix A.3.1.
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Furthermore, a special case of this operation is associated to the
severe congestion situation occurring simultaneously on the forward
and reverse paths. An example of this operation is given in Appendix
A.3.2.
Simulation results associated with these procedures can be found in
[DiKa08].
QNE(Ingress) QNE (int.) QNE (int.) QNE (int.) QNE (Egress)
NTLP stateful NTLP st.less NTLP st.less NTLP st.less NTLP stateful
user| | | | |
data| user | | | |
--->| data | user data | |user data |
|--------------->| | S |
| |--------------------------->S (#marked bytes)
| | | S-------------->|
| | | S(#unmarked bytes)
| | | S-------------->|Term
| | | S |flow?
| | NOTIFY (PDR) S |YES
|<------------------------------------------------------------|
|RESERVE(RMD-QSpec) | S |
|"forward - T tear" | S |
|--------------->| | RESERVE(RMD-QSpec):|
| |--------------------------->S"forward - T tear"
| | | S-------------->|
| | | RESERVE(RMD-QSpec): |
| | | "reverse - T tear" |
| RESERVE(RMD-QSpec): | |<--------------|
|"reverse - T tear" |<-------------S |
|<-----------------------------| S |
Figure 20: Intra-domain RMD severe congestion handling for
bi-directional reservation (congestion on path QNE(Ingress)
towards QNE(Egress))
Figure 20 shows the scenario where the severe congested node is
located in the "forward" path. The QNE Egress node has to generate an
end-to-end NOTIFY(PDR) message. In this way the QNE Ingress will be
able to receive the (#marked and #unmarked) that were measured by the
QNE Egress node on the congested "forward path". Note that in this
situation it is assumed that the "reverse path" is not congested.
This scenario is very similar to the
severe congestion handling scenario described in Section 4.6.1.6.2
and shown in Figure 14. The difference is related to the release
procedure, which is accomplished in the same way as described in
Section 4.6.2.4.
Figure 21 shows the scenario where the severe congested node is
located in the "reverse" path. Note that in this situation it is
assumed that the "forward path" is not congested. The main difference
between this scenario and the scenario shown in Figure 20 is that no
end-to-end NOTIFY(PDR) message has to be generated by the QNE Egress
node.
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This is because now the severe congestion occurs on the "reverse
path" and the QNE Ingress node receives the (#marked and #unmarked)
user data passing through the severely congested "reverse path". The
QNE Ingress node will be able to calculate the number of flows that
have to be terminated or forwarded in a lower priority queue.
QNE (Ingress) QNE (int.) QNE (int.) QNE (int.) QNE (Egress)
NTLP stateful NTLP st.less NTLP st.less NTLP st.less NTLP stateful
user| | | | |
data| user | | | |
--->| data | user data | |user data |
|--------------->| | | |
| |--------------------------->|user data |user
| | | |-------------->|data
| | | | |--->
| | | user | |<---
| user data | | data |<--------------|
| (#marked bytes)| S<----------| |
|<--------------------------------S | |
| (#unmarked bytes) S | |
Term|<--------------------------------S | |
Flow? | S | |
YES |RESERVE(RMD-QSpec): S | |
|"forward - T tear" s | |
|--------------->| RESERVE(RMD-QSpec): | |
| | "forward - T tear" | |
| |--------------------------->| |
| | S |-------------->|
| | S RESERVE(RMD-QSpec):
| | S "reverse - T tear" |
| RESERVE(RMD-QSpec) S |<--------------|
| "reverse - T tear" S<----------| |
|<--------------------------------S | |
Figure 21: Intra-domain RMD severe congestion handling for
bi-directional reservation (congestion on path QNE(Egress)
towards QNE(Ingress)
For the flows that have to be terminated a release procedure, see
Section 4.6.2.4, is initiated to release the reserved resources
on the "forward" and "reverse" paths.
4.6.2.6 Admission control using congestion notification based on
probing
This section describes the admission control scheme that uses the
congestion notification function based on probing when RMD
intra-domain bi-directional reservations are supported.
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QNE(Ingress) Interior QNE (int.) Interior QNE (Egress)
NTLP stateful not NSIS aware not NSIS aware not NSIS aware NTLP stateful
user| | | | |
data| | | | |
--->| | user data | |user data |
|-------------------------------------------->S (#marked bytes)
| | | S-------------->|
| | | S(#unmarked bytes)
| | | S-------------->|
| | | S |
| | RESERVE(re-marked DSCP in GIST)):|
| | | S |
|-------------------------------------------->S |
| | | S-------------->|
| | | S |
| | RESPONSE(unsuccessful INFO-SPEC) |
|<------------------------------------------------------------|
| | | S |
Figure 22: Intra-domain RMD congestion notification based on probing
for bi-directional admission control (congestion on path
from QNE(Ingress) towards QNE(Egress))
This procedure is similar to the congestion notification for
admission control procedure described in Section 4.6.1.7. The main
difference is related to the location of the severe congested node,
i.e., "forward" path (i.e., path between QNE Ingress towards QNE
Egress) or "reverse" path (i.e., path between QNE Egress towards
QNE Ingress).
Figure 22 shows the scenario where the severe congested node is
located in the "forward" path. The functionality of providing
admission control is the same as the one described in Section
4.6.1.7, Figure 15.
Figure 23 shows the scenario where the congested node is located in
the "reverse" path. The probe RESERVE message sent in the "forward"
direction will not be affected by the severe congested node, while
the DSCP value in the IP header of any packet of the "reverse"
direction flow and also of the GIST message that carries the
probe RESERVE message sent in the "reverse" direction will be
remarked by the congested node. The QNE ingress is in this way
notified that a congestion occurred in the network and therefore it
is able to refuse the new initiation of the reservation.
Note that the "not NSIS aware" Interior nodes MUST be configured
such that they can detect the congestion/severe congestion
situations and remark packets in the same way as the Interior
"NSIS aware" nodes do.
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QNE (Ingress) Interior QNE (int.) Interior QNE (Egress)
NTLP stateful not NSIS aware NTLP st.less not NSIS aware NTLP stateful
user| | | | |
data| | | | |
--->| | user data | | |
|-------------------------------------------->|user data |user
| | | |-------------->|data
| | | | |--->
| | | | |user
| | | | |data
| | | | |<---
| S | user data | |
| S user data |<--------------------------|
| user data S<---------------| | |
|<---------------S | | |
| user data S | | |
| (#marked bytes)S | | |
|<---------------S | | |
| S RESERVE(unmarked DSCP in GIST)): |
| S | | |
|----------------S------------------------------------------->|
| S RESERVE(re-marked DSCP in GIST) |
| S<-------------------------------------------|
|<---------------S | | |
Figure 23: Intra-domain RMD congestion notification for
bi-directional admission control (congestion on path
QNE(Egress) towards QNE(Ingress))
4.7 Handling of additional errors
During the QSpec processing, additional errors MAY occur. The way
in which these additional errors are handled and notified is
specified in [QSP-T] and [QoS-NSLP].
5. Security Considerations
I. INTRODUCTION
A design goal of the RMD-QOSM protocol is to be "lightweight" in
terms of the number of exchanged signaling message and the amount of
state established at involved signaling nodes (with and without
reduced state operation). A side-effect of this design decision is to
introduce second-class signaling nodes, namely QNE Interior nodes,
that are restricted in their ability to perform QoS signaling
actions. Only the QNE Ingress and the QNE Egress nodes are allowed to
initiate certain signaling messages.
Moreover, RMD focuses on an intra-domain deployment only.
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The above description has the following implications for security:
1) QNE Ingress and QNE Egress nodes require more security and fault
protection than QNE Interior nodes because their uncontrolled
behavior has larger implications for the overall stability of the
network. QNE Ingress and QNE Egress nodes share a security
association and utlize GIST security for protection of their
signaling messages. Intra-domain signaling messages used for RMD
signaling do not use GIST security and therefore they do not store
security associations.
2) The focus on intra-domain QoS signaling simplifies trust
management and reduces overall complexity. See Section 2 of RFC 4081
for a more detailed discussion about the complete set of
communication models available for end-to-end QoS signaling
protocols. The security of RMD-QOSM does not depend on interior nodes
and hence the cryptographic protection of intra-domain messages via
GIST is not utilized.
It is important to highlight that RMD always uses the message
exchange shown in Figure 24 even if there is no end-to-end signaling
session. If the RMD-QOSM is triggered based on an E2E signaling
exchange then the RESERVE message is created by a node outside the
RMD domain and will subsequently travel further on (e.g., to the data
receiver). Such an exchange is shown in Figure 3. As such, an
evaluation of RMD's security always has to be seen as a combination
of the two signaling sessions, (1) and (2) of Figure 24. Note that
for the E2E message, such as the RESERVE and the RESPONSE message, a
single "hop" refers to the communication between the QNE Ingress and
the QNE Egress since QNE Interior nodes do not participate in the
exchange.
QNE QNE QNE QNE
Ingress Interior Interior Egress
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
| RESERVE (1) | | |
+--------------------------------------------->|
| RESERVE` (2) | | |
+-------------->| | |
| | RESERVE` | |
| +-------------->| |
| | | RESERVE` |
| | +------------->|
| | | RESPONSE` (2)|
|<---------------------------------------------+
| | | RESPONSE (1) |
|<---------------------------------------------+
Figure 24: RMD message exchange
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Authorizing quality of service reservations is accomplished using the
AAA framework and the functionality is inherited from the underlying
NSIS QoS NSLP, see [QoS-NSLP], and not described again in this
document. As a technical solution mechanism Diameter QoS application
[Diameter-QoS] may be used. The end-to-end reservation request
arriving at the ingress node will trigger the authorization procedure
with the backend AAA infrastructure. The end-to-end reservation is
typically triggered by a human interaction with a software
application, such as a voice-over-IP client when making a call. When
authorization is successful then no further user initiated QoS
authorization check is expected to be performed within the RMD domain
for the intra-domain reservation.
II. SECURITY THREATS
In the RMD-QOSM, the ingress node constructs both end-to- end and
intra-domain signaling messages based on the end-to-end message
initiated by the sender end node.
The Interior nodes within the RMD network ignore the end-to-end
signaling message, but process, modify, and forward the intra-domain
signaling messages towards the egress node. In the meantime, resource
reservation states are installed, modified or deleted at each
interior node along the data path according to the content of each
intra-domain signaling message. The edge nodes of an RMD network are
critical components that require strong security protection.
Therefore, they act as security gateways for incoming and outgoing
signaling messages. Moreover, a certain degree of trust has to be
placed into Interior nodes within the RMD-QOSM network, such that
these nodes can perform signaling message processing and take the
necessary actions.
With the RMD-QOSM we assume that the ingress and the egress nodes are
not controlled by an adversary and the communication between the
ingress and the egress nodes is secured using standard GIST security,
(see Section 6 of [GIST]) mechanisms and experiences integrity,
replay and confidentiality protection.
Note that this only affects messages directly addressed by these two
nodes and not any other message that needs to be processed by
intermediaries. The SESSION ID object of the end-to-end communication
is visible, via GIST, to the Interior nodes.
In order to define the security threats that are associated with the
RMD-QOSM we consider that an adversary that may be located inside the
RMD domain and could drop, delay, duplicate, inject, or modify
signaling packets.
Depending on location of adversary, we speak about an on-path
adversary or an off-path adversary, see also RFC 4081 [RFC4081].
II-A. On-path Adversary
The on-path adversary is a node, which supports RMD-QOSM and is able
to observe RMD-QOSM signaling message exchanges.
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1) Dropping signaling messages
An adversary could drop any signaling messages after receiving them.
This will cause a failure of reservation request for new sessions or
deletion of resource units (bandwidth) for on-going sessions due to
states timeout.
It may trigger the ingress node to retransmit the lost signaling
messages. In this scenario the adversary drops selected signaling
messages, for example intra-domain reserve messages. In the RMD-QOSM,
the retransmission mechanism can be provided at the ingress node to
make sure that signaling messages can reach the egress node. However,
the retransmissions triggered by the adversary dropping messages may
cause certain problems. Therefore, it is recommended to disable the
use of retransmissions in the RMD-QOSM aware network, see also
section 4.6.1.1.1.
2) Delaying Signaling Messages
Any signaling message could be delayed by an adversary.
For example, if RESERVE` messages are delayed over the duration of
the refresh period then the resource units (bandwidth) reserved along
the nodes for corresponding sessions will be removed. In this
situation, the ingress node does not receive the RESPONSE within a
certain period, and considers that the signaling message is failed,
which may cause a retransmission of the 'failed' message. The egress
node may distinguish between the two messages, i.e., the delayed
message and the retransmitted message, and it could take a proper
response.
However, interior nodes suffer from this retransmission and they may
reserve twice the resource units (bandwidth) requested by the ingress
node.
3) Replaying Signaling Messages
An adversary may want to replay signaling messages.
It first stores the received messages and decides when to replay
these message and at what rate (packets/per seconds).
When the RESERVE` message carried a RII object, the egress will reply
with a RESPONSE` message towards the ingress node. The ingress node
can then detect replays by comparing the value of RII in the
RESPONSE` messages with the stored value.
4) Injecting Signaling Messages
Similar to the replay-attack scenario, the adversary may store a part
of the information carried by signaling messages, for example, the
RSN object. When the adversary injects signaling messages, it puts
the stored information together with its own generated parameters
(RMD-Qspec <TMOD-1> parameter, RII, etc.) into the injected messages
and then sends them out. Interior nodes will process these messages
by default, reserve the requested resource units (bandwidth) and pass
them to downstream nodes.
Bader, et al. [Page 82]
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It may happen that the resource units (bandwidth) on the Interior
nodes are exhausted if these injected messages consume much
bandwidth.
5) Modifying Signaling Messages
On-path adversaries are capable of modifying any part of the
signaling message. For example, the adversary can modify the <M>, <S>
and <O> parameters of the RMD-QSPEC messages. The egress node
will then use the SESSION ID and subsequently the BOUND SESSION ID
objects to refer to that flow to be terminated or set to lower
priority. It is also possible for the adversary to modify the
RMD-Qspec <TMOD-1> parameter and/or <PHB Class> parameter, which
could cause a modification of an amount of the requested resource
units (bandwidth) changes.
II-B. Off-path Adversary
In this case the adversary is not located on-path and it does not
participate in the exchange of RMD-QOSM signaling messages, and
therefore is unable to eavesdrop signaling messages. Hence, the
adversary does not know valid RIIs, RSNs, SESSION IDs. Hence, the
adversary has to generate new parameters and constructs new signaling
messages. Since Interior nodes operate in reduced state mode,
injected signaling messages are treated as new once, which causes
Interior nodes to allocate additional reservation state.
III. SECURITY REQUIREMENTS
The following security requirements are set as goals for the intra-
domain communication, namely:
* Nodes, which are never supposed to participate in the NSIS
signaling exchange, must not interfere with QNE Interior nodes. Off-
path nodes (off-path with regard to the path taken by a particular
signaling message exchange) must not be able to interfere with other
on-path signaling nodes.
* The actions allowed by a QNE Interior node should be minimal (i.e.,
only those specified by the RMD-QOSM). For example, only the QNE
Ingress and the QNE Egress nodes are allowed to initiate certain
signaling messages. QNE Interior nodes are, for example, allowed to
modify certain signaling message payloads.
Note that the term `interfere` refers to all sorts of security
threats, such as denial of service, spoofing, replay, signaling
message injection, etc.
Bader, et al. [Page 83]
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IV. SECURITY MECHANISMS
An important security mechanism that was built into RMD-QOSM was the
ability to tie the end-to-end RESERVE and the RESERVE` messages
together using the BOUND SESSION ID and to allow the ingress node to
match the RESERVE` with the RESPONSE` by using the RII. These
mechanisms enable the edge nodes to detect unexpected signaling
messages.
We assume that the RESERVE/RESPONSE is sent with hop-by-hop channel
security provided by GIST and protected between the QNE Ingress and
the QNE Egress. GIST security mechanisms MUST be used to offer
authentication, integrity, and replay protection. Furthermore,
encryption MUST be used to prevent an adversary located along the
path of the RESERVE message to learn information about the session
that can later be used to inject a RESERVE` message.
The following messages need to be mapped to each other to make sure
that the occurrence of one message is not without the other one:
a) the RESERVE and the RESERVE` relate to each other at the QNE
Egress and
b) the RESPONSE and the RESERVE relate to each other at the QNE
Ingress and
c) the RESERVE` and the RESPONSE` relate to each other. The RII is
carried in the RESERVE` message and the RESPONSE` message that is
generated by the QNE Egress node contains the same RII as the
RESERVE`. The RII can be used by the QNE Ingress to match the
RESERVE` with the RESPONSE`. The QNE Egress is able to determine
whether the RESERVE` was created by the QNE Ingress node since the
intra-domain session, which sent the RESERVE`, is bound to an end-to-
end session via the BOUND_SESSION_ID value included in the intra-
domain QoS-NSLP operational state maintained at the QNE Egress.
The RESERVE and the RESERVE` message are tied together using the
BOUND_SESSION_ID(s) maintained by the intra-domain and end-to-end
QoS-NSLP operational states maintained at the QNE edges, see Section
4.3.1, 4.3.2, 4.3.3. Hence, there cannot be a RESERVE` without a
corresponding RESERVE. The SESSION_ID can fulfill this purpose quite
well if the aim is to provide protection against off-path adversaries
that do not see the SESSION_ID carried in the RESERVE and the
RESERVE` messages.
If, however, the path changes (due to re-routing or due to mobility)
then an adversary could inject RESERVE` messages (with a previously
seen SESSION_ID) and could potentially cause harm.
An off-path adversary can, of course, create RESERVE` messages that
cause intermediate nodes to create some state (and cause other
actions) but the message would finally hit the QNE Egress node. The
QNE Egress node would then be able to determine that there is
something going wrong and generate an error message.
Bader, et al. [Page 84]
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The severe congestion handling can be triggered by intermediate nodes
(unlike other messages). In many cases, however, intermediate nodes
experiencing congestion use refresh messages modify the <S> and <O>
parameters of the message. These messages are still initiated by the
QNE Ingress node and carry the SESSION_ID. The QNE Egress node will
use the SESSION_ID and subsequently the BOUND_SESSION_ID, maintained
by the intra-domain QoS-NSLP operational state, to refer to a flow
that might be terminated. The aspect of intermediate nodes initiating
messages for severe congestion handling is for further study.
During the refresh procedure a RESERVE` creates a RESPONSE`, see
Figure 25. The RII is carried in the RESERVE` message and the
RESPONSE` message that is generated by the QNE Egress node contains
the same RII as the RESERVE`.
The RII can be used by the QNE Ingress to match the RESERVE` with the
RESPONSE`.
A further aspect is marking of data traffic. Data packets can be
modified by an intermediary without any relationship to a signaling
session (and a SESSION_ID). The problem appears if an off-path
adversary injects spoofed data packets.
QNE Ingress QNE Interior QNE Interior QNE Egress
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
| REFRESH RESERVE` | |
+-------------->| REFRESH RESERVE` |
| (+RII) +-------------->| REFRESH RESERVE`
| | (+RII) +------------->|
| | | (+RII) |
| | | |
| | | REFRESH |
| | | RESPONSE`|
|<---------------------------------------------+
| | | (+RII) |
Figure 25: RMD REFRESH message exchange
The adversary thereby needs to spoof data packets that relate to the
flow identifier of an existing end-to-end reservation that SHOULD be
terminated. Therefore the question arises how an off-path adversary
SHOULD create a data packet that matches an existing flow identifier
(if a 5-tuple is used). Hence, this might not turn out to be simple
for an adversary unless we assume the previously mentioned
mobility/re-routing case where the path through the network changes
and the set of nodes that are along a path changes over time.
6. IANA Considerations
This section defines additional codepoint assignments in the QSPEC
Parameter ID registry, in accordance with BCP 26 [RFC5226].
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6.1. Assignment of QSPEC Container IDs
This document specifies the following QSPEC containers to be assigned
within the QSPEC Parameter ID registry created in
[QSP-T]:
<PHR_Resource_Request> container (Section 4.1.2 above, suggested
ID=17)
<PHR_Release_Request> container (Section 4.1.2 above, suggested
ID=18)
<PHR_Refresh_Update> container (Section 4.1.2 above, suggested ID=19)
<PDR_Reservation_Request> container (Section 4.1.3 above, suggested
ID=20)
<PDR_Refresh_Request> container (Section 4.1.3 above, suggested
ID=21)
<PDR_Release_Request> container (Section 4.1.3 above, suggested
ID=22)
<PDR_Reservation_Report> container (Section 4.1.3 above, suggested
ID=23)
<PDR_Refresh_Report> container (Section 4.1.3 above, suggested ID=24)
<PDR_Release_Report> container (Section 4.1.3 above, suggested ID=25)
<PDR_Congestion_Report> container (Section 4.1.3 above, suggested
ID=26)
7. Acknowledgments
The authors express their acknowledgement to people who have worked
on the RMD concept: Z. Turanyi, R. Szabo, G. Pongracz, A. Marquetant,
O. Pop, V. Rexhepi, G. Heijenk, D. Partain, M. Jacobsson, S.
Oosthoek, P. Wallentin, P. Goering, A. Stienstra, M. de Kogel, M.
Zoumaro-Djayoon, M. Swanink, R. Klaver G. Stokkink, J. W. van
Houwelingen, D. Dimitrova, T. Sealy, H. Chang, J. de Waal.
Bader, et al. [Page 86]
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8. Authors' Addresses
Attila Bader
Ericsson Research
Ericsson Hungary Ltd.
Laborc 1, Budapest, Hungary, H-1037
EMail: Attila.Bader@ericsson.com
Lars Westberg
Ericsson Research
Torshamnsgatan 23
SE-164 80 Stockholm, Sweden
EMail: Lars.Westberg@ericsson.com
Georgios Karagiannis
University of Twente
P.O. BOX 217
7500 AE Enschede, The Netherlands
EMail: g.karagiannis@ewi.utwente.nl
Cornelia Kappler
DeZem GmbH
Knesebeckstr. 86/87
10623 Berlin
Germany
Email: cornelia.kappler@googlemail.com
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
EMail: Hannes.Tschofenig@nsn.com
URI: http://www.tschofenig.priv.at
Tom Phelan
Sonus Networks
250 Apollo Dr.
Chelmsford, MA USA 01824
EMail: tphelan@sonusnet.com
Attila Takacs
Ericsson Research
Ericsson Hungary Ltd.
Laborc 1, Budapest, Hungary, H-1037
EMail: Attila.Takacs@ericsson.com
Bader, et al. [Page 87]
INTERNET-DRAFT RMD-QOSM
Andras Csaszar
Ericsson Research
Ericsson Hungary Ltd.
Laborc 1, Budapest, Hungary, H-1037
EMail: Andras.Csaszar@ericsson.com
9. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[QoS-NSLP] Manner, J., Karagiannis, G.,McDonald, A.,
"NSLP for Quality-of-Service signaling", draft-ietf-nsis-qos-
nslp (work in progress).
[QSP-T] Ash, J., Bader, A., Kappler C., "QoS-NSLP QSpec Template"
draft-ietf-nsis-qspec (work in progress).
[GIST] Schulzrinne, H., Hancock, R., "GIST: General Internet
Messaging Protocol for Signaling", draft-ietf-nsis-ntlp
(work in progress).
10. Informative References
[AdCa03] Adler, M., Cai, J.-Y., Shapiro, J. K., Towsley, D.,
"Estimation of congestion price using probabilistic packet marking",
Proc. IEEE INFOCOM, pp. 2068-2078, 2003.
[AnHa06] Lachlan L. H. Andrew and Stephen V. Hanly, "The Estimation
Error of Adaptive Deterministic Packet Marking", 44th Annual Allerton
Conference on Communication, Control and Computing, 2006.
[AtLi01] Athuraliya, S., Li, V. H., Low, S. H., Yin, Q., "REM: active
queue management", IEEE Network, vol. 15, pp. 48-53, May/June 2001.
[Chan07] H. Chang, "Security support in RMD-QOSM", Masters thesis,
University of Twente, 2007.
[CsTa05] Csaszar, A., Takacs, A., Szabo, R., Henk, T., "Resilient
Reduced-State Resource Reservation", Journal of Communication and
Networks, Vol. 7, Nr. 4, December 2005.
[DiKa08] Dimitrova, D., Karagiannis, G., de Boer, P.-T., "Severe
congestion handling approaches in NSIS RMD domains with bi-
directional reservations", Journal of Computer Communications,
Elsevier, vol. 31, pp. 3153-3162, 2008.
[Diameter-QoS] Sun, D., McCann, P., Tschofenig, H., ZOU), T.,
Doria, A., and G. Zorn, "Diameter Quality of Service Application",
draft-ietf-dime-diameter-qos (work in progress).
Bader, et al. [Page 88]
INTERNET-DRAFT RMD-QOSM
[Extens-NSIS] Manner, J., Bless, R., Loughney, J., and E. Davies,
"Using and Extending the NSIS Protocol Family", draft-ietf-nsis-ext
(work in progress).
[JaSh97] Jamin, S., Shenker, S., Danzig, P., "Comparison of
Measurement-based Admission Control Algorithms for Controlled-Load
Service", Proceedings IEEE Infocom `97, Kobe, Japan, April 1997.
[GrTs03] Grossglauser, M., Tse, D.N.C, "A Time-Scale Decomposition
Approach to Measurement-Based Admission Control", IEEE/ACM
Transactions on Networking, Vol. 11, No. 4, August 2003
[Part94] C. Partridge, Gigabit Networking, Addison Wesley
Publishers (1994).
[RFC1633] Braden R., Clark D., Shenker S., "Integrated Services in
the Internet Architecture: an Overview", RFC 1633.
[RFC2215] Shenker, S., and J. Wroclawski, "General Characterization
Parameters for Integrated Service Network Elements", RFC 2215,
September 1997.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
and W. Weiss, "An Architecture for Differentiated Services", RFC
2475, December 1998
[RFC2638] Nichols K., Jacobson V., Zhang L. "A Two-bit
Differentiated Services Architecture for the Internet", RFC 2638,
July 1999
[RFC2983] D. Black, "Differentiated Services and Tunnels",
RFC 2983, October 2000.
[RFC2998] Bernet Y., Ford, P., Yavatkar, R., Baker, F., Zhang, L.,
Speer, M., Braden, R., Davie, B., Wroclawski, J. and E.
Felstaine, "Integrated Services Operation Over Diffserv
Networks", RFC 2998, November 2000.
[RFC3175] Baker, F., Iturralde, C. Le Faucher, F., Davie, B.,
"Aggregation of RSVP for IPv4 and IPv6 Reservations",
RFC 3175, 2001.
[RFC3726] M. Brunner, "Requirements for Signaling Protocols",
RFC 3726, April 2004.
[RFC4125] Le Faucheur & Lai, "Maximum Allocation Bandwidth
Constraints Model for Diffserv-aware MPLS Traffic Engineering",
RFC 4125, June 2005.
[RFC4127] Le Faucheur et al, Russian Dolls Bandwidth Constraints
Model for Diffserv-aware MPLS Traffic Engineering, RFC 4127, June
2005.
Bader, et al. [Page 89]
INTERNET-DRAFT RMD-QOSM
[RFC4081] Tschofenig, H. and D. Kroeselberg, "Security Threats for
Next Steps in Signaling (NSIS)", RFC 4081, June 2005.
[RFC5226] Narten, T., Alvestrand, H., "Guidelines for Writing an
IANA Considerations Section in RFCs," RFC 5226, May 2008.
[RMD1] Westberg, L., et al., "Resource Management in Diffserv
(RMD): A Functionality and Performance Behavior Overview", IFIP
PFHSN`02
[RMD2] G. Karagiannis, et al., "RMD - a lightweight application
of NSIS" Networks 2004, Vienna, Austria.
[RMD3] Marquetant A., Pop O., Szabo R., Dinnyes G., Turanyi Z.,
"Novel Enhancements to Load Control - A Soft-State, Lightweight
Admission Control Protocol", Proc. of the 2nd Int. Workshop on
Quality of Future Internet Services, Coimbra, Portugal,
Sept 24-26, 2001, pp. 82-96.
[RMD4] A. Csaszar et al., "Severe congestion handling with
resource management in diffserv on demand", Networking 2002
[TaCh99] P. P. Tang, T-Y Charles Tai, "Network Traffic
Characterization Using Toket Bucket Model",
IEEE Infocom 1999, The Conference on Computer Communications, no. 1,
March 1999, pp. 51-62.
[ThCo04] Thommes, R. W., Coates, M. J., "Deterministic packet marking
for congestion packet estimation" Proc. IEEE Infocom, 2004.
Bader, et al. [Page 90]
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Appendix A.1.1 Example of a remarking operation during severe
congestion in the Interior nodes
This appendix describes an example of a remarking operation during
severe congestion in the Interior nodes.
Per supported PHB, the interior node can support the operation states
depicted in Figure A.1, when the per-flow congestion notification
based on probing signaling scheme is used in combination with this
severe congestion type. Figure A.2 depicts the same functionality
when the per-flow congestion notification based on probing scheme is
not used in combination with the severe congestion scheme. The
description given in this and the following appendices, focuses
on the situation that during the congestion notification state, the
"notified DSCP" marking and during the severe congestion state the
"encoded DSCP" and "affected DSCP" markings are used. In this case,
the "notified DSCP" marking is used during the congestion
notification state to mark all packets passing through an interior
node that operates in the congestion notification state. In this way,
and in combination with probing, an flow-based ECMP solution can be
provided for the congestion notification state. The "encoded DSCP"
marking is used to encode and signal the excess rate, measured at
interior nodes, to the egress nodes. The "affected DSCP" marking is
used to mark all packets that are passing through a severe congested
node and are not "encoded DSCP" marked.
Another possible situation could be derived where both congestion
notification and severe congestion state are using the "encoded DSCP"
marking, without using the "notified DSCP" marking. The "affected
DSCP" marking is used to mark all packets that are passing through
an Interior node that is in severe congestion state and are not
"encoded DSCP" marked. In addition, the probe packet that is carried
by an intra-domain RESERVE message and pass through Interior nodes
SHOULD be "encoded DSCP" marked if the Interior node is in
congestion notification or severe congestion states. Otherwise the
probe packet will remain unmarked. In this way an ECMP solution can
be provided for both congestion notification and severe congestion
states. The"encoded DSCP" packets are signaling excess rate that is
not only associated with interior nodes that are in severe congestion
state, but also with interior nodes that are in congestion
notification state. The algorithm at the Interior node, is similar
to the algorithm described in the following appendix sections.
However, this method is not described in detail in this example.
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---------------------------------------------
| event B |
| V
---------- ------------- ----------
| Normal | event A | Congestion | event B | Severe |
| state |---------->| notification|-------->|congestion|
| | | state | | state |
---------- ------------- ----------
^ ^ | |
| | event C | |
| ----------------------- |
| event D |
------------------------------------------------
Figure A.1: States of operation, severe congestion combined with
congestion notification based on probing
---------- -------------
| Normal | event B | Severe |
| state |-------------->| congestion |
| | | state |
---------- -------------
^ |
| event E |
---------------------------
Figure A.2: States of operation, severe congestion without
congestion notification based on probing
The terms used in Figure A.1 and Figure A.2 are:
Normal state: represents the normal operation conditions of the
node, i.e. no congestion
Severe congestion state: it represents the state when state the
interior node is severely congested related to a certain PHB. It is
important to emphasize that one of the targets of the severe
congestion state solution to change the severe congestion state
behaviour directly to the normal state.
Congestion notification: state where the load is relatively high,
close to the level when congestion can occur
event A: this event occurs when the incoming PHB rate is higher than
the "congestion notification detection" threshold and lower than the
severe congestion detection". This threshold is used by the
congestion notification based on probing scheme, see
Section 4.6.1.7, 4.6.2.6.
event B: this event occurs when the incoming PHB rate is higher than
the "severe congestion detection" threshold.
Bader, et al. [Page 92]
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event C: this event occurs when the incoming PHB rate is lower than
or equal to the "congestion notification detection" threshold.
event D: this event occurs when the incoming PHB rate is lower than
or equal to the "severe_congestion_restoration" threshold. It is
important to emphasize that this even supports one of the targets of
the severe congestion state solution to change the severe congestion
state behaviour directly to the normal state.
event E: this event occurs when the incoming PHB rate is lower than
or equal to the "severe congestion restoration" threshold.
Note that the "severe congestion detection", "severe congestion
restoration" and admission thresholds SHOULD be higher than the
"congestion notification detection" threshold, i.e.,:
"severe congestion detection" > "congestion notification detection"
and "severe congestion restoration" > "congestion notification
detection"
Furthermore, the "severe congestion detection" threshold SHOULD be
higher than or equal to the admission threshold that is used by the
reservation based and NSIS measurement based signaling schemes.
"severe congestion detection" >= admission threshold
Moreover, the "severe congestion restoration" threshold SHOULD be
lower than or equal to the "severe congestion detection" threshold
that is used by the reservation based and NSIS measurement based
signaling schemes, i.e.,:
"severe congestion restoration" <= "severe congestion detection"
During severe congestion the interior node calculates, per traffic
class (PHB), the incoming rate that is above the "severe congestion
restoration" threshold, denoted as signaled_overload_rate, in the
following way:
* A severe congested interior node SHOULD take into account that
packets might be dropped. Therefore, before queuing and eventually
dropping packets, the interior node SHOULD count the total number of
unmarked and remarked bytes received by the severe congested node,
denote this number as total_received_bytes. Note that there are
situations when more than one interior nodes in the same path become
severe congested. Therefore, any interior node located behind a
severe congested node MAY receive marked bytes.
When the "severe congestion detection" threshold per PHB is set
equal to the maximum capacity allocated to one PHB used by the RMD-
QOSM it means that if the maximum capacity associated to a PHB is
fully utilized and a packet belonging to this PHB arrives, then it is
assumed that the interior node will not forward this packet
downstream.
Bader, et al. [Page 93]
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In other words this packet will either be dropped or set to another
PHB. Furthermore, this also means that after the severe congestion
situation is solved, then the ongoing flows will be able to send
their associated packets up to a total rate equal to the maximum
capacity associated to the PHB. Therefore, when more than one
interior nodes located on the same path will be severe congested and
when the interior node receives "encoded DSCP" marked packets, then
it will mean that an interior node located upstream is also severely
congested.
When the "severe congestion detection" threshold per PHB
is set equal to the maximum capacity allocated to one PHB, then this
interior node MUST forward the "encoded DSCP" marked packets and it
SHOULD NOT consider these packets during its local remarking process.
In other words, the egress should see the excess rates encoded by the
different severe congested interior nodes as independent, and
therefore, these independent excess rates will be added.
When the "severe congestion detection" threshold per PHB
is not set equal to the maximum capacity allocated to one PHB then
this means that after the severe congestion situation is solved, the
ongoing flows will not be able to send their associated packets
up to a total rate equal to the maximum capacity associated to the
PHB, but only up to the "severe_congestion_threshold". When more than
one interior nodes located on the same communication path are severe
congested and when one of these interior node receives "encoded_DSCP"
marked packets then this interior node SHOULD NOT mark unmarked,
i.e., either "original DSCP" or "affected DSCP" or "notified DSCP""
encoded packets, up to a rate equal to the difference between the
maximum PHB capacity and the "severe congestion threshold", when the
incoming "encoded DSCP"" marked packets are already able to signal
this difference. In this case the "severe congestion threshold"
SHOULD be configured in all interior nodes, which are located in the
RMD domain, and equal to:
"severe_congestion_threshold" =
= Maximum PHB capacity - threshold_offset_rate
The threshold_offset_rate represents rate and SHOULD have the same
value in all interior nodes.
* before queuing and eventually dropping the packets, at the end of
each measurement interval of T seconds, calculate the current
estimated overloaded rate, say measured_overload_rate, by using the
following equation:
measured_overload_rate =
=((total_received_bytes)/T)-severe_congestion_restoration)
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To provide reliable estimation of the encoded information several
techniques can be used, see [AtLi01], [AdCa03], [ThCo04], [AnHa06].
Note that since marking is done in interior nodes, the decisions are
made at egress nodes, and termination of flows are performed by
ingress nodes, there is a significant delay until the overload
information is learned by the ingress nodes, see Section 6 of
[CsTa05]). The delay consists of the trip time of data packets from
the severe congested interior node to the egress, the measurement
interval, i.e., T, and the trip time of the notification signaling
messages from egress to ingress. Moreover, until the overload
decreases at the severe congested interior node, an additional trip
time from the ingress node to the severe congested interior node MUST
expire. This is because immediately before receiving the congestion
notification, the ingress MAY have sent out packets in the flows that
were selected for termination. That is, a terminated flow MAY
contribute to congestion for a time longer that is taken from the
ingress to the interior node. Without considering the above, interior
nodes would continue marking the packets until the measured
utilization falls below the severe congestion restoration threshold.
In this way, at the end more flows will be terminated than necessary,
i.e., an over-reaction takes place. [CsTa05] provides a solution to
this problem, where the interior nodes use a sliding window memory to
keep track of the signaling overload in a couple of previous
measurement intervals. At the end of a measurement intervals, T,
before encoding and signaling the overloaded rate as "encoded DSCP"
packets, the actual overload is decreased with the sum of already
signaled overload stored in the sliding window memory, since that
overload is already being handled in the severe congestion handling
control loop. The sliding window memory consists of an integer number
of cells, i.e, n = maximum number of cells. Guidelines for
configuring the sliding window parameters are given in [CsTa05].
At the end of each measurement interval, the newest calculated
overload is pushed into the memory, and the oldest cell is dropped.
If Mi is the overload_rate stored in ith memory cell (i = [1..n]),
then at the end of every measurement interval, the overload rate that
is signaled to the egress node, i.e., signaled_overload_rate is
calculated as follows:
Sum_Mi =0
For i =1 to n
{
Sum_Mi = Sum_Mi + Mi
}
signaled_overload_rate = measured_overload_rate - Sum_Mi,
where Sum_Mi is calculated as above.
Next, the sliding memory is updated as follows:
for i = 1..(n-1): Mi <- Mi+1
Mn <- signaled_overload_rate
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The bytes that have to be remarked to satisfy the signaled overload
rate: signaled_remarked_bytes, are calculated using the
following pseudo code:
IF severe_congestion_threshold <> Maximum PHB capacity
THEN
{
IF (incoming_encoded-DSCP_rate <> 0) AND
(incoming_encoded-DSCP_rate =< termination_offset_rate)
THEN
{ signaled_remarked_bytes =
= ((signaled_overload_rate - incoming_encoded-DSCP_rate)*T)/N
}
ELSE IF (incoming_encoded-DSCP_rate > termination_offset_rate)
THEN signaled_remarked_bytes =
= ((signaled_overload_rate - termination_offset_rate)*T)/N
ELSE IF (incoming_encoded-DSCP_rate =0)
THEN signaled_remarked_bytes =
= signaled_overload_rate*T/N
}
ELSE signaled_remarked_bytes = signaled_overload_rate *T/N
Where the incoming "encoded DSCP" rate is calculated as follows:
incoming_encoded-DSCP_rate =
= (received number of "encoded_DSCP" during T) * N)/T;
The signal_remarked_bytes represents also the number of
the outgoing packets (after the dropping stage) that MUST be
remarked, during each measurement interval T, by a node when operates
in severe congestion mode.
Note that in order to process an overload situation higher than 100%
of the maintained severe congestion threshold all the nodes within
the domain MUST be configured and maintain a scaling parameter, e.g.,
N used in the above equation, which in combination with the marked
bytes, e.g., signaled_remarked_bytes, such a high overload situation
can be calculated and represented. N can be equal or higher than 1.
Note that when incoming remarked bytes are dropped, the operation of
the severe congestion algorithm MAY be affected, e.g., the algorithm
MAY become in certain situations slower. An implementation of the
algorithm MAY assure as much as possible that the incoming marked
bytes are not dropped. This could for example be accomplished by
using different dropping rate thresholds for marked and unmarked
bytes.
Note that when the "affected DSCP" marking is used by a node
that is congested due to a a severe congestion situation then all
the outgoing packets that are not marked (i.e., by using the "encoded
DSCP") have to be remarked using the "affected DSCP" marking.
The "encoded DSCP" and the "affected DSCP" marked packets (when
applied in the whole RMD domain) are propagated to the QNE edge
nodes.
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Furthermore, note that when the congestion notification based on
probing is used in combination with severe congestion, then in
addition to the possible "encoded DSCP" and "affected DSCP" another
DSCP for the remarking of the same PHB is used, see Section 4.6.1.7.
This additional DSCP is denoted in this document as "notified
DSCP". When an interior node operates
in the severe congested state, see Figure A.2, and receives "notified
DSCP" packets, these packets are considered to be unmarked packets
(but not "affected DSCP" packets). This means that during severe
congestion also the "notified DSCP" packets can be remarked and
encoded as either "encoded DSCP" or "affected DSCP" packets.
Appendix A.1.2 Example of a detailed severe congestion operation in the
Egress nodes
This appendix describes an example of a detailed severe congestion
operation in the Egress nodes.
The states of operation in Egress nodes are similar to the ones
described in A.1.1. The definition of the events, see below, is
however different than the definition of the events given in Figure
A.1 and Figure A.2:
* event A: when the egress receives a predefined rate of "notified
DSCP" marked bytes/packets then event_A is activated, see Section
4.6.1.7 and A.2.2. The predefined rate of "notified DSCP" marked
bytes is denoted as the congestion notification detection threshold.
Note this congestion notification detection threshold can also be
zero, meaning that the event_A is activated when the egress node,
during an interval T, receives at least one "notified DSCP" packet.
* event B: this event occurs when the egress receives packets marked
as either "encoded DSCP" or "affected DSCP" (when "affected DSCP" is
applied in the whole RMD domain).
* event C: this event occurs when the rate of incoming
"notified DSCP" packets decreases below the congestion notification
detection threshold. In the situation that the congestion
notification detection threshold is zero, this will mean that event C
is activated when the egress node, during an interval T, does not
receive any "notified DSCP" marked packets.
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* event D: this event occurs when the egress, during an interval T,
does not receive packets marked as either "encoded DSCP" or "affected
DSCP" (when "affected DSCP" is applied in the whole RMD domain).
Note that when "notified DSCP" is applied in the whole RMD domain for
the support of congestion notification, then this event could cause
the following change in operation state.
When the egress, during an interval T, does not receive (1) packets
marked as either "encoded DSCP" or "affected DSCP" (when "affected
DSCP" is applied in the whole RMD domain) and (2) it does NOT receive
"notified DSCP" marked packets then the change in the operation state
occurs from the "Severe congestion state" to "Normal state".
When the egress, during an interval T, does not receive (1) packets
marked as either "encoded DSCP" or "affected DSCP" (when "affected
DSCP" is applied in the whole RMD domain) and (2) it does receive
"notified DSCP" marked packets then the change in the operation state
occurs from the "Severe congestion state" to "Congestion notification
state".
* event E: this event occurs when the egress, during an interval T,
does not receive packets marked as either "encoded DSCP" or
"affected DSCP" (when "affected DSCP" is applied in the whole RMD
domain)
An example of the algorithm for calculation of the number of flows
associated with each priority class that have to be terminated is
explained by the pseudo-code below.
The edge nodes are able to support severe congestion handling by: (1)
identifying which flows were affected by the severe congestion and
(2) selecting and terminating some of these flows such that the
quality of service of the remaining flows is recovered.
The "encoded DSCP" and the "affected DSCP" marked packets (when
applied in the whole RMD domain) are received by the QNE edge node.
The QNE edge nodes keep per flow state and therefore they can
translate the calculated bandwidth to be terminated, to number of
flows. The QNE egress node records the excess rate and the identity
of all the flows, arriving at the QNE egress node, with
"encoded DSCP" and with "affected DSCP" (when applied in the whole
RMD domain); only these flows, which are the ones passing through the
severely congested interior node(s), are candidates for termination.
The excess rate is calculated by measuring the rate of all the
"encoded DSCP" data packets that arrive at the QNE egress node. The
Measured excess rate is converted by the egress node, by multiplying
it by the factor N, which was used by the QNE interior node(s) to
encode the overload level.
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When different priority flows are supported all the low priority
flows that arrived at the egress node are terminated first. Next all
the medium priority flows are stopped and finally, if necessary, even
high priority flows are chosen. Within a priority class both "encoded
DSCP" and "aected DSCP" are considered before the mechanism moves to
higher priority class. Finally, for each flow that has to be
terminated the egress node sends a NOTIFY message to the ingress node
which stops the flow.
Below this algorithm is described in detail.
First, when the egress operates in the severe congestion state then
the total amount of remarked bandwidth associated with the PHB
traffic class, say total_congested_bandwidth, is calculated.
Note that when the node maintains information about
each ingress/egress pair aggregate, then the
total_congested_bandwidth MUST be calculated per ingress/egress pair
reservation aggregate. This bandwidth represents the severe congested
bandwidth that SHOULD be terminated. The total_congested_bandwidth
can be calculated as follows:
total_congested_bandwidth = N*input_remarked_bytes/T
Where, input_remarked_bytes represents the number of "encoded DSCP"
marked bytes that arrive at the egress, during one measurement
interval T, N is defined as in Section 4.6.1.6.2.1 and A.1.1. The
term denoted as terminated_bandwidth is a temporal variable
representing the total bandwidth that have to be terminated,
belonging to the same PHB traffic class. The
terminate_flow_bandwidth(priority_class) is the total of bandwidth
associated with flows of priority class equal to priority_class. The
parameter priority_class is an integer fulfilling
0 =< priority_class =< Maximum_priority.
The QNE egress node records the identity of the QNE Ingress Node that
forwarded each flow, the total_congested_bandwidth and the identity
of all the flows, arriving at the QNE Egress Node, with "encoded
DSCP" and "affected DSCP" (when applied in whole RMD domain). This
ensures that only these flows, which are the ones passing through the
severely overloaded QNE interior node(s), are candidates for
termination. The selection of the flows to be terminated is described
in the pseudo-code that is given below, which is realized by the
function denoted below as calculate_terminate_flows().
The calculate_terminate_flows() function uses the
terminate_bandwidth_class value and translates this bandwidth value
to number of flows that have to be terminated. Only the "encoded
DSCP" flows and "affected DSCP" (when applied in whole RMD domain)
flows, which are the ones passing through the severely overloaded
interior node(s), are candidates for termination.
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After the flows to be terminated are selected the
sum_bandwidth_terminate(priority_class) value is calculated that is
the sum of the bandwidth associated with the flows, belonging to a
certain priority class, which will certainly be terminated.
The constraint of finding the total number of flows that have to
be terminated is that sum_bandwidth_terminate(priority_class), SHOULD
be smaller or approximatelly equal to the variable
terminate_bandwidth(priority_class).
terminated_bandwidth = 0;
priority_class = 0;
while terminated_bandwidth < total_congested_bandwidth
{
terminate_bandwidth(priority_class) =
= total_congested_bandwidth - terminated_bandwidth
calculate_terminate_flows(priority_class);
terminated_bandwidth =
= sum_bandwidth_terminate(priority_class) + terminated_bandwidth;
priority_class = priority_class + 1;
}
If the egress node maintains ingress/egress pair reservation
aggregates, then the above algorithm is performed for each
ingress/egress pair reservation aggregate.
Finally, for each flow that has to be terminated the QNE egress node
sends a NOTIFY message to the QNE ingress node to terminate the flow.
Appendix A.2.1 Example of a detailed remarking admission control
(congestion notification) operation in Interior nodes
This appendix describes an example of a detailed remarking admission
control (congestion notification) operation in Interior nodes.
The predefined congestion notification threshold, see Appendix A.1.1,
is set according to, and usually less than, an engineered bandwidth
limitation, i.e., admission threshold, based on e.g. agreed Service
Level Agreement or a capacity limitation of specific links.
The difference between the congestion notification threshold and the
engineered bandwidth limitation, i.e., admission threshold, provides
an interval where the signaling information on resource limitation is
already sent by a node but the actual resource limitation is not
reached. This is due to the fact that data packets associated with an
admitted session have not yet arrived, while allows the admission
control process available at the egress to interpret the signaling
information and reject new calls before reaching congestion.
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Note that in the situation when the data rate is higher than the
preconfigured congestion notification rate, also data packets are
re-marked, see section 4.6.1.6.2.1. To distinguish between congestion
notification and severe congestion, two methods MAY be used (see
Appendix 1.1.1):
* using different DSCP values (re-marked DSCP values). The remarked
DSCP that is used for this purpose is denoted as "notified DSCP" in
this document. When this method is used and when the interior node is
in "congestion notification" state, see A.1.1, then the node SHOULD
remark all the unmarked bytes passing through the node using the
"notified DSCP". Note that this method can only be applied if all
nodes in RMD domain use the "notified" DSCP marking. In this way,
also probe packets that will pass through the interior node that
operates in congestion notification state are being encoded using the
"notified DSCP" marking.
* Using the "encoded DSCP" marking for congestion notification and
severe congestion. This method is not described in detail in this
example appendix.
Appendix A.2.2 Example of a detailed admission control (congestion
notification) operation in Egress nodes
This appendix describes an example of a detailed admission control
(congestion notification) operation in Egress nodes.
The admission control congestion notification procedure can be
applied only if the egress maintains the ingress/egress pair
aggregate. When the operation state of the ingress/egress pair
aggregate is the "congestion notification", see Appendix A.1.2, then
the implementation of the algorithm depends on how the congestion
notification situation is notified to the egress. As mentioned in
Section A.2.1, two methods are used:
* using the "notified DSCP". During a measurement interval T, the
egress counts the number of "notified DSCP" marked bytes that belong
to the same PHB and are associated with the same ingress/egress pair
aggregate, say input_notified_bytes. We denote the rate as
incoming_notified_rate.
* using the "encoded DSCP". In this case, during a measurement
interval T, the egress measures the input_notified_bytes by counting
the "encoded DSCP" bytes.
Below only the detail description of the first method is given.
The incoming congestion_rate can be then calculated as follows:
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incoming_congestion_rate = input_notified_bytes/T
If the incoming_congestion_rate is higher than a preconfigured
congestion notification threshold, then the communication path
between ingress and egress is considered to be congested. Note that
the pre-congestion notification threshold can be set to zero. In this
case the egress node will operate in congestion notification state at
the moment that it receives at least one "notified DSCP" encoded
packet.
When the egress node operates in "congestion notification" state
and if the end-to-end RESERVE (probe) arrives at the egress, then
this request SHOULD be rejected. Note that this is happening
only when the probe packet is either "notified DSCP" or "encoded
DSCP" marked. In this way it is ensured that the end-to-end RESERVE
(probe) packet passed through the node that it is congested. This
feature is very useful when ECMP based routing is used to detect
Only flows that are passing through the congested router.
If such an ingress/egress pair aggregated state is not available when
the (probe) RESERVE message arrives at the egress, then this request
is accepted if the DSCP of the packet carrying the RESERVE messsage
is unmarked. Otherwise (if the packet is either "notified DSCP" or
"encoded DSCP" marked), it is rejected.
Appendix A.3.1 Example of selecting bi-directional flows for termination
during severe congestion
This appendix describes an example of selecting bi-directional flows
for termination during severe congestion.
When a severe congestion occurs on e.g., in the forward path, and
when the algorithm terminates flows to solve the severe congestion in
forward path, then the reserved bandwidth associated with the
terminated bidirectional flows is also released. Therefore, a careful
selection of the flows that have to be terminated SHOULD take place.
A possible method of selecting the flows belonging to the same
priority type passing through the severe congestion point on a
unidirectional path can be the following:
* the egress node SHOULD select, if possible, first unidirectional
flows instead of bidirectional flows
* the egress node SHOULD select, if possible, bidirectional flows
that reserved a relatively small amount of resources on the path
reversed to the path of congestion.
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Appendix A.3.2 Example of a severe congestion solution for bi-
directional flows congested simultaneously on forward and reverse path
This appendix describes an example of a severe congestion solution
for bi-directional flows congested simultaneously on forward and
reverse path.
This scenario describes a solution using the combination of the
severe congestion solutions described in Section 4.6.2.5.2.
It is considered that the severe congestion occurs simultaneously on
forward and reverse directions, which MAY affect the same bi-
directional flows.
When the QNE Edges maintain per-flow intra-domain QoS-NSLP
operational states then the steps can be the following, see Figure
A.3. Consider that the egress node selects a number of bi-directional
flows to be terminated. In this case the egress will send for each
bi-directional flows a NOTIFY message to ingress. If the Ingress
receives these NOTIFY messages and its operational state (associated
with reverse path) is in the severe congestion state (see Figure A.1
and A.2), then the ingress operates in the following way:
* For each NOTIFY message, the Ingress SHOULD identify the
bidirectional flows have to be terminated.
* The ingress then calculates the total bandwidth that SHOULD be
released in the reverse direction (thus not in forward direction) if
the bidirectional flows will be terminated (preempted), say
"notify_reverse_bandwidth". This bandwidth can be calculated by the
sum of the bandwidth values associated with all the end-to-end
sessions that received a (severe congestion) NOTIFY message.
* Furthermore, using the received marked packets (from the reverse
path) the ingress will calculate, using the algorithm used by an
egress and described in A.1.2, the total bandwidth that has to be
terminated in order to solve the congestion in the reverse path
direction, say "marked_reverse_bandwidth".
* The ingress then calculates the bandwidth of the additional flows
that have to be terminated, say "additional_reverse_bandwidth", in
order to solve the severe congestion in reverse direction, by taking
into account:
** the bandwidth in the reverse direction of the bidirectional flows
that were appointed by the egress (the ones that received a NOTIFY
message) to be preempted, i.e., "notify_reverse_bandwidth"
** the total amount of bandwidth in the reverse direction that has
been calculated by using the received marked packets, i.e.,
"marked_reverse_bandwidth".
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QNE (Ingress) NE (int.) NE (int.) NE (int.) QNE (Egress)
NTLP stateful NTLP stateful
data| user | | | |
--->| data | #unmarked bytes| | |
|--------------->S #marked bytes | | |
| S--------------------------->| |
| | | |-------------->|data
| | | | |--->
| | | | Term.?
| NOTIFY | | |Yes
|<------------------------------------------------------------|
| | | | |data
| | | user | |<---
| user data | | data |<--------------|
| (#marked bytes)| S<----------| |
|<--------------------------------S | |
| (#unmarked bytes) S | |
Term|<--------------------------------S | |
Flow? | S | |
YES |RESERVE(RMD-QSpec): S | |
|"forward - T tear" s | |
|--------------->| RESERVE(RMD-QSpec): | |
| | "forward - T tear" | |
| |--------------------------->| |
| | S |-------------->|
| | S RESERVE(RMD-QSpec):
| | S "reverse - T tear" |
| RESERVE(RMD-QSpec) S |<--------------|
| "reverse - T tear" S<----------| |
|<--------------------------------S | |
Figure A.3: Intra-domain RMD severe congestion handling for
bi-directional reservation (congestion on both forward and
reverse direction)
This additional bandwidth can be calculated using the following
algorithm:
IF ("marked_reverse_bandwidth" > "notify_reverse_bandwidth") THEN
"additional_reverse_bandwidth" =
= "marked_reverse_bandwidth"- "notify_reverse_bandwidth";
ELSE
"additional_reverse_bandwidth" = 0
* Ingress terminates the flows that experienced a severe congestion
in the "forward" path and received a (severe congestion) NOTIFY
message
* If possible the ingress SHOULD terminate unidirectional flows that
are using the same egress-ingress reverse direction communication
path to satisfy the release of a total bandiwtdh up equal to the:
"additional_reverse_bandwidth", see Appendix 3.1.
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* If the number of REQUIRED uni-directional flows (to satisfy the
above issue) is not available, then a number of bi-directional flows
that are using the same egress-ingress reverse direction
communication path MAY be selected for pre-emption in order to
satisfy the release of a total bandiwtdh equal up to the:
"additional_reverse_bandwidth". Note that using the guidelines given
in Appendix A.3.1, first the bidirectional flows that reserved a
relatively small amount of resources on the path reversed to the path
of congestion SHOULD be selected for termination.
When the QNE Edges maintain aggregated intra-domain QoS-NSLP
operational states then the steps can be the following.
* The egress calculates the bandwidth to be terminated using the same
method as described in Section 4.6.1.6.2.2. The egress includes this
bandwidth value in a <PDR Bandwidth> within a "PDR_Congestion_Report"
container that is carried by the end-to-end NOTIFY message.
* The Ingress receives the NOTIFY message and reads the <PDR
Bandwidth> value included in the "PDR_Congestion_Report" container.
Note that this value is denoted as "notify_reverse_bandwidth" in the
situation that the QNE edges maintain per flow intra-domain QoS-NSLP
operational states, but is calculated differently. The variables
"marked_reverse_bandwidth" and "additional_reverse_bandwidth are
calculated using the same steps as explained for the situation that
the QNE edges maintain per flow intra-domain QoS-NSLP states.
* Regarding the termination of flows that are using the same egress-
ingress reverse direction communication path, the Ingress can follow
the same procedures as the situation that the QNE edges
maintain per-flow intra-domain QoS-NSLP operational states.
The RMD aggregated (reduced state) reservations maintained by the
interior nodes, can be reduced in the "forward" and "reverse"
directions by using the procedure described in Section 4.6.2.3 and
including in the "Peak Data Rate-1 (p)" value of the local RMD-QSpec
<TMOD-1> parameter of the RMD-QOSM <QoS Desired> field carried by the
"forward" intra-domain RESERVE the value equal to
"notify_reverse_bandwidth" and by including the
"additional_reverse_bandwidth" value in the <PDR Bandwidth> parameter
within the "PDR_Release_Request" container that is carried by the
same intra-domain RESERVE message.
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Appendix A.4 Example of pre-emption handling during admission control
This appendix describes an example of how pre-emption handling is
supported during admission control.
This section describes the mechanism that can be supported by the
QNE Ingress, QNE Interior and QNE Egress nodes to satisfy
pre-emption during the admission control process.
This mechanism uses the pre-emption building blocks specified in
[QoS-NSLP].
A.4.1 Pre-emption handling in QNE Ingress nodes
If a QNE Ingress receives a RESERVE for a session that causes other
session(s) to be pre-empted, for each of these to be pre-empted
sessions, then the QNE Ingress follows the following steps:
Step_1:
The QNE Ingress MUST send a tearing RESERVE downstream and add a
BOUND_SESSION_ID, with Binding_Code value equal to "Indicated session
caused pre-emption" that indicates the SESSION_ID of the session that
caused the pre-emption. Furthermore, an INFO-SPEC object with error
code value equal to "Reservation pre-empted" has to be included in
each of these tearing RESERVE messages.
The selection of which flows have to be preempted can be based on
predefined policies. For example, this selection process can be based
on the MRI associated with the high and low priority sessions. In
particular, the QNE Ingress can select low(er) priority session(s)
where their MRI is "close" (especially the target IP) to the one
associated with the higher priority session. This means that
typically the high priority session and the to be preempted lower
priority sessions are following the same communication path and are
passing through the same QNE Egress node.
Furthermore, the amount of lower priority sessions that have to be
pre-empted per each high priority session, has to be such that the
requested resources by the higher priority session SHOULD be lower or
equal than the sum of the reserved resources associated with the
lower priority sessions that have to be pre-empted.
Step_2:
For each of the sent tearing RESERVE(s) the QNE Ingress will send a
NOTIFY message with an INFO-SPEC objects with error code value equal
to "Reservation pre-empted" towards the QNI.
Step_3:
After sending the pre-empted (tearing) RESERVE(s), the Ingress QNE
will send the (reserving) RESERVE, which caused the pre-emption,
downstream towards the QNE Egress.
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A.4.2 Pre-emption handling in QNE Interior nodes
The QNE Interior upon receiving the first (tearing) RESERVE that
carries the BOUND_SESSION_ID object with Binding_Code value equal to
"Indicated session caused pre-emption" and an INFO-SPEC object with
error code value equal to "Reservation preempted" it considers that
this session has to be pre-empted.
In this case the QNE Interior creates a so called "pre-emption
state", which is identified by the SESSION_ID carried in the
pre-emption related BOUND_SESSION_ID object. Furthermore, this
"pre-emption state" will include the SESSION_ID of the session
associated with the (tearing) RESERVE. If subsequently additional
tearing RESERVE(s) are arriving including the same values of
BOUND_SESSION_ID and INFO-SPEC objects, then the associated
SESSION_IDs of these (tearing) RESERVE message will be included in
the already created "pre-emption state". The QNE will then set a
timer, with a value that is high enough to ensure that it will not
expire before the (reserving) RESERVE arrives.
Note that when the "pre-emption state" timer expires then the
bandwidth associated with the pre-empted session(s) will have to be
released, following a normal RMD-QOSM bandwidth release procedure..
If the QNE interior node will not receive the all to be pre-empted
(tearing) RESERVE messages sent by the QNE Ingress before their
associated (reserving) RESERVE message arrives, then the (reserving)
RESERVE message will not reserve any resources and this message will
be "M" marked, see Section 4.6.1.2. Note that this situation is not a
typical situation. Typically, this situation can only occur when at
least one of (tearing) RESERVe messages are dropped due to an error
condition.
Otherwise, if the QNE Interior receives the all to be pre-empted
(tearing) RESERVE messages sent by the QNE Ingress, then the QNE
Interior will remove the pending resources, and make the new
reservation using normal RMD-QOSM bandwidth release and reservation
procedures.
A.4.3 Pre-emption handling in QNE Egress nodes
Similar to the QNE Interior operation, the QNE Egress upon receiving
the first (tearing) RESERVE that carries the BOUND_SESSION_ID object
with Binding_Code value equal to "Indicated session caused
pre-emption" and an INFO-SPEC object with error code value equal to
"Reservation preempted" it considers that this session has to be pre-
empted. Similar to the QNE Interior operation the QNE Egress creates
a so called "pre-emption state", which is identified by the
SESSION_ID carried in the pre-emption related BOUND_SESSION_ID
object. This "pre-emption state" will store the same type of
information and use the same timer value as specified in section
A.4.2.
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If subsequently additional tearing RESERVE(s) are arriving including
the same values of BOUND_SESSION_ID and INFO-SPEC objects, then the
associated SESSION_IDs of these (tearing) RESERVE message will be
included in the already created "pre-emption state".
If the (reserving) RESERVE sent by the QNE Ingress node arrived and
is not "M" marked and if all the to be pre-empted (tearing) RESERVE
messages arrived then the QNE Egress will remove the pending
resources and make the new reservation using normal RMD-QOSM
procedures.
If the QNE Egress receives a "M" marked RESERVE message then the QNE
Egress will use the normal partial RMD-QOSM procedure to release the
partial reserved resources associated with the "M" marked RESERVE,
see Section 4.6.1.2.
If the QNE Egress will not receive all the to be pre-empted (tearing)
RESERVE messages sent by the QNE Ingress before their associated and
not "M" marked (reserving) RESERVE message arrives, then the
following steps can be followed:
* If the QNE Egress uses an end-to-end QOSM supports the pre-emption
handling then the QNE Egress have to calculate and select new
lower priority sessions that have to be terminated. The way of how
the to be pre-empted sessions are selected and signalled to the
downstream QNEs is similar to the operation specified in Section
A.4.1.
* If the QNE Egress does not use an end-to-end QOSM that supports
the pre-emption handling then the QNE Egress has to reject the
requesting (reserving) RESERVE associated with the high priority
session, see Section 4.6.1.2.
Note that typically, the situation that the QNE Egress does not
receive all the to be pre-empted (tearing) RESERVE messages sent by
the QNE Ingress can only occur when at least one of (tearing) RESERVe
messages are dropped due to an error condition.
A.5 Example of a retransmission procedure within the RMD domain
This appendix describes an example of a retransmission procedure that
can be used in the RMD domain.
If the retransmission of intra-domain RESERVE messages within the RMD
domain is not disallowed then all the QNE Interior nodes SHOULD use
the functionality described in this section.
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In this situation we enable QNE Interior nodes to maintain a replay
cache in which each entry contains the <RSN>, <SESSION_ID> (available
via GIST), <REFRESH_PERIOD> (available via the QoS NSLP [QoS-NSLP])
and the last received "PHR Container" <Container ID> carried by the
RMD-QSpec for each session [QSP-T]. Thus this solution uses
information carried by QOS-NSLP objects [QoS-NSLP] and parameters
carried by the RMD-QSpec "PHR Container". The following phases can be
distinguished:
Phase 1: Create Replay Cache Entry
When an Interior node receives an intra-domain RESERVE
message and its cache is empty or there is no matching entry, it
reads the <Container ID> field of the "PHR container" of the received
message. If the <Container ID> is a PHR_RESOURCE_REQUEST, which
indicates that the intra-domain Reserve message is a reservation
request, then the QNE Interior node creates a new entry in the cache
and copies the <RSN>, <SESSION_ID> and <Container ID> to the entry
and sets the <REFRESH_PERIOD>.
By using the information stored in the List the Interior node
verifies whether the received intra-domain RESERVE message is sent
by an adversary or not. For example, if the <SESSION_ID> and <RSN> of
a received intra-domain RESERVE message match the values stored in
the List then the Interior node checks the <Container ID> part.
If the <Container_ID> is different then:
Situation D1: <Container ID> in its own list is
PHR_RESOURCE_REQUEST, and <Container ID> in the message is
PHR_REFRESH_UPDATE;
Situation D2: <Container ID> in its own list is
PHR_RESOURCE_REQUEST or PHR_REFRESH_UPDATE, and <Container ID>
in the message is PHR_RELEASE_REQUEST;
Situation D3: <Container ID> in its own list is PHR_REFRESH_UPDATE,
and <Container ID> in the message is PHR_RESOURCE_REQUEST;
For Situation D1, the QNE Interior node processes this message by
RMD-QoSM default operation, reserves bandwidth, updates the entry
and passes the message to downstream nodes. For Situation D2, the
QNE Interior node processes this message by RMD-QoSM default
operation, releases bandwidth, deletes all entries associated with
the session and passes the message to downstream nodes. For
situation D3, the QNE Interior node does not use/process the
local RMD-QSpec <TMOD-1> parameter carried by the received intra-
domain RESERVE message. Furthermore, the <K> flag in the "PHR
Container" have to be set such that the local RMD-QSpec <TMOD-1>
parameter carried by the intra-domain RESERVE message is not
processed/used by a QNE Interior node.
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If the <Container_ID> is the same then:
Situation S1: <Container ID> is equal to PHR_RESOURCE_REQUEST;
Situation S2: <Container ID> is equal to PHR_REFRESH_UPDATE;
For situation S1, the QNE Interior node does not process the
intra-domain RESERVE message but it just passes it to
downstream nodes, because
it might have been retransmitted by the QNE Ingress node;
For situation S2, the QNE Interior node processes the first
incoming intra-domain (refresh) RESERVE message within a refresh
period and updates the entry and forwards it to the downstream
nodes.
If only <Session_ID> is matched to the list, then the QNE Interior
Node checks the <RSN>. Here also two situations can be
distinguished:
If a rerouting takes place, see Section 5.2.5.2 in [QoS-NSLP], the
<RSN> in the message will be equal either to <RSN + 2> in the
stored list if it is not a tearing RESERVE or to <RSN -1> in the
stored list if it is a tearing RESERVE:
The QNE Interior node will check the <Container ID> part;
If the <RSN> in the message is equal to <RSN + 2> in the
stored list and the <Container ID> is a PHR_RESOURCE_REQUEST or
PHR_REFRESH_UPDATE then the received intra-domain RESERVE
message has to be interpreted and processed as a typical
(non tearing) RESERVE message, which is caused by rerouting, see
Section 5.2.5.2 in [QoS-NSLP].
If the <RSN> in the message is equal to <RSN-1> in the
stored list and the <Container ID> is a PHR_RELEASE_REQUEST
then the received intra-domain RESERVE message has to be
interpreted and processed as a typical (tearing) RESERVE
message, which is caused by rerouting, see Section 5.2.5.2 in
[QoS-NSLP].
If other situations occur than the ones described above, then
the QNE Interior node does not use/process the local RMD-QSpec
<TMOD-1> parameter carried by the received intra-domain RESERVE
message. Furthermore, the <K> paramer has to be set, see above.
Phase 2: Update Replay Cache Entry
When a QNE Interior node receives an intra-domain RESERVE message,
it retrieves the corresponding entry from the cache and compares the
values. If the message is valid, the Interior node will update
<Container ID> and <REFRESH_PERIOD> in the List entry.
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Phase 3: Delete Replay Cache Entry
When a QNE Interior node receives an intra-domain (tear) RESERVE
message and an entry in the replay cache can be found, then the
QNE Interior node will delete this entry after processing the
message. Furthermore, the Interior node will delete cache entries,
if it did not receive an intra-domain (refresh) Reserve message
during the <REFRESH_PERIOD> period with a <Container_ID> value equal
to PHR_REFRESH_UPDATE.
A.6. Example on matching the initiator QSPEC to the local RMD-QSPEC
Section 3.4 of [QSP-T] describes an example of how the QSPEC can be
Used within QOS-NSLP. Figure A.4 illustrates a situation where a QNI
and a QNR are using an end to end QOSM, denoted in this context as Z-
e2e. It is considered that the QNI access network side is a wireless
access network built on a generation "X" technology with QoS support
as defined by generation "X", while QNR access network is a
wired/fixed access network with its own defined QoS support.
Furthermore, it is considered that the shown QNE edges are located at
the boundary of a RMD domain and that the shown QNE Interior nodes
are located inside the RMD domain.
The QNE edges are able to run both the Z-e2e QOSM and the RMD-QOSM,
while the QNE interior nodes can only run the RMD-QOSM. The QNI that
is considered to e.g., be a wireless laptop, while the QNR a PC.
|------| |------| |------| |------|
|Z-e2e |<->|Z-e2e |<------------------------->|Z-e2e |<->|Z-e2e |
| QOSM | | QOSM | | QOSM | | QOSM |
| | |------| |-------| |-------| |------| | |
| NSLP | | NSLP |<->| NSLP |<->| NSLP |<->| NSLP | | NSLP |
|Z-e2e | | RMD | | RMD | | RMD | | RMD | | Z-e2e|
| QOSM | | QOSM | | QOSM | | QOSM | | QOSM | | QOSM |
|------| |------| |-------| |-------| |------| |------|
-----------------------------------------------------------------
|------| |------| |-------| |-------| |------| |------|
| NTLP |<->| NTLP |<->| NTLP |<->| NTLP |<->| NTLP |<->| NTLP |
|------| |------| |-------| |-------| |------| |------|
QNI QNE QNE QNE QNE QNR
(End) (Ingress Edge) (Interior) (Interior) (Egress Edge) (End)
Figure A.4. Example of Initiator & Local Domain QOSM Operation
The QNI sets QoS Desired and QoS Available QSPEC objects in the
initiator QSPEC, and initializes QoS Available to QoS Desired. In
this example, the <Minimum QoS> object is not populated. The QNI
populates QSPEC parameters to ensure correct treatment of its traffic
in domains down the path. Additionally, to ensure correct treatment
further down the path, the QNI includes <PHB Class> in <QoS Desired>.
The QNI therefore includes in the QSPEC
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QoS Desired = <TMOD> <PHB Class>
QoS Available = <TMOD> <Path Latency>
In this example it is assumed that the <TMOD> parameter is used to
encode the traffic parameters of a VoIP application that uses RTP and
the G.711 Codec, see Appendix B in [QSP-T].
The below text is copied from [QSP-T].
"In the simplest case the Minimum Policed Unit m is the sum of the
IP-, UDP- and RTP- headers + payload. The IP header in the IPv4 case
has a size of 20 octets (40 octets if IPv6 is used). The UDP header
has a size of 8 octets and RTP uses a 12 octet header. The G.711
Codec specifies a bandwidth of 64 kbit/s (8000 octets/s). Assuming
RTP transmits voice datagrams every 20ms, the payload for one
datagram is 8000 octets/s * 0.02 s = 160 octets.
IPv4+UDP+RTP+payload: m=20+8+12+160 octets = 200 octets
IPv6+UDP+RTP+payload: m=40+8+12+160 octets = 220 octets
The Rate r specifies the amount of octets per second. 50 datagrams
Are sent per second.
IPv4: r = 50 1/s * m = 10,000 octets/s
IPv6: r = 50 1/s * m = 11,000 octets/s
The bucket size b specifies the maximum burst. In this example a
burst of 10 packets is used.
IPv4: b = 10 * m = 2000 octets
IPv6: b = 10 * m = 2200 octets ", from [QSP-T].
In our example we will assume that IPV4 is used and therefore, the
<TMOD-1> values will be set as follows:
m = 200 octets
r = 10000 octets/s
b = 2000 octets
The Peak Data Rate-1 (p) and MPS are not specified above, but in our
example we will assume:
p = r = 10000 octets/s
MPS = 220 octets.
The <PHB Class> is set in such a way that the Expedited Forwarding
(EF) PHB is used.
Since <Path Latency> and <QoS Class> are not vital parameters from
the QNI's perspective, it does not raise their M flags.
Each QNE, which supports the Z-e2e QOSM on the path, reads and
interprets those parameters in the initiator QSPEC.
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When an end-to-end RESERVE message is received at a QNE Ingress node
at the RMD domain border then the QNE ingress can 'hide' the
initiator end-to-end RESERVE message so that only the QNE edges
process the initiator (end-to-end) RESERVE message, which then
bypasses intermediate nodes between the edges of the domain, and
issues its own local RESERVE message (see Section 6). For this new
local RESERVE message, the QNE Ingress node generates the local RMD-
QSpec. The RMD-QSpec corresponding to the RMD-QOSM is generated based
on the original initiator QSPEC according to the procedures described
in Section 4.5 of [QoS-NSLP] and in Section 6 of this draft. The RMD
QNE ingress maps the <TMOD-1> parameters contained in the original
Initiator QSPEC into the equivalent <TMOD-1> parameter representing
only the peak bandwidth in the local RMD-QSpec.
In this example the initial <TMOD-1> parameters are mapped into the
RMD-QSpec <TMOD-1> parameters as follows.
As specified the RMD-QOSM bandwidth equivalent <TMOD-1> parameter of
RMD-QSpec should have:
r = p of initial e2e <TMOD-1> parameter
m = large;
b = large;
For the RMD-QSpec <TMOD-1> parameter the following values are
calculated:
r = p of initial e2e <TMOD-1> parameter = 10000 octets/s
m is set in this example to large as follows:
m = MPS of initial e2e <TMOD-1> parameter = 220 octets
The maximum value of b = 250 Gbytes, but in our example this value is
quite large. The b parameter specifies the extent to which the data
rate can exceed the sustainable level for short periods of time.
In order to get a large b, in this example we consider that for a
period of certain period of time the data rate can exceed the
sustainable level, which in our example is the peak rate (p).
Thus in our example we calculate b as:
b = p * "period of time".
For this VoIP example, we can assume that this period of time is 1.5
seconds, see below:
b = 10000 octets/s * 1.5 seconds = 15000 octets
Thus the local RMD-QSpec <TMOD-1> values are:
r = 10000 octets/s
p = 10000 octets/s
m = 220 octets
b = 15000 octets
MPS = 220 octets
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The bit level format of the RMD-QSpec is given in Section 4.1. In
particular, The Initiator/Local QSPEC bit, i.e., <I> is set to
"Local" (i.e., "1") and the <Qspec Proc> is set as follows:
* Message Sequence = 0: Sender initiated
* Object combination = 0: <QoS Desired> for RESERVE and
<QoS Reserved> for RESPONSE
The <QSPEC Version> used by RMD-QOSM is the default version, i.e.,
"0", see [QSP-T]. The <QSPEC Type> value used by the RMD-QOSM is
specified in [QSP-T] and is equal to: "2".
The <Traffic Handling Directives> contains the following fields:
<Traffic Handling Directives> = <PHR container> <PDR container>
The Per Hop Reservation container (PHR container) and
the Per Domain Reservation container (PDR container) are specified
in Section 4.1.2 and 4.1.3, respectively. The <PHR container>
contains the traffic handling directives for intra-domain
communication and reservation. The <PDR container> contains
additional traffic handling directives that is needed for
edge-to-edge communication. The RMD-QOSM <QoS Desired> and
<QoS Reserved>, are specified in Section 4.1.1.
In RMD-QOSM the <QoS Desired> and <QoS Reserved> objects contain the
following parameters:
<QoS Desired> = <TMOD-1> <PHB Class> <Admission Priority>
<QoS Reserved> = <TMOD-1> <PHB Class> <Admission Priority>
The bit format of the <PHB Class> (see [QSP-T] and Figure 4 and
Figure 5) and <Admission Priority> complies to the bit format
specified in [QSP-T].
In this example the RMD-QSpec <TMOD-1> values are the ones that were
calculated and given above. Furthermore, the <PHB Class>, is
representing the EF PHB class. Moreover, in this example the RMD
reservation is established without an <Admission Priority> parameter,
which is equivalent to a reservation established with an <Admission
Priority> whose value is 1.
The RMD QNE egress node updates QoS Available on behalf of the entire
RMD domain if it can. If it cannot (since the M flag is not set for
<Path Latency>) it raises the parameter-specific, 'not-supported'
flag, warning the QNR that the final latency value in QoS Available
is imprecise.
In the "Y" access domain, the initiator QSPEC is processed by the QNR
in the similar was as it was processed in the "X" wireless access
domain, by the QNI.
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If the reservation was successful, eventually the RESERVE request
arrives at the QNR (otherwise the QNE at which the reservation failed
would have aborted the RESERVE and sent an error RESPONSE back to the
QNI). If the RII was included in the QoS NSLP message, the QNR
generates a positive RESPONSE with QSPEC objects QoS Reserved and QoS
Available. The parameters appearing in QoS Reserved are the same as
in QoS Desired, with values copied from QoS Available. Hence, the QNR
includes the following QSPEC objects in the RESPONSE:
QoS Reserved = <TMOD> <PHB Class>
QoS Available = <TMOD> <Path Latency>
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