NSIS Working Group Attila Bader
INTERNET-DRAFT Lars Westberg
Ericsson
Expires: 23 December 2006 Georgios Karagiannis
University of Twente
Cornelia Kappler
Siemens
Tom Phelan
Sonus
June 23, 2006
RMD-QOSM - The Resource Management in Diffserv QOS Model
<draft-ietf-nsis-rmd-07.txt>
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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 preemption 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
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . .4
3. Overview of RMD and RMD-QOSM . . . . . . . . . . . . . .. . .4
3.1 RMD . . . . . . . . . . . . . . . . . . . . . . . . . . .4
3.2 Basic features of RMD-QOSM . . . . . . . . . . . . . . . 7
3.2.1 Role of the QNEs . . . . . . . .. . . . . . . . . .7
3.2.2 RMD-QOSM signaling . . . . . . . . . . . . . . . . 8
3.2.3 RMD-QOSM Applicability and considerations. . . . . 9
4. RMD-QOSM, Detailed Description . . . . . . . . . . . .. . . 10
4.1 RMD-QSpec Definition . . . . . . . . . . . . . . . . . .11
4.1.1 RMD-QOSM QoS Description . . . . . . . . . . . . 11
4.1.2 PHR RMD-QOSM control information . . . . . . . . .12
4.1.3 PDR RMD-QOSM control information . . . . . . . . 14
4.2 Message format . . . . . . . . . . . . . . . . . . . . .15
4.3 RMD node state management . . . . . . . . . . . . . . . 16
4.3.1 Aggregated versus per flow reservations at the
QNE edges . . . . . . . . . . . . . . . . . . . . 17
4.3.2 Measurement-based method . . . . . . . . . . . . .17
4.3.3 Reservation-based method . .. . . . . . . . . . . 18
4.4 Transport of RMD-QOSM messages . . . . . . . . . . . . .19
4.5 Edge discovery and addressing of messages . . . . . . . 20
4.6 Operation and sequence of events . . . . . . . . . . . .20
4.6.1 Basic unidirectional operation . . . . . . . . . .20
4.6.1.1 Successful reservation. . . . . . . . . . . .21
4.6.1.2 Unsuccessful reservation . . . . . . . . . . 29
4.6.1.3 RMD refresh reservation. . . . . . . . . . . 31
4.6.1.4 RMD modification of aggregated reservation . 35
4.6.1.5 RMD release procedure. . . . . . . . . . . . 36
4.6.1.6 Severe congestion handling . . . . . . . . .44
4.6.1.7 Admission control using congestion
notification based on probing . . . . . . . 49
4.6.2 Bidirectional operation . . . . . . . . . . . . . 51
4.6.2.1 Successful and unsuccessful reservation . . .53
4.6.2.2 Refresh reservation . . . . . . . . . . . . .58
4.6.2.3 Modification of aggregated reservation . . . 58
4.6.2.4 Release procedure . . . . . . . . . . . . . .59
4.6.2.5 Severe congestion handling . . . . . . . . . 60
4.6.2.6 Admission control using congestion
notification based on probing . . . . . . . .63
4.7 Handling of additional errors . . . . . . . . . . . . . 64
5. Security Consideration. . . . . . . . . . . . . . . . . . . 65
6. IANA Considerations. . . . . . . . . . . . . . . . . . . . .68
7. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . .68
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8. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . 68
9. Normative References . . . . . . . . . . . . . . . . . . . .69
10. Informative References . . . . . . . . . . . . . . . . . . 69
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 model 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) 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. 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
Internally to the RMD network, RMD-QOSM 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]).
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In the RMD-QOSM, only routers at the edges of a Diffserv domain
(Ingress and Egress nodes) support the QoS-NSLP stateful operation.
Interior nodes support either the QoS-NSLP stateless operation, or a
reduced-state operation with coarser granularity than the edge nodes.
The remainder of this draft is structured following the suggestions
in Appendix B of [QSP-T] for the description of QoS Signaling
Policies.
After the terminology in Section 2, we give an overview of RMD and
the RMD-QOSM in Section 3. 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 RFC 2119.
The terminology defined by GIST [GIST] and QoS-NSLP [QoS-NSLP]
applies to this draft.
In addition, the following terms are used:
Edge node: an (NSIS-capable) node on the boundary of some
administrative domain.
Ingress node: An edge node that handles the traffic as it enters the
domain.
Egress node: An edge node that handles the traffic as it leaves the
domain.
Interior nodes: the set of (NSIS-capable) nodes which form an
administrative domain, excluding the edge nodes.
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
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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 subscription-time Service Level Agreements (SLAs)
that statically define the parameters of the traffic that will be
accepted from a customer.
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. In particular, 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.
In RMD two basic admission control modes are described:
reservation-based and measurement-based admission control.
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 classes, and signal
changes in the class reservations as necessary. The reservation is
quantified in terms of resource units. 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. Once
an admission decision is made, no record of the decision need be
kept. The advantage of measurement-based resource management
protocols is that they do not require pre-reservation state nor
explicit release of the reservations. 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.
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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 are 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. In this way the edges can admit or reject flows that are
requesting resources. Note that in this situation, in addition to the
probe packet, also ordinary data packets passing though the congested
node are re-marked.The rate of the re-marked data packets is used to
detect a congestion situation that can influence the admission
control decissions.
* 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, giving
the possibility to apply measuring techniques, see e.g., [JaSh97],
[GrTs03], that are using current and past information on NSIS
sessions that requested resources from an NSIS aware interior node.
The admission decision is 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 some alpha. Otherwise, the admission
decision is negative.
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.
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* 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 mainly QoS-NSLP aware nodes. 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).
|------| |-------| |------| |------|
| 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
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Note that the RMD domain may contain Interior nodes that are
not NSIS aware nodes (not shown in the figure). 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).
3.2.2 RMD-QOSM Signaling
The basic RMD-QOSM signaling is shown in Figure 3. A RESERVE
message is created by a QNI with an Initiator QSpec describing the
reservation and forwarded along the path towards the QNR. When the
original RESERVE message arrives at the Ingress node, an RMD-QSpec
is constructed based on the top-most QSPEC in the message (usually
the Initiator QSPEC). The RMD-QSpec is sent in a local, independent
RESERVE message through the Interior nodes towards the QNR. This
local RESERVE message uses the NTLP hop-by-hop datagram signaling
mechanism. Meanwhile, the original RESERVE message is sent to the
Egress node on the path to the QNR using the reliable transport mode
of NTLP.
QNE QNE QNE QNE
Ingress Interior Interior Egress
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
RESERVE | | | |
-------->| RESERVE | | |
+--------------------------------------------->|
| RESERVE' | | |
+-------------->| | |
| | RESERVE' | |
| +-------------->| |
| | | RESERVE' |
| | +------------->|
| | | | RESERVE
| | | +------->
| | | |RESPONSE
| | | |<-------
| | | RESPONSE |
|<---------------------------------------------+
RESPONSE| | | |
<--------| | | |
Figure 3: Sender-initiated reservation with Reduced State Interior
Nodes
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Each QoS-NSLP node on the data path processes the local RESERVE
message and checks the availability of resources with either the
reservation-based or the measurement-based method. When the message
reaches the Egress node, and the reservation is successful in each
Interior nodes, the original 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 a RESPONSE message is sent directly the Ingress node.
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 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, where the use bandwidth
as a signaled <QoS Desired> parameter is required. The RMD-QOSM is
not able to support the full set of (Assured Forwarding) AF-like
functionality where multiple PHBs/DSCPs are used. This is because
the signaled <QoS Desired> parameter should contain two token
buckets needed to signal AF in full generality. Note however, that
RMD-QOSM could also support a single AF PHB, as far as the traffic
or the upper limit of the traffic can be characterized by a single
bandwidth parameter.
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.
The available RMD-QOSM 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)
* 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)
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* per aggregate RMD NSIS measurement based admission control (see
Sections 4.3.1, 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)
* per flow RMD reservation based in combination with severe
congestion handling by the RMD-QOSM refresh procedure (see Sections
4.3.1, 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)
* per flow RMD reservation based in combination with severe
congestion handling by proportional data packet marking procedure
(see Sections 4.3.1, 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)
* per aggregate RMD reservation based in combination with
severe congestion handling by the RMD-QOSM refresh procedure (see
Sections 4.3.1, 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)
* per aggregate RMD reservation based in combination with
severe congestion handling by proportional data packet marking
procedure (see Sections 4.3.1, 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)
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.
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4.1. RMD-QSpec Definition
The QSPEC format is specified in [QSP-T] and is as follows:
QSPEC = <QSPEC Version> <QOSM ID> <QSPEC Control Information>
<QoS Description>
The <QSPEC Version> and <QoSM ID> used by the RMD-QOSM are
assigned by IANA, see Section 6. The <QSPEC Control Information>
contains the following fields:
<QSPEC Control Information> = <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 QoS specific control information for intra-domain
communication and reservation. The <PDR container> contains
additional control information that is needed for edge-to-edge
communication.
The <QoS Description> contains the <RMD-QOSM QoS description field>
that is specified in Section 4.1.1. The <RMD-QOSM QoS Description>
field, 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 Description
The RMD-QOSM QoS Description carried by the RESERVE message only
contains the QoS Desired object [QSP-T]. The QoS Reserved object is
carried by the RESPONSE message.
<RMD-QOSM QoS Description> = <QoS Desired> for RESERVE
<RMD-QOSM QoS Description> = <QoS Reserved> for RESPONSE
<QoS Desired> = <Bandwidth> <PHB Class> <Admission Priority>
<QoS Reserved> = <Bandwidth> <PHB Class> <Admission Priority>
The bit format of the <Bandwidth> (see Figure 4), <PHB Class> (see
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.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|E|0|T| 2 |r|r|r|r| 1 ||
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Bandwidth parameter
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|E|0|T| 6 |r|r|r|r| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DSCP |0 0 0 0 0 0 0 0 0 0| Reserved |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 5: PHB_Class parameter
4.1.2. PHR Container
This section describes the parameters used by the PHR container.
<PHR container> = <Overload %>, <S>,<M>,
<Admitted Hops>, <B>, <Hop_U> <Time Lag>
The bit format of the PHR container can be seen in Figure 6. Note
that in Figure 6 <Hop U> is represented as <U>.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|E|N|T| Container ID |r|r|r|r| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|M| Admitted Hops|B|U| Time Lag | Overload % | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: PHR container
Parameter/Container ID:
8 bit field, indicating the PHR type: PHR_Resource_Request,
PHR_Release_Request, PHR_Refresh_Update. It is used to further
specify QoS-NSLP RESERVE and RESPONSE messages.
"PHR_Resource_Request" (Container ID = 1): initiate or
update the traffic class reservation state on all nodes located on
the communication path between the QNE(Ingress) and QNE(Egress)
nodes.
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"PHR_Refresh_Update" (Container ID = 2): 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.
"PHR_Release_Request" (Container ID = 3): explicitly release, by
subtraction, the reserved resources for a particular flow
from a traffic class reservation state.
<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 sever congestion occurs. Congested Interior nodes SHOULD
notify Edge QNEs about the congestion by setting the
S bit.
<Overload %>:
8 bits In case of severe congestion the level of overload is
indicated by the Overload %. Overload % SHOULD be higher than 0 if
S bit is set. If overload in a node is greater than the overload
in a previous node then Overload % SHOULD be updated.
<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 is
increased by one at each Interior QNE. 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.
<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.
<B>: 1 bit. Indicates bi-directional reservation.
<Time Lag>: 8 bit field. The time lag used in a sliding window
over the refresh period.
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4.1.3. PDR container
This section describes the parameters of the PDR container.
The bit format of the PDR container can be seen in Figure 7.
<PDR container> = <Overload %> <S> <M> <Max
Admitted Hops> <B> [<PDR Reverse Requested Resources>]
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|E|N|T| Container ID |r|r|r|r| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|M| Max Adm Hops |B| Overload % | Empty | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PDR Reverse Requested Resources(32-bit IEEE floating p.number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: PDR container
Parameter/Container ID:
8-bit field identifying the type of PDR container field.
"PDR_Reservation_Request" (Parameter/Container ID = 4): 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" (Parameter/Container ID = 5): 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" (Parameter/Container ID = 6): generated and
sent by the QNE(Ingress) node to the QNE(Egress) node to release
the per domain reservation states explicitly
"PDR_Reservation_Report" (Parameter/Container ID = 7): 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" control information fields have been
received and that the request has been admitted or rejected
"PDR_Refresh_Report" (Parameter/Container ID = 8) generated and sent
by the QNE(Egress) node in case needed, to the QNE(Ingress) node
to report that a "PHR_Refresh_Update" control information
field has been received and has been processed
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"PDR_Release_Report" (Parameter/Container ID = 9) 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" control information fields have been
received and have been processed.
"PDR_Congestion_Report" (Parameter/Container ID = 10): generated and
sent by the QNE(Egress) node to the QNE(Ingress) node and used for
congestion notification
<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.
<Overload %>:
8-bit. It includes the Overload % of the
"PHR_Resource_Request" or "PHR_Refresh_Update" control
information fields, indicating the level of overload to the Ingress
node.
<M> (PDR Marked):
1-bit. Carries the <M> value of the "PHR_Resource_Request" or
"PHR_Refresh_Update" control information 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 Reverse Requested Resources>:
32 bits. This field only applies when the "B" flag is set to
"1". It specifies the requested number of units of resources
that have to be reserved by a node in the reverse direction
when the intra-domain signaling procedures require a bi-
directional reservation procedure.
4.2. Message Format
The format of the messages used by the RMD-QOSM complies with the
QoS-NSLP specification. As specified in [QoS-NSLP], for each
QoS-NSLP message type, there is a set of rules for the permissible
choice of object types. These rules are specified using Backus-Naur
Form (BNF) augmented with square brackets surrounding optional
sub-sequences. The BNF implies an order for the objects in a
message. However, in many (but not all) cases, object order makes no
logical difference. An implementation SHOULD create messages with
the objects in the order shown here, but accept the objects in any
permissible order.
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The format of a local (intra-domain) RESERVE message used by the
RMD-QOSM is:
RESERVE = COMMON_HEADER
RSN [ RII ] [ REFRESH_PERIOD ]
[ *BOUND_SESSION_ID ]
[[ PACKET_CLASSIFIER ] [ RMD-QSPEC ]]
The format of an intra-domain Query message that may be used by the
RMD-QOSM is as follows:
QUERY = COMMON_HEADER
[ RII ] [ *BOUND_SESSION_ID ]
[ PACKET_CLASSIFIER ] RMD-QSPEC
A QUERY message MUST contain an RII object to indicate a RESPONSE is
desired, unless the QUERY is being used to initiate reverse-path
state for a receiver-initiated reservation.
The format of a local (intra-domain) RESPONSE message used by
the RMD-QOSM is as follows:
intra-domain RESPONSE = COMMON_HEADER
[ RII / RSN ] INFO_SPEC [ RMD-QSPEC ]
The format of an end-to-end RESPONSE message that is used by the
RMD-QOSM to carry an intra-domain RMD-QSPEC object is as follows:
RESPONSE = COMMON_HEADER [RII/RSN] INFO_SPEC [QSPEC] [RMD-QSPEC]
The format of an intra-domain NOTIFY message used by the RMD-QOSM is
as follows:
NOTIFY = COMMON_HEADER INFO_SPEC [ RMD-QSPEC ]
The format of an end-to-end NOTIFY message that is used by the
RMD-QOSM to carry an intra-domain RMD-QSPEC object is as follows:
NOTIFY = COMMON_HEADER INFO_SPEC [QSPEC] [RMD-QSPEC]
All objects, except RMD-QSPEC objects, are specified in [QoS-NSLP].
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.
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4.3.1 Aggregated versus per flow reservations at the QNE Edges
The QNE Edges maintain for the RMD QoS model either per flow, or
aggregated QoS-NSLP reservation states. Each per flow or aggregated
QoS-NSLP reservation state, associated with the RMD-QOS model, is
identified by a NTLP SESSION_ID (see [GIST]). In RMD, these states
are denoted as PDR states.
When the QNE Edges use aggregated QoS-NSLP reservation states the
SESSION_ID of the aggregated state, the IP addresses of the Ingress
and Egress nodes, the PHB value and the size of the aggregated
reservation, e.g., reserved bandwidth have to be maintained.
The size of the aggregation is specified in Section 1.4.4 of
[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 it aggregates. 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 endeavoring 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).
4.3.2 Measurement-based method
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 traffic belonging to a PHB traffic class a
predefined congestion 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.
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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. Note that in this situation, in addition to the probe
packet, also ordinary data packets passing though the congested node
are re-marked. The rate of the re-marked data packets is used to
detect a congestion situation that can influence the admission
control decissions.
* NSIS measurement-based admission control:
The measurement based admission control is implemented in NSIS aware
stateless routers. 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 local 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
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
from the QNE Ingress node up to the QNE Egress node. This state
represents the number of currently reserved resource units. 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]. The simplified concept
that is used by the per traffic class admission control process, is
based on the following equation:
last + p <= T,
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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 are soft states, which are
refreshed by sending periodic refresh local RESERVE messages. If a
refresh message corresponding to a number of reserved resource units
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 PHR
release message. 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 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.
4.4. Transport of RMD-QOSM messages
The intra-domain (local) messages used by the RMD-QOSM MUST operate
in the NTLP/GIST Datagram mode (see [GIST]). Therefore, the NSLP
functionality available in all QoS NSLP nodes that are able to
support the RMD-QOSM MUST require the intra-domain GIST
functionality available in these nodes to operate in the datagram
mode, i.e., require GIST 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
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* 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.
All the intra-domain local messages are transported using the GIST
data messages (see [GIST]). At the ingress the original (end-to-end)
RESERVE message is forwarded but ignored by the stateless or reduced-
state nodes, see Figure 3. The intermediate (interior) nodes are
bypassed using multiple levels of the router alert option
(see [QoS-NSLP]. In that
case, interior routers are configured to handle only certain levels
of router alert (RAO) values. 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.
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 QoS signaling
messages that are processed only by the Edge nodes use the peer-peer
addressing of the GIST connection (C) mode. RMD QoS 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. RMD QoS signaling messages that are addressed to
the data path end nodes are intercepted by the Egress nodes.
4.6. Operation and sequence of events
4.6.1. Basic unidirectional operation
This section describes the basic unidirectional operation and
sequence of events of the RMD-QOSM. The following basic operation
cases are distinguished:
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* 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 Edge can also operate as a
QNI or as a QNR. Note that the described functionality applies to the
RMD reservation-based and to the NSIS measurement-based admission
control methods. 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.
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].
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. Note that when the QOSM ID of the end-to-end QoS
model is not known to the Ingress node (QNE), the Ingress MUST
interpret at least the mandatory parameters (see [QSP-T]). If the
QSPEC object contains also optional parameters that are not used by
the RMD-QOSM, then the N-flag of each of these objects MUST be set.
Subsequently, the RMD QoS Description: <Bandwidth> and <PHB Class>
are derived from the QoS Description of the end-to-end QSpec. The
Ingress QNE performs then the following functionality.
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If the requested <Bandwidth> parameter cannot be satisfied locally,
then an end to end RESPONSE message has to be generated. An end-to-
end QSpec object MUST be included in the 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
<Bandwidth> 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: 0x04 Transient Failure
Error code value: 0x07 Total 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].
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 messages. These 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.
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 0x01 (Tunnel and end-to-end sessions). If the QNE Edge nodes
maintain intra-domain aggregated QoS-NSLP reservation states then the
value of Binding_Code MUST be set to 0x03 (Aggregate sessions).
The intra-domain RESERVE SHOULD contain in the BOUND_SESSION_ID the
SESSION_ID of its bound end-to-end session. The value of the
Binding_Code MUST be set to 0x01 (Tunnel and end-to-end sessions).
Note that the end to end RESERVE is tunneled within the RMD domain.
Therefore, the T-flag of the QSPEC parameters has to be processed/set
according to the [QSP-T] specification.
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.
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If no QOS-NSLP aggregation procedure at the QNE Edges is possible
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 MUST be sent using the NTLP datagram
mode (see Section 4.4). In addition, the intra-domain RESERVE (RMD-
QSPEC) message MUST include a PHR container (PHR_Resource_Request)
and the "RMD QOS Description" field.
The end-to-end RESERVE message includes the end-to-end QSpec and it
is sent towards the Egress QNE. If the end-to-end QSpec does not
carry an RII object, then an RII object has to be generated and
included into the end-to-end RESERVE message.
Note that after completing the initial discovery phase, the GIST
connection mode can be used between the QNE Ingress and QNE Egress.
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, which corresponds to a RAO 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
levels of router alert (RAO) values.
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.
The (initial) intra-domain RESERVE message MUST be sent by the QNE
Ingress and it MUST contain the following values:
* the value of the <RSN> object SHOULD be the same as the value
of the RSN object of the end-to-end RESERVE message;
* the value of the <BOUND_SESSION_ID> object MUST be the SESSION_ID
associated to the end-to-end RESERVE message. Furthermore, if
the QNE Edge nodes maintain per flow QoS-NSLP reservation states
then the value of Binding_Code MUST be set to 0x01 (Tunnel and
end-to-end sessions).
* 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 boundary nodes and the QNE Interior nodes
MUST be configured as Interior (intermediary) nodes;
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* The <RII> object MUST not included in this message;
* The flag REPLACE MUST be set to FALSE = 0;
* the value of the <REFRESH_PERIOD> object MUST be calculated
and set by the QNE Ingress node, see also Section 4.6.1.3;
* the value of the <PACKET_CLASSIFIER> object SHOULD be associated
with the path-coupled routing 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 SHOULD be obtained from the
MRI values obtained from GIST.
* the PHR resource units MUST be included into the <Bandwidth>
parameter of the "RMD QoS Description" field;
* the value of the Parameter/Container ID field of the PHR container
MUST be set to 1, (i.e., PHR_Resource_Request;)
* the value of the <Admitted Hops> parameter in the PHR container
MUST be set to "1";
* the value of the <Hop_U> parameter in the PHR container MUST be
set to "0";
* If the end-to-end RESERVE message carried an <Admission Priority>
parameter, then this parameter should be copied 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.
* In a single-domain case the PDR container MAY not be included into
the message.
When an end-to-end RESPONSE(PDR) message is received by the QNE
Ingress node, the RMD-QSPEC, see Section 4.6.1.1.3, has to be
identified, processed and removed from the end-to-end RESPONSE
message. The QoS-NSLP state in the QNE Ingress stores and maintains
the binding between each end-to-end session and each intra-domain
session. In this way the QNE Ingress can match the PHR container that
has been carried by the intra-domain RESERVE with the received PDR
container that has been carried by the end-to-end RESPONSE message.
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The RMD QoS model functionality is notified by reading the <M>
parameter of the "PDR RMD control information" container that the
reservation has been successful.
Furthermore, the INFO_SPEC object SHOULD be read by the QoS-NSLP
functionality. In case of successful reservation the INFO_SPEC object
SHOULD have the following values:
* Error Severity Class: 0x02 Success
* Error Code value: 0x01 Reservation successful
If the end-to-end RESPONSE message has to be forwarded to a
node outside the RMD-QOSM aware domain then the non-default 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.
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:
* the values of the <RSN>, <RII>, <PACKET_CLASSIFIER>,
<REFRESH_PERIOD>, <BOUND_SESSION_ID> 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 value of the DSCP value SHOULD be obtained via the MRI
parameters that the QoS-NSLP receives from GIST.
* The flag REPLACE MUST be set to FALSE = 0;
* the value of <Bandwidth> parameter of the "RMD QoS Description"
field is used by the QNE Interior node for admission control, see
Section 4.3.2 and Section 4.3.3. Furthermore, if the <Admission
Priority> parameter is carried by the "RMD QoS Description" field
this parameter is processed as described in the following bullet.
* in case of the RMD reservation-based procedure, and if these
resources are admitted (see Section 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.
Bader, et al. [Page 25]
INTERNET-DRAFT RMD-QOSM
* If the bandwidth allocated for the PHB_high_priority traffic is
fully utilized, and a high priority request arrives, other
policies can be used, which are beyond the scope of this document.
One example for these policies can be that the high priority
session is admitted through preemption of ongoing lower priority
sessions, when the bandwidth reserved by the lower priority
sessions can satisfy the high priority bandwidth request.. When
the available bandwidth for the PHB_lower_priority
and for the PHB_normal_priority is not enough to support the high
priority traffic, then it will generate congestion for these PHB
traffic classes. A solution to this congestion problem can be
accomplished by using the severe congestion detection mechanism
specified in Section 4.6.1.6.2.1. The degree of this congested
bandwidth is indicated by using a specific DSCP (see Section
4.6.1.6.2.1) by marking the bytes proportionally to the degree of
congestion. Other mechanisms may also be used as queues for the
new high priority requests until capacity becomes available for
the high priority sessions.
* in case of the RMD measurement based method, and if these
resources are admitted (see Section 4.3.2), using a MBAC
algorithm, the number of this resources will be used to update the
MBAC algorithm.
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 SHOULD be removed.
Note that the received end to end RESERVE was tunneled within the RMD
domain. Therefore, the T-flag of the QSPEC parameters has to be
processed/set according to the [QSP-T] specification.
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If the 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. Furthermore, note
that the Egress should use a timer, that uses a pre-configured value,
which can be used to synchronize the arrival of the end to end
RESERVE and the intra-domain RESERVE (RMD-QSPEC) messages. If these
two messages do not arrive during the time defined by the timer, then
the reservation is considered as being failed. In this case a
RESPONSE message is sent towards the QNE ingress with the following
INFO_SPEC values:
Error Class: 0x04 Transient Failure
Error Code: 0x05 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. The session included
in the <BOUND_SESSION_ID> object is the session associated with the
end-to-end RESERVE message.
Note that if the QNE Edge nodes maintain per flow QoS-NSLP
reservation states then the value of Binding_Code = 0x01 (Tunnel and
end-to-end sessions) is used.
Note that when the interior nodes are using mechanisms to admit high
priority session through preemption of ongoing lower priority
sessions, the mechanisms of solving the congestion on a low priority
traffic PHB may use the solution specified in Section 4.6.1.6.2.2.
The QNE Egress MUST wait for the end-to-end RESPONSE message that has
the same SESSION ID and RII object as the end-to-end RESERVE message
forwarded towards QNR.
The non-default values of the objects contained in the end-to-end
RESPONSE(PDR) message MUST be used and/or set by the QNE Egress as
follows:
* 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: 0x02 Success,
Error Code value: 0x01 Reservation successful,
Furthermore, an end-to-end QSpec object MUST be included in the
RESPONSE message. The parameters included in the QSPEC <QoS
Reserved> object are copied from the original <QoS Desired> values.
Bader, et al. [Page 27]
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) |
| | |------------------->|
| | | RESERVE
| | | |-->
| | | RESPONSE
| | | |<--
| |RESPONSE(PDR) | |
|<------------------------------------------------------------|
RESPONSE | | |
<---| | | |
Figure 8: Basic operation of successful reservation procedure used by
the RMD-QOSM
In addition to the above, the QNE Egress MUST also generate a RMD-
QSPEC object that is carried by the end-to-end RESPONSE(PDR)
message, see Section 4.2.
The following parameters of the RMD-QSPEC object MUST be used and/or
set in the following way:
* the value of the Parameter/Container ID field of the PDR container
MUST be set "7" (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.
The end-to-end RESPONSE(PDR) message is addressed and sent to its
upstream QoS-NSLP neighbor, i.e., QNE Ingress node. Note that for all
upstream messages the RAO is not set. Therefore, all Interior nodes
ignore the end-to-end RESPONSE messages.
Bader, et al. [Page 28]
INTERNET-DRAFT RMD-QOSM
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 the same 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 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 and to the NSIS measurement-based admission control methods.
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.
4.6.1.2.1 Operation in the Ingress nodes
When an end-to-end RESERVE message arrives at the QNE Ingress and
if there are no resources available locally, the QNE Ingress MUST
reject this end-to-end RESERVE message and sends a 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(PDR) message is received by an Ingress
node, see Section 4.6.1.2.3, the following actions take place. The
non-default values of the objects contained in the end-to-end
RESPONSE (PDR) message MUST be used and/or set by the QNE Ingress
node as follows:
* the values of the <RII/RSN>, [<INFO_SPEC> ], [QSPEC] objects are
set according to the QoS-NSLP procedures. Furthermore, the
INFO_SPEC object, generated by the Egress is read by the QoS-NSLP
functionality.
* the RMD-QSPEC object, see Section 4.2, has to be processed
and removed. The RMD Resource Management Function (RMF) is
notified by reading the <M> parameter of the PDR container that
the reservation has been unsuccessful. 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).
Bader, et al. [Page 29]
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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.
Furthermore, the "E" flag associated with the QSPEC <QoS Desired>
object and the "E" flag associated with the <Bandwidth> 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 <Bandwidth> parameter SHOULD be set.
In general, if a QNE Interior node receives a QSpec <Bandwidth>
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 QoS Description" field MUST NOT be
processed.
4.6.1.2.3 Operation in the Egress nodes
In the RMD reservation based and the RMD measurement based scenario,
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 session
included in its BOUND_SESSION_ID object MUST be bound. The session
in the <BOUND_SESSION_ID> object is the session associated with the
end-to-end RESERVE.
The QNE Egress node MUST generate an end-to-end RESPONSE message
that has to be sent to its previous stateful QoS-NSLP hop.
* the values of the <RII/RSN>, <INFO_SPEC> objects are set
by the standard QoS-NSLP protocol functions. In case of
unsuccessful reservation the INFO_SPEC object SHOULD have the
following values:
Error Severity Class: 0x04, Transient Failure
Error Code value: 0x07 Total 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 QSPEC <QoS Reserved> object and the "E" flag associated with the
<Bandwidth> parameter are set.
Bader, et al. [Page 30]
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:M =1) |
| |------------------>| |
| | | RESERVE(RMD-QSPEC:M=1)
| | |------------------->|
| |RESPONSE(PDR) | |
|<------------------------------------------------------------|
RESPONSE | | |
<---| | | |
RESERVE(RMD-QSPEC: Tear=1, M=1, <Admitted Hops>=<Max_Admitted Hops>
|------------------->| | |
Figure 9: Basic operation during unsuccessful reservation
initiation used by the RMD-QOSM
In addition to the above, similarly to the successful operation,
see Section 4.6.1.1.3, the QNE Egress MUST also generate an RMD-QSPEC
object that is carried by the end-to-end RESPONSE message.
The following fields of the RMD-QSPEC object MUST be used and/or set
in the following way:
* the value of the <PDR Control Type> of the PDR container MUST be
set to "7" (PDR_Reservation_Report);
* the value of the <Admitted Hops> parameter of the PHR container
included in the received <M> marked PDR container 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 set to
"1".
4.6.1.3 RMD refresh reservation
In case of RMD measurement-based method, QoS-NSLP states in the RMD
domain are not maintained, therefore, the end-to-end RESERVE
(refresh) message is sent directly to the QNE Egress.
Bader, et al. [Page 31]
INTERNET-DRAFT RMD-QOSM
The refresh procedure in case of RMD reservation-based method
follows a similar scheme as the reservation process, shown in Figure
3. 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. 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 QoS Description"
field and a PHR container (i.e., PHR_Refresh_Update).
The selection of the IP source and destination address of this
message depends on if and how the different inter domain
(end-to-end) flows can be aggregated by the QNE Ingress node (see
Section 4.3.1). Note that this QoS-NSLP aggregation procedure is
different than the RMD traffic class aggregation procedure. One
example is the approach used by the RSVP aggregation scenario
([RFC3175]), where the IP source address of this message is the IP
address of the aggregator (i.e., QNE Ingress) and the IP destination
address of this message is the IP address of the De-aggregator
(i.e., QNE Egress). An alternative approach is the one used
in "RSVP Refresh Overhead Reduction Extensions" ([RFC2961]). If no
QOS-NSLP aggregation procedure at the QNE edges is possible 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.
An example of this RMD specific refresh operation can be seen in
Figure 10.
Bader, et al. [Page 32]
INTERNET-DRAFT RMD-QOSM
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
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 flag REPLACE MUST be set to FALSE = 0;
* the PHR resource units MUST be included into the <Bandwidth>
parameter. The value of the <Bandwidth> 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). If no QOS-NSLP aggregation is
accomplished by the QNE Ingress node, the value of the <Bandwidth>
parameter SHOULD be equal to the <Bandwidth> parameter of its
associated new (initial) intra-domain RESERVE (RMD-QSPEC) message;
* the value of the Parameter/Container field of the "PHR RMD-QOSM
control information" container MUST be set to "2",
i.e., "PHR_Refresh_Update";
* In a single-domain case the PDR container field
is not needed in the message.
* the value of the <RII> object MUST contain the Response
Identification Information value of the Ingress QNE, that is
unique within a session and different for each message (see
[QoS-NSLP]).
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>, [*QSPEC] objects are
processed by the standard QoS-NSLP protocol functions (see Section
4.6.1.1);
Bader, et al. [Page 33]
INTERNET-DRAFT RMD-QOSM
* the PDR has to be processed and removed 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) (in case of the flow aggregation procedure 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" control information 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:
* the value of <Bandwidth> parameter of the "RMD QoS Description"
field is used by the QNE Interior node for refreshing the RMD
traffic class state. These resources (included in <Bandwidth>),
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 Section 4.3.3. If the
refresh procedure cannot be fulfilled then the <M> parameter of the
PHR container MUST be set to "1". Furthermore, the "E" flag
associated with <QoS Desired> object and the "E" flag associated
with the <Bandwidth> parameter SHOULD be set.
Any PHR container of type "PHR_Refresh_Update", and its associated
"RMD QoS Description" field (i.e., <Bandwidth>), whether it is
marked or not and independent of the "E" flag value of the
<Bandwdith> parameter, is always processed, but marked bits are not
changed.
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INTERNET-DRAFT RMD-QOSM
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 intra-domain RESPONSE (RMD-QSPEC) message MUST be sent to the
QNE Ingress node, i.e., the previous stateful hop. The address of the
QNE Ingress node can be found using the existing messaging
association between the QNE Egress and QNE Ingress nodes. This state
is associated with the end-to-end session and identified by the
SESSION ID that is bound to the session of the intra-domain
RESPONSE(RMD-QSPEC) message.
* the values of the <RII/RSN>, <INFO_SPEC> objects are set
by the standard QoS-NSLP protocol functions.
* The value of the <PDR Control Type> parameter of the PDR container
MUST be set "8" (i.e. PDR_Refresh_Report).
In case of successful reservation the INFO_SPEC object SHOULD
have the following values:
Error Severity Class: 0x02, Success
Error Code value: 0x01 Reservation successful
* In case of unsuccessful reservation the INFO_SPEC object SHOULD
have the following values:
Error Severity Class: 0x04, Transient Failure
Error Code value: 0x07 Total reservation failure
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 <Bandwidth> parameter are set.
4.6.1.4. RMD modification of aggregated reservations
In the case when the QNE edges maintain QoS-NSLP aggregated
reservation states and the aggregated reservation has to be
modified (see Section 4.3.1) the following procedure is applied:
Bader, et al. [Page 35]
INTERNET-DRAFT RMD-QOSM
* When the modification request requires an increase of the reserved
resources, the QNE Ingress node MUST include the corresponding
value into the <Bandwidth> parameter of the "RMD QoS Description"
field, 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" control information that is associated with
the <Bandwidth> parameter MUST be marked. 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 <Bandwidth> parameter of the "RMD QoS Description" field.
Subsequently an RMD release procedure SHOULD be accomplished (see
Section 4.6.1.5).
4.6.1.5 RMD release procedure
If a refresh RESERVE message does not arrive at a QNE Interior node
within the refresh time-out period then the resources associated
with this message are removed. 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.
When the RMD-RMF of a QNE edge or QNE Interior node processes a
"PHR_Release_Request" control information 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. 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"
control information.
Bader, et al. [Page 36]
INTERNET-DRAFT RMD-QOSM
When a node (QNE edge or QNE Interior) receives the
"PHR_Release_Request" control information, 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 <Bandwidth> parameter of
the "RMD QoS Description" field that has been sent together with the
"PHR_Release_Request" control information container, but not below
zero.
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 that includes one
of the following error codes, see Section 4.7:
0x01 - Informational
0x03 - Protocol error
0x04 - Transient Failure
0x05 - Permanent failure
0x06 - QoS-related Error
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
has to be notified.
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INTERNET-DRAFT RMD-QOSM
Similar to 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, which
corresponds to a RAO value that will be used by the GIST message that
carries the end-to-end RESPONSE message to bypass the QNE Interior
nodes. It will generate an intra-domain RESERVE(RMD-QSPEC) message.
Before generating this message, the RMD RMF is using the RMD traffic
class (PHR) resources (specified in <Bandwidth>) and the PHB type
(specified in <PHB Class>) for a RMD release procedure. This can be
achieved by subtracting the amount of the requested resources from
the total reserved amount of resources stored in the RMD traffic
class state.
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
The intra-domain RESERVE (RMD-QSPEC) message MUST include a "RMD
QoS Description" field and a PHR container, (i.e.,
"PHR_Resource_Release") 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:
Bader, et al. [Page 38]
INTERNET-DRAFT RMD-QOSM
* The flag REPLACE MUST be set to FALSE = 0;
* The <RII> object MUST not included in this message. This is
because the QNE Ingress node does not need to receive a
response from the QNE Egress node;
* the TEAR flag MUST be set to ON;
* the PHR resource units MUST be included into the <Bandwidth>
parameter of the "RMD QoS Description" field;
* 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 "3" (i.e.,
PHR_Resource_Release).
The intra-domain tear RESERVE (RMD-QSPEC) message is received and
processed by the QNE Interior nodes. Most of the non-default
values of the objects contained in this refresh intra-domain RESERVE
(RMD-QSPEC) message are set by a QNE Interior node in the same way
as described in Section 4.6.1.1. The following objects are set and
processed differently:
* Any QNE Interior node that receives the combination of the "RMD
QoS Description" field and the "PHR_Resource_Release" control
information container MUST identify the traffic class (PHB)
and release the requested resources included in the <Bandwidth>
parameter. This can be achieved by subtracting the amount of RMD
traffic class requested resources, included in the <Bandwidth>
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_Resource_Release" container is used during the release
procedure as explained in Section 4.6.1.5.
The intra-domain tear RESERVE (RMD-QSPEC) message is received and
processed by the QNE Egress node. The "RMD QoS Description" and the
"PHR RMD-QOSM control " container (and if available the "PDR RMD-QOSM
control information" container) are read and processed by the RMD QoS
node.
Bader, et al. [Page 39]
INTERNET-DRAFT RMD-QOSM
The value of the <Bandwidth>
parameter of the "RMD QoS Description" field and the value of the
<Time Lag> field of the PHR container MUST be used by the RMD release
procedure. This can be achieved by subtracting the amount of RMD
traffic class requested resources, included in the <Bandwidth>
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 the above described procedure applies to the situation that
the QNE edges maintain a per flow QoS-NSLP reservation state. 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
in this Section.
4.6.1.5.2 Triggered by a marked RESPONSE or NOTIFY message
This RMD explicit release procedure can be triggered by either an
end-to-end RESPONSE message with a <M> marked PDR container (see
Section 4.6.1.2) an intra-domain RESPONSE message with a <S> marked
PDR container (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: 0x01 Informational
Error Code value: 0x05 Congestion situation
The RMD specific release procedure that is triggered by an
end-to-end RESPONSE message with a <M> marked PDR container (see
Section 4.6.1.2) can be terminated at any QNE edge
or any QNE Interior node using the <Max_Admitted Hops> field.
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The RMD specific explicit release procedure that is terminated at a
QNE Interior (or QNE edge) node is denoted as RMD partial release
procedure. This explicit release procedure can be used, for example,
during a RMD specific operation for unsuccessful reservation (see
Section 4.6.1.2). When the RMD QoS signaling model functionality of a
QNE Ingress node receives a <M> or <S> marked PDR container of type
"PDR_Reservation_Report" or "PDR_Congestion_Report", it MUST start an
RMD partial release procedure. The QNE Ingress node generates an
intra-domain RESERVE (RMD-QSPEC) message. Before generating this
message, the RMD-QOSM functionality is using the RMD traffic class
(PHR) resource units for a RMD release procedure. This can be
achieved by subtracting the amount of RMD traffic class requested
resources from the total reserved amount of resources stored in the
RMD traffic class state.
When the generation of the intra-domain RESERVE (RMD-QSPEC) message
is triggered by an end-to-end NOTIFY message, which does not carry a
PDR container, but it carries an INFO_SPEC object with the following
values, then the intra-domain RESERVE(RMD-QSPEC) message MUST include
an <RMD QoS Description> field and a PHR container, (i.e.,
PHR_Resource_Release) and it MAY include a PDR container, (i.e.,
PDR_Release_Request). Note that this procedure is accomplished during
the severe congestion handling by proportional data packet marking,
see Section 4.6.1.6.2. The error code values carried by this NOTIFY
message are:
Error Severity Class: 0x01 Informational
Error Code value: 0x05 Congestion situation
Furthermore, note that the tear intra-domain RESERVE message is
generated as it is shown in Figure 12, when it is triggered by either
a NOTIFY message or RESPONSE message that do not carry a PDR
container, but the INFO_SPEC object includes one of the following
error codes, see Section 4.7:
0x01 - Informational
0x03 - Protocol error
0x04 - Transient Failure
0x05 - Permanent failure
0x06 - QoS-related Error
An example of this message exchange can be seen in Figure 12.
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.
Bader, et al. [Page 41]
INTERNET-DRAFT RMD-QOSM
The following objects MUST be used and/or set differently:
* The flag REPLACE MUST be set to FALSE;
* 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.
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=SET) | |
| ---------------->|RESERVE(RMD-QSPEC:Tear=1, M=1,S=SET) |
| | | |
| |----------------->| |
| | RESERVE(RMD-QSPEC:Tear=1, M=1,S=SET)
| | |----------------->|
Figure 12: Basic operation during RMD explicit release procedure
triggered by NOTIFY used by the RMD-QOSM
When the generation of the intra-domain RESERVE(RMD-QSPEC) message
is triggered by an end-to-end RESPONSE(PDR) message then this
generated intra-domain RESERVE(RMD-QSPEC) message MUST include a
<RMD QoS Description> field and a PDR container, (i.e.,
PHR_Resource_Release) and it MAY include a PDR container, (i.e.,
PDR_Release_Request). 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 flag REPLACE MUST be set to FALSE;
* The value of the <M> parameter of the PHR container MUST be set
to "1".
* The RESERVE message MAY include a PDR container.
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* When the tear intra-domain RESERVE message is triggered by an
intra-domain RESPONSE(RMD-QSPEC) message, then the value of the
<Max Admitted Hops> parameter of the PDR container included in the
received <M> or <S> marked intra-domain RESPONSE(PDR) message
MUST be included in the <Max Admitted Hops> parameter of the PDR
container of the RESERVE message. Note that this procedure is
applied for the severe congestion handling by the RMD-QOSM refresh
procedure (see Section 4.6.1.6.1). The tear intra-domain RESERVE
message propagates in this case until the QNE egress (similar to
Figure 12).
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, <Admitted Hops>=<Max_Admitted Hops>)
|------------------->| | |
| | | |
Figure 13: Basic operation during RMD explicit release procedure
Triggered by RESPONSE used by the RMD-QOSM
Any QNE edge or QNE Interior node that receives the
"RMD QoS Description" field and the PHR container MUST identify the
traffic class state (PHB), using the <PHB Class> parameter, and
release the requested resources included in the <Bandwidth> field.
This can be achieved by subtracting the amount of RMD traffic class
requested resources, included in the <Bandwidth> field, 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 Section 4.6.1.5.
The <Admitted Hops> value included in the PHR container is increased
by one. If the value of <M> parameter of the "PHR_Resource_Release"
control information container is "1" and if the value of the <S>
parameter is set to "0" then the <Max_Admitted Hops> value included
in the PDR container MUST be compared with the calculated <Admitted
Hops> value. When these two values are equal then the intra-domain
RESERVE(RMD-QSPEC) has to be terminated and it will not be forwarded
downstream. The reason of this is that the QNE node that is
currently processing this message was the last QNE node that
successfully processed the "RMD QoS Description" field 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
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INTERNET-DRAFT RMD-QOSM
reservation request, therefore, this QNE node marked the <M>
parameter of the "PHR_Resource_Request" control information. When
the values of the <M> and <S> parameters are set to "0", then this
message will not be terminated by a QNE Interior node, but it will be
forwarded in the downstream direction. The QNE Egress node will
receive and process the PHR_Resource_Release control information.
Afterwards, the QNE Egress node MUST terminate the intra-domain
RESERVE(RMD-QSPEC) message.
Note that the above described procedure applies to the situation that
the QNE edges maintain a per flow QoS-NSLP reservation state. 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
in this section.
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
The QoS-NSLP and RMD are able to cope with congested situations
using the refresh procedure, see Section 4.6.1.3. If the refresh is
not successful in an QNE Interior node, edge nodes are notified by
"S" marking the refresh messages and by including the percentage of
overload into the <Overload %> field in the "PHR_Refresh_Update"
container, carried by the intra-domain RESERVE message.
The intra-domain RESPONSE message that is sent by the QNE Egress
towards QNE Ingress will contain a PDR container with a
Parameter/Container ID = 10, i.e., "PDR_Congestion_Report". The
values of the <S> and <Overload %> fields of this container should
be set equal to the values of the <S> and <Overload %> fields,
respectively, carried by the "PHR_Refresh_Update" message. Part of
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INTERNET-DRAFT RMD-QOSM
the flows, corresponding to the <Overload %>, 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. Note that
the above described functionality applies to the RMD reservation-
based and to the NSIS measurement-based admission control schemes.
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 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. The use of this DSCP
type eliminates the possibility that, due to e.g. 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.
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It is RECOMMENDED that the total number of additional DSCPs needed
for severe congestion handling within an RMD domain should be as low
as possible and it should not exceed the limit of 16. 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, independently from their dropping
precedence. Assuming 4 AF classes and 1 EF class, and using one DSCP
per traffic class then the number of DSCPs used in this situation for
severe congestion is 5. If two additional DSCP's are used then the
total number in this case is 10.
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
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. 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
states.
The ingress/egress pair aggregated 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, i.e., <Preemption Priority>
& <Defending Priority> parameter, or by using a local defined policy.
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.
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INTERNET-DRAFT RMD-QOSM
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 a 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:
* the values of the <INFO_SPEC> object is set by the standard
QoS-NSLP protocol functions.
* the INFO_SPEC object SHOULD include information that notifies that
the end-to-end flow SHOULD be terminated. This information is as
follows:
Error Severity Class: 0x01 Informational
Error Code value: 0x05 Congestion situation
The selection and notification process of the end-to-end is identical
for the scenarios where the QNE Edges maintain per-flow or aggregated
QoS-NSLP reservation states.
Furthermore, 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 not be restored if
there is an SLA agreement between domains that a downstream domain
handles the remarking problem.
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), or shifting them to an alternative RMD
traffic class (PHB). This operation is depicted in Figure 14, where
the QNE Ingress, for each flow (session) to be terminated, receives a
NOTIFY message. The NOTIFY message SHOULD include an INFO-SPEC object
with the following information:
Error Severity Class: 0x1 Informational
Error Code value: 0x05 Congestion situation
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INTERNET-DRAFT RMD-QOSM
When the QNE Ingress node receives the end-to-end NOTIFY message, it
associates this NOTIFY message with its bound intra-domain session,
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 |flow?
|<----------------|------------------|------------------|YES
|RESERVE(RMD-QSPEC:Tear=1,M=1,S=SET) | |
| --------------->|RESERVE(RMD-QSPEC:T=1, M=1,S=SET) |
| | | |
| |----------------->| |
| | RESERVE(RMD-QSPEC:Tear=1, M=1,S=SET)
| | |----------------->|
Figure: 14 RMD severe congestion handling
Note that the above functionality applies to the RMD reservation-
based and to both measurement-based admission control methods (i.e.,
congestion notification based on probing and the NSIS measurement-
based admission control). The above functionality applies also for
the scenario where the QNE Edge nodes maintain either per flow QoS-
NSLP reservation states or aggregated QoS-NSLP reservation states.
In the case that the edges support aggregated QoS-NSLP reservation
states the following actions take place. When the QNE Ingress node
receives the end-to-end NOTIFY message, it associates the NOTIFY
message with the intra-domain aggregated QoS-NSLP state via the
BOUND_SESSION_ID information included in the end-to-end per-flow QoS-
NSLP state. The QNE Ingress node should reduce the bandwidth
associated with the end-to-end flow from the aggregated bandwidth
associated with its bound aggregated QoS-NSLP reservation state. This
is accomplished by triggering the RMD modification for aggregated
reservations procedure described in Section 4.6.1.4.
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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.
If the ingress is configured to neither process this type of
admission control nor any other admission control scheme specified in
the previous sections, then the <NON QOSM Hop> parameter that is
carried by the end-to-end QSpec SHOULD be set.
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.
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. Using
standard functionalties 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 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.
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INTERNET-DRAFT RMD-QOSM
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 state for each supported PHB.
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.
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: 0x04, Transient failure
Error Code value: 0x07 Total 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 <Bandwidth> 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 not be restored if there is an
SLA agreement between domains that a downstream domain handles the
remarking problem.
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INTERNET-DRAFT RMD-QOSM
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
4.6.2 Bi-directional operation
RMD assumes asymmetric routing by default. Combined sender-receiver
initiated reservation cannot be efficiently done in the RMD domain
because upstream NTLP states are not stored in Interior routers.
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.
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INTERNET-DRAFT RMD-QOSM
This 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 <Bandwidth> parameters
for both directions, i.e., QNE Ingress towards QNE Egress and QNE
Egress towards QNE Ingress, then the QNE Ingress MAY include both
<Bandwidth> 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
the <BOUND_SESSION_ID> object at the QNE Ingress and QNE Egress.
|------ 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 bi-directional reservation scenario in the RMD domain
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.
The first BOUND_SESSION_ID object is applied 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. 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 0x01 (Tunnel and end-
to-end sessions). If the QNE Edge nodes maintain intra-domain
aggregated QoS-NSLP reservation states then the value of Binding_Code
MUST be set to 0x03 (Aggregate sessions).
The intra-domain RESERVE SHOULD contain in the BOUND_SESSION_ID the
SESSION_ID of its bound end to end session. The value of the
Binding_Code MUST be set to 0x01 (Tunnel and end-to-end sessions).
Bader, et al. [Page 52]
INTERNET-DRAFT RMD-QOSM
The SESSION_ID field of the second BOUND_SESSION_ID object depends on
the direction of the message. An upstream RMD QoS-NSLP message SHOULD
contain the SESSION_ID of the bound downstream end-to-end flow. A
downstream RMD QoS-NSLP message SHOULD contain the SESSION_ID of the
bound upstream end-to-end flow. In both cases the value of the
Binding_Code associated with this BOUND_SESSION_ID object SHOULD be
equal to 0x02.
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".
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 <Bandwidth> parameters
for both directions, i.e., QNE Ingress towards QNE Egress and
QNE Egress towards QNE Ingress.
4.6.2.1 Successful and unsuccessful reservations
This section describes the operation of the RMD-QOSM where a RMD
bi-directional reservation operation 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. 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 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:
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* Two BOUND_SESSION_ID objects MUST be used. The first
BOUND_SESSION_ID object contains the SESSION_ID of its bound
End-to-end session. The value of the Binding_Code MUST be set to
0x01 (Tunnel and end-to-end sessions). The SESSION_ID field of
the second BOUND_SESSION_ID object SHOULD contain the SESSION_ID
of the bound "reverse" end-to-end flow. The value of the
Binding_Code associated with this BOUND_SESSION_ID object SHOULD
be equal to 0x02.
* the RII object MUST NOT included in the message. This is because
no RESPONSE message is expected to arrive.
* the <B> bit of the PHR container indicates a bi-directional
reservation and it MUST be set to "1".
* the PDR container is also included into the RESERVE(RMD-QSPEC):
"forward" message. The value of the Parameter/Container ID is
"4", 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 Reverse Requested Resources> 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:
Bader, et al. [Page 54]
INTERNET-DRAFT RMD-QOSM
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
* two BOUND_SESSION_ID objects SHOULD be used.
The first BOUND_SESSION_ID object contains the SESSION ID of its
bound end to end session. The value of the Binding_Code = 0x01
(Tunnel and end-to-end sessions). The SESSION_ID field of
the second BOUND_SESSION_ID object SHOULD contain the SESSION_ID
of the bound "forward" end-to-end flow. The value of the
Binding_Code associated with this BOUND_SESSION_ID object SHOULD
be equal to 0x02.
* the RII object is not included in the message. This is because no
RESPONSE message is expected to arrive;
* the value of the <Bandwidth> parameter is set equal to the value
of the <PDR Reverse Requested Resources> field included in the
RESERVE(RMD-QSPEC):"forward" message that triggered the
generation of this RESERVE(RMD-QSPEC): "reverse" message;
* 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
Parameter/Container ID is "7", i.e., "PDR_Reservation_Report";
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* 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 <Bandwidth> 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 <Bandwidth> 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
<Bandwidth> it MUST mark the <M> bit, i.e., set to value "1", of
the RESERVE(RMD-QSPEC): "forward".
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 difference
is that the QNE Egress generates an intra-domain (local)
RESPONSE(PDR) message that is sent towards QNE Ingress node.
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) | M |
|"forward - T tear" | M |
|----------------> | 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 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
<Bandwidth> it MUST mark the <M> bit, i.e., set to value "1",
the RESERVE(RMD-QSPEC):"reverse".
* 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 (local) RESERVE(RMD-QSPEC):
"forward - T tear" message. This message carriers a
"PHR_Release_Request" and a "PDR_Release_Request" control
information. This message is sent to QNE Egress node.
The QNE Egress node by using the information contained in the
"PHR_Release_Request" and the "PDR_Release_Request" control
info containers it generates a RESERVE(RMD-QSPEC):"reverse - T
tear" message that is sent towards the QNE Ingress node.
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): M | |
|"forward - T tear" M | |
|--------------->| RESERVE(RMD-QSPEC): | |
| | "forward - T tear" | |
| |-------------------------------->| |
| | M |------------->|
| | M RESERVE(RMD-QSPEC):
| | M reverse - T tear" |
| | 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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4.6.2.2 Refresh reservations
This section describes the operation of the RMD-QOSM where a RMD
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 Parameter/Container ID of the PHR container is
"2", i.e., "PHR_Refresh_Update".
* the value of the Parameter/Container ID of the PDR container is
"5", 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 Parameter/Container ID of the PHR container is
"2", i.e., "PHR_Refresh_Update".
* the value of the Parameter/Container ID of the PDR container is
"8", i.e., "PDR_Refresh_Report".
4.6.2.3 Modification of aggregated reservations
This section describes the operation of the RMD-QOSM where a RMD
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:
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INTERNET-DRAFT RMD-QOSM
* When the modification request requires an increase of the reserved
resources, the QNE Ingress node MUST include the corresponding value
into the <Bandwidth> parameter of the "RMD QoS Description" field,
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" control information associated with the
<Bandwidth> parameter MUST be marked. In this situation the RMD
specific operation for unsuccessful reservation will be applied (see
Section 4.6.2.1).
* When the modification request requires a decrease of the
reserved resources, the QNE Ingress node MUST include this value
into the <Bandwidth> parameter of the "RMD QoS Description" field.
Subsequently an RMD release procedure SHOULD be accomplished (see
Section 4.6.2.4).
4.6.2.4 Release procedure
This section describes the operation of the RMD-QOSM where a RMD
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 Parameter/Container ID of the PHR container is
"3", i.e."PHR_Release_Request";
* the value of the Parameter/Container ID of the PDR container is
"6", 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 Parameter/Container ID of the PHR container is
"3", i.e., "PHR_Release_Request";
* the PDR container is not included in the RESERVE (RMD-QSPEC):
"reverse" message.
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4.6.2.5 Severe congestion handling
This section describes the severe congestion handling operation used
in combination with 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 bi-directional
reservation procedure.
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))
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INTERNET-DRAFT RMD-QOSM
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" path (i.e.,
path between QNE Ingress towards QNE Egress) or "reverse" path (i.e.,
path between QNE Egress towards QNE Ingress). Another difference is
associated with the way of how the egress node selects the flows that
have to be terminated. Note that when a severe congestion situation
occurs on e.g.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.
Furthermore, a special case of this operation is associated to the
severe congestion situation occuring simultaneously on the forward
and reverse paths. An example of this operation is given in Appendix
A.3.2.
Figure 20 shows the scenario where the severe congested node is
located in the "forward" path. 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.
Bader, et al. [Page 61]
INTERNET-DRAFT RMD-QOSM
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
| | | | |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))
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Figure 21 shows the scenario where the severe congested node is
located in the "reverse" path. The main difference between this
scenario and the scenario shown in Figure 20 is that no intra-domain
NOTIFY(PDR) message has to be generated by the QNE Egress node. This
is because the (#marked and #unmarked) user data is arriving at the
QNE Ingress. 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.
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 bi-directional
reservations are supported.
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).
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))
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Figure 22 shows the scenario where the severe congested node is
located in the "forward" path. The functionality of providing
admission control is very similar to 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 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.
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
of how these additional errors are handled and notified is specified
in [QSP-T] and [QoS-NSLP].
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5. Security Considerations
A router implementing a QoS signaling protocol can, similar to a
router without QoS signaling, do a lot of harm to a system. If taken
over by an adversary, a router can delay, drop, inject, duplicate or
modify packets. Additional threats are, however, introduced with new
protocols and they are subject for a discussion below.
The RMD-QOSM aims to 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. This implies the usage of the Datagram Mode which
does not allow channel security to be used. As such, RMD signaling is
targeted towards intra-domain signaling only.
In the context of RMD-QOSM signaling a classification between
on-path adversaries and off-path adversaries needs to be made.
Furthermore, it might be necessary to differentiate between off-path
nodes that never participate in the RMD signaling exchange and nodes
that are only off-path with regard to a specific signaling session
whereby routing asymmetry might even mean that the downstream and the
upstream signaling direction matters for this classification.
QNE QNE QNE QNE
Ingress Interior Interior Egress
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
| RESERVE (1) | | |
+--------------------------------------------->|
| RESERVE' (2) | | |
+-------------->| | |
| | RESERVE' | |
| +-------------->| |
| | | RESERVE' |
| | +------------->|
| | | |
| | | RESPONSE (1) |
|<---------------------------------------------+
| | | |
Figure 24: RMD message exchange
Note 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 must
always been seen as a combination of the two signaling sessions, (1)
and (2) of Figure 24.
Bader, et al. [Page 65]
INTERNET-DRAFT RMD-QOSM
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, SHOULD NOT interfere with QNE Interior nodes. Off-path
nodes (off-path with regard to the path taken by a particular
signaling message exchange) SHOULD 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.
If we assume that the RESERVE/RESPONSE is sent in C-Mode and
protected between the QNE Ingress and the QNE Egress node then we can
be sure that the payloads of these messages MUST be authenticated,
integrity, replay protected and encrypted. Encryption is necessary to
prevent an adversary that is located along the path of the RESERVE
message to learn information about the session that can later be used
to inject a valid RESERVE'. The following messages need to relate 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' (carried in the RESPONSE) relate to
each other
The RESERVE and the RESERVE' message are tied together using the
BOUND_SESSION_ID. 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.
Bader, et al. [Page 66]
INTERNET-DRAFT RMD-QOSM
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.
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
<Overload %> 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 to refer to a flow that might be terminated. The
aspect of intermediate nodes initiating messages for severe
congestion handling is for further study.
QNE QNE QNE QNE
Ingress Interior Interior Egress
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
| REFRESH | | |
| RESERVE' | | |
+-------------->| REFRESH | |
| (+RII) | RESERVE' | |
| +-------------->| REFRESH |
| | (+RII) | RESERVE' |
| | +------------->|
| | | (+RII) |
| | | |
| | | REFRESH |
| | | RESPONSE'|
|<---------------------------------------------+
| | | (+RII) |
| | | |
Figure 25: RMD REFRESH message exchange
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'. The QNE Egress is able to determine whether the RESERVE'
(as a refresh) was created by the QNE Ingress node since the
BOUND_SESSION_ID is included in the RESERVE' message.
Bader, et al. [Page 67]
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With the initial RESERVE'/RESERVE exchange there is a one-to-one
mapping between the RESERVE and the RESERVE' message based on the
SESSION_ID that is used in the two messages and the BOUND_SESSION_ID.
With the REFRESH' message this is not the case since they relate to
one RESERVE message exchange.
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. 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
RMD-QOSM requires a new IANA registry for RMD QoS Model
Identifiers. It is a 32-bit value carried in a QSPEC object [QSP-T].
RMD-QOSM defines 2 new objects for the QSPEC Template: PHR container
and PDR container, see 4.1.2 and 4.1.3. For these new containers, new
IDs in the QSPEC Template Object Type registry should be assigned.
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
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
Bader, et al. [Page 68]
INTERNET-DRAFT RMD-QOSM
Georgios Karagiannis
University of Twente
P.O. BOX 217
7500 AE Enschede, The Netherlands
EMail: g.karagiannis@ewi.utwente.nl
Cornelia Kappler
Siemens AG
Siemensdamm 62
Berlin 13627, Germany
Email: cornelia.kappler@siemens.com
Hannes Tschofenig
Siemens AG
Otto-Hahn-Ring 6
Munich 81739, Germany
EMail: Hannes.Tschofenig@siemens.com
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
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., Van de Bosch,
S., "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).
10. Informative References
[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.
Bader, et al. [Page 69]
INTERNET-DRAFT RMD-QOSM
[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
[RFC2961] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.
and S. Molendini, "RSVP Refresh Overhead Reduction Extensions",
RFC 2961, April 2001.
[RFC3175] Baker, F., Iturralde, C. Le Faucher, F., Davie, B.,
"Aggregation of RSVP for IPv4 and IPv6 Reservations",
IETF RFC 3175, 2001.
[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
[GIST] Schulzrinne, H., Hancock, R., "GIST: General Internet
Messaging Protocol for Signaling", draft-ietf-nsis-ntlp
(work in progress).
[RFC1633] Braden R., Clark D., Shenker S., "Integrated Services in
the Internet Architecture: an Overview", RFC 1633
[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
[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.
Bader, et al. [Page 70]
INTERNET-DRAFT RMD-QOSM
[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
Appendix A.1.1 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.
---------------------------------------------
| 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
Bader, et al. [Page 71]
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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
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. 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.
event C: this event occurs when the incoming PHB rate is lower than
the "congestion notification detection" threshold.
event D: this event occurs when the incoming PHB rate is lower than
the "severe_congestion_restoration" threshold.
event E: this event occurs when the incoming PHB rate is lower than
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:
Bader, et al. [Page 72]
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* 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.
* 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)
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
where 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, in 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.
Bader, et al. [Page 73]
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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
The bytes that have to be remarked to satisfy the signaled overload
rate: signaled_remarked_bytes, are calculated as follows:
signaled_remarked_bytes = signaled_overload_rate*T/N
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
ca be calculated and represented.
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.
Bader, et al. [Page 74]
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Note that when the "affected DSCP" marking is applied by a severe
congested node then all the outgoing packets that are not marked
(i.e., by using the "encoded DSCP") have to be remarked using the
"affected DSCP" code. 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 might
be used, see Section 4.6.1.7. This additional DSCP might be 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).
Appendix A.1.2 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 how
ever different than the definition of the events given in Figure A.1
and Figure A.2:
* event A: the egress node measures the rate of the incoming
"notified_DSCP" marked packets and compare it with a predefined
congestion notification detection threshold at the egress. When the
measured rate of "notified DSCP" bytes is higher than this threshold
then event_A is activated, see Section 4.6.1.7 and A.2.2. This is
applied when the whole RMD domain uses "notified DSCP" for this
purpose. If the "notified DSCP" marking is not used in the whole RMD
domain, the "encoded_DSCP" marking is used to notify the congestion
notification state. In this case the egress should measure the rate
of the incoming "encoded_DSCP" marked packets and compare it with a
predefined congestion notification detection threshold and to a
severe congestion detection threshold in the egress. Note that the
detection thresholds used in the egress for congestion notification
and severe congestion may be different than the ones used in interior
nodes. When the measured rate of "encoded DSCP" bytes is higher than
the congestion notification threshold but lower than the severe
congestion threshold then event_A is activated.
* 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). However, when the "encoded_DSCP"
marking is also used for congestion notification detection purposes,
see description of event_A, then event_B is only activated if either
"affected DSCP" packets are received or if the rate of the incoming
"encoded_DSCP" marked packets is higher than the preconfigured severe
congestion detection egress threshold.
Bader, et al. [Page 75]
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* event C: this event occurs when the rate of incoming
"notified DSCP" packets decreases below the congestion notification
detection threshold. This is applied when whole RMD domain uses
"notified DSCP" for this purpose. When the "encoded_DSCP" marking is
also used for congestion notification detection, see description of
event_A, then event_C is activated when the rate of incoming "encoded
DSCP" packets decreases below the congestion notification threshold.
* event D: this event occurs when the egress does not receive packets
marked as either "encoded DSCP" or "affected DSCP" (when "affected
DSCP" is applied in the whole RMD domain). When the "encoded_DSCP"
marking is also used for congestion notification detection, see
description of event_A, event_B, event_C, then the event_D is only
activated if either "affected DSCP" packets are not anymore received
or if the rate of the incoming "encoded_DSCP" marked packets is
slower than the preconfigured severe congestion restoration threshold
in egress.
* event E: this event occurs when the egress 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 pseudocode below.
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
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 marked bytes
that arrive at the ingress, during one measurement interval T, N is
defined as in Section 4.6.1.6.2.1. 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
Bader, et al. [Page 76]
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0 < priority_class =< Maximum_priority.
The calculate_terminate_flows(priority_class) function determines the
Flows for a given priority class and per PHB that has to be
Terminated. This function also calculates the term
sum_bandwidth_terminate(priority_class), which is the sum of the
bandwith associated with the flows that will 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 aggregates, then the
above algorithm is performed for each ingress/egress pair aggregate.
Appendix A.2.1 Example of a detailed remarking admission control
(congestion notification) operation in Interior nodes
In particular, the predefined congestion notification threshold 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. 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):
Bader, et al. [Page 77]
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* using different DSCP values (re-marked DSCP values). The remarked D
SCP 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 the unmarked bytes using the "notified DSCP". Note that this
method can only be applied if all nodes in RMD domain use the
"notified" DSCP marking.
* Using the "encoded DSCP" marking for congestion notification and
severe congestion. This situation is applied when the "notified DSCP"
marking is not applied in the RMD domain. When this method is used
and when the interior node is in "congestion notification" state, see
A.1.1, then the node should remark the unmarked bytes using the
"encoded DSCP".
Note that if a node starts dropping packets belonging to a PHB that
suports both "severe congestion" and "congestion notification"
states, see section 4.6.1.6.2.1, then it is considered that the
packet rate associated to this PHB is higher than the severe
congestion detection threshold and that the operation state of this
node has moved to the severe congestion state, see Appendix A.1.1.
Appendix A.2.2 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 maintais 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
instead of the "notified DSCP", the "encoded DSCP" bytes.
The incoming congestion_rate can be then calculated as follows:
incoming_congestion_rate = N*input_notified_bytes/T
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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. In this
situation if the end-to-end RESERVE (probe) arrives at the egress,
then this request SHOULD be rejected. Note that this choice is
independent of the DSCP marking status of the packet that carries the
RESERVE message.
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
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.
Appendix A.3.2 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. This situation is depicted in 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.
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INTERNET-DRAFT RMD-QOSM
QNE (Ingress) NE (int.) NE (int.) NE (int.) QNE (Egress)
NTLP stateful NTLP stateful
user| | | | |
data| user | | | |
--->| data | #unmarked bytes| | |
|--------------->S #marked bytes | | |
| S--------------------------->| |
| | | |-------------->|data
| | | | |--->
| | | | |Term.?
| NOTIFY | | |Yes
|<------------------------------------------------------------|
| | | | |
| | | | |data
| | | | |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)
* 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".
* 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".
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INTERNET-DRAFT RMD-QOSM
* 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".
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 received a (preemption) 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.
* 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 preemption in order to satisfy
the release of a total bandiwtdh up equal 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.
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INTERNET-DRAFT RMD-QOSM
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