Next Steps in Signaling J. Manner (ed.)
Internet-Draft University of Helsinki
Expires: September , 2006 G. Karagiannis
University of Twente/Ericsson
A. McDonald
Siemens/Roke Manor Research
March 2006
NSLP for Quality-of-Service Signaling
<draft-ietf-nsis-qos-nslp-10.txt>
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Copyright (C) The Internet Society (2006).
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Abstract
This draft describes an NSIS Signaling Layer Protocol (NSLP) for
signaling QoS reservations in the Internet. It is in accordance with
the framework and requirements developed in NSIS. Together with
GIST, it provides functionality similar to RSVP and extends it. The
QoS NSLP is independent of the underlying QoS specification or
architecture and provides support for different reservation models.
It is simplified by the elimination of support for multicast flows.
This draft explains the overall protocol approach, design decisions
made and provides examples. It specifies object and message formats
and processing rules.
Table of Contents
1 Introduction ................................................. 4
1.1 Scope and background ....................................... 4
1.2 Model of operation ......................................... 5
2 Terminology .................................................. 8
3 Protocol Overview ............................................ 9
3.1 Overall approach ........................................... 9
3.1.1 GIST Interactions ........................................ 9
3.1.2 Protocol messages ........................................ 10
3.1.3 QoS Models and QoS Specifications ........................ 11
3.1.4 Policy control ........................................... 12
3.2 Design decisions ........................................... 13
3.2.1 Soft-state ............................................... 13
3.2.2 Sender-receiver initiation ............................... 14
3.2.3 Message sequencing ....................................... 14
3.2.4 Explicit state installation confirmation and responses
3.2.5 Reduced refresh .......................................... 15
3.2.6 Message scoping .......................................... 15
3.2.7 Session binding .......................................... 16
3.2.8 Layering ................................................. 16
3.2.8.1 Local QoS models ....................................... 16
3.2.8.2 Local control plane properties ......................... 17
3.2.8.3 Aggregate reservations ................................. 17
3.2.9 Priority ................................................. 18
3.2.10 Rerouting ............................................... 18
4 Examples of QoS NSLP Operation ............................... 20
4.1 Basic sender-initiated reservation ......................... 20
4.2 Sending a Query ............................................ 22
4.3 Basic receiver-initiated reservation ....................... 22
4.4 Bidirectional Reservations ................................. 24
4.5 Use of Local QoS Models .................................... 25
4.6 Aggregate Reservations ..................................... 26
4.7 Reduced State or Stateless Interior Nodes .................. 27
4.8 Re-routing scenario ........................................ 30
4.9 Authorization Model Examples ............................... 31
4.9.1 Authorization for the two party approach ................. 31
4.9.2 Token based three party approach ......................... 31
4.9.3 Generic three party approach ............................. 32
5 QoS NSLP Functional specification ............................ 33
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5.1 QoS NSLP Message and Object Formats ........................ 33
5.1.1 Common header ............................................ 33
5.1.2 Message formats .......................................... 34
5.1.2.1 RESERVE ................................................ 34
5.1.2.2 QUERY .................................................. 36
5.1.2.3 RESPONSE ............................................... 37
5.1.2.4 NOTIFY ................................................. 37
5.1.3 Object Formats ........................................... 38
5.1.3.1 Request Identification Information (RII) ............... 39
5.1.3.2 Reservation Sequence Number (RSN) ...................... 39
5.1.3.3 REFRESH_PERIOD ......................................... 39
5.1.3.4 BOUND_SESSION_ID ....................................... 40
5.1.3.5 PACKET_CLASSIFIER ...................................... 40
5.1.3.6 INFO_SPEC .............................................. 41
5.1.3.7 QSPEC .................................................. 45
5.2 General Processing Rules ................................... 46
5.2.1 State Manipulation ....................................... 46
5.2.2 Message Forwarding ....................................... 47
5.2.3 Standard Message Processing Rules ........................ 47
5.2.4 Retransmissions .......................................... 47
5.2.5 Rerouting ................................................ 48
5.2.5.1 Last node behavior ..................................... 48
5.2.5.2 Reservation maintenance on route change ................ 49
5.2.5.3 Upstream route change notification ..................... 50
5.2.5.4 Route change oscillation ............................... 50
5.3 Object Processing .......................................... 51
5.3.1 Reservation Sequence Number (RSN) ........................ 51
5.3.2 Request Identification Information (RII) ................. 52
5.3.3 BOUND_SESSION_ID ......................................... 53
5.3.4 REFRESH_PERIOD ........................................... 53
5.3.5 INFO_SPEC ................................................ 55
5.3.5.1 Informational INFO_SPEC ................................ 55
5.3.5.2 Success INFO_SPEC ...................................... 55
5.3.5.3 Protocol Error INFO_SPEC ............................... 56
5.3.5.4 Transient Failure INFO_SPEC ............................ 57
5.3.5.5 Permanent Failure INFO_SPEC ............................ 57
5.3.5.6 NSLP-specific Error INFO_SPEC .......................... 58
5.3.6 QSPEC .................................................... 58
5.4 Message Processing Rules ................................... 58
5.4.1 RESERVE Messages ......................................... 59
5.4.2 QUERY Messages ........................................... 62
5.4.3 RESPONSE Messages ........................................ 62
5.4.4 NOTIFY Messages .......................................... 64
6 IANA considerations .......................................... 64
7 QoS use of GIST service interface ............................ 65
7.1 Example sender-initiated reservation ....................... 65
7.2 Session identification ..................................... 66
7.3 Support for bypassing intermediate nodes ................... 66
7.4 Support for peer change identification ..................... 67
7.5 Support for stateless operation ............................ 67
7.6 Last node detection ........................................ 67
7.7 Re-routing detection ....................................... 68
7.8 Priority of signaling messages ............................. 68
7.9 Knowledge of intermediate QoS NSLP unaware nodes ........... 68
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7.10 NSLP Data Size ............................................ 69
7.11 Notification of GIST 'D' flag value ....................... 69
7.12 NAT Traversal ............................................. 69
8 Assumptions on the QoS Model ................................. 69
8.1 Resource sharing ........................................... 69
8.2 Reserve/commit support ..................................... 69
9 Security Considerations ...................................... 70
9.1 Introduction and Threat Overview ........................... 70
9.2 Trust Model ................................................ 71
9.3 Computing the authorization decision ....................... 73
10 Acknowledgments ............................................. 73
11 Contributors ................................................ 74
12 References .................................................. 74
12.1 Normative References ...................................... 74
12.2 Informative References .................................... 74
1. Introduction
1.1. Scope and background
This document defines a Quality of Service (QoS) NSIS Signaling Layer
Protocol (NSLP), henceforth referred to as the "QoS NSLP". This
protocol establishes and maintains state at nodes along the path of a
data flow for the purpose of providing some forwarding resources for
that flow. It is intended to satisfy the QoS-related requirements of
RFC 3726 [RFC3726]. This QoS NSLP is part of a larger suite of
signaling protocols, whose structure is outlined in the NSIS
framework [RFC4080]; this defines a common NSIS Transport Layer
Protocol (NTLP) which QoS NSLP uses to carry out many aspects of
signaling message delivery. A specification of the NTLP, GIST [I-
D.ietf-nsis-ntlp] is done in another document.
The design of QoS NSLP is conceptually similar to RSVP, RFC 2205
[RFC2205], and uses soft-state peer-to-peer refresh messages as the
primary state management mechanism (i.e., state installation/refresh
is performed between pairs of adjacent NSLP nodes, rather than in an
end-to-end fashion along the complete signaling path). Although there
is no backwards compatibility at the level of protocol messages,
interworking with RSVP at a signaling application gateway would be
possible in some circumstances. QoS NSLP extends the set of
reservation mechanisms to meet the requirements of RFC 3726
[RFC3726], in particular support of sender or receiver-initiated
reservations, as well as, a type of bi-directional reservation and
support of reservations between arbitrary nodes, e.g., edge-to-edge,
end-to-access, etc. On the other hand, there is no explicit support
for IP multicast.
A distinction is made between the operation of the signaling protocol
and the information required for the operation of the Resource
Management Function (RMF). This document describes the signaling
protocol, whilst [I-D.ietf-nsis-qspec] describes the RMF- related
information carried in the QSPEC (QoS Specification) object in QoS
NSLP messages. This is similar to the decoupling between RSVP and the
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IntServ architecture, RFC 1633 [RFC1633]. The QSPEC carries
information on resources available, resources required, traffic
descriptions and other information required by the RMF.
This document is structured as follows. The overall approach to
protocol design is outlined in Section 3.1. The operation and use of
QoS NSLP is then clarified by means of a number of examples in
Section 4. These sections should be read by readers interested in the
protocol capabilities. The functional specification Section 5
contains more detailed object and message formats and processing
rules and should be the basis for implementers. The subsequent
sections describe extensibility (IANA), requirements on GIST API and
security considerations.
1.2. Model of operation
This section presents a logical model for the operation of the QoS-
NSLP and associated provisioning mechanisms within a single node.
The model is shown in Figure 1.
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+---------------+
| Local |
|Applications or|
|Management (e.g|
|for aggregates)|
+---------------+
^
V
V
+----------+ +----------+ +---------+
| QoS NSLP | | Resource | | Policy |
|Processing|<<<<<<>>>>>>>|Management|<<<>>>| Control |
+----------+ +----------+ +---------+
. ^ | * ^
| V . * ^
+----------+ * ^
| NTLP | * ^
|Processing| * V
+----------+ * V
| | * V
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
. . * V
| | * .............................
. . * . Traffic Control .
| | * . +---------+.
. . * . |Admission|.
| | * . | Control |.
+----------+ +------------+ . +---------+.
<-.-| Input | | Outgoing |-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.->
| Packet | | Interface | .+----------+ +---------+.
===>|Processing|====| Selection |===.| Packet |====| Packet |.==>
| | |(Forwarding)| .|Classifier| Scheduler|.
+----------+ +------------+ .+----------+ +---------+.
.............................
<.-.-> = signaling flow
=====> = data flow (sender --> receiver)
<<<>>> = control and configuration operations
****** = routing table manipulation
Figure 1: QoS NSLP in a Node
This diagram shows an example implementation scenario where QoS
conditioning is performed on the output interface. However, this does
not limit the possible implementations. For example, in some cases
traffic conditioning may be performed on the incoming interface, or
it may be split over the input and output interfaces. Also, the
interactions with the Policy Control component may be more complex,
involving more than a simple interaction with the Resource Management
Function.
From the perspective of a single node, the request for QoS may result
from a local application request, or from processing an incoming QoS-
NSLP message.
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o The request from a local application includes not only user
applications (e.g., multimedia applications) but also network
management (e.g. initiating a tunnel to handle an aggregate, or
interworking with some other reservation protocol - such as RSVP)
and the policy control module (e.g., for explicit teardown
triggered by AAA). In this sense, the model does not distinguish
between hosts and routers.
o Incoming messages are captured during input packet processing
and handled by GIST. Only messages related to QoS are passed to
the QoS NSLP. GIST may also generate triggers to the QoS NSLP
(e.g., indications that a route change has occurred).
The QoS request is handled by a local 'resource management'
function, which coordinates the activities required to grant and
configure the resource. It also handles policy-specific aspects of
QoS signaling.
o The grant processing involves two local decision modules,
'policy control' and 'admission control'. Policy control
determines whether the user has administrative permission to make
the reservation. Admission control determines whether the node has
sufficient available resources to supply the requested QoS.
o If both checks succeed, parameters are set in the packet
classifier and in the link layer interface (e.g., in the packet
scheduler) to obtain the desired QoS. Error notifications are
passed back to the request originator. The resource management
function may also manipulate the forwarding tables at this stage,
to select (or at least pin) a route; this must be done before
interface-dependent actions are carried out (including forwarding
outgoing messages over any new route), and is in any case
invisible to the operation of the protocol.
Policy control is expected to make use of a AAA service external to
the node itself. Some discussion can be found in a separate document
on AAA issues [NSIS-AAA] and one on authorization issues [QOS-AUTH].
More generally, the processing of policy and resource management
functions may be outsourced to an external node leaving only 'stubs'
co-located with the NSLP; this is not visible to the protocol
operation, although it may have some influence on the detailed design
of protocol messages to allow the stub to be minimally complex. A
more detailed discussion of authentication and authorization can be
found in Section 3.1.4.
The group of user plane functions, which implement QoS for a flow
(admission control, packet classification, and scheduling) is
sometimes known as 'traffic control'.
Admission control, packet scheduling, and any part of policy control
beyond simple authentication have to be implemented using specific
definitions for types and levels of QoS; Our assumption is that the
QoS NSLP is independent of the QoS parameters (e.g., IntServ service
elements). These are captured in a QoS Model and interpreted only by
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the resource management and associated functions, and are opaque to
the QoS NSLP itself. QoS Models are discussed further in Section
3.1.3.
The final stage of processing for a resource request is to indicate
to the QoS NSLP protocol processing that the required resources have
been configured. The QoS NSLP may generate an acknowledgment message
in one direction, and may forward the resource request in the other.
Message routing is (by default) carried out by the GIST module. Note
that while Figure 1 shows a unidirectional data flow, the signaling
messages can pass in both directions through the node, depending on
the particular message and orientation of the reservation.
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 [I-D.ietf-nsis-ntlp] applies to this
draft.
In addition, the following terms are used:
QNE: an NSIS Entity (NE), which supports the QoS NSLP.
QNI: the first node in the sequence of QNEs that issues a
reservation request for a session.
QNR: the last node in the sequence of QNEs that receives a
reservation request for a session.
Session: A "session" is essentially a signaling application
concept, since it is only used in non-trivial state management
actions that are application specific. A session defines an
association between a QNI and QNR related to a data flow. All QNEs
on the path, including the QNI and QNR, use the same identifier to
refer to the state stored for the association. The same QNI and
QNR may have more than one session active at any one time. The
session identifier should be (probabilistically) globally unique,
and it should not be modified end-to-end.
Session Identification (SESSION_ID, SID): This is a
cryptographically random and (probabilistically) globally unique
identifier of the application layer session that associated with a
certain flow. For a given flow, different signaling applications
may or may not use the same session identifier. Often there will
only be one flow for a given session, but in mobility/multihoming
scenarios there may be more than one and they may be differently
routed [RFC4080].
Source or message source: The one of two adjacent NSLP peers that
is sending a signaling message (maybe the upstream or the
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downstream peer). Note that this is not necessarily the QNI.
QoS NSLP operation state: State used/kept by QoS NSLP processing
to handle messaging aspects.
QoS reservation state: State used/kept by Resource Management
Function to describe reserved resources for a session.
Flow ID: This is essentially the Message Routing Information (MRI)
in GIST for path-coupled signaling.
Figure 2 shows the components that have a role in a QoS NSLP
signaling session. The flow sender and receiver would in most cases
be part of the QNI and QNR nodes. Yet, these may be separate nodes,
too.
QoS NSLP nodes
IP address (QoS unaware NSIS nodes are IP address
= Flow not shown) = Flow
Source | | | Destination
Address | | | Address
V V V
+--------+ Data +------+ +------+ +------+ +--------+
| Flow |-------|------|------|------|-------|------|---->| Flow |
| Sender | Flow | | | | | | |Receiver|
+--------+ | QNI | | QNE | | QNR | +--------+
| | | | | |
+------+ +------+ +------+
=====================>
<=====================
Signaling
Flow
Figure 2: Components of the QoS NSLP architecture.
A glossary of terms and abbreviations used in this document can be
found in Appendix A.
3. Protocol Overview
3.1. Overall approach
3.1.1. GIST Interactions
The QoS NSLP uses GIST for delivery of all its messages. Messages are
normally passed from the NSLP to GIST via an API (defined in Appendix
D of [I-D.ietf-nsis-ntlp]), which also specifies additional
information, including an identifier for the signaling application
(e.g., 'QoS NSLP'), the flow/session identifier, and an indication of
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the intended direction - towards data sender or receiver. On
reception, GIST provides the same information to the QoS NSLP. In
addition to the NSLP message data itself, other meta-data (e.g.
session identifier, flow routing information) can be transferred
across this interface.
The QoS NSLP does not provide any method of interacting with
firewalls or Network Address Translators (NATs). It assumes that a
basic NAT traversal service is provided by GIST.
3.1.2. Protocol messages
The QoS NSLP uses four message types:
RESERVE: The RESERVE message is the only message that manipulates
QoS NSLP reservation state. It is used to create, refresh, modify
and remove such state. The RESERVE message is idempotent; the
resultant effect is the same whether a message is received once or
many times.
QUERY: A QUERY message is used to request information about the
data path without making a reservation. This functionality can be
used to 'probe' the network for path characteristics, for
receiver- initiated reservations or for support of certain QoS
models. The information obtained from a QUERY may be used in the
admission control process of a QNE (e.g., in case of measurement-
based admission control). Note that a QUERY does not change
existing reservation state. It does not cause QoS NSLP state to be
installed in nodes other than the one that generated the QUERY.
RESPONSE: The RESPONSE message is used to provide information
about the result of a previous QoS NSLP message. This includes
explicit confirmation of the state manipulation signaled in the
RESERVE message, the response to a QUERY message or an error code
if the QNE or QNR is unable to provide the requested information
or if the response is negative. The RESPONSE message is impotent,
it does not cause any reservation state to be installed or
modified.
NOTIFY: NOTIFY messages are used to convey information to a QNE.
They differ from RESPONSE messages in that they are sent
asynchronously and need not refer to any particular state or
previously received message. The information conveyed by a NOTIFY
message is typically related to error conditions. Examples would
be notification to an upstream peer about state being torn down or
to indicate when a reservation has been pre-empted.
QoS NSLP messages are sent peer-to-peer. This means that a QNE
considers its adjacent upstream or downstream peer to be the source
of the each message.
Each protocol message has a common header which indicates the message
type and contains flags. Message formats are defined in Section
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5.1.2. Message processing rules are defined in Section 5.4.
QoS NSLP messages contain three types of objects:
1. Control Information: Control information objects carry general
information for the QoS NSLP processing, such as sequence numbers
or whether a response is required.
2. QoS specifications (QSPECs): QSPEC objects describe the actual
resources that are required and depend on the QoS model being
used. Besides any resource description they may also contain other
control information used by the RMF's processing.
3. Policy objects: Policy objects contain data used to authorize
the reservation of resources.
Object formats are defined in Section 5.1.3. Object processing rules
are defined in Section 5.3.
3.1.3. QoS Models and QoS Specifications
QoS NSLP provides flexibility over the exact patterns of signaling
messages that are exchanged. The decoupling of QoS NSLP and QSPEC
allows the QoS NSLP to be ignorant about the ways in which traffic,
resources, etc. are described, and it can treat the QSPEC as an
opaque object.
The QSPEC fulfills a similar purpose to the TSpec, RSpec and AdSpec
objects used with RSVP and specified in RFC 2205 [RFC2205] and RFC
2210 [RFC2210]. At each QNE, its content is interpreted by the
Resource Management Function and the Policy Control Function for the
purposes of policy control and traffic control (including admission
control and configuration of the packet classifier and scheduler).
QoS NSLP does not mandate any particular behavior for the RMF,
instead demanding interoperability at the signaling protocol whilst
leaving the validation of RMF behavior to SLAs or contracts external
to the protocol itself. The RMF may make use of various elements from
the QoS NSLP message, not only the QSPEC object.
The QSPEC carries a collection of objects that can describe QoS
specifications in a number of different ways. A QSPEC will usually
contain some objects which need to be understood by all
implementations, and it can also be enhanced with additional objects
to provide a more exact definition to the RMF, which may be better
able to use its specific resource management mechanisms (which may,
e.g., be link specific) as a result.
A QoS Model defines the behavior of the RMF, including inputs and
outputs, and how QSPEC information is used to describe resources
available, resources required, traffic descriptions, and control
information required by the RMF. A QoS Model also describes the
minimum set of parameters QNEs should use in the QSPEC when signaling
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about this QoS Model.
QoS Models may be local (private to one network), implementation/
vendor specific, or global (implementable by different networks and
vendors). The authors are currently aware of three efforts related to
QoS Model specification: IntServ Controlled Load [QOSM-CL], ITU
Y.1541 [Y.1541], and Resource Management for DiffServ (RMD) [RMD].
The definition of a QoS model may also have implications on how local
behavior should be implemented in the areas where the QoS NSLP gives
freedom to implementers. For example, it may be useful to identify
recommended behavior for how a RESERVE message that is forwarded
relates to that received, or when additional signaling sessions
should be started based on existing sessions, such as required for
aggregate reservations. In some cases, suggestions may be made on
whether state that may optionally be retained should be held in
particular scenarios. Moreover, a QoS model may specify reservation
pre-emption, e.g., an incoming resource request may cause removal of
an earlier reservation.
An ongoing effort attempts to specify a QSPEC template [I-D.ietf-
nsis-qspec]. The QSPEC template contains object formats for generally
useful elements of the QoS description, which is designed to ensure
interoperability when using the basic set of objects.
3.1.4. Policy control
Getting access to network resources typically involves some kind of
policy control. One example of this is authorization of the resource
requester. Policy control for QoS NSLP resource reservation signaling
is conceptually organized as illustrated below in Figure 3.
+-------------+
| Policy |
| Decision |
| Point (PDP) |
+------+------+
|
/-\-----+-----/\
//// \\\\
|| ||
| Policy transport |
|| ||
\\\\ ////
\-------+------/
|
+-------------+ QoS signaling +------+------+
| Entity |<==============>| QNE = Policy|<=========>
| requesting | Data Flow | Enforcement |
| resource |----------------|-Point (PEP)-|---------->
+-------------+ +-------------+
Figure 3: Policy control with the QoS NSLP signaling.
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From QoS NSLP point of view, the policy control model is essentially
a two-party model between neighboring QNEs. The actual policy
decision may depend on the involvement of a third entity (the policy
decision point, PDP), but this happens outside of the QoS NSLP
protocol by means of existing policy infrastructure (COPS, Diameter,
etc). The policy control model for the entire end-to-end chain of
QNEs is therefore one of transitivity, where each of the QNEs
exchanges policy information with its QoS NSLP policy peer.
The input to policy control is referred to as "Policy data". The QoS
NSLP may carry some policy control information in this "Policy Data".
However, the default operation is to use GIST mechanisms, which are
provided across the GIST API. Policy data itself is opaque to the QoS
NSLP, which simply passes it to policy control when required. The
policy data is independent from the QoS model in use.
Two options are currently considered for support by QoS NSLP policy
control:
a. Reuse of GIST channel security mechanisms
b. Carrying authorization data within the QoS NSLP.
The fist option is preferred as it relies on existing security
measures. This can be controlled through the GIST API. The second
option is currently under study [NSLP-AUTH].
It is generally assumed that policy enforcement is likely to
concentrate on border nodes between administrative domains. In some
cases policy objects transmitted across the domain traverse an
intermediate Policy Ignorant Node (PIN) that is allowed to process
QoS NSLP message but does not handle policy information. The policy
peering between ingress and egress edge of a domain therefore relies
on the internal chain of trust between the nodes in the domain. If
this is not acceptable, a separate signaling session can be set up
between the edge node in order to exchange policy information. This
is similar to the aggregation mechanism.
3.2. Design decisions
QoS NSLP was designed according to ten principles. These are defined
in this section.
3.2.1. Soft-state
The NSIS protocol suite takes a soft-state approach to state
management. This means that reservation state in QNEs must be
periodically refreshed. The frequency with which state installation
is refreshed is expressed in the REFRESH_PERIOD object. This object
contains a value in milliseconds indicating how long the state that
is signaled for remains valid. Maintaining the reservation beyond
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this lifetime can be done by sending periodically a RESERVE message.
3.2.2. Sender-receiver initiation
QoS NSLP supports both sender-initiated and receiver-initiated
reservations. For a sender-initiated reservation, RESERVE messages
travel in the same direction as the data flow that is being signaled
for (the QNI is at the side of the source of the data flow).
For a receiver-initiated reservation, RESERVE messages travel in the
opposite direction (the QNI is at the side of the receiver of the
data flow). Before sending the RESERVE, the sender of the data first
sends a QUERY message with the R-bit set that creates the required
GIST path state. The QUERY message is needed due to the asymmetric
nature of IP routing.
Note: these definitions follow the definitions in Section 3.3.1. of
RFC 4080 [RFC4080]. The question is, which node is in charge of
requesting and maintaining the resource reservation. In a receiver-
initiated reservation, even though the sender sends the initial
QUERY, the receiver is still in charge of making the actual resource
request, and maintaining the reservation.
3.2.3. Message sequencing
RESERVE messages affect the installed reservation state. Unlike
NOTIFY, QUERY and RESPONSE messages, the order in which RESERVE
messages are received influences the eventual reservation state that
will be stored at a QNE, that is, the most recent RESERVE message
replaces the current reservation. Therefore, in order to protect
against RESERVE message re-ordering or duplication, the QoS NSLP uses
a Reservation Sequence Number (RSN).
The RSN has local significance only, i.e., between QNEs. Attempting
to make an identifier that was unique in the context of a SESSION_ID
but the same along the complete path would be very hard. Since
RESERVE messages can be sent by any node on the path that maintains
reservation state (e.g., for path repair) we would have the difficult
task of attempting to keep the identifier synchronized along the
whole path. Since message ordering only ever matters between a pair
of peer QNEs, we can make the RSN unique just between a pair of
neighboring stateful QNEs. By managing the sequence numbers in this
manner, the source of the RESERVE does not need to determine how the
next QNE will process the message.
Note that, since the RSN is unique within a SESSION_ID, it can be
used together with a SESSION_ID to refer to a particular installed
state.
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3.2.4. Explicit state installation confirmation and responses
A QoS NSLP instance MAY request an explicit confirmation of its state
installation actions from the immediate upstream or downstream peer.
This is achieved by using an ACKNOWLEDGE (A) flag in the message
header. This mechanism enables a QoS NSLP instance to rapidly detect
a failure of the peer QoS NSLP instance or the underlying transport,
i.e., either GIST itself or the used transport protocol below, e.g.,
TCP.
In addition to this, a QNE may require other information such as a
confirmation that the end-to-end reservation is in place or a reply
to a query along the path. For such requests, it must be able to keep
track of which request each response refers to. This is supported by
including a Request Identification Information (RII) object in a QoS
NSLP message.
3.2.5. Reduced refresh
For scalability, QoS NSLP supports an abbreviated form of refresh
RESERVE message. In this case, the refresh RESERVE references the
reservation using the RSN and the SESSION_ID, and does not include
the full reservation specification (including QSPEC). These reduced
refreshes require an explicit acknowledgment of state installation to
ensure that the RSN reference will be understood. It is up to a QNE
that receives a message containing an RII to decide whether it wants
to accept reduced refreshes and provide this explicit acknowledgment.
3.2.6. Message scoping
A QNE may use local policy when deciding whether to propagate a
message or not. The QoS NSLP also includes an explicit mechanism to
restrict message propagation by means of a scoping mechanism.
For a RESERVE or a QUERY message, a SCOPING flag limits the part of
the path on which state is installed or the downstream nodes that can
respond. When set to zero, it indicates that the scope is "whole
path" (default). When set to one, the scope is "single hop".
The propagation of a RESPONSE message is limited by the RII object,
which ensures that it is not forwarded back along the path further
than the node that requested the RESPONSE.
This specification does not support an explicit notion of a region
scope or "to a mobility-related path branch/merge point". If needed,
this can be easily proposed as an extension later on, e.g., based on
LRSVP [LRSVP].
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3.2.7. Session binding
Session binding is defined as the enforcement of a relation between
different QoS NSLP sessions (i.e., signaling flows with different
SESSION_ID (SID) as defined in GIST [I-D.ietf-nsis-ntlp]).
Session binding indicates a (possibly asymmetric) dependency relation
between two or more sessions by including a BOUND_SESSION_ID object.
A session with SID_A (the binding session) can express its relation
to another session with SID_B (the bound session) by including a
BOUND_SESSION_ID object containing SID_B in its messages. The
dependency is asymmetric if the session with SID_B does not carry a
BOUND_SESSION_ID object containing SID_A.
The concept of session binding is used to indicate the dependency
between the end-to-end session and the aggregate session in case of
aggregate reservations. In case of bidirectional reservations, it is
used to express the dependency between the sessions used for forward
and reverse reservation. Note that the dependency indicated by
session binding is purely informative in nature and does not
automatically trigger any action in a QNE. However, a QNE may use the
information for local resource optimization or to tear down
reservations that are no longer useful.
A message may include more than one BOUND_SESSION_ID object. This may
happen, e.g., in certain aggregation and bi-directional reservation
scenarios, where a session needs to be bound to another session for
the reverse path, and also to a reservation aggregation within a
domain.
3.2.8. Layering
QoS NSLP supports layered reservations. Layered reservations may
occur when certain parts of the network (domains) implement one or
more local QoS models, or when they locally apply specific control
plane characteristics (e.g., GIST unreliable transfer mode instead of
reliable transfer mode). They may also occur when several per-flow
reservations are locally combined into an aggregate reservation.
3.2.8.1. Local QoS models
A domain may have local policies regarding QoS model implementation,
i.e., it may map incoming traffic to its own locally defined QoS
models. QoS NSLP supports this by allowing QSPEC objects to be
stacked.
When a domain wants to apply a certain QoS model to an incoming per-
flow reservation request, each edge of the domain is configured to
map the incoming QSPEC object to a local QSPEC object and push that
object onto the stack of QSPEC objects (typically immediately
following the Common Control Information, i.e., before the first
QSPEC that is found in the message). QNEs inside the domain look at
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the top of the QSPEC object stack to determine which QoS model to
apply for the reservation.
The position of the local QSPEC object in the stack implies a trade-
off between the speed with which incoming messages can be processed
and the time it takes to construct the outgoing message (if any). By
mandating the locally valid object to be on top of the stack we value
ease of processing over ease of message construction.
Note that the use of multiple QSPEC objects may require complex
processing. While processing the QSPEC on the top of the stack, a QNE
may also need to process inner QSPEC objects. For example, a domain
may want to hide its existence from the end hosts, and for doing that
may need to process objects and fields in the inner QSPEC used
originally by the end hosts.
3.2.8.2. Local control plane properties
The way signaling messages are handled is mainly determined by the
parameters that are sent over GIST-NSLP API and by the Common Control
Information. A domain may have a policy to implement local control
plane behavior. It may, for instance, elect to use an unreliable
transport locally in the domain while still keeping end-to-end
reliability intact.
The QoS NSLP supports this situation by allowing two sessions to be
set up for the same reservation. The local session has the desired
local control plane properties and is interpreted in internal QNEs.
This solution poses two requirements: the end-to-end session must be
able to bypass intermediate nodes and the egress QNE needs to bind
both sessions together.
Intermediate node bypass is achieved with GIST. The local session and
the end-to-end session are bound at the egress QNE by means of the
BOUND_SESSION_ID object.
3.2.8.3. Aggregate reservations
In some cases it is desirable to create reservations for an
aggregate, rather than on a per-flow basis, in order to reduce the
amount of reservation state needed, as well as, the processing load
for signaling messages. The QoS NSLP, therefore, provides aggregation
facilities similar to RFC 3175 [RFC3175]. However, the aggregation
scenarios supported are wider than that proposed there. Note that QoS
NSLP does not specify how reservations need to be combined in an
aggregate or how end-to-end properties need to be computed but only
provides signaling support for it.
The essential difference with the layering approaches described in
Section 3.2.8.1 and Section 3.2.8.2 is that the aggregate reservation
needs a Flow ID, i.e., MRI, that describes all traffic carried in the
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aggregate (e.g., a DSCP in case of IntServ over DiffServ). The need
for a different Flow ID mandates the use of two different sessions,
similar to Section 3.2.8.2 and to the RSVP aggregation solution in
RFC 3175 [RFC3175].
Edge QNEs of the aggregation domain that want to maintain some end-
to-end properties may establish a peering relation by sending the
end-to-end message transparently over the domain (using the
intermediate node bypass capability described above). Updating the
end-to-end properties in this message may require some knowledge of
the aggregated session (e.g., for updating delay values). For this
purpose, the end-to-end session contains a BOUND_SESSION_ID carrying
the SESSION_ID of the aggregate session.
3.2.9. Priority
This specification acknowledges the fact that in some situations,
some messages or some reservations may be more important than others
and therefore foresees mechanisms to give these messages or
reservations priority.
Priority of certain signaling messages over others may be required in
mobile scenarios when a message loss during call set-up is less
harmful than during handover. This situation only occurs when GIST or
QoS NSLP processing is the congested part or scarce resource.
Priority of certain reservations over others may be required when QoS
resources are oversubscribed. In that case, existing reservations may
be preempted in order to make room for new higher-priority
reservations. A typical approach to deal with priority and preemption
is through the specification of a setup priority and holding priority
for each reservation. The resource management function at each QNE
then keeps track of the resource consumption at each priority level.
Reservations are established when resources, at their setup priority
level, are still available. They may cause preemption of reservations
with a lower holding priority than their setup priority.
Support of reservation priority is a QSPEC parameter and therefore
outside the scope of this specification. The GIST specification
provides a mechanism to support a number of levels of message
priority that can be requested over the NSLP-GIST API.
3.2.10. Rerouting
QoS NSLP needs to adapt to route changes in the data path. This
assumes the capability to detect rerouting events, perform QoS
reservation on the new path and optionally tear down reservations on
the old path.
Rerouting detection can be performed at three levels. First, routing
modules may detect route changes through their interaction with
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routing protocols. Certain QNEs or GIST implementations may interact
with local routing module to receive quick notification of route
changes. This is largely implementation-specific and outside of the
scope of NSIS. Second, route changes may be detected at the GIST
layer. GIST is able to provide information on such events over the
API. This is outside the scope of the QoS NSLP specification. Third,
rerouting may be detected at the NSLP layer. A QoS NSLP node is able
to detect changes in its QoS NSLP peers by keeping track of a Source
Identification Information (SII) handle that provides information
similar in nature to the RSVP_HOP object described in RFC 2205
[RFC2205]. When a RESERVE message with an existing SESSION_ID and a
different SII is received, the QNE knows its upstream or downstream
peer has changed, for sender- and receiver-oriented reservations,
respectively.
Reservation on the new path happens when a RESERVE message arrives at
the QNE beyond the point where the old and new paths diverge. A
refreshing RESERVE (with no QSpec) will be identified as an error by
a QNE on the new path. It will send back an error message which
results in a full RESERVE message being sent. Depending on the
transfer mode, this may require installation of a new messaging
association. Rapid recovery at the NSLP layer therefore requires
short refresh periods. Detection before the next RESERVE message
arrives is only possible at the IP layer or through monitoring of
GIST peering relations (e.g., by TTL counting the number of GIST hops
between NSLP peers or the observing changes in the outgoing interface
towards GIST peer). These mechanisms can provide implementation
specific optimizations, and are outside the scope of this
specification.
When the QoS NSLP is aware of the route change, it needs to set up
the reservation on the new path. This is done by sending a new
RESERVE message. If the next QNE is, in fact, unchanged then this
will be used to refresh/update the existing reservation. Otherwise it
will lead to the reservation being installed on the new path.
After the reservation on the new path is set up, the branching
nodenode may want to tear down the reservation on the old path
(sooner than would result from normal soft-state time-out). This
functionality is supported by keeping track of the old SII-Handle
provided over the GIST API. This handle can be used by the QoS NSLP
to route messages explicitly to the next node.
A QNI or a branch node may wish to keep the reservation on the old
branch. This could for instance be the case when a mobile node has
experienced a mobility event and wishes to keep reservation to its
old attachment point in case it moves back there. For this purpose, a
REPLACE flag is foreseen in the common header, which, when set to
FALSE, indicates that the reservation on the old branch should be
kept.
The design of the QoS-NSLP allows reservations to be installed at a
subset of the nodes along a path, including cases where those nodes
might not included the endpoints of the application data flow.
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In the case where the data flow receiver does not support the QoS-
NSLP, some particular considerations must be given to node discovery
and rerouting at the end of the signaling path.
There are three cases for the last node on the signaling path: 1)
Last node is the data receiver 2) Last node is a configured proxy for
the data receiver 3) Last node is not the data receiver and is not
explicitly configured to act as a signaling proxy on behalf of the
data receiver.
Cases (1) and (2) can be handled by the QoS-NSLP itself during the
initial path setup, since the QNE knows that it should terminate the
signaling. Case (3) requires some assistance from GIST which provides
messages across the API to indicate that no further QoS-NSLP
supporting GIST nodes are present downstream, and downstream route
change probing needs to continue once the reservation is installed to
detect any changes in this situation.
4. Examples of QoS NSLP Operation
The QoS NSLP can be used in a number of ways. The examples given here
give an indication of some of the basic processing. However, they are
not exhaustive and do not attempt to cover the details of the
protocol processing.
4.1. Basic sender-initiated reservation
QNI QNE QNE QNR
| | | |
| RESERVE | | |
+--------->| | |
| | RESERVE | |
| +--------->| |
| | | RESERVE |
| | +--------->|
| | | |
| | | RESPONSE |
| | |<---------+
| | RESPONSE | |
| |<---------+ |
| RESPONSE | | |
|<---------+ | |
| | | |
| | | |
Figure 4: Basic Sender Initiated Reservation
To make a new reservation, the QNI constructs a RESERVE message
containing a QSPEC object, from its chosen QoS model, which describes
the required QoS parameters.
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The RESERVE message is passed to GIST which transports it to the next
QNE. There it is delivered to the QoS NSLP processing which examines
the message. Policy control and admission control decisions are made.
The exact processing also takes into account the QoS model being
used. The node performs appropriate actions (e.g., installing
reservation) based on the QSPEC object in the message.
The QoS NSLP then generates a new RESERVE message (usually based on
the one received). This is passed to GIST, which forwards it to the
next QNE.
The same processing is performed at further QNEs along the path, up
to the QNR. The determination that a node is the QNR may be made
directly (e.g., that node is the destination for the data flow), or
using some GIST functionality to determine that there are no more
QNEs between this node and the data flow destination.
A node can ask a confirmation of the installed state from its
immediate peer. It does so by setting the A flag, which causes a
RESPONSE message to be sent by the immediate peer. One use of this is
to confirm the installation of state, which allows the use of reduced
refreshes that later refer to that state. A RESPONSE message can also
indicate an error when, e.g., a reservation has failed to be
installed.
Any node may include a request for a RESPONSE in its RESERVE
messages. It does so by including a Request Identification
Information (RII) object in the RESERVE message. If the message
already includes an RII, an interested QNE must not add a new RII
object nor replace the old RII object, but may simply remember that
RII to match the related RESPONSE it is interested in later. When it
receives the RESPONSE, it forwards the RESPONSE upstream towards the
RII originating node.
The RESPONSE is forwarded peer-to-peer along the reverse of the path
that the RESERVE message took (using GIST path state), and so is seen
by all the QNEs on the reverse-path. It is only forwarded as far as
the node which requested the RESPONSE originally.
The reservation can subsequently be refreshed by sending further
RESERVE messages containing the complete reservation information, as
for the initial reservation. The reservation can also be modified in
the same way, by changing the QSPEC data to indicate a different set
of resources to reserve.
The overhead required to perform refreshes can be reduced, in a
similar way to that proposed for RSVP in RFC 2961 [RFC2961]. Once a
RESPONSE message has been received indicating the successful
installation of a reservation, subsequent refreshing RESERVE messages
can simply refer to the existing reservation, rather than including
the complete reservation specification.
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4.2. Sending a Query
QUERY messages can be used to gather information from QNEs along the
path. For example, it can be used to find out what resources are
available before a reservation is made.
In order to perform a query along a path, the QNE constructs a QUERY
message. This message includes a QSPEC containing the actual query to
be performed at QNEs along the path. It also contains an object used
to match the response back to the query, and an indicator of the
query scope (next node, whole path). The QUERY message is passed to
GIST to forward it along the path.
A QNE (including the QNR) receiving a QUERY message should inspect it
and create a new message, based on that received with the query
objects modified as required. For example, the query may request
information on whether a flow can be admitted, and so a node
processing the query might record the available bandwidth. The new
message is then passed to GIST for further forwarding (unless it
knows it is the QNR, or is the limit for the scope in the QUERY).
At the QNR, a RESPONSE message must be generated if the QUERY message
includes a Request Identification Information (RII) object. Into this
is copied various objects from the received QUERY message. It is then
passed to GIST to be forwarded peer-to-peer back along the path.
Each QNE receiving the RESPONSE message should inspect the RII object
to see if it 'belongs' to it (i.e., it was the one that originally
created it). If it does not then it simply passes the message back to
GIST to be forwarded back down the path.
4.3. Basic receiver-initiated reservation
As described in the NSIS framework [RFC4080] in some signaling
applications, a node at one end of the data flow takes responsibility
for requesting special treatment - such as a resource reservation -
from the network. Both ends then agree whether sender or receiver-
initiated reservation is to be done. In case of a receiver initiated
reservation, both ends agree whether a "One Pass With Advertising"
(OPWA) [_XREF_OPWA95] model is being used. This negotiation can be
accomplished using mechanisms that are outside the scope of NSIS.
To make a receiver-initiated reservation, the QNR constructs a QUERY
message, which may contain a QSPEC object from its chosen QoS model
(see Figure 5). The QUERY must have the R-bit set. This QUERY message
does not need to trigger a RESPONSE message and therefore, the QNI
must not include the RII object (Section 5.4.2), into the QUERY
message. The QUERY message may be used to gather information along
the path, which is carried by the QSPEC object. An example of such
information is the "One Pass With Advertising" (OPWA) [_XREF_OPWA95].
This QUERY message causes GIST reverse-path state to be installed.
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QNR QNE QNE QNI
sender receiver
| | | |
| QUERY | | |
+--------->| | |
| | QUERY | |
| +--------->| |
| | | QUERY |
| | +--------->|
| | | |
| | | RESERVE |
| | |<---------+
| | RESERVE | |
| |<---------+ |
| RESERVE | | |
|<---------+ | |
| | | |
| RESPONSE | | |
+--------->| | |
| | RESPONSE | |
| +--------->| |
| | | RESPONSE |
| | +--------->|
| | | |
Figure 5: Basic Receiver Initiated Reservation
The QUERY message is transported by GIST to the next downstream QoS
NSLP node. There it is delivered to the QoS NSLP processing which
examines the message. The exact processing also takes into account
the QoS model being used and may include gathering information on
path characteristics that may be used to predict the end-to-end QoS.
The QNE generates a new QUERY message (usually based on the one
received). This is passed to GIST, which forwards it to the next QNE.
The same processing is performed at further QNEs along the path, up
to the flow receiver. The receiver detects that this QUERY message
carries the R-bit and by using the information contained in the
received QUERY message, such as the QSPEC, constructs a RESERVE
message.
The RESERVE is forwarded peer-to-peer along the reverse of the path
that the QUERY message took (using GIST reverse path state). Similar
to the sender-initiated approach, any node may include an RII in its
RESERVE messages. The RESPONSE is sent back to confirm the resources
are set up.
The reservation can subsequently be refreshed in the same way as for
the sender-initiated approach. This RESERVE message may be also used
to refresh GIST reverse path state. Alternatively, refreshing GIST
reverse path state could be performed by sending periodic QUERY
messages, which are needed in case of route changes anyway.
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4.4. Bidirectional Reservations
Bidirectional reservations are supported by binding two uni-
directional sessions together. We distinguish two cases:
o Binding two sender-initiated reservations, e.g., one sender-
initiated reservation from QNE A to QNE B and another one from QNE B
to QNE A.
o Binding a sender-initiated and a receiver-initiated reservation,
e.g., a sender-initiated reservation from QNE A towards QNE B, and a
receiver-initiated reservation from QNE A towards QNE B for the data
flow in the opposite direction (from QNE B to QNE A). This case is
particularly useful when one end of the communication has all
required information to set up both sessions.
Both ends have to agree on which bi-directional reservation type they
need to use. This negotiation/agreement can be accomplished using
mechanisms that are outside the scope of NSIS.
The scenario with two sender-initiated reservations is shown on
Figure 6. Note that RESERVE messages for both directions may visit
different QNEs along the path because of asymmetric routing. Both
directions of the flows are bound by inserting the BOUND_SESSION_ID
object at the QNI and QNR. RESPONSE messages are optional and not
shown on the picture for simplicity.
A QNE QNE B
| | FLOW-1 | |
|===============================>|
|RESERVE-1 | | |
QNI+--------->|RESERVE-1 | |
| +-------------------->|QNR
| | | |
| | FLOW-2 | |
|<===============================|
| | |RESERVE-2 |
| RESERVE-2 |<---------+QNI
QNR|<--------------------+ |
| | | |
Figure 6: Bi-directional reservation for sender+sender scenario
The scenario with a sender-initiated and a receiver-initiated
reservation is shown on Figure 7. In this case, QNI B sends out two
RESERVE messages, one for the sender-initiated and one for the
receiver-initiated reservation.
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A QNE QNE B
| | FLOW-1 | |
|===============================>|
| QUERY-1 | | |
QNI+--------->| QUERY-1 | |
| +-------------------->|QNR
| | | |
| |RESERVE-1 | |
|RESERVE-1 +<--------------------|QNR
QNI+<---------| | |
| | | |
| | FLOW-2 | |
|<===============================|
| | |RESERVE-2 |
|RESERVE-2 | |<---------+QNI
QNR|<--------------------+ |
| | | |
Figure 7: Bi-directional reservation for sender+receiver scenario
4.5. Use of Local QoS Models
In some cases it may be required to use a different QoS model along a
particular segment of the signaling. In this case a node at the edge
of this region needs to add the additional local QSPEC information,
based on the end-to-end QSPEC. This allows the QoS description to be
tailored to the QoS provisioning mechanism available in the network.
+-------- QoSM2 domain -------+
| |
| |
+----+ +----+ +----+ +----+ +----+
|QNI | |edge| |int.| |edge| |QNR |
| |========>|QNE |========>|QNE |========>|QNE |========>| |
+----+ RESERVE +----+ RESERVE +----+ RESERVE +----+ RESERVE +----+
QSPEC1 | QSPEC2 QSPEC2 | QSPEC1
| {QSPEC1} {QSPEC1} |
| |
+-----------------------------+
Figure 8: Reservation with local QoS Models
This initially proceeds as for the basic example, with peer-to-peer
installation of reservations. However, within a region of the network
a different QoSM (QoSM2) needs to be used. At the edge of this region
the QNEs support both the end-to-end and local QoS models. When the
RESERVE message reaches the QNE at the ingress, the initial
processing of the RESERVE proceeds as normal. However, the QNE also
determines the appropriate description using QoSM2. The RESERVE
message to be sent out is constructed mostly as usual but with a
second QSPEC object added on top, which becomes the 'current' one.
When this RESERVE message is received at an node internal to the
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QoSM2 domain the QoS NSLP only uses the local QSPEC, rather than the
end-to-end QSPEC. Otherwise, processing proceeds as usual. The
RESERVE message that it generates should include both of the QSPECs
from the message it received.
At the QNE at the egress of the region the local QSPEC is removed
from the message so that subsequent QNEs receive only the end-to-end
QSPEC.
A message can contain at most two QSPEC objects, i.e., the end-to-end
QSPEC and a local QSPEC.
4.6. Aggregate Reservations
In order to reduce signaling and per-flow state in the network, the
reservations for a number of flows may be aggregated together.
QNI QNE QNE/QNI' QNE' QNR'/QNE QNR
aggregator deaggregator
| | | | | |
| RESERVE | | | | |
+--------->| | | | |
| | RESERVE | | | |
| +--------->| | | |
| | | RESERVE | | |
| | +-------------------->| |
| | | RESERVE' | | |
| | +=========>| RESERVE' | |
| | | +=========>| RESERVE |
| | | | +--------->|
| | | | RESPONSE'| |
| | | RESPONSE'|<=========+ |
| | |<=========+ | |
| | | | | RESPONSE |
| | | | RESPONSE |<---------+
| | |<--------------------+ |
| | RESPONSE | | | |
| |<---------+ | | |
| RESPONSE | | | | |
|<---------+ | | | |
| | | | | |
| | | | | |
Figure 9: Sender Initiated Reservation with Aggregation
An end-to-end per-flow reservation is initiated as normal (with
messages shown in Figure 9 as "RESERVE").
At the aggregator a reservation for the aggregated flow is initiated
(shown in Figure 9 as "RESERVE'"). This may use the same QoS model as
the end-to-end reservation but has a flow identifier for the
aggregated flow (e.g., tunnel) instead of for the individual flows.
This document does not specify how the QSPEC of the aggregate session
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can be derived from the QSPECs of the end-to-end sessions.
The messages used for the signaling of the individual reservation
need to be marked such that the intermediate routers will not inspect
them. The marking MUST be accomplished by the Aggregator by
modifying the QoS-NSLP default NSLP-ID value to a NSLP-ID predefined
value. The De-aggregator MUST stop this marking process by
reassigning the QoS-NSLP default NSLP-ID value to these signaling
messages. The deaggregator then becomes the next hop QNE for the end-
to-end per-flow reservation.
Aggregator Deaggregator
+---+ +---+ +---+ +---+
|QNI|-----|QNE|-----|QNE|-----|QNR| aggregate
+---+ +---+ +---+ +---+ reservation
+---+ +---+ ..... ..... +---+ +---+
|QNI|-----|QNE|-----. .-----. .-----|QNE|-----|QNR| end-to-end
+---+ +---+ ..... ..... +---+ +---+ reservation
The deaggregator acts as the QNR for the aggregate reservation.
Information is carried in the reservations to enable the deaggregator
to associate the end-to-end and aggregate reservations with one
another.
The key difference between this example and previous ones is that the
flow identifier for the aggregate is expected to be different to that
for the end-to-end reservation. The aggregate reservation can be
updated independently of the per-flow end-to-end reservations.
4.7. Reduced State or Stateless Interior Nodes
This example uses a different QoS model within a domain, in
conjunction with GIST and NSLP functionality which allows the
interior nodes to avoid storing GIST and QoS NSLP state. As a result
the interior nodes only store the QSPEC-related reservation state, or
even no state at all. This allows the QoS model to use a form of
"reduced-state" operation, where reservation states with a coarser
granularity (e.g., per-class) are used, or a "stateless" operation
where no QoS NSLP state is needed (or created).
The key difference between this example and the use of different QoS
models in Section 4.5 is that the transport characteristics for the
´local' reservation can be different from that of the end-to-end
reservation, i.e., GIST can be used in a different way for the edge-
to-edge and hop-by-hop sessions. The reduced state reservation can be
updated independently of the per-flow end-to-end reservations.
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QNE QNE QNE QNE
ingress interior interior egress
GIST stateful GIST stateless GIST stateless GIST stateful
| | | |
RESERVE | | | |
-------->| RESERVE | | |
+--------------------------------------------->|
| RESERVE' | | |
+-------------->| | |
| | RESERVE' | |
| +-------------->| |
| | | RESERVE' |
| | +------------->|
| | | | RESERVE
| | | +-------->
| | | | RESPONSE
| | | |<--------
| | | RESPONSE |
|<---------------------------------------------+
RESPONSE| | | |
<--------| | | |
Figure 11: Sender-initiated reservation with Reduced State Interior
Nodes
The QNI performs the same processing as before to generate the
initial RESERVE message, and it is forwarded by GIST as usual. At the
QNEs at the edges of the stateless or reduced-state region the
processing is different and the nodes support two QoS models.
At the ingress the original RESERVE message is forwarded but ignored
by the stateless or reduced-state nodes. This is accomplished by
marking this 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. The egress MUST stop this
marking process by reassigning the QoS-NSLP default NSLP-ID value to
the original RESERVE message. An example of such operation is given
in [RMD].
The egress node is the next QoS NSLP hop for that session. After the
initial discovery phase using unreliable GIST transfer mode, reliable
GIST transfer mode between the ingress and egress can be used. At the
egress node the RESERVE message is then forwarded normally.
At the ingress a second RESERVE' message is also built. This makes
use of a QoS model suitable for a reduced state or stateless form of
operation (such as the RMD per hop reservation). Since the original
RESERVE and the RESERVE' messages are addressed identically, RESERVE'
visits the same nodes that were visited, including the egress QNE.
When processed by interior (stateless) nodes the QoS NSLP processing
exercises its options to not keep state wherever possible, so that no
per flow QoS NSLP state is stored. Some state, e.g., per class, for
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the QSPEC related data may be held at these interior nodes. The QoS
NSLP also requests that GIST use different transport characteristics
(i.e., sending of messages in unreliable GIST transfer mode). It also
requests the local GIST processing not to retain messaging
association state or reverse message routing state.
Nodes, such as those in the interior of the stateless or reduced-
state domain, that do not retain reservation state cannot send back
RESPONSE messages (and so cannot use reduced refreshes).
At the egress node the RESERVE' message is interpreted in conjunction
with the reservation state from the end-to-end RESERVE message (using
information carried in the message to correlate the signaling flows).
The RESERVE message is only forwarded further if the processing of
the RESERVE' message was successful at all nodes in the local domain,
otherwise the end-to-end reservation is regarded as having failed to
be installed.
Since GIST neighbor relations are not maintained in the reduced-state
region, only sender initiated signaling can be supported. If a
receiver-initiated reservation over a stateless or reduced state
domain is required this can be implemented as shown below.
QNE QNE QNE
ingress interior egress
GIST stateful GIST stateless GIST stateful
| | |
QUERY | | |
-------->| QUERY | |
+------------------------------>|
| | | QUERY
| | +-------->
| | | RESERVE
| | |<--------
| | RESERVE |
|<------------------------------+
| RESERVE | RESERVE |
|-------------->|-------------->|
RESERVE | | |
<--------| | |
Figure 12: Receiver-initiated reservation with Reduced State Interior
Nodes
The RESERVE message that is received by the egress QNE of the
stateless domain is sent transparently to the ingress QNE (known as
the source of the QUERY message). When the RESERVE message reaches
the ingress, the ingress QNE knows it needs to send both a sender-
initiated RESERVE over the stateless domain and send a RESERVE
message further upstream.
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4.8. Re-routing scenario
The QoS NSLP needs to adapt to route changes in the data path. This
assumes the capability to detect rerouting events, perform QoS
reservation on the new path and optionally tear down reservations on
the old path.
When the QoS NSLP is aware of the route change, it needs to set up
the reservation on the new path. This is done by incrementing the RSN
and sending a RESERVE message. On links that are common to the old
and the new path, this RESERVE message is interpreted as a refreshing
RESERVE. On new links, it creates the reservation.
After the reservation on the new path is set up, the branching node
or the merging node may want to tear down the reservation on the old
path (faster than what would result from normal soft-state time-out).
This functionality is supported by keeping track of the old SII, as
provided over the GIST API. The SII is opaque to the QoS NSLP, i.e.,
QoS NSLP does not make any assumptions on how this identifier is
constructed. When passed over the API from the NSLP to GIST, it
allows QoS NSLP to indicate that its messages should be sent to the
QNE identified by that SII.
In case of a receiver-initiated reservation, a QNE can detect a route
change by receiving a RESERVE message with a different SII. In case
of a sender-initiated reservation, the same information is learned
from a RESPONSE message, or from a NOTIFY message sent by the
downstream peer. A QNE that has detected the route change via the SII
change sends a RESERVE message towards the QNR on the old path (using
the old SII) with the TEAR flag set. Note that in case of receiver-
initiated reservations, this involves a QNE that is notified of the
route change in another way and wants to tear down the old branch
needs to send the RESERVE on the new path with an RII object. When
it receives the RESPONSE message back, it can check whether its peer
has effectively changed and send a RESERVE with the TEAR flag set if
it has. Otherwise, teardown is not needed. A QNE that is unable to
support an RII or does not receive a RESPONSE needs to rely on soft-
state timeout on the old branch.
A QNI or a branch node may wish to keep the reservation on the old
branch. This could for instance be the case when a mobile node has
experienced a mobility event and wishes to keep reservation to its
old attachment point in case it moves back there. In that case, it
sets the REPLACE flag in the common header to zero. Note that keeping
old reservations affects the resources available to other nodes.
Thus, the operator of the access network must make the final decision
on whether this behavior is allowed. Also, the QNEs in the access
network may add this flag even if the mobile node has not used the
flag initially.
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4.9. Authorization Model Examples
Various authorization models can be used in conjunction with the QoS
NSLP.
4.9.1. Authorization for the two party approach
The two party approach is conceptually the simplest authorization
model.
+-------------+ QoS request +--------------+
| Entity |----------------->| Entity |
| requesting | | authorizing |
| resource |granted / rejected| resource |
| |<-----------------| request |
+-------------+ +--------------+
^ ^
+...........................+
financial establishment
Figure 13: Two party approach
In this example the authorization decision only involves the two
entities, or makes use of previous authorization using an out-of-band
mechanism to avoid the need for active participation of an external
entity during the NSIS protocol execution.
This type of model may be applicable, e.g., between two neighboring
networks (inter-domain signaling) where a long-term contract (or
other out-of-band mechanisms) exists to manage charging and provides
sufficient information to authorize individual requests.
4.9.2. Token based three party approach
An alternative approach makes use of authorization tokens, such as
those described in RFC 3520 [RFC3520] and RFC 3521 [RFC3521] or used
as part of the Open Settlement Protocol [OSP]. The former
('authorization tokens') are used to associate two different
signaling protocols (i.e., SIP and NSIS) and their authorization with
each other whereas the latter is a form of digital money. As an
example, with the authorization token mechanism, some form of
authorization is provided by the SIP proxy, which acts as the
resource authorizing entity in Figure 14. If the request is
authorized, then the SIP signaling returns an authorization token
which can be included in the QoS signaling protocol messages to refer
to the previous authorization decision. The tokens themselves may
take a number of different forms, some of which may require the
entity performing the QoS reservation to query external state.
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Authorization
Token Request +--------------+
+-------------->| Entity C | financial settlement
| | authorizing | <..................+
| | resource | .
| +------+ request | .
| | +--------------+ .
| | .
| |Authorization .
| |Token .
| | .
| | .
| | .
| | QoS request .
+-------------+ + Authz. Token +--------------+ .
| Entity |----------------->| Entity B | .
| requesting | | performing | .
| resource |granted / rejected| QoS | <..+
| A |<-----------------| reservation |
+-------------+ +--------------+
Figure 14: Token based three party approach
For the digital money type of systems (e.g., OSP tokens), the token
represents a limited amount of credit. So, new tokens must be sent
with later refresh messages once the credit is exhausted.
4.9.3. Generic three party approach
Another method is for the node performing the QoS reservation to
delegate the authorization decision to a third party, as illustrated
in Figure 15.
+--------------+
| Entity C |
| authorizing |
| resource |
| request |
+-----------+--+
^ |
| |
QoS | | QoS
authz| |authz
req.| | res.
QoS | v
+-------------+ request +--+-----------+
| Entity |----------------->| Entity B |
| requesting | | performing |
| resource |granted / rejected| QoS |
| A |<-----------------| reservation |
+-------------+ +--------------+
Figure 15: Three party approach
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Authorization may be performed on a per-request basis, periodically,
or on a per-session basis. The authorization request might make use
of EAP authentication between entities A and C, and a subsequent
protocol exchange between A and B to create a secure channel for
further communications. Such a technique gives flexibility in terms
of the authentication and key exchange protocols used.
A further extension to this model is to allow Entity C to reference a
AAA server in the user's home network when making the authorization
decision.
5. QoS NSLP Functional specification
5.1. QoS NSLP Message and Object Formats
A QoS NSLP message consists of a common header, followed by a body
consisting of a variable number of variable-length, typed "objects".
The common header and other objects are encapsulated together in a
GIST NSLP-Data object. The following subsections define the formats
of the common header and each of the QoS NSLP message types. In the
message formats, the common header is denoted as COMMON_HEADER.
For each QoS NSLP message type, there is a set of rules for the
permissible choice of object types. These rules are specified using
the Augmented Backus-Naur Form (ABNF) specified in RFC 4234
[RFC4234]. The ABNF 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 order, except
for QSPEC object(s) which always appear last in the message, and
whose mutual order matters.
5.1.1. Common header
All GIST NSLP-Data objects for the QoS NSLP MUST contain this common
header as the first 32 bits of the object (this is not the same as
the GIST Common Header).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | Message Flags | Generic Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields in the common header are as follows:
Msg Type: 8 bits
1 = RESERVE
2 = QUERY
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3 = RESPONSE
4 = NOTIFY
Message-specific flags: 8 bits
These flags are defined as part of the specfication of individual
messages.
Generic flags: 16 bits
There exists currently one generic flag, the Scoping bit (S). The
use of the S-bit is described with each message that makes use of
it.
The set of appropriate flags depends on the particular message being
processed. Any bit not defined as a flag for a particular message
MUST be set to zero on sending and MUST be ignored on receiving.
5.1.2. Message formats
5.1.2.1. RESERVE
The format of a RESERVE message is as follows:
RESERVE = COMMON_HEADER
RSN [ RII ] [ REFRESH_PERIOD ] [ *BOUND_SESSION_ID ]
[ [ PACKET_CLASSIFIER ] QSPEC [ QSPEC ] ]
The RSN is the only mandatory object and MUST always be present in
all cases. At least one QSPEC MUST be included in the initial RESERVE
sent towards the QNR. A PACKET_CLASSIFIER MAY be provided. If the
PACKET_CLASSIFIER is not provided, then the full set of information
provided in the GIST MRI for the session should be used for packet
classification purposes.
Subsequent RESERVE messages meant as reduced refreshes, where no
QSPEC is provided, MUST NOT include a PACKET_CLASSIFIER either.
If any QSPEC objects are present in a RESERVE message, they MUST
occur at the end of the message. There are no other requirements on
transmission order, although the above order is recommended.
Three message-specific flags are defined for use in the common header
with the RESERVE message. These are:
+-+-+-+-+-+-+-+-+
|Reserved |T|A|R|
+-+-+-+-+-+-+-+-+
TEAR (T) - when set, indicates that reservation state and QoS NSLP
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operation state should be torn down. This is indicated to the RMF.
Depending on the QoS model, the tear message may include a QSPEC
to further specify state removal.
ACKNOWLEDGE (A) - when set, indicates that an explicit
confirmation of the state installation action is REQUIRED. This
flag SHOULD be set on transmission by default.
REPLACE (R) - when set the flag has two meanings. First, it
indicates that a RESERVE with different Message Routing
Information (MRI) replaces an existing one, so the old one MAY be
torn down immediately. This is the default situation. This flag
may be unset to indicate a desire from an upstream node to keep an
existing reservation on an old branch in place. Second, this flag
is also used to indicate whether the reserved resources on the old
branch should be torn down or not when the data path change
happens. In this case, the MRI is the same and only the route path
is changed.
One generic flag is used with the RESERVE message:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
SCOPING (S) - when set, indicates that the message is scoped and
should not travel down the entire path but only as far as the next
QNE (scope="next hop"). By default, this flag is not set (default
scope="whole path").
If the REFRESH_PERIOD is not present, a default value of 30 seconds
is assumed.
If the session of this message is bound to another session, then the
RESERVE message MUST include the SESSION_ID of that other session in
a BOUND_SESSION_ID object.
A "reservation collision" may occur if the sender believes that a
sender-initiated reservation should be performed for a flow, whilst
the other end believes that it should be starting a receiver-
initiated reservation. If different session identifiers are used then
this error condition is transparent to the QoS NSLP though it may
result in an error from the RMF, otherwise the removal of the
duplicate reservation is left to the QNIs/QNRs for the two sessions.
If a reservation is already installed and a RESERVE message is
received with the same session identifier from the other direction
(i.e., going upstream where the reservation was installed by a
downstream RESERVE message, or vice versa) then an error indicating
"RESERVE received from wrong direction" MUST be sent in a RESPONSE
message to the signaling message source for this second RESERVE.
A refresh right along the path can be forced by requesting a RESPONSE
from the far end (i.e., by including an RII object in the RESERVE
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message). Without this, a refresh RESERVE would not trigger RESERVE
messages to be sent further along the path, as each hop has its own
refresh timer. If the routing path changed due to mobility, the
mobile node's IP address changed, and it sent a Mobile IP binding
update, the resulting refresh is a new RESERVE. This RESERVE includes
a new MRI and will be propagated end-to-end without requesting a
RESPONSE.
Note: It is possible for a host to use this mechanism to constantly
force the QNEs on the path to send refresh RESERVE messages. It may,
therefore, be appropriate for QNEs to perform rate limiting on the
refresh messages that they send.
5.1.2.2. QUERY
The format of a QUERY message is as follows:
QUERY = COMMON_HEADER
[ RII ][ *BOUND_SESSION_ID ]
[ PACKET_CLASSIFIER ] QSPEC [ QSPEC ]
QUERY messages MUST always include at least one QSPEC. QUERY messages
MAY include a PACKET_CLASSIFIER. If a PACKET_CLASSIFIER is not
included then the full GIST MRI should be used for packet
classification purposes.
A QUERY message for requesting information about network resources
MUST contain an RII object to match an incoming RESPONSE to the
QUERY.
A QUERY message MAY contain two QSPEC objects. The QSPEC object
describes what is being queried for and may contain objects that
gather information along the data path. QSPEC objects MUST occur at
the end of the message. There are no other requirements on
transmission order, although the above order is recommended.
One message-specific flag is defined for use in the common header
with the QUERY message. This is:
+-+-+-+-+-+-+-+-+
|Reserved |R|
+-+-+-+-+-+-+-+-+
RESERVE-INIT (R) - when this is set, the QUERY is meant as a trigger
for the recipient to make a resource reservation by sending a
RESERVE.
One generic flag is defined for use in the common header with the
QUERY message. This is:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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SCOPING (S) - when set, indicates that the message is scoped an
should not travel down the entire path but only as far as the next
QNE (scope="next hop"). By default, this flag is not set (default
scope="whole path").
If the session of this message is bound to another session, then the
RESERVE message MUST include the SESSION_ID of that other session in
a BOUND_SESSION_ID object.
5.1.2.3. RESPONSE
The format of a RESPONSE message is as follows:
RESPONSE = COMMON_HEADER
[ RII / RSN ] INFO_SPEC
[ QSPEC ] [ QSPEC ]
A RESPONSE message MUST contain an INFO_SPEC object which indicates
the success of a reservation installation or an error condition.
Depending on the value of the INFO_SPEC, the RESPONSE MAY also
contain a QSPEC object.
If any QSPEC objects are present, they MUST occur at the end of the
message. There are no other requirements on transmission order,
although the above order is recommended.
No message-specific flags are defined.
One generic flag is defined for use in the common header with the
RESPONSE message. This is:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
SCOPING (S) - when set, indicates that the message is scoped and
should not travel down the entire path but only as far as the next
QNE (scope="next hop"). By default, this flag is not set (default
scope="whole path").
5.1.2.4. NOTIFY
The format of a NOTIFY message is as follows:
NOTIFY = COMMON_HEADER
INFO_SPEC [ QSPEC ] [ QSPEC ]
A NOTIFY message MUST contain an INFO_SPEC object indicating the
reason for the notification. Depending on the INFO_SPEC value, it MAY
contain one or two QSPEC objects providing additional information.
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No flags are defined for use with the NOTIFY message.
5.1.3. Object Formats
The QoS NSLP uses the Type-Length-Value (TLV) object format defined
by GIST [I-D.ietf-nsis-ntlp]. Every object consists of one or more
32-bit words with a one-word header. For convenience the standard
object header is shown here:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|B|r|r| Type |r|r|r|r| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value for the Type field comes from QoS NSLP object type space,
the various objects are presented in subsequent sections. The Length
field is given in units of 32 bit words and measures the length of
the Value component of the TLV object (i.e., it does not include the
standard header).
The bits marked 'A' and 'B' are extensibility flags, and used to
signal the desired treatment for objects whose treatment has not been
defined in the protocol specification (i.e., whose Type field is
unknown at the receiver). The following four categories of object
have been identified, and are described here.
AB=00 ("Mandatory"): If the object is not understood, the entire
message containing it MUST be rejected, and an error message
sent back.
AB=01 ("Ignore"): If the object is not understood, it MUST be
deleted and the rest of the message processed as usual.
AB=10 ("Forward"): If the object is not understood, it MUST be
retained unchanged in any message forwarded as a result of
message processing, but not stored locally.
AB=11 ("Refresh"): If the object is not understood, it should be
incorporated into the locally stored signaling application state
for this flow/session, forwarded in any resulting message, and
also used in any refresh or repair message which is generated
locally.
The remaining bits marked 'r' are reserved. The extensibility flags
follow the definition in the GIST specification. All objects defined
in this specification MUST be understood by all QNEs, thus, they MUST
have the AB-bits set to "00".
The object diagrams here use '//' to indicate a variable sized field
and ':' to indicate a field that is optionally present.
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A QoS NSLP implementation must recognize objects of the following
types: RII, RSN, REFRESH_PERIOD, BOUND_SESSION_ID, INFO_SPEC, and
QSPEC.
The object header is followed by the Value field, which varies for
different objects. The format of the Value field for currently
defined objects is specified below.
5.1.3.1. Request Identification Information (RII)
Type: RII
Length: Fixed - 1 32-bit word
Value: An identifier which must be (probabilistically) unique within
the context of a SESSION_ID, and SHOULD be different every time a
RESPONSE is desired. Used by a QNE to match back a RESPONSE to a
request in a RESERVE or QUERY message.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Response Identification Information (RII) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.1.3.2. Reservation Sequence Number (RSN)
Type: RSN
Length: Fixed - 2 32-bit words
Value: An incrementing sequence number that indicates the order in
which state modifying actions are performed by a QNE, and an epoch
identifier to allow the identification of peer restarts. The RSN has
local significance only, i.e., between a pair of neighboring stateful
QNEs.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reservation Sequence Number (RSN) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Epoch Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.1.3.3. REFRESH_PERIOD
Type: REFRESH_PERIOD
Length: Fixed - 1 32-bit word
Value: The refresh timeout period R used to generate this message; in
milliseconds.
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh Period (R) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.1.3.4. BOUND_SESSION_ID
Type: BOUND_SESSION_ID
Length: Fixed - 5 32-bit words
Value: contains an 8-bit Binding_Code that indicates the nature of
binding. The rest specifies the SESSION_ID (as specified in GIST [I-
D.ietf-nsis-ntlp]) of the session that must be bound to the session
associated with the message carrying this object.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED | Binding Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Session ID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Currently defined Binding Codes are:
o 0x01 - Tunnel and end-to-end sessions
o 0x02 - Bi-directional sessions
o 0x03 - Aggregate sessions
o 0x04 - Dependent sessions (one session is alive only if the
other session is also alive)
More binding codes maybe defined based on the above four atomic
binding actions. Note a message may include more than one
BOUND_SESSION_ID object. This may be needed in case one needs to
define more specifically the reason for binding, or if the session
must be bound to more than one other session (with possibly different
reasons).
5.1.3.5. PACKET_CLASSIFIER
Type: Packet Classifier
Length: Variable
Value: Contains a 2 byte value indicating the MRM being used, and
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then additional variable length MRM-specific data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message-Routing-Method | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
// Method-specific classifier data (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For the basic path-coupled routing MRM, the method specific data is
two bytes long and consists of a set of flags:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X|Y|P|T|F|S|A|B| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The flags are:
X - Source Address and Prefix
Y - Destination Address and Prefix
P - Protocol
T - Traffic Class
F - Flow Label
S - SPI
A - Source Port
B - Destination Port
The flags indicate which fields from the MRI should be used by the
packet classifier. This allows a subset of the information in the MRI
to be used for identifying the set of packets which are part of the
reservation. Flags MUST only be set if the data is present in the MRI
(i.e., where there is a corresponding flag in the GIST MRI, the
PACKET_CLASSIFIER flag can only be set if the corresponding GIST MRI
flag is set). It should be noted that some flags in the
PACKET_CLASSIFIER (X and Y) relate to data that is always present in
the MRI, but are optional to use for QoS NSLP packet classification.
The appropriate set of flags set may depend, to some extent, on the
QoS model being used.
5.1.3.6. INFO_SPEC
Type: INFO
Length: Variable
Value: Contains a 4-bit error class, a 12-bit error code, an 8-bit
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QoS model-specific error subcode, an 8-bit error source identifier
length, an error source identifier and optionally variable length
error-specific information.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Class | Error Code | Error subcode | ESI-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Error Source Identifier //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional error-specific information //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The first four bits of the object indicate the error severity class.
The currently defined severity classes are:
o 0x01 - Informational
o 0x02 - Success
o 0x03 - Protocol Error
o 0x04 - Transient Failure
o 0x05 - Permanent Failure
o 0x06 - QoS model-specific Error
Within each error severity class a number of error values are
defined.
o Informational:
* 0x01 - Unknown BOUND_SESSION_ID: the message refers to an
unknown SESSION_ID in its BOUND_SESSION_ID object.
* 0x02 - Route Change: possible route change occurred on
downstream path.
o Success:
* 0x01 - State installation succeeded
* 0x02 - Reservation created: reservation installed on
complete path (sent by last node).
* 0x03 - Reservation accepted: reservation installed at this
QNE, but not yet installed on the rest of the path.
* 0x04 - Reservation created but modified: reservation
installed, but bandwidth reserved was not the maximum
requested.
o Protocol Error:
* 0x01 - Illegal message type: the type given in the Message
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Type field of the common header is unknown.
* 0x02 - Wrong message length: the length given for the
message does not match the length of the message
data.
* 0x03 - Bad flags value: an undefined flag or combination
of flags was set.
* 0x04 - Mandatory object missing: an object required in a
message of this type was missing.
* 0x05 - Illegal object present: an object was present which
must not be used in a message of this type.
* 0x06 - Unknown object present: an object of an unknown type
was present in the message.
* 0x07 - Wrong object length: the length given for the object
did not match the length of the object data present.
* 0x08 - Unknown QSPEC type: the QoS Model ID refers to a QoS
Model which is not known by this QNE.
* 0x09 - RESERVE received from wrong direction.
* 0x0a - Unknown object field value: a field in ab object had
an unknown value.
* 0x0b - Invalid Flag-Field combination: An object contains an
invalid combination of flags and/or fields.
* 0x0c - Duplicate object present.
o Transient Failure:
* 0x01 - Requested resources not available
* 0x02 - Insufficient bandwidth available
* 0x03 - Delay requirement cannot be met
* 0x04 - Transient RMF-related error
* 0x05 - Resources pre-empted
* 0x06 - No GIST reverse-path forwarding state
* 0x07 - NSLP soft-state expired
* 0x08 - No path state for RESERVE, when doing a receiver-
oriented reservation
* 0x09 - Reservation pre-empted
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* 0x0a - RII conflict
* 0x0b - Full QSPEC required
* 0x0c - Mismatch synchronization between end-to-end RESERVE
and intra-domain RESERVE
o Permanent Failure:
* 0x01 - Authentication failure
* 0x02 - Unable to agree transport security with peer
* 0x03 - Internal or system error
* 0x04 - Resource request denied (authorization failed)
* 0x05 - Permanent RMF-related error
o QoS model-specific Error:
This error class may be used, if a QoS model needs to indicate
errors, which do not fit any of the pre-defined error levels.
The interpretation of these errors is defined in each QoS model
document separately.
Values in the error subcode field are defined in each QoS model
specification separately. The default value for the subcode is 0x00.
A default value means that the QoS model does not want or does not
need to give more information about the error/result, anything else
in the subcode must be defined in the QoS model specification.
Error Source Identifier
The Error Source Identifier is for diagnostic purposes and its
inclusion is OPTIONAL. It is suggested that implementations might
use this for the IP address, host name or other identifier of the
QNE generating the INFO_SPEC to aid diagnostic activities.
If a QNE encounters protocol errors, it MAY include additional
information, mainly for diagnostic purposes. Additional
information may be included if the type of an object is erroneous,
or a field has an erroneous value.
If the type of an object is erroneous, the following optional
error-specific information may be included at the end of the
INFO_SPEC.
Object Type Info:
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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Object Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This object provides information about the type of object which
caused the error.
If a field in an object had in incorrect value, the following
optional error-specific information may be added at the end of the
INFO_SPEC.
Object Value Info:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rsvd | Real Object Length | Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Object //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Real Object Length: Since the length in the original TLV header
may be inaccurate, this field provides the actual length of the
object (including the TLV Header) included in the error message.
Offset: The byte in the object at which the QNE node found the
error.
Object: The invalid TLV object (including the TLV Header).
This object carries information about a TLV object which was found
to be invalid in the original message. An error message may
contain more than one Object Value Info object.
5.1.3.7. QSPEC
Type: QSPEC
Length: Variable
Value: Variable length QSPEC (QoS specification) information, which
is QoS Model dependent.
The contents and encoding rules for this object are specified in
other documents. See [I-D.ietf-nsis-qspec].
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// QSPEC Data //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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5.2. General Processing Rules
5.2.1. State Manipulation
The processing of a message and its component objects involves
manipulating the QoS NSLP and reservation state of a QNE.
For each flow, a QNE stores (RMF-related) reservation state which
depends on the QoS model / QSPEC used and QoS NSLP operation state
which includes non-persistent state (e.g., the API parameters while a
QNE is processing a message) and persistent state which is kept as
long as the session is active.
The persistent QoS NSLP state is conceptually organized in a table
with the following structure. The primary key (index) for the table
is the SESSION_ID:
SESSION_ID
A large identifier provided by GIST or set locally.
The state information for a given key includes:
Flow ID
Copied from GIST. Several entries are possible in case of mobility
events.
SII-Handle for each upstream and downstream peer
The SII-Handle is a local identifier generated by GIST and passed
over the API. It is a handle that allows to refer to a particular
GIST next hop. See SII-Handle in [I-D.ietf-nsis-ntlp] for more
information.
RSN from each upstream peer
The RSN is a 32 bit counter.
Current own RSN
A 32 bit counter.
List of RII for outstanding responses with processing information.
The RII is a 32 bit number.
State lifetime
The state lifetime indicates how long the state that is being
signaled for remains valid.
BOUND_SESSION_ID
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The BOUND_SESSION_ID is a 128 bit identifier.
Adding the state requirements of all these items gives an upper bound
on the state to be kept by a QNE. The need to keep state depends on
the desired functionality at the NSLP layer.
5.2.2. Message Forwarding
QoS NSLP messages are sent peer-to-peer along the path. The QoS NSLP
does not have the concept of a message being sent along the entire
path. Instead, messages are received by a QNE, which may then send
another message (which may be identical to the received message, or
contain some subset of objects from it) to continue in the same
direction (i.e., towards QNI or QNR) as the message received.
The decision on whether to generate a message to forward may be
affected by the value of the SCOPING flag or by the presence of an
RII object.
5.2.3. Standard Message Processing Rules
If a mandatory object is missing from a message then the receiving
QNE MUST NOT propagate the message any further. It MUST construct a
RESPONSE message indicating the error condition and send it back to
the peer QNE that sent the message.
If a message contains an object of an unrecognised type, then the
behavior depends on the AB extensibility flags.
5.2.4. Retransmissions
There are two retransmission mechanisms for RESERVE, one for
retransmissions between two directly adjacent QNEs (using the ACK
flag), and one for end-to-end retransmissions, e.g., between QNI and
QNR (using an RII object).
First, in case a QNE transmits a RESERVE with a set ACK flag it
awaits a RESPONSE (either positive or an error) from the receiving
QNE as acknowledgment of processing the REQUEST. If there is no such
acknowledgment, the sender may resend the same message after a
timeout of QOSNSLP_ACK_WAIT with an initial value of 500 ms. The
timeout may be dynamically determined like the RTO for TCP in rules
2.2 and 2.3 from [RFC 2988]. An implementation MAY cache the last RTO
measurement as the initial value for future requests to the QNE.
Further retransmissions may be initiated with exponentially
increasing wait intervals (doubling the wait interval each time) up
to QOSNSLP_ACK_WAIT_MAX (defaults to 2s) after the initial
transmission. The latter limit is provided to ensure a fast reaction
to failures and to avoid conflicts with a potential retransmission
when an included RII object will trigger another retransmission. In
case no RII object is contained in the RESERVE, a failure should be
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indicated to the signaling application.
Second, in case a QNE transmits a RESERVE with an RII object set it
waits for a RESPONSE from the responding QNE. QoS-NSLP messages for
which a response is requested by including an RII object, but fail to
elicit a response are retransmitted. The initial retransmission
occurs after a QOSNSLP_REQUEST_RETRY wait period. Retransmissions
MUST be made with exponentially increasing wait intervals (doubling
the wait each time). QoS-NSLP messages should be retransmitted until
either a response (which might be an error) has been obtained, or
until QOSNSLP_RETRY_MAX seconds after the initial transmission. In
the latter case, a failure should be indicated to the signaling
application.
QOSNSLP_REQUEST_RETRY: 2 seconds Wait interval before initial
retransmit of the message
QOSNSLP_RETRY_MAX: 30 seconds Give up retrying to send the
message
5.2.5. Rerouting
5.2.5.1. Last node behavior
As discussed in section 3.2.10 particular mechanisms need to be used
at the QNR when it is not also the data receiver or a configured
proxy for the data receiver.
Two particular cases for rerouting need to be considered in this
situation. In the first, referred to as "Path Extension", rerouting
occurs such that an additional QNE is inserted into the signaling
path between the old last node and the data receiver, as shown in
Figure 16.
/-------\ Initial route
/ v
/-\
/--|B|--\ +-+
/ \-/ \ |x| = QoS-NSLP aware
+-+ /-\ +-+
----|A| |D|
+-+ \-/ /-\
\ +-+ / |x| = QoS-NSLP unaware
\--|C|--/ \-/
+-+
\ ^
\-------/ Updated route
Figure 16: Path Extension
When rerouting occurs, the data path changes from A-B-D to A-C-D.
Initially the signaling path ends at A. Despite initially being the
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last node, node A MUST continue to attempt to send messages
downstream to probe for path changes, unless it has been explicitly
configured as a signaling proxy for the data flow receiver. This is
required so that the signaling path change is detected, and C will
become the new last QNE.
In a second case, referred to as "Path Truncation", rerouting occurs
such that the QNE that was the last node on the signaling path is no
longer on the data path. This is shown in Figure 17.
/-------\ Initial route
/ v
+-+
/--|B|--\ +-+
/ +-+ \ |x| = QoS-NSLP aware
+-+ /-\ +-+
----|A| |D|
+-+ \-/ /-\
\ /-\ / |x| = QoS-NSLP unaware
\--|C|--/ \-/
\-/
\ ^
\-------/ Updated route
Figure 17: Path Truncation
When rerouting occurs, the data path again changes from A-B-D to A-C-
D. The signaling path initially ends at C, but this node is not on
the new path. In this case, the normal GIST path change detection
procedures at A will detect the path change and notify the QoS-NSLP.
GIST will also notify the signaling application that no downstream
GIST nodes supporting the QoS-NSLP are present. Node A MUST take over
as the last node on the signaling path.
5.2.5.2. Reservation maintenance on route change
QoS NSLP is notified by GIST when GIST believes that a rerouting
event may have occurred. As part of the API, GIST provides an SII-
Handle which can be used by the NSLP to direct a signaling message to
a particular peer. The current SII-Handle will change if the
signaling peer changes. However, it is not guaranteed to remain the
same after a rerouting event where the peer does not change.
Therefore, the QoS NSLP mechanism for reservation maintenance after a
route change includes robustness mechanisms to avoid accidentally
tearing down a reservation in situations where the peer QNE has
remained the same after a 'route change' notification from GIST.
When a QNE detects that its neighbor QNE in the direction of the QNR
has changed, it SHOULD send a RESERVE message, including the full
QSPEC. This RESERVE message MUST include an RII, to request a
response from the QNR. When sending this message the RSN MUST be
incremented by two (and this becomes the current RSN value). An SII
MUST NOT be specified when passing this message over the API to GIST,
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so that it is correctly routed to the new peer QNE.
When the QNE receives the RESPONSE message that relates to that the
RESERVE message sent down the new path, it SHOULD send a RESERVE
message with the TEAR flag sent down the old path, by specifying the
SII relating to the old peer QNE. When sending this RESERVE message
the RSN field MUST be set to one less than the current RSN value (and
the current RSN value remains unchanged). This 'RSN-1' will cause the
message to be reject by the next peer if the old and new next peers
are actually the same.
Depending on the particular route change, there may be a 'merge
point' (or 'crossover node') where the old and new paths merge.
Initially this has a reservation installed by the old peer QNE,
identified by an old SII. When the new reservation is installed after
the route change the new peer QNE will be identified by a new SII. At
a later point the crossover node may receive a RESERVE message with
the TEAR flag set from the QNE identified by the old SII. A node
receiving a RESERVE message with the TEAR flag set which does not
come from the current peer QNE, identified by its SII, MUST be
ignored and MUST NOT be forwarded.
5.2.5.3. Upstream route change notification
GIST may notify QoS NSLP that a possible upstream route change has
occurred over the GIST API. On receiving such a notification, QoS
NSLP SHOULD send a NOTIFY message with Informational code 0x02 for
signaling sessions associated with the identified MRI.
On receiving such a NOTIFY message, QoS NSLP SHOULD use the
InvalidateRoutingState API call to inform GIST that routing state may
be out of date. QoS NSLP SHOULD send a NOTIFY message upstream.
5.2.5.4. Route change oscillation
In some circumstances a route change may occur, but the path then
falls back to the original route.
After a route change the routers on the old path will continue to
refresh the reservation until soft state times out, or an explicit
TEAR is received.
After detecting an upstream route change a QNE SHOULD consider the
new upstream peer as current and not fall back to the old upstream
peer unless:
- it stops receiving refreshes from the old upstream peer for at
least
the soft state timeout period and then starts receiving messages
from
the old upstream peer again
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- or, it stops receiving refreshes from the new upstream peer for at
least the soft state timeout period
GIST routing state keeps track of the latest upstream peer it has
seen, and so may spuriously indicate route changes occur when the old
upstream peer refreshes its routing state until the state at that
node is explicitly torn down or times out.
5.3. Object Processing
5.3.1. Reservation Sequence Number (RSN)
A QNE's own RSN is a sequence number which applies to a particular
signaling session (i.e., with a particular SESSION_ID). It MUST be
incremented for each new RESERVE message where the reservation for
the session changes. The RSN is manipulated using the serial number
arithmetic rules from [RFC1982], which also defines wrapping rules
and the meaning of 'equals', 'less than' and 'greater than' for
comparing sequence numbers in a circular sequence space.
The RSN object also contains an Epoch Identifier, which provides a
method for determining when a peer has restarted (e.g., due to node
reboot or software restart). The exact method for providing this
value is implementation defined. Options include storing a serial
number which is incremented on each restart, picking a random value
on each restart or using the restart time.
On receiving a RESERVE message a QNE examines the Epoch Identifier to
determine if the peer sending the message has restarted. If the Epoch
Identifier is different to that stored for the reservation then the
RESERVE message MUST be treated as an updated reservation (even if
the RSN is less than the current stored value), and the stored RSN
and Epoch Identifier MUST be updated to the new values.
When receiving a RESERVE message a QNE uses the RSN given in the
message to determine whether the state being requested is different
to that already stored. If the RSN is equal to that stored for the
current reservation the current state MUST be refreshed. If the RSN
is greater than the current stored value, the current reservation
MUST be modified appropriately (provided that admission control and
policy control succeed), and the stored RSN value updated to that for
the new reservation. If the RSN is less than the current value, then
it indicates an out-of-order message and the RESERVE message MUST be
discarded.
If the QNE does not store per-session state (and so does not keep any
previous RSN values) then it MAY ignore the value of the RSN. It MUST
also copy the same RSN into the RESERVE message (if any) it sends as
a consequence of receiving this one.
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5.3.2. Request Identification Information (RII)
A QNE sending QUERY or RESERVE messages may require a response to be
sent. It does so by including a Request Identification Information
(RII) object. When creating an RII object the QNE MUST select the
value for the RII such that it is probabilistically unique within the
given session. A RII object is typically set by the QNI.
A number of choices are available when implementing this.
Possibilities might include using a totally random value, or a node
identifier together with a counter. If the value collides with one
selected by another QNE for a different QUERY then RESPONSE messages
may be incorrectly terminated, and not passed back to the node that
requested them.
The node that created the RII object MUST remember the value used in
the RII to match back any RESPONSE it will receive. The node SHOULD
use a timer to identify situations where it has taken too long to
receive the expected RESPONSE. If the timer expires without receiving
a RESPONSE it MAY perform a retransmission as discussed in Section
5.2.4. In this case this QNE MUST not generate any RESPONSE or
NOTIFY message to notify this error.
If an intermediate QNE wants to request a response for an outgoing
message, but the message already included an RII when it arrived, the
QNE must not add a new RII object nor replace the old RII object, but
may simply remember that RII to match the related RESPONSE it is
interested in later. When it receives the RESPONSE, it forwards the
RESPONSE upstream towards the RII originating node. Note that only
the node that originally created the RII can set up a retransmission
timer. Thus, if an intermediate QNE decides to use the RII already
contained in the message, it MUST NOT set up a retransmission timer,
but rely on the retransmission timer set up by the QNE that inserted
the RII.
When receiving a message containing an RII object the node MUST send
a RESPONSE if either
o The SCOPING flag is set ('next hop' scope), or
o This QNE is the last one on the path for the given session.
and the QNE keeps per-session state for the given session.
A message contains at most one RII object that is unique within a
session and different for each message, in order to allow responses
to be matched back to requests (without incorrectly matching at other
nodes). Downstream nodes that desire responses may keep track of this
RII to identify the RESPONSE when it passes back through them.
In the rare event that the QNE wants to request a response for a
message that already included an RII, and this RII value conflicts
with an existing RII value on the QNE, the node should interrupt the
processing the message, and send an error message upstream to
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indicate an RII collision, and request a retry with a new RII value.
5.3.3. BOUND_SESSION_ID
As shown in the examples in Section 4, the QoS NSLP can relate
multiple sessions together. It does this by including the SESSION_ID
from one session in a BOUND_SESSION_ID object in messages in another
session.
When receiving a message with a BOUND_SESSION_ID object, a QNE MUST
copy the BOUND_SESSION_ID object into all messages it sends for the
same session. A QNE that stores per-session state MUST store the
value of the BOUND_SESSION_ID.
The BOUND_SESSION_ID is only indicative in nature. However, a QNE
implementation MAY use BOUND_SESSION_ID information to optimize
resource allocation, e.g., for bidirectional reservations. When
receiving a tearing RESERVE for an aggregate reservation, it MAY use
this information to initiate a tearing RESERVE for end-to-end
sessions bound to the aggregate. The BOUND_SESSION_ID processing must
be ready to process more than one such object within a single
message.
5.3.4. REFRESH_PERIOD
Refresh timer management values are carried by the REFRESH_PERIOD
object which has local significance only. At the expiration of a
"refresh timeout" period, each QNE independently examines its state
and sends a refreshing RESERVE message to the next QNE peer where it
is absorbed. This peer-to-peer refreshing (as opposed to the QNI
initiating a refresh which travels all the way to the QNR) allows
QNEs to choose refresh intervals as appropriate for their
environment. For example, it is conceivable that refreshing intervals
in the backbone, where reservations are relatively stable, are much
larger than in an access network. The "refresh timeout" is calculated
within the QNE and is not part of the protocol; however, it must be
chosen to be compatible with the reservation lifetime as expressed by
the REFRESH_PERIOD, and an assessment of the reliability of message
delivery.
The details of timer management and timer changes (slew handling and
so on) are identical to the ones specified in Section 3.7 of RFC 2205
[RFC2205].
There are two time parameters relevant to each QoS NSLP state in a
node: the refresh period R between generation of successive refreshes
for the state by the neighbor node, and the local state's lifetime L.
Each RESERVE message may contain a REFRESH_PERIOD object specifying
the R value that was used to generate this (refresh) message. This R
value is then used to determine the value for L when the state is
received and stored. The values for R and L may vary from peer to
peer. This peer-to-peer refreshing (as opposed to the QNI initiating
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a refresh which travels all the way to the QNR) allows QNEs to choose
refresh intervals as appropriate for their environment. For example,
it is conceivable that refreshing intervals in the backbone, where
reservations are relatively stable, are much larger than in an access
network.
In more detail (quoting directly from RFC2205):
1. Floyd and Jacobson [_XREF_FJ94] have shown that periodic
messages generated by independent network nodes can become
synchronized. This can lead to disruption in network services as
the periodic messages contend with other network traffic for link
and forwarding resources. Since QoS NSLP sends periodic refresh
messages, it must avoid message synchronization and ensure that
any synchronization that may occur is not stable. For this reason,
it is recommended that the refresh timer should be randomly set to
a value in the range [0.5R, 1.5R].
2. To avoid premature loss of state, L must satisfy L >= (K +
0.5)*1.5*R, where K is a small integer. Then in the worst case,
K-1 successive messages may be lost without state being deleted.
To compute a lifetime L for a collection of state with different R
values R0, R1, ..., replace R by max(Ri).
Currently K = 3 is suggested as the default. However, it may be
necessary to set a larger K value for hops with high loss rate. K
may be set either by manual configuration per interface, or by
some adaptive technique that has not yet been specified.
3. Each RESERVE message carries a REFRESH_PERIOD object containing
the refresh time R used to generate refreshes. The recipient node
uses this R to determine the lifetime L of the stored state
created or refreshed by the message.
4. The refresh time R is chosen locally by each node. If the node
does not implement local repair of reservations disrupted by route
changes, a smaller R speeds up adaptation to routing changes,
while increasing the QoS NSLP overhead. With local repair, a
router can be more relaxed about R since the periodic refresh
becomes only a backstop robustness mechanism. A node may therefore
adjust the effective R dynamically to control the amount of
overhead due to refresh messages.
The current suggested default for R is 30 seconds. However, the
default value Rdef should be configurable per interface.
5. When R is changed dynamically, there is a limit on how fast it
may increase. Specifically, the ratio of two successive values
R2/R1 must not exceed 1 + Slew.Max.
Currently, Slew.Max is 0.30. With K = 3, one packet may be lost
without state timeout while R is increasing 30 percent per refresh
cycle.
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6. To improve robustness, a node may temporarily send refreshes
more often than R after a state change (including initial state
establishment).
7. The values of Rdef, K, and Slew.Max used in an implementation
should be easily modifiable per interface, as experience may lead
to different values. The possibility of dynamically adapting K
and/or Slew.Max in response to measured loss rates is for future
study.
5.3.5. INFO_SPEC
The INFO_SPEC object is carried by the RESPONSE and NOTIFY messages
and it is used to report a successful, an unsuccessful, or an error
situation. In case of an error situation the error messages SHOULD
be generated even if no RII object is included in the RESERVE or
QUERY messages. Note that when the "T" flag is set in the RESERVE
message an error situation SHOULD not trigger the generation of a
RESPONSE message.
Six classes of the INFO_SPEC object are identified and specified in
Section 5.1.3.6. The message processing rules for each class are
defined in the following subsections.
5.3.5.1. Informational INFO_SPEC
This INFO_SPEC class MUST be generated by a last QNE when a RESERVE
or a QUERY message carries a BOUND_SESSION_ID that refers to a
SESSION_ID that is not available in the QNE's QoS-NSLP operational
state. A RESPONSE message MUST carry this object towards the QNI. The
RESPONSE message MUST be forwarded unconditionally up to the QNI. The
actions that SHOULD be undertaken by the QNI that receives this
INFO_SPEC object are specified by the local policy of the QoS model
supported by this QNE.
The default action is that the QNI that receives this INFO_SPEC
object SHOULD not trigger any other QoS-NSLP procedure.
5.3.5.2. Success INFO_SPEC
This INFO_SPEC class MUST be generated by a stateful QoS-NSLP QNE
when a RESERVE message triggers the following successful actions:
* State installation succeeded: the QOS-NSLP state is
successfully installed.
* Reservation is created on the complete path. Note that in
this case the INFO_SPEC object is generated by the last
QNE when the reservation is successfully created on the
complete path.
* Reservation accepted by the QNE. The reservation is accepted
by the QNE.
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* Reservation created but modified. The reservation is installed,
but bandwidth reserved was not the maximum requested.
A RESPONSE message MUST carry this object, which MUST be forwarded
unconditionally towards the upstream QNE, which generated the RESERVE
message that triggered the generation of this INFO_SPEC object.
The actions that SHOULD be undertaken by the QNE that receives this
INFO_SPEC object are specified by the local policy of the QoS model
supported by this QNE.
The default action is that the QNI that receives this INFO_SPEC
object SHOULD not trigger any other QOS-NSLP procedure.
5.3.5.3. Protocol Error INFO_SPEC
This INFO_SPEC class MUST be generated by a stateful QoS-NSLP QNE
when a RESERVE or QUERY message is received by the QNE and the
following protocol error codes are identified:
* Illegal message type: the type given in the
Message Type field of the common header is unknown.
* Wrong message length: the length given for the
message does not match the length of the message data.
* Bad flags value: an undefined flag or combination
of flags was set.
* Mandatory object missing: an object required in a
message of this type was missing.
* Illegal object present: an object was present
which must not be used in a message of this type.
* Unknown object present: an object of an unknown
type was present in the message.
* Wrong object length: the length given for the
object did not match the length of the object data present.
* Unknown QSPEC type (Unknown QOSM): the QOSM ID
refers to a QOSM which is not known by this QNE.
A RESPONSE message MUST carry this object, which MUST be forwarded
unconditionally towards the upstream QNE that generated the RESERVE
or QUERY message that triggered the generation of this INFO_SPEC
object.
The actions that SHOULD be undertaken by the QNE that receives this
INFO_SPEC object are specified by the local policy of the QoS model
supported by this QNE.
The default action is that the QNE that receives this INFO_SPEC
object SHOULD not trigger any other QOS-NSLP procedure.
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5.3.5.4. Transient Failure INFO_SPEC
This INFO_SPEC class MUST be generated by a stateful QoS-NSLP QNE
when a RESERVE or QUERY message is received by the QNE and the
following error codes are identified:
* Requested resources not available
* Insufficient bandwidth available
* Delay requirement cannot be met
* Transient RMF-related error: this error class must be specified
by the supported QoS model.
* Resources pre-empted: cannot be met
* No GIST reverse-path forwarding state
* NSLP soft-state expired
* No path state for RESERVE, when doing a receiver-oriented
reservation
* Reservation pre-empted: cannot be met
* RII conflict; a QNE may receive a
message with an RII that is already in use, which is a conflict
situation
A RESPONSE message MUST carry this object, which MUST be forwarded
unconditionally towards the upstream QNE that generated the RESERVE
or QUERY message that triggered the generation of this INFO_SPEC
object. The transient RMF-related error MAY also be carried by a
NOTIFY message. The actions that SHOULD be undertaken by the QNE
that receives this INFO_SPEC object are specified by the local policy
of the QoS model supported by this QNE.
The default action is that the QNE that receives this INFO_SPEC
object SHOULD re-trigger the retransmission of the RESERVE or QUERY
message that triggered the generation of the INFO_SPEC object.
5.3.5.5. Permanent Failure INFO_SPEC
This INFO_SPEC class MUST be generated by a stateful QoS-NSLP QNE
when a RESERVE or QUERY message is received by a QNE and the
following error codes are identified:
* Authentication failure: the authentication procedure failed
* Unable to agree transport security with peer
* Internal or system error
* Resource request denied (authorization failed)
* Permanent RMF-related error: this error class must be specified
by the supported QoS model.
A RESPONSE message MUST carry this object, which MUST be forwarded
unconditionally towards the upstream QNE that generated the RESERVE
or QUERY message that triggered this protocol error. The permanent
RMF-related, the internal or system errors MAY also be carried by a
NOTIFY message.
The actions that SHOULD be undertaken by the QNE that receives this
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INFO_SPEC object are specified by the local policy of the QoS model
supported by this QNE.
The default action is that the QNE that receives this INFO_SPEC
object SHOULD not trigger any other QoS-NSLP procedure.
5.3.5.6. NSLP-specific Error INFO_SPEC
This error class may be used, if an NSLP needs to indicate errors,
which do not fit in each NSLP separately. For QoS-NSLP, these are
defined in the different QoS model specifications.
5.3.6. QSPEC
The contents of the QSPEC depends on the QoS model being used. A
template for QSPEC objects can be found in [I-D.ietf-nsis-qspec].
Upon reception, the complete QSPEC is passed to the Resource
Management Function (RMF), along with other information from the
message necessary for the RMF processing.
A QNE that receives a QSPEC stack may need to inspect the top most or
both of the QSPEC objects in the stack, e.g., an domain edge QNE may
need to add or remove a local QSPEC. Yet, if the top most QSPEC
(i.e., te first QSPEC in the message) defines an unknown QOSM not
understood by the RMF, the QNE MUST send an RESPONSE containing an
INFO_SPEC and MUST NOT attempt to recover by inspecting the other
QSPEC at the bottom of the stack.
Parameters of the QoS Model that is being signaled for are carried in
the QSPEC object. A domain may have local policies regarding QoS
model implementation, i.e., it may map incoming traffic to its own
locally defined QoS Models. The QoS NSLP supports this by allowing
QSPEC objects to be stacked.
When a domain wants to apply a certain QoS Model to an incoming per-
flow reservation request, each edge of the domain is configured to
map the incoming QSPEC object to a local QSPEC object and push that
object onto the stack of QSPEC objects (so that it becomes the first
QSPEC in the message).
A QNE that knows it is the last QNE to understand a local QSPEC
object (e.g., by configuration of the egress QNEs of a domain) MUST
remove the topmost QSPEC object from the stack. It SHOULD update the
underlying QoS Model's writable parameters, e.g., QoS Available.
5.4. Message Processing Rules
This section provides rules for message processing. Not all possible
error situations are considered. A general rule for dealing with
erroneous messages is that a node should evaluate the situation
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before deciding how to react. There are two ways to react to
erroneous messages:
a) Silently drop the message, or
b) Drop the message, and reply with an error code to the sender.
The default behavior, in order to protect the QNE from a possible DoS
attack, is to silently drop the message. However, if the QNE is able
to authenticate the sender, e.g., through GIST, the QNE may send a
proper error message back to sender in order to let it know that
there is an inconsistency in the states of adjacent QNEs.
Yet, there is a third possible mode of operation when receiving an
unexpected or erroneous message. The QNE may consider the incoming
message as fully acceptable, and operate as if there was no error in
the processing. This may happen, for example, if the QNE knows it has
just rebooted and has lost its signaling states. Now, the QNE may try
to act as if "nothing happened". Note that an implementation must
carefully consider this behavior.
5.4.1. RESERVE Messages
The RESERVE message is used to manipulate QoS reservation state in
QNEs. A RESERVE message may create, refresh, modify or remove such
state. A QNE sending a RESERVE may require a response to be sent by
including a Request Identification Information (RII) object, see
Section 5.3.2.
RESERVE messages MUST only be sent towards the QNR. A QNE that
receives a RESERVE message checks the message format. In case of
malformed messages, the QNE MAY send a RESPONSE message with the
appropriate INFO_SPEC.
Before performing any state changing actions a QNE MUST determine
whether the request is authorized. The way to do this check depends
on the authorization model being used.
When the RESERVE is authorized, a QNE checks the COMMON_HEADER flags.
If the TEAR flag is set, the message is a tearing RESERVE which
indicates complete QoS NSLP state removal (as opposed to a
reservation of zero resources). On receiving such a RESERVE message
the QNE MUST inform the RMF that the reservation is no longer
required. The QNE SHOULD remove the QoS NSLP state. It MAY signal to
GIST (over the API) that reverse path state for this reservation is
no longer required. Depending on the QoS model, the tear message may
include a QSPEC to further specify state removal. If the QoS model
requires a QSPEC, and none is provided, the QNE should reply with an
error message, and not remove the reservation. If the tearing
RESERVE includes a QSPEC, but none is required by the QoS model, the
QNE may silently discard the QSPEC and proceed as if it did not exit
in the message.
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As discussed in section 5.2.5.2, to avoid incorrect removal of state
after a rerouting event, a node receiving a RESERVE message with the
TEAR flag set which does not come from the current peer QNE,
identified by its SII, MUST be ignored and MUST NOT be forwarded.
If the QNE has reservations which are bound to this session (they
contained the SESSION_ID of this session in their BOUND_SESSION_ID
object), it MUST send a NOTIFY message for each of these reservations
with an appropriate INFO_SPEC. The QNE MAY elect to send RESERVE
messages with the TEAR flag set for these reservations.
The default behavior of a QNE that receives a RESERVE with a
SESSION_ID for which it already has state installed but with a
different flow ID is to replace the existing reservation (and tear
down the reservation on the old branch if the RESERVE is received
with a different SII).
In some cases, this may not be the desired behavior. In that case,
the QNI or a QNE may set the REPLACE flag in the common header to
zero to indicate that the new session does not replace the existing
one.
A QNE that receives a RESERVE with the REPLACE flag set to zero but
with the same SII, will indicate REPLACE=0 to the RMF (where it will
be used for the resource handling). Furthermore, if the QNE maintains
a QoS-NSLP state then it will also add the new flow ID in the QoS-
NSLP state. If the SII is different, this means that the QNE is a
merge point. In that case, in addition to the operations specified
above, the value REPLACE=0 is also indicating that a tearing RESERVE
SHOULD NOT be sent on the old branch.
When a QNE receives a RESERVE message with an unknown SESSION_ID and
this message contains no QSPEC because it was meant as a refresh then
the node MUST send a RESPONSE message with an INFO_SPEC that
indicates a missing QSPEC to the upstream peer ("Full QSPEC
required"). The upstream peer SHOULD send a complete RESERVE (i.e.,
one containing a QSPEC) on the new path (new SII).
At a QNE, resource handling is performed by the RMF. For sessions
with the REPLACE flag set to zero, we assume that the QoS model
includes directions to deal with resource sharing. This may include,
adding the reservations, or taking the maximum of the two or more
complex mathematical operations.
This resource handling mechanism in the QoS Model is also applicable
to sessions with different SESSION_ID but related through the
BOUND_SESSION_ID object. Session replacement is not an issue here,
but the QoS Model may specify whether to let the sessions that are
bound together share resources on common links or not.
Finally, it is possible that a RESERVE is received with no QSPEC at
all. This is the case of a reduced refresh. In this case, rather than
sending a refreshing RESERVE with the full QSPEC, only the SESSION_ID
and the SII are sent to refresh the reservation. Note that this
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mechanism just reduces the message size (and probably eases
processing). One RESERVE per session is still needed.
If the REPLACE flag is set, the QNE SHOULD update the reservation
state according to the QSPEC contained in the message (if the QSPEC
is missing the QNE should indicate this error by replying with a
RESPONSE containing the corresponding INFO_SPEC "Full QSPEC
required"). It MUST update the lifetime of the reservation. If the
REPLACE flag is not set, a QNE SHOULD NOT remove the old reservation
state if the SII which is passed by GIST over the API is different
than the SII that was stored for this reservation. The QNE MAY elect
to keep sending refreshing RESERVE messages.
If the ACKNOWLEDGE flag is set, the QNE MUST acknowledge its state
installation action. It does so by sending a RESPONSE with an
INFO_SPEC indicating that the reservation is installed at the QNE
(code 0x03).
If the SCOPING flag is set, or if the QNE is the last QNE on the path
to the destination, the QNE MUST send a RESPONSE message.
When a QNE receives a RESERVE message, its processing may involve
sending out another RESERVE message. When sending a RESERVE message,
the QNE may insert or remove 'local' QSPEC objects from the message.
If any QSPEC is present, the first QSPEC MUST NOT be removed when
sending on the RESERVE message.
Upon transmission, a QNE SHOULD set the ACKNOWLEDGE flag. It MUST do
so if it wishes to use the reduced overhead refresh mechanism
described in Section 3.2.5. It MUST NOT send a reduced overhead
refresh message (i.e., a RESERVE with a non-incremented RSN and no
QSPEC) unless it has received a RESPONSE message for that RESERVE
message.
If the session of this message is bound to another session, then the
RESERVE message MUST include the SESSION_ID of that other session in
a BOUND_SESSION_ID object.
In case of receiver-initiated reservations, the RESERVE message must
follow the same path that has been followed by the QUERY message.
Therefore, GIST is informed, over the QoS NSLP/GIST API, to pass the
message upstream, i.e., by setting GIST "D" flag, see GIST [I-D.ietf-
nsis-ntlp].
The QNE must create a new RESERVE and send it to its next peer, when:
- A new resource set up was done,
- A new resource set up was not done, but the QOSM still defines that
a RESERVE must be propagated,
- The RESERVE is a refresh and includes new MRI, or
- If the R-bit is included in an arrived QUERY.
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5.4.2. QUERY Messages
A QUERY message is used to request information about the data path
without making a reservation. This functionality can be used to
'probe' the network for path characteristics or for support of
certain QoS models, or for initiating a receiver-initiated
reservation.
A QNE sending a QUERY indicates a request for a response by including
a Request Identification Information (RII) object, see Section 5.3.2.
A request to initiate a receiver-initiated reservation is done
through the R-flag, see Section 5.1.2.2.
When a QNE receives a QUERY message the QSPEC is passed to the RMF
for processing. The RMF may return a modified QSPEC which is used in
any QUERY or RESPONSE message sent out as a result of the QUERY
processing.
When processing a QUERY message, a QNE checks whether the R-bit is
set. If the bit is set, the QUERY is used to install reverse path
state. In this case, if the QNE is not the QNI, it creates a new
QUERY message to send downstream. If the QUERY contained a QSPEC,
this MUST be passed to the RMF where it MAY be modified by QoS Model
specific QUERY processing. If the QNE is the QNI, the QNE creates a
RESERVE message, which contains a QSPEC received from the RMF and
which MAY be based on the received QSPEC. If this node was not
expecting to perform a receiver-initiated reservation then an error
MUST be sent back along the path.
If an RII object is present, and if the QNE is the QNR or the SCOPING
flag is set, the QNE MUST generate a RESPONSE message and pass it
back along the reverse of the path used by the QUERY.
In other cases, the QNE MUST generate a QUERY message which is then
forwarded further along the path using the same MRI, Session ID and
Direction as provided when the QUERY was received over the GIST API.
The QSPEC to be used is that provided by the RMF as described
previously. When generating a QUERY to send out to pass the query
further along the path, the QNE MUST copy the RII object (if present)
into the new QUERY message unchanged. A QNE that is also interested
in the response to the query keeps track of the RII to identify the
RESPONSE when it passes through it.
Note that QUERY messages with the R-bit set should always be answered
by the QNR. This feature may be used, e.g., following handovers, to
set up new path state in GIST, and request the other party to send a
RESERVE back on this new GIST path.
5.4.3. RESPONSE Messages
The RESPONSE message is used to provide information about the result
of a previous QoS NSLP message, e.g., confirmation of a reservation
or information resulting from a query. The RESPONSE message is
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impotent, it does not cause any state to be installed or modified.
A RESPONSE message MUST be sent when the QNE is the last node to
process a RESERVE or QUERY message containing an RII object (based on
scoping of the RESERVE or QUERY, or because this is the last node on
the path). In this case, the RESPONSE MUST copy the RII object from
the RESERVE or QUERY. In case of a successful RESPONSE carrying an
INFO_SPEC class 0x02 the error code must not be set to 0x02 unless
the RESPONSE is really generated by the QNR.
In addition, a RESPONSE message MUST be sent when the ACKNOWLEDGE
flag is set or when an error occurs while processing a received
message. If the received message contains an RII object and the
ACKNOWLEDGE flag is set, a QNE generates a RESPONSE without RII if
the QNE is not the QNR. In this case a successful RESPONSE carries
the INFO_SPEC with success code 0x01 and the received message is
forwarded further along the path towards the QNR. In case the QNR
receives a message with an ACKNOWLEDGE flag and an RII object it
generates two RESPONSE messages: one for the ACK towards the previous
upstream hop as above (without RII) and one as RESPONSE containing
the RII (and if the request was successful an INFO_SPEC with code
either 0x02 if the reservation is installed on complete path (sent by
last node) or 0x04 if the reservation is installed, but the bandwidth
reserved was not the maximum requested.
On receipt of a RESPONSE message containing an RII object, the
stateful QoS-NSLP QNE MUST attempt to match it to the outstanding
response requests for that signaling session. If the match succeeds,
then the RESPONSE MUST NOT be forwarded further along the path if it
contains an INFO_SPEC class informational or success. If the QNE did
not insert this RII itself, if must forward the RESPONSE to the next
peer. Thus, for RESPONSES indicating success, forwarding should only
stop if the QNE inserted the RII by itself, If the RESPONSE carries
an INFO_SPEC indicating an error, forwarding SHOULD continue upstream
towards the QNI by using RSNs as described in the next paragraph.
On receipt of a RESPONSE message containing an RSN object, a stateful
QoS-NSLP QNE MUST compare the RSN to that of the appropriate
signaling session. If the match succeeds then the INFO_SPEC MUST be
processed. If the INFO_SPEC object is used to notify errors then the
node MUST use the stored upstream peer RSN value, associated with the
same session, and forward the RESPONSE message further along the path
towards the QNI.
The INFO_SPEC object used to notify errors can be of the following
types:
* Protocol Error INFO_SPEC (see Section 5.3.5.3)
* Transient Failure INFO_SPEC (see Section 5.3.5.4)
* Permanent Failure INFO_SPEC (see Section 5.3.5.5)
* NSLP-specific Error INFO_SPEC (see Section 5.3.5.6)
If the INFO_SPEC is not used to notify error situations, see above,
then if the RESPONSE message carries an RSN, the message MUST NOT be
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forwarded further along the path.
If there is no match for RSN, the message should be silently dropped.
On receipt of a RESPONSE message containing neither an RII nor an RSN
object, the RESPONSE MUST NOT be forwarded further along the path.
In the typical case RESPONSE messages do not change the states
installed in intermediate QNEs. However, depending on the QoS model,
there may be situations where states are affected, e.g.,
- if the RESPONSE includes an INFO_SPEC describing an error situation
resulting in reservations to be removed, or
- the QoS model allows a QSPEC to define [min,max] limits on the
resources requested, and downstream QNEs gave less resources than
their upstream nodes, which means that the upstream nodes may
release a part of the resource reservation.
5.4.4. NOTIFY Messages
NOTIFY messages are used to convey information to a QNE
asynchronously. NOTIFY messages are impotent. They do not cause any
state to be installed. However, if the notification indicates an
error, the indicated state may be removed. The exact operation
depends on the QoS model. NOTIFY message do not directly cause other
messages to be sent. NOTIFY messages are sent asynchronously, rather
than in response to other messages. They may be sent in either
direction (upstream or downstream).
6. IANA considerations
This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values related to the QoS
NSLP, in accordance with BCP 26 RFC 2434 [RFC2434].
The QoS NSLP requires IANA to create a number of new registries.
The QoS NSLP Message Type is a 8 bit value. The allocation of values
for new message types requires standards action. This specification
defines four QoS NSLP message types, which form the initial contents
of this registry: RESERVE, QUERY, RESPONSE and NOTIFY.
QoS NSLP Messages have a messages-specific 8 bit flags/reserved field
in their header, and a 16-bit Generic Flags field. All currently used
flags are specified in Section 5.1.2. The allocation of new flags is
done as needed through IANA.
The QoS Model Identifier (QoS Model ID) is carried in a QSPEC object.
The allocation of new QoS Model IDs is done by IANA.
This specification defines an NSLP for use with GIST. Consequently, a
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new identifier must be assigned for it from GIST NSLP Identifier
registry.
This document also defines seven new objects for the QoS NSLP: RII,
RSN, REFRESH_PERIOD, BOUND_SESSION_ID, PACKET_CLASSIFIER, QSPEC and
INFO_SPEC. Values are to be assigned for them from NSLP Object Type
registry.
In addition it defines a number of Error Codes for the QoS NSLP.
These can be found in Section 5.1.3.6 and are to be assigned values
from NSLP Error Code registry.
Further consideration of IANA issues can be found in a separate draft
[NSIS-EXT].
7. QoS use of GIST service interface
This section describes the use of GIST service interface to implement
QoS NSLP requirements on GIST.
7.1. Example sender-initiated reservation
We first describe the use of the service interface in a very basic
scenario: message reception and transmission for a RESERVE message in
a sender-initiated reservation.
A QNE that wishes to initiate a sender-initiated reservation
constructs a new RESERVE message to send downstream. The use of GIST
service interface in this case is explained on Figure 18.
GIST QoS NSLP
| |
|<=====================================|
| SendMessage{ |
| NSLP-Data=RESERVE, |
| NSLP-Data-Size=X bytes, |
| NSLP-Message-Handle=NULL, |
| NSLP-Id=QoS, |
| Session-ID=SID_X, |
| MRI=MRI, |
| SII-Handle=empty, |
| Transfer-attributes=default, |
| Timeout=default, |
| IP-TTL=default |
| GHC=default} |
| |
Figure 18: GIST service interface usage for
sending a sender-initiated reservation
Note that an explicit preference for a particular type of transport,
such as reliable/unreliable, may change the values of some service
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interface parameters (e.g., Transfer-attributes=unreliable).
The message is received by the peer QNE. The use of GIST service
interface when receiving a RESERVE message for a sender-initiated
reservation is explained on Figure 19.
GIST QoS NSLP
| |
|=====================================>|
| RecvMessage{ |
| NSLP-Data=RESERVE, |
| NSLP-Data-Size=X bytes, |
| NSLP-Id=QoS, |
| Session-ID=SID_X, |
| MRI=MRI, |
| Adjacency-Check=default, |
| SII-Handle=empty, |
| Transfer-attributes=default, |
| IP-TTL=TTL_X, |
| IP-Distance=0 |
| GHC=default} |
| |
Figure 19: GIST service interface usage for message
reception of sender-initiated reservation
7.2. Session identification
The QoS NSLP keeps message and reservation state per session. A
session is identified by a Session Identifier (SESSION_ID). The
SESSION_ID is the primary index for stored NSLP state and needs to be
constant and unique (with a sufficiently high probability) along a
path through the network. On Figure 18, QoS NSLP picks a value SID_X
for Session-ID. This value is subsequently used by GIST and QoS NSLP
to refer to this session.
7.3. Support for bypassing intermediate nodes
The QoS NSLP may want to restrict the handling of its messages to
specific nodes. This functionality is needed to support layering
(explained in Section 3.2.8), when only the edge QNEs of a domain
process the message. This requires a mechanism at GIST level (which
can be invoked by the QoS NSLP) to bypass intermediate nodes between
the edges of the domain.
The intermediate nodes are bypassed using multiple levels of the
router alert option. In that case, internal routers are configured to
handle only certain levels of router alerts. This is accomplished by
marking the signaling messages, i.e., modifying the QoS-NSLP default
NSLP-ID value to another NSLP-ID predefined value. The marking MUST
be accomplished by the ingress edge by modifying the QoS-NSLP default
NSLP-ID value to a NSLP-ID predefined value. The egress MUST stop
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this marking process by reassigning the QoS-NSLP default NSLP-ID
value to the original RESERVE message. The exact operation of
modifying the NSLP-ID must be specified in the relevant QoS model
specification.
7.4. Support for peer change identification
There are several circumstances where it is necessary for a QNE to
identify the adjacent QNE peer, which is the source of a signaling
application message; e.g., it may be to apply the policy that "state
can only be modified by messages from the node that created it" or it
might be that keeping track of peer identity is used as a (fallback)
mechanism for rerouting detection at the NSLP layer.
This functionality is implemented in GIST service interface with SII-
handle. As shown in the above example, we assume the SII- handling
will support both own SII and peer SII.
Keeping track of the SII of a certain reservation also provides a
means for the QoS NSLP to detect route changes. When a QNE receives a
RESERVE referring to existing state but with a different SII, it
knows that its upstream peer has changed. It can then use the old SII
to initiate a teardown along the old section of the path. This
functionality is supported in GIST service interface when the peer's
SII which is stored on message reception is passed to GIST upon
message transmission.
7.5. Support for stateless operation
Stateless or reduced state QoS NSLP operation makes the most sense
when some nodes are able to operate in a stateless way at GIST level
as well. Such nodes should not worry about keeping reverse state,
message fragmentation and reassembly (at GIST), congestion control or
security associations. A stateless or reduced state QNE will be able
to inform the underlying GIST of this situation. GIST service
interface supports this functionality with the Retain-State attribute
in the MessageReceived primitive.
7.6. Last node detection
There are situations in which a QNE needs to determine whether it is
the last QNE on the data path (QNR), e.g., to construct and send a
RESPONSE message.
A number of conditions may result in a QNE determining that it is the
QNR:
o the QNE may be the flow destination
o the QNE have some other prior knowledge that it should act as
the QNR
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o the QNE may be the last NSIS-capable node on the path
o the QNE may be the last NSIS-capable node on the path
supporting the QoS NSLP
Of these four conditions, the last two can only be detected by GIST.
We rely on GIST to inform the QoS NSLP about these cases by providing
a trigger to the QoS NSLP when it determines that it is the last NE
on the path, which supports the QoS NSLP. GIST supports this by the
MessageDeliverError primitive. The error type 'no next node found'
which is given as an example can be used. It is expected that
additional error codes need to be defined.
7.7. Re-routing detection
Route changes may be detected at GIST layer or the information may be
obtained by GIST through local interaction with or notification from
routing protocols or modules. GIST allows to pass such information
over the service interface using the NetworkNotification primitive
with the appropriate 'downstream route change' or 'upstream route
change' notification.
7.8. Priority of signaling messages
The QoS NSLP will generate messages with a range of performance
requirements for GIST. These requirements may result from a
prioritization at the QoS NSLP (Section 3.2.9) or from the
responsiveness expected by certain applications supported by the QoS
NSLP.
GIST design should be able to ensure that performance for one class
of messages was not degraded by aggregation with other classes of
messages. GIST service interface supports this with the 'priority'
transfer attribute.
7.9. Knowledge of intermediate QoS NSLP unaware nodes
In some cases it is useful to know that a reservation has not been
installed at every router along the path. It is not possible to
determine this using only NSLP functionality.
GIST should be able to provide information to the NSLP about whether
the message has passed through nodes that did not provide support for
this NSLP.
GIST service interface supports this by keeping track of IP-TTL and
Original-TTL in the RecvMessage primitive. A difference between the
two indicates the number of QoS NSLP unaware nodes.
The QSPEC template also includes a bit "<NON QOSM Hop>" telling that
one or more QOSM-aware QNE were encountered on the path from the QNI
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to the QNR [I-D.ietf-nsis-qspec].
7.10. NSLP Data Size
When GIST passes the QoS NSLP data to the NSLP for processing, it
must also indicate the size of that data. This is supported by the
NSLP-Data-Size attribute.
7.11. Notification of GIST 'D' flag value
When GIST passes the QoS NSLP data to the NSLP for processing, it
must also indicate the value of the 'D' (Direction) flag for that
message. This is done in the Direction attribute of the SendMessage
and RecvMessage primitives.
7.12. NAT Traversal
The QoS NSLP relies on GIST for NAT traversal.
8. Assumptions on the QoS Model
8.1. Resource sharing
This specification assumes that resource sharing is possible between
flows with the same SESSION_ID that originate from the same QNI or
between flows with a different SESSION_ID that are related through
the BOUND_SESSION_ID object. For flows with the same SESSION_ID,
resource sharing is only applicable when the existing reservation is
not just replaced (which is indicated by the REPLACE flag in the
common header.
The Resource Management Function (RMF) reserves resources for each
flow. We assume that the QoS model supports resource sharing between
flows. A QoS Model may elect to implement a more general behavior of
supporting relative operations on existing reservations, such as
ADDING or SUBTRACTING a certain amount of resources from the current
reservation. A QoS Model may also elect to allow resource sharing
more generally, e.g., between all flows with the same DSCP.
8.2. Reserve/commit support
Reserve/commit behavior means that the time at which the reservation
is made may be different from the time when the reserved resources
are actually set aside for the requesting session. This specification
acknowledges the usefulness of such a mechanism but assumes that its
implementation is opaque to QoS NSLP and is fully handled by the QoS
Model.
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9. Security Considerations
9.1. Introduction and Threat Overview
The security requirement for the QoS NSLP is to protect the signaling
exchange for establishing QoS reservations against identified
security threats. For the signaling problem as a whole, these threats
have been outlined in NSIS threats [RFC4081]; the NSIS framework
[RFC4080] assigns a subset of the responsibility to GIST and the
remaining threats need to be addressed by NSLPs. The main issues to
be handled can be summarized as:
Authorization:
The QoS NSLP must assure that the network is protected against theft-
of-service by offering mechanisms to authorize the QoS reservation
requester. A user requesting a QoS reservation might want proper
resource accounting and protection against spoofing and other
security vulnerabilities which lead to denial of service and
financial loss. In many cases authorization is based on the
authenticated identity. The authorization model must provide
guarantees that replay attacks are either not possible or limited to
a certain extent. Authorization can also be based on traits which
enables the user to remain anonymous. Support for user identity
confidentiality can be accomplished.
Message Protection:
Signaling message content should be protected against modification,
replay, injection and eavesdropping while in transit. Authorization
information, such as authorization tokens, need protection. This type
of protection at the NSLP layer is necessary to protect messages
between NSLP nodes which includes end-to-middle, middle-to-middle and
even end-to-end protection.
Rate Limitation:
QNEs should perform rate limiting on the refresh messages that they
send. An attacker could send erroneous messages on purpose, forcing
the QNE to constantly reply with an error message. Authentication
mechanisms would help in figuring out if error situations should be
reported to the sender, or silently ignored. If the sender is
authenticated, the QNE should reply promptly.
In addition to the above-raised issues we see the following
functionality provided at the NSLP layer:
Prevention of Denial of Service Attacks:
GIST and QoS NSLP nodes have finite resources (state storage,
processing power, bandwidth). The protocol mechanisms s in this
document try to minimize exhaustion attacks against these
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resources when performing authentication and authorization for QoS
resources.
To some extent the QoS NSLP relies on the security mechanisms
provided by GIST which by itself relies on existing authentication
and key exchange protocols. Some signaling messages cannot be
protected by GIST and hence should be used with care by the QoS NSLP.
An API must ensure that the QoS NSLP implementation is aware of the
underlying security mechanisms and must be able to indicate which
degree of security is provided between two GIST peers. If a level of
security protection for QoS NSLP messages is required which goes
beyond the security offered by GIST or underlying security
mechanisms, additional security mechanisms described in this document
must be used. The different usage environments and the different
scenarios where NSIS is used make it very difficult to make general
statements without reducing its flexibility.
9.2. Trust Model
This specification is based on a model which requires trust between
neighboring NSLP nodes to establish a chain-of-trust along the QoS
signaling path. The model is simple to deploy, was used in previous
QoS authorization environments (such as RSVP) and seems to provide
sufficiently strong security properties. We refer to this model as
the
On the New Jersey Turnpike, motorists pick up a ticket at a toll
booth when entering the highway. At the highway exit the ticket is
presented and payment is made at the toll booth for the distance
driven. For QoS signaling in the Internet this procedure is roughly
similar. In most cases the data sender is charged for transmitted
data traffic where charging is provided only between neighboring
entities.
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+------------------+ +------------------+ +------------------+
| Network | | Network | | Network |
| X | | Y | | Z |
| | | | | |
| -----------> -----------> |
| | | | | |
| | | | | |
+--------^---------+ +------------------+ +-------+----------+
| .
| .
| v
+--+---+ Data Data +--+---+
| Node | ==============================> | Node |
| A | Sender Receiver | B |
+------+ +------+
Legend:
----> Peering relationship which allows neighboring
networks/entities to charge each other for the
QoS reservation and data traffic
====> Data flow
..... Communication to the end host
Figure 20: New Jersey Turnpike Model
The model shown in Figure 20 uses peer-to-peer relationships between
different administrative domains as a basis for accounting and
charging. As mentioned above, based on the peering relationship a
chain-of-trust is established. There are several issues which come to
mind when considering this type of model:
o The model allows authorization on a request basis or on a per-
session basis. Authorization mechanisms are elaborated in Section
4.9. The duration for which the QoS authorization is valid needs
to be controlled. Combining the interval with the soft-state
interval is possible. Notifications from the networks also seem to
be viable approach.
o The price for a QoS reservation needs to be determined somehow
and communicated to the charged entity and to the network where
the charged entity is attached. Price distribution protocols are
out of scope. The model assumes, per default, that the data sender
is authorizing the QoS reservation. Please note that this is only
a simplification and further extensions are possible in the
future.
o This architecture is simple enough to allow a scalable solution
(ignoring reverse charging, multicast issues and price
distribution).
Charging the data sender as performed in the model simplifies
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security handling by demanding only peer-to-peer security protection.
Node A would perform authentication and key establishment. The
established security association (together with the session key)
would allow the user to protect QoS signaling messages. The identity
used during the authentication and key establishment phase would be
used by Network X (see Figure 20) to perform the so-called policy-
based admission control procedure. In our context this user
identifier would be used to establish the necessary infrastructure to
provide authorization and charging. Signaling messages later
exchanged between the different networks are then also subject to
authentication and authorization. The authenticated entity thereby
is, however, the neighboring network and not the end host.
The New Jersey Turnpike model is attractive because of its
simplicity. S. Schenker et. al. [shenker-pricing] discuss various
accounting implications and introduced the edge pricing model. The
edge pricing model shows similarity to the model described in this
section with the exception that mobility and the security
implications itself are not addressed.
9.3. Computing the authorization decision
Whenever an authorization decision has to be made then there is the
question which information serves as an input to the authorizing
entity. The following information items have been mentioned in the
past for computing the authorization decision (in addition to the
authenticated identity):
Price
QoS objects
Policy rules
Policy rules include attributes like time of day, subscription to
certain services, membership, etc. into consideration when computing
an authorization decision.
A detailed description of the authorization handling is handled in
other documents. The authors assume that the QoS NSLP needs to
provide a number of attributes to support the large range of
scenarios.
10. Acknowledgments
The authors would like to thank Eleanor Hepworth, Ruediger Geib,
Roland Bless, Nemeth Krisztian, Markus Ott, Mayi Zoumaro-Djayoon,
Martijn Swanink, and Ruud Klaver for their useful comments. Roland,
especially, has done deep reviews of the document, making sure the
protocol is well defined.
Bob Braden provided helpful comments and guidance which were
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gratefully received.
11. Contributors
This draft combines work from three individual drafts. The following
authors from these drafts also contributed to this document: Robert
Hancock (Siemens/Roke Manor Research), Hannes Tschofenig and Cornelia
Kappler (Siemens AG), Lars Westberg and Attila Bader (Ericsson) and
Maarten Buechli (Dante) and Eric Waegeman (Alcatel).
Sven Van den Bosch was the first editor of the draft. Since version
06 of the draft, Jukka Manner has taken the editorship.
Yacine El Mghazli (Alcatel) contributed text on AAA.
Charles Shen and Henning Schulzrinne suggested the use of the reason
field in the BOUND_SESSION_ID.
12. References
12.1. Normative References
[I-D.ietf-nsis-ntlp] Schulzrinne, H., and R. Hancock, "GIST: General
Internet Messaging Protocol for Signaling", Work in Progress.
[I-D.ietf-nsis-qspec] Ash, J., "QoS NSLP QSPEC Template", Work in
Progress.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
12.2. Informative References
[LRSVP] Manner, J., "Localized RSVP", Work in Progress.
[NSIS-AAA] Tschofenig, H., "NSIS Authentication, Authorization and
Accounting Issues", Work in Progress.
[NSIS-EXT] Loughney, J. "NSIS Extensibility Model", Work in Progress.
[NSLP-AUTH] Manner, J., Stiemerling, M., Tschofenig, H.,
"Authorization for NSIS Signaling Layer Protocols", Work in Progress.
[OSP] ETSI, "Telecommunications and Internet protocol harmonization
over networks (tiphon); open settlement protocol (osp) for inter-
domain pricing, authorization, and usage exchange", Technical
Specification 101 321, version 2.1.0.
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[QOS-AUTH] Tschofenig, H., "QoS NSLP Authorization Issues", Work in
Progress.
[QOSM-CL] Kappler, C., "A QoS Model for Signaling IntServ Controlled-
Load Service with NSIS", Work in Progress.
[RFC1633] Braden, B., Clark, D., and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview", RFC 1633, June
1994.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification", RFC 2205, September 1997.
[RFC2210] Wroclawski, J., "The Use of RSVP with IETF Integrated
Services", RFC 2210, September 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated Services", RFC
2475, December 1998.
[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 Faucheur, F., and B. Davie,
"Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC 3175,
September 2001.
[RFC3520] Hamer, L-N., Gage, B., Kosinski, B., and H. Shieh,
"Session Authorization Policy Element", RFC 3520, April 2003.
[RFC3521] Hamer, L-N., Gage, B., and H. Shieh, "Framework for
Session Set-up with Media Authorization", RFC 3521, April 2003.
[RFC3583] Chaskar, H., "Requirements of a Quality of Service (QoS)
Solution for Mobile IP", RFC 3583, September 2003.
[RFC3726] Brunner, M., "Requirements for Signaling Protocols", RFC
3726, April 2004.
[RFC4080] Hancock, R., "Next Steps in Signaling: Framework", RFC
4080, December 2004.
[RFC4081] Tschofenig, H. and D. Kroeselberg, "Security Threats for
NSIS", RFC 4081, October 2004.
[RFC4234] Crocker, D., and Overell, P., "Augmented BNF for Syntax
Specifications: ABNF". RFC 4234, October, 2005.
[RMD] Bader, A., "RMD-QOSM - The Resource Management in DiffServ QoS
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model", Work in Progress.
[shenker-pricing] Shenker, S., Clark, D., Estrin, D., and S. Herzog,
"Pricing in computer networks: Reshaping the research agenda", Proc.
of TPRC 1995, 1995.
[Y.1541] Ash, J., "Y.1541 QoS Model for Networks Using Y.1541 QoS
Classes", Work in Progress.
[_XREF_FJ94] Jacobson, V., "Synchronization of Periodic Routing
Messages", IEEE/ACM Transactions on Networking , Vol. 2 , No. 2 ,
April 1994.
[_XREF_OPWA95] Breslau, L., "Two Issues in Reservation
Establishment", Proc. ACM SIGCOMM '95 , Cambridge , MA , August 1995.
Authors' Addresses
Jukka Manner
Department of Computer Science University of Helsinki
P.O. Box 68 (Gustav Hallstromin katu 2b)
HELSINKI, FIN-00014
Finland
Phone: +358-9-191-51298
Email: jmanner@cs.helsinki.fi
Sven Van den Bosch
Alcatel
Francis Wellesplein 1
Antwerpen B-2018
Belgium
Email: sven.van_den_bosch@alcatel.be
Georgios Karagiannis
University of Twente/Ericsson
P.O. Box 217
Enschede 7500 AE
The Netherlands
Email: karagian@cs.utwente.nl
Andrew McDonald
Siemens/Roke Manor Research
Roke Manor Research Ltd.
Romsey, Hants SO51 0ZN
UK
Email: andrew.mcdonald@roke.co.uk
Appendix A. Glossary
AAA: Authentication, Authorization and Accounting
EAP: Extensible Authentication Protocol
MRI: Message Routing Information (see [I-D.ietf-nsis-ntlp])
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NAT: Network Address Translator
NSLP: NSIS Signaling Layer Protocol (see [RFC4080])
NTLP: NSIS Transport Layer Protocol (see [RFC4080])
OPWA: One Pass With Advertising
OSP: Open Settlement Protocol
PIN: Policy Ignorant Node
QNE: an NSIS Entity (NE), which supports the QoS NSLP (see Section 2)
QNI: the first node in the sequence of QNEs that issues a reservation
request for a session (see Section 2)
QNR: the last node in the sequence of QNEs that receives a
reservation request for a session (see Section 2)
QSPEC: Quality of Service Specification
RII: Request Identification Information
RMD: Resource Management for DiffServ
RMF: Resource Management Function
RSN: Reservation Sequence Number
RSVP: Resource Reservation Protocol (see [RFC2205])
SII: Source Identification Information
SIP: Session Initiation Protocol
SLA: Service Level Agreement
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