Next Steps in Signalling S. Van den Bosch
Internet-Draft Alcatel
Expires: April 25, 2005 G. Karagiannis
University of Twente/Ericsson
A. McDonald
Siemens/Roke Manor Research
October 25, 2004
NSLP for Quality-of-Service signalling
draft-ietf-nsis-qos-nslp-05.txt
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Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This draft describes an NSIS Signalling Layer Protocol (NSLP) for
signalling QoS reservations in the Internet. It is in accordance
with the framework and requirements developed in NSIS.
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Together with GIMPS, 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 . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Scope and background . . . . . . . . . . . . . . . . . . . 5
1.2 Model of operation . . . . . . . . . . . . . . . . . . . . 6
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 9
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . 10
3.1 Overall approach . . . . . . . . . . . . . . . . . . . . . 10
3.1.1 GIMPS Interactions . . . . . . . . . . . . . . . . . . 10
3.1.2 Protocol messages . . . . . . . . . . . . . . . . . . 10
3.1.3 QoS Signalling Models and QoS specifications . . . . . 11
3.1.4 Authentication and authorization . . . . . . . . . . . 12
3.2 Design decisions . . . . . . . . . . . . . . . . . . . . . 15
3.2.1 Soft-state . . . . . . . . . . . . . . . . . . . . . . 15
3.2.2 Sender-receiver initiation . . . . . . . . . . . . . . 15
3.2.3 Message sequencing . . . . . . . . . . . . . . . . . . 15
3.2.4 Explicit state installation confirmation and
responses . . . . . . . . . . . . . . . . . . . . . . 16
3.2.5 Summary refreshes . . . . . . . . . . . . . . . . . . 16
3.2.6 Message scoping . . . . . . . . . . . . . . . . . . . 16
3.2.7 Session binding . . . . . . . . . . . . . . . . . . . 17
3.2.8 Layering . . . . . . . . . . . . . . . . . . . . . . . 17
3.2.9 Priority . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.10 Rerouting (SII) . . . . . . . . . . . . . . . . . . 19
4. Examples of QoS NSLP Operation . . . . . . . . . . . . . . . 21
4.1 Basic sender-initiated reservation . . . . . . . . . . . . 21
4.2 Sending a Query . . . . . . . . . . . . . . . . . . . . . 22
4.3 Basic receiver-initiated reservation . . . . . . . . . . . 23
4.4 Bidirectional Reservations . . . . . . . . . . . . . . . . 25
4.5 Use of Local QoS Models . . . . . . . . . . . . . . . . . 26
4.6 Aggregate Reservations . . . . . . . . . . . . . . . . . . 27
4.7 Reduced State or Stateless Interior Nodes . . . . . . . . 29
4.8 Re-routing scenario . . . . . . . . . . . . . . . . . . . 32
4.9 Authorization Model Examples . . . . . . . . . . . . . . . 33
4.9.1 Authorization for the two party approach . . . . . . . 33
4.9.2 Token based three party approach . . . . . . . . . . . 33
4.9.3 Generic three party approach . . . . . . . . . . . . . 34
5. QoS NSLP Functional specification . . . . . . . . . . . . . 36
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5.1 QoS NSLP Message and Object Formats . . . . . . . . . . . 36
5.1.1 Common header . . . . . . . . . . . . . . . . . . . . 36
5.1.2 Message formats . . . . . . . . . . . . . . . . . . . 37
5.1.3 Object Formats . . . . . . . . . . . . . . . . . . . . 39
5.2 General Processing Rules . . . . . . . . . . . . . . . . . 43
5.2.1 State Manipulation . . . . . . . . . . . . . . . . . . 44
5.2.2 Message Forwarding . . . . . . . . . . . . . . . . . . 45
5.2.3 Standard Message Processing Rules . . . . . . . . . . 45
5.3 Object Processing . . . . . . . . . . . . . . . . . . . . 45
5.3.1 Reservation Sequence Number (RSN) . . . . . . . . . . 45
5.3.2 Request Identification Information (RII) . . . . . . . 46
5.3.3 BOUND_SESSION_ID . . . . . . . . . . . . . . . . . . . 47
5.3.4 REFRESH_PERIOD . . . . . . . . . . . . . . . . . . . . 47
5.3.5 ERROR_SPEC . . . . . . . . . . . . . . . . . . . . . . 49
5.3.6 QSPEC . . . . . . . . . . . . . . . . . . . . . . . . 49
5.4 Message Processing Rules . . . . . . . . . . . . . . . . . 50
5.4.1 RESERVE Messages . . . . . . . . . . . . . . . . . . . 50
5.4.2 QUERY Messages . . . . . . . . . . . . . . . . . . . . 52
5.4.3 RESPONSE Messages . . . . . . . . . . . . . . . . . . 53
5.4.4 NOTIFY Messages . . . . . . . . . . . . . . . . . . . 54
6. IANA considerations . . . . . . . . . . . . . . . . . . . . 55
7. QoS use of GIMPS service interface . . . . . . . . . . . . . 56
7.1 Example sender-initiated reservation . . . . . . . . . . . 56
7.2 Session identification . . . . . . . . . . . . . . . . . . 57
7.3 Support for bypassing intermediate nodes . . . . . . . . . 57
7.4 Support for peer change identification . . . . . . . . . . 58
7.5 Support for stateless operation . . . . . . . . . . . . . 58
7.6 Last node detection . . . . . . . . . . . . . . . . . . . 58
7.7 Re-routing detection . . . . . . . . . . . . . . . . . . . 59
7.8 Priority of signalling messages . . . . . . . . . . . . . 59
7.9 Knowledge of intermediate QoS NSLP unaware nodes . . . . . 59
7.10 NSLP Data Size . . . . . . . . . . . . . . . . . . . . . 60
7.11 Notification of GIMPS 'D' flag value . . . . . . . . . . 60
7.12 NAT Traversal . . . . . . . . . . . . . . . . . . . . . 60
8. Assumptions on the QSM . . . . . . . . . . . . . . . . . . . 61
8.1 Resource sharing . . . . . . . . . . . . . . . . . . . . . 61
8.2 Reserve/commit support . . . . . . . . . . . . . . . . . . 61
9. Open issues . . . . . . . . . . . . . . . . . . . . . . . . 62
9.1 Peering agreements on interdomain links . . . . . . . . . 62
9.2 Protocol Operating Environment Assumptions . . . . . . . . 62
10. Security Considerations . . . . . . . . . . . . . . . . . . 64
10.1 Introduction and Threat Overview . . . . . . . . . . . . 64
10.2 Trust Model . . . . . . . . . . . . . . . . . . . . . . 65
10.3 Computing the authorization decision . . . . . . . . . . 67
11. Change History . . . . . . . . . . . . . . . . . . . . . . . 68
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 70
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 71
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 72
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14.1 Normative References . . . . . . . . . . . . . . . . . . . 72
14.2 Informative References . . . . . . . . . . . . . . . . . . 72
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 74
A. POLICY_DATA Class . . . . . . . . . . . . . . . . . . . . . 76
A.1 Base Format . . . . . . . . . . . . . . . . . . . . . . . 76
A.2 Options . . . . . . . . . . . . . . . . . . . . . . . . . 76
A.3 Policy Elements . . . . . . . . . . . . . . . . . . . . . 77
A.3.1 Authorization token Policy Element . . . . . . . . . . 77
A.3.2 OSP Token Policy Element . . . . . . . . . . . . . . . 79
A.3.3 User Identity Policy element . . . . . . . . . . . . . 79
Intellectual Property and Copyright Statements . . . . . . . 80
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1. Introduction
1.1 Scope and background
This document defines a Quality of Service (QoS) NSIS Signalling
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 signalling protocols, whose structure is outlined in
the NSIS framework [I-D.ietf-nsis-fw]; this defines a common NSIS
Transport Layer Protocol (NTLP) which QoS-NSLP uses to carry out many
aspects of signalling message delivery. A specification of the NTLP,
GIMPS [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 signalling path). Although
there is no backwards compatibility at the level of protocol
messages, interworking with RSVP at a signalling 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 support for IP
multicast.
QoS-NSLP does not mandate any specific 'QoS Signalling Model' (QSM),
i.e. a particular QoS provisioning method or QoS architecture; this
is similar to (but stronger than) the decoupling between RSVP and the
IntServ architecture, RFC 1633 [RFC1633]. It should be able to carry
information for various QSMs; the specification of Integrated
Services for use with RSVP given in RFC 2210 [RFC2210] could form the
basis of one QSM.
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 GIMPS API and
security considerations.
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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.
+---------------+
| Local |
|Applications or|
|Management (e.g|
|for aggregates)|
+---------------+
^
^
V
V
+-------------+ +------------+----------+ +---------+
|Common NSLP | |QSM-specific| Resource | | Policy |
| Processing +<<>>>| NSLP |Mgmt. Fct.|<<>| Control |
| | | Processing | | | |
+-------------+ +------------+----------+ +---------+
. ^ | * ^
| V . * ^
+----------+ * ^
| GIMPS | * ^
|Processing| * V
+----------+ * V
| | * V
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
. . * V
| | * .............................
. . * . Traffic Control .
| | * . +---------+.
. . * . |Admission|.
| | * . | Control |.
+----------+ +------------+ . +---------+.
<-.-| Input | | Outgoing |-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.->
| Packet | | Interface | .+----------+ +---------+.
===>|Processing|====| Selection |===.| Packet |====| Packet |.==>
| | |(Forwarding)| .|Classifier| Scheduler|.
+----------+ +------------+ .+----------+ +---------+.
.............................
<.-.-> = signalling flow
=====> = data flow (sender --> receiver)
<<<>>> = control and configuration operations
****** = routing table manipulation
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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.
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.
o The 'local application case' 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 The 'incoming message' case requires NSIS messages to be captured
during input packet processing and handled by GIMPS. Only
messages related to QoS are passed to the QoS-NSLP. GIMPS 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 QoS Signalling Policy-specific message
aspects.
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 [I-D.tschofenig-nsis-aaa-issues] and one on
auhorization issues [I-D.tschofenig-nsis-qos-authz-issues]. More
generally, the processing of policy and resource management functions
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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 on authentication and authorization can be found
in Section 3.1.4. The definition of the POLICY_DATA class is given
in Appendix A.
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 Signalling Policy and
interpreted only by the resource management and associated functions,
and are opaque to the QoS-NSLP itself. QoS Signalling Policy is
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 acknowledgement
message in one direction, and may propagate the resource request
forwards in the other. Message routing is (by default) carried out
by GIMPS module. Note that while Figure 1 shows a unidirectional
data flow, the signalling messages can pass in both directions
through the node, depending on the particular message and orientation
of the reservation.
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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 GIMPS [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.
Source or message source: The one of two adjacent NSLP peers that is
sending a signalling message (maybe the upstream or the downstream
peer). NB: 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.
QoS NSLP nodes
IP address (QoS unware 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 | +--------+
| | | | | |
+------+ +------+ +------+
=====================>
<=====================
Signalling
Flow
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3. Protocol Overview
3.1 Overall approach
3.1.1 GIMPS Interactions
The QoS NSLP uses GIMPS for delivery of all its messages. Messages
are normally passed from the NSLP to the GIMPS via an API, which also
specifies additional information, including an identifier for the
signalling application (e.g. 'QoS-NSLP'), the flow/session
identifier, and an indication of the intended direction - towards
data sender or receiver. On reception, GIMPS 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 the GIMPS.
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.
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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
5.1.2. Message processing rules are defined in Section 5.4.
QoS NSLP messages contain three types of objects:
Control Information: Control information objects carry general
information for the QoS NSLP processing, such as sequence numbers
or whether a response is required. This may include some
mechanisms that are useful for many QSMs (Common Control
Information) and some that are for a particular QSM only (QSM
specific Control Information). QSM specific Control Information
is specified together with a QSM. This specification only defines
Common Control Information. Currently, Common Control Information
is defined for session identification, message sequencing,
response request, message scoping and session lifetime.
QoS specifications (QSPECs): QSPEC objects describe the actual
resources that are required and are specific to the QSM being
used. Besides any resource description they may also contain QSM
specific control information used by the QSM's processing.
Policy objects: Policy objects contain data used to authorise 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 Signalling Models and QoS specifications
A QoS Signalling Model (QSM) is a mechanism which allows QNEs to
signal for QoS reservations in the Internet using QoS NSLP. It does
not define new QoS provisioning methods or architectures, which we
collectively denote as a "QoS model", but rather enables signalling
for existing ones. Integrated Services [RFC1633], Differentiated
Services [RFC2475] and RMD [I-D.westberg-rmd-framework] are all
examples of QoS architectures for which a QSM can be specified.
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There is no restriction on the number of QSMs that can be defined.
QSMs 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 QSM specification: IntServ Controlled Load
[I-D.kappler-nsis-qosmodel-controlledload], based on ITU
[I-D.ash-nsis-nslp-qos-sig-proof-of-concept] and Resource Management
for DiffServ (RMD)
[I-D.bader-rmd-qos-model][I-D.bader-nsis-rmd-diffserv-qsm].
The specification of a QSM includes a description of its QoS
parameter information, as well as how that information should be
treated or interpreted in the network. In that sense, the QSM goes
beyond the QoS NSLP protocol level in that it could also describe the
role of QNEs in this QoS Model and a certain QSPEC. Specification of
a certain QSPEC may include specifying generic and optional
parameters (including how generic parameters not used in this QSM are
mapped onto parameters defined therein) and QSM-specific message
formats or state management.
The information needed to signal for a QSM is carried in QoS NSLP
inside a QoS specification (QSPEC) object. The QSPEC is opaque to
the QoS NSLP and similar in purpose to the TSpec, RSpec and AdSpec
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).
An ongoing effort attempts to specify a QSPEC template. The QSPEC
template contains object formats for generally useful elements of the
QoS description, which is expected to enhance interoperability. The
QSPEC template defines a QSM ID, QSM-specific Control Information and
a QoS Description. A QSM specifies which generic parameters may be
carried in the QSPEC, or restricts the values these parameters can
take. A QSM may also define additional QSM-specific parameters.
3.1.4 Authentication and authorization
The QoS signalling protocol needs to exchange information which is
subsequently used as input to the AAA infrastructure. The response
from the AAA infrastructure must also be returned and processed by
the respective entities.
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+-------------+
| Entity |
| authorizing |
| resource |
| request |
+-----+-------+
|
|
/-\----+-----/\
//// \\\\
|| ||
| AAA Cloud |
|| ||
\\\\ ////
\-------+-----/
|
+-------------+ QoS signalling +---+--+
| Entity |<=================>| |<=========>
| requesting | Data Flow | QNE |
| resource |-------------------|------|---------->
+-------------+ +------+
QoS NSLP requests allow particular user(s) to obtain preferential
access to network resources. To prevent abuse, some form of an
access control (also known as policy based admission control) will
generally be required on users who make reservations. Typically,
such authorization is expected to make use of an AAA service external
to the node itself. In any case, cryptographic user identification
and selective admission will generally be needed when a reservation
is requested.
The QoS NSLP request is handled by a local 'resource management'
function, which coordinates the activities required to grant and
configure the resource. The grant processing involves two local
decision modules, 'policy control' and 'admission control'. Policy
control determines whether the user is sufficiently authorized to
make the reservation. Admission control determines whether the node
has sufficient available resources to offer the requested QoS.
3.1.4.1 Policy Ignorant Nodes
It is generally assumed that policy enforcement is likely to
concentrate on border nodes between administrative domains. Figure 4
below illustrates a simple administrative domain with:
o two boundary nodes (A, C), which represent QNEs authorized by AAA
entities.
o A core node (B) represents an Policy Ignorant QNE (PIN) with
capabilities limited to default admission control handling.
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Authorizing Entity 1 Authorizing Entity 2
| |
| |
+---+ +---+ +---+
| A +---------+ B +---------+ C |
+---+ +---+ +---+
QNE1 PIN QNE2
Figure 4: Administrative Domain scenario
Here, policy objects transmitted across the domain traverse an
intermediate PIN node (B) that is allowed to process QoS NSLP message
but does not handle policy information.
3.1.4.2 Policy Data
The input to policy control is referred to as "Policy data", which
QoS NSLP carries in the POLICY_DATA object. Policy data may include
credentials identifying entities and traits depending on the
authorization model in use (2-party, 3-party, token-based 3-party).
There are no requirements for all nodes to process this object.
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 QSM in use.
Policy control depends on successful user authentication and
authorization of a QoS NSLP reservation request. The authorization
decision might be valid for a certain amount of time or even for the
entire lifetime of the session. It is a decision of the involved
party to trigger a re-authorization procedure. This feature is
supported by the Policy Refresh Timer (PRT) option of the Policy
object.
Policy objects are carried by QoS NSLP messages and contain policy
information. All policy-capable nodes (at any location in the
network) can generate, modify, or remove policy objects, even when
senders or receivers do not provide, and may not even be aware of
policy data objects.
The exchange of Policy objects between policy-capable QNEs along the
data path, supports the generation of consistent end-to-end policies.
Furthermore, such policies can be successfully deployed across
multiple administrative domains when border nodes manipulate and
translate Policy objects according to established sets of bilateral
agreements.
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3.2 Design decisions
QoS NSLP was designed according to the principles and supports the
functionality outlined below.
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 signalled for remains valid. Maintaining the reservation beyond
this lifetime can be done by sending a ("refreshing") 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 dataflow that is being signalled
for (the QNI is at the side of the source of the dataflow). 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)
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. Therefore, QoS NSLP supports detection of
RESERVE message re-ordering or duplication with 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
neighbouring 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
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used together with a SESSION_ID to refer to particular installed
state.
3.2.4 Explicit state installation confirmation and responses
A QNE may desire 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.
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 Summary refreshes
For scalability, QoS NSLP supports an abbreviated form of refreshing
RESERVE message ("summary refresh"). In this case, the refreshing
RESERVE references the reservation using the RSN and the SESSION_ID,
rather than including the full reservation specification (including
QSPEC, ...). Summary 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 summary 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 the CRN". If needed, this can be easily proposed as an
extension later on,e.g. based on LRSVP [I-D.manner-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. signalling flows with different
SESSION_ID (SID) as defined in GIMPS [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 optimisation or to tear down
reservations that are no longer useful.
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. GIMPS 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 QSM implementation, i.e.
it may map incoming traffic to its own locally defined QSMs. QoS
NSLP supports this by allowing QSPEC objects to be stacked.
When a domain wants to apply a certain QSM 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. the first QSPEC that is found in
the message). QNEs inside the domain look at the top of the QSPEC
object stack to determine which QSM to apply for the reservation.
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The position of the local QSPEC object in the stack implies a
tradeoff 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.
3.2.8.2 Local control plane properties
The way signalling messages are handled is mainly determined by the
parameters that are sent over GIMPS-NSLP API and by the Common
Control Information. A domain may have a policy to implement local
control plane behaviour. 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 GIMPS. 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
signalling 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 signalling 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 FlowID that describes all traffic carried in the aggregate
(e.g. a DSCP in case of IntServ over DiffServ). The need for a
different FlowID mandates the use of two different sessions, similar
to Section 3.2.8.2 and to the RSVP aggregation solution 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
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end-to-end message transparantly 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 signalling messages over others may be required
in mobile scenarios when a message loss during call set-up is less
harmful then during handover. This situation only occurs when GIMPS
or QoS NSLP processing is the congested part or scarce resource.
This specification requests GIMPS design to foresee a mechanism to
support a number of levels of message priority that can be requested
over the NSLP-GIMPS API.
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 QSM specific issue and therefore
outside the scope of this specification.
3.2.10 Rerouting (SII)
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
routing protocols. Certain QNEs or GIMPS implementations may
interact with local routing module to receive quick notification of
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route changes. This is largely implementation-specific and outside
of the scope of NSIS. Second, route changes may be detected at GIMPS
layer. This specification requests GIMPS design to foresee
notification of this information 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) object that is 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 peer has changed.
Reservation on the new path happens when a refreshing RESERVE message
arrives at the QNE where the old and the new path diverge. The
refreshing RESERVE will be interpreted as a new RESERVE on the new
path. 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 GIMPS peering relations (e.g. by TTL counting the
number of GIMPS hops between NSLP peers or the observing changes in
the outgoing interface towards GIMPS peer). These mechanisms can
provide implementation specific optimisations, 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 incrementing the
RSN and then sending a new 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.
This specification requests GIMPS design to provide support for an
SII that is interpreted as a random identifier at the QoS NSLP but
that allows, when passed over the API, to forward QoS NSLP messages
to the QNE identified by that SII.
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.
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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 5: Basic Sender Initiated Reservation
To make a new reservation, the QNI constructs a RESERVE message
containing a QSPEC object, from its chosen QSM, which describes the
required QoS parameters.
The RESERVE message is passed to GIMPS 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 QSM 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 GIMPS, 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 GIMPS functionality to determine that there are no more
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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
summary refreshes that later refer to that state. A RESPONSE message
can also indicate an error when, for example, 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. The RESPONSE is
forwarded peer-to-peer along the reverse of the path that the RESERVE
message took (using GIMPS 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.
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 QSM-specific 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.
4.2 Sending a Query
QUERY messages can be used to gather information from QNEs along to
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 QSM-specific objects 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 GIMPS 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
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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 GIMPS 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 GIMPS 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 GIMPS to be forwarded back down the path.
4.3 Basic receiver-initiated reservation
As described in the NSIS framework [I-D.ietf-nsis-fw] in some
signalling 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, see Section 9.2.
To make a receiver-initiated reservation, the QNI constructs a QUERY
message, which may contain a QSPEC object from its chosen QSM (see
Figure 6). 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 GIMPS
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 6: Basic Receiver Initiated Reservation
The QUERY message is transported by GIMPS 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 QSM being used and may include gathering information on path
characteristics that may be used to predict the end-to-end QoS.
The QoS NSLP then generates a new QUERY message (usually based on the
one received). This is passed to GIMPS, which forwards it to the
next QNE. The same processing is performed at further QNEs along the
path, up to the receiver, which in this situation is the QNR. The
QNR detects that this QUERY message does not carry an RII object 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 GIMPS reverse path state).
Similar to the sender-initiated approach, any node may include an RII
in its RESERVE messages.
The reservation can subsequently be refreshed in the same way as for
the sender-initiated approach. This RESERVE message may be also used
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to refresh GIMPS reverse path state. Alternatively, refreshing GIMPS
reverse path state could be performed by sending periodic QUERY
messages, which are needed in case of route changes anyway.
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-intiated 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, see Section 9.2.
The scenario with two sender-initiated reservation is shown on Figure
7. 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 7: Bi-directional reservation for sender+sender scenario
The scenario with a sender-initiated and a receiver-initiated
reservation is shown on Figure 8. In this case, QNI B sends out two
RESERVE messages, one for the sender-initiated and one for the
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receiver-initiated reservation.
A QNE QNE B
| | FLOW-1 | |
|===============================>|
| QUERY-1 | | |
QNI+--------->| QUERY-1 | |
| +-------------------->|QNR
| | | |
|RESERVE-1 | | |
QNI+<---------|RESERVE-1 | |
| +<--------------------|QNR
| | | |
| | FLOW-2 | |
|<===============================|
| | |RESERVE-2 |
|RESERVE-2 | |<---------+QNI
QNR|<--------------------+ |
| | | |
Figure 8: 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 QSM along a
particular segment of the signalling. In this case a node at the
edge of this region needs to map between the two resource
descriptions (and any auxiliary data).
+-------- QSM2 domain --------+
| |
| |
+----+ +----+ +----+ +----+ +----+
|QNI | |edge| |int.| |edge| |QNR |
| |========>|QNE |========>|QNE |========>|QNE |========>| |
+----+ RESERVE +----+ RESERVE +----+ RESERVE +----+ RESERVE +----+
QSPEC1 | QSPEC2 QSPEC2 | QSPEC1
| {QSPEC1} {QSPEC1} |
| |
+-----------------------------+
Figure 9: 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 QSM (QSM2) needs to be used. At the edge of this
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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 QSM2. 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 QSM2
domain the QoS NSLP only uses the QSPEC at the top of the stack (i.e.
the 'current' one), rather than the end-to-end QSPEC. Otherwise,
processing proceeds as usual. The RESERVE message that it generates
should include the complete stack of 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.
QSPECs can be stacked in this way to an arbitrary depth.
4.6 Aggregate Reservations
In order to reduce signalling and per-flow state in the network, the
reservations for a number of flows may be aggregated together.
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QNI QNE QNE/QNI' QNE' QNR'/QNE QNR
aggregator deaggregator
| | | | | |
| RESERVE | | | | |
+--------->| | | | |
| | RESERVE | | | |
| +--------->| | | |
| | | RESERVE | | |
| | +-------------------->| |
| | | RESERVE' | | |
| | +=========>| RESERVE' | |
| | | +=========>| RESERVE |
| | | | +--------->|
| | | | RESPONSE'| |
| | | RESPONSE'|<=========+ |
| | |<=========+ | |
| | | | | RESPONSE |
| | | | RESPONSE |<---------+
| | |<--------------------+ |
| | RESPONSE | | | |
| |<---------+ | | |
| RESPONSE | | | | |
|<---------+ | | | |
| | | | | |
| | | | | |
Figure 10: Sender Initiated Reservation with Aggregation
An end-to-end per-flow reservation is initiated as normal (with
messages shown in Figure 10 as "RESERVE").
At the aggregator a reservation for the aggregated flow is initiated
(shown in Figure 10 as "RESERVE'"). This may use the same QSM 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 can
be derived from the QSPECs of the end-to-end sessions.
Markings are used so that intermediate routers do not need to inspect
the individual flow reservations. The deaggregator then becomes the
next hop QNE for the end-to-end per-flow reservation.
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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 QSM within a domain, in conjunction
with GIMPS and NSLP functionality which allows the interior nodes to
avoid storing GIMPS and QoS NSLP state. As a result the interior
nodes only store the QSM-specific reservation state, or even no state
at all. This allows the QSM 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 QSMs
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. GIMPS 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
GIMPS stateful GIMPS stateless GIMPS stateless GIMPS stateful
| | | |
RESERVE | | | |
-------->| RESERVE | | |
+--------------------------------------------->|
| RESERVE' | | |
+-------------->| | |
| | RESERVE' | |
| +-------------->| |
| | | RESERVE' |
| | +------------->|
| | | | RESERVE
| | | +-------->
| | | | RESPONSE
| | | |<--------
| | | RESPONSE |
|<---------------------------------------------+
RESPONSE| | | |
<--------| | | |
Figure 12: 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 GIMPS 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. The egress node is the next
QoS NSLP hop for that session. After the initial discovery phase
using unreliable GIMPS transfer mode, reliable GIMPS 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 QSM 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
excercises 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 the QSM related data may be held at these interior nodes. The
QoS NSLP also requests that GIMPS use different transport
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characteristics (i.e. sending of messages in unreliable GIMPS
transfer mode). It also requests the local GIMPS 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 summary 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 signalling
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 GIMPS neighbour relations are not maintained in the
reduced-state region, only sender initiated signalling 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
GIMPS stateful GIMPS stateless GIMPS stateful
| | |
QUERY | | |
-------->| QUERY | |
+------------------------------>|
| | | QUERY
| | +-------->
| | | RESERVE
| | |<--------
| | RESERVE |
|<------------------------------+
| RESERVE | RESERVE |
|-------------->|-------------->|
RESERVE | | |
<--------| | |
Figure 13: Receiver-initiated reservation with Reduced State Interior
Nodes
The RESERVE message that is received by the egress QNE of the
stateless domain is sent transparantly 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
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message further upstream.
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.
This specification requests GIMPS design to provide support for an
SII. 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, 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.
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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 14: Two party approach
In this example the authorization decision only involves the two
entities, or makes use of previous authorisation 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, for example, between two
neighbouring networks (inter-domain signalling) 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
signalling 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 15. If the request is
authorized, then the SIP signalling returns an authorization token
which can be included in the QoS signalling 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 15: 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 16.
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+--------------+
| 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 16: Three party approach
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.
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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
GIMPS 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 (BNF) specified in RFC 2234 [RFC2234].
The BNF implies an order for the objects in a message. However, in
many (but not all) cases, object order makes no logical difference.
An implementation should create messages with the objects in the
order shown here, but accept the objects in any permissible order.
5.1.1 Common header
All GIMPS NSLP-Data objects for the QoS NSLP MUST contain this common
header as the first 32 bits of the object.
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 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields in the common header are as follows:
Msg Type: 16 bits
1 = RESERVE
2 = QUERY
3 = RESPONSE
4 = NOTIFY
Flags: 16 bits
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.
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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 ]
[ POLICY_DATA ] [ *QSPEC ]
The RSN is the only mandatory object and MUST always be present.
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.
Four flags are defined for use in the common header with the RESERVE
message. These are:
TEAR (T) - when set, indicates that reservation state and QoS NSLP
operation state should be torn down. This is indicated to the
RMF.
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").
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, indicates that a RESERVE with different
Flow Routing Information (FRI) 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.
If the REFRESH_PERIOD is not present, a default value of 30 seconds
is assumed.
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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.
5.1.2.2 QUERY
The format of a QUERY message is as follows:
QUERY = COMMON_HEADER
[ RII ][ BOUND_SESSION_ID ]
[ POLICY_DATA ] [ *QSPEC ]
A QUERY message MUST contain an RII object to match an incoming
RESPONSE to the QUERY, unless the QUERY is being used to initiate
reverse-path state for a receiver-initiated reservation.
A QUERY message MAY contain one or more QSPEC objects and a
POLICY_DATA object. The QSPEC object describes what is being queried
for and may contain objects that gather information along the data
path. The POLICY_DATA object authorizes the requestor of the QUERY
message. 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.
One flag is defined for use in the common header with the QUERY
message. This is:
SCOPING - 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 ] ERROR_SPEC
[ *QSPEC ]
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A RESPONSE message MUST contain an ERROR_SPEC object which indicates
the success of a reservation installation or an error condition.
Depending on the value of the ERROR_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.
One flag is defined for use in the common header with the RESPONSE
message. This is:
SCOPING - 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
ERROR_SPEC [ QSPEC ]
A NOTIFY message MUST contain an ERROR_SPEC object indicating the
reason for the notification. Depending on the ERROR_SPEC value, it
MAY contain a QSPEC providing additional information.
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 GIMPS [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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|r|r|r|r| Type |r|r|r|r| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value for the Type field comes from GIMPS object type space. The
Length field is given in units of 32 bit words and and measures the
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length of the Value component of the TLV object (i.e. it does not
include the standard header).
The object diagrams here use '//' to indicate a variable sized field
and ':' to indicate a field that is optionally present.
A QoS NSLP implementation must recognize objects of the following
types: RII, RSN, REFRESH_PERIOD, BOUND_SESSION_ID, ERROR_SPEC, QSPEC
and POLICY_DATA.
NB: This draft does not currently include the codepoints for the QoS
NSLP related object types. To aid those writing experimental early
implementations a temporary set of NSIS-related numbers are given at
<http://nsis.srmr.co.uk/nsis-numbers.html>.
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 - 1 32-bit word
Value: An incrementing sequence number that indicates the order in
which state modifying actions are performed by a QNE. The RSN has
local significance only, i.e. between a pair of neighbouring
stateful QNEs.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reservation Sequence Number (RSN) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh Period (R) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.1.3.4 BOUND_SESSION_ID
Type: BOUND_SESSION_ID
Length: Fixed - 4 32-bit words
Value: Specifies the SESSION_ID (as specified in GIMPS
[I-D.ietf-nsis-ntlp]) of the session that must be bound to the
session associated with the message carrying this object.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Session ID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.1.3.5 ERROR_SPEC
The error object shares a common format with GIMPS and is specified
in the GIMPS [I-D.ietf-nsis-ntlp] specification.
Type: ERROR
Length: Variable
Value: Contains a 1 byte error class and 3 byte error code, an error
source identifier and optionally variable length error-specific
information.
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Class | Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ESI-Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Error Source Identifier //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional error-specific information //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The first byte of the error code indicates the severity level. The
currently defined severity levels are:
o 0x01 - Informational
o 0x02 - Success
o 0x03 - Protocol Error
o 0x04 - Transient Failure
o 0x05 - Permanent Failure
Within each severity class a number of error values are defined.
o Informational:
* 0x01000001 - Unknown BOUND_SESSION_ID: the message refers to an
unknown SESSION_ID in its BOUND_SESSION_ID object.
o Success:
* 0x02000001 - State installation succeeded
* 0x02000002 - Reservation created: reservation installed on
complete path (sent by last node).
* 0x02000003 - Reservation accepted: reservation installed at
this QNE, but not yet installed on the rest of the path.
* 0x02000004 - Reservation created but modified: reservation
installed, but bandwidth reserved was not the maximum
requested.
o Protocol Error:
* 0x03000001 - Illegal message type: the type given in the
Message Type field of the common header is unknown.
* 0x03000002 - Wrong message length: the length given for the
message does not match the length of the message data.
* 0x03000003 - Bad flags value: an undefined flag or combination
of flags was set.
* 0x03000004 - Mandatory object missing: an object required in a
message of this type was missing.
* 0x03000005 - Illegal object present: an object was present
which must not be used in a message of this type.
* 0x03000006 - Unknown object present: an object of an unknown
type was present in the message.
* 0x03000007 - Wrong object length: the length given for the
object did not match the length of the object data present.
* 0x03000008 - Unknown QSPEC type (Unknown QSM): the QSM ID
refers to a QSM which is not known by this QNE.
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o Transient Failure:
* 0x04000001 - Requested resources not available
* 0x04000002 - Insufficient bandwidth available
* 0x04000003 - Delay requirement cannot be met
* 0x04000004 - Transient QSM-specific error
* 0x04000005 - Resources pre-empted
* 0x04000006 - No GIMPS reverse-path forwarding state
* 0x04000007 - NSLP soft-state expired
o Permanent Failure:
* 0x05000001 - Authentication failure
* 0x05000002 - Unable to agree transport security with peer
* 0x05000003 - Internal or system error
* 0x05000004 - Resource request denied (authorization failed)
* 0x05000005 - Permanent QSM-specific error
5.1.3.6 QSPEC
Type: QSPEC
Length: Variable
Value: This object contains a 4 byte QSM ID and a variable length
QSPEC (QoS specification) information, which is QSM specific.
Such a QSM can be a standardized one, a private one, or a
well-known one.
The contents and encoding rules for this object are specified in
other documents, prepared by QSPEC template designers.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QoS Signaling Policy Identifier (QSP ID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// QSpec Data //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.1.3.7 POLICY_DATA
POLICY_DATA objects may contain various items to authenticate the
user and allow the reservation to be authorised. Some possible
contents are given in Appendix A, and some issues are also discussed
in Section 3.1.4.
5.2 General Processing Rules
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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 (QSM specific) reservation state which is
different for each QSM 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 organised 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 GIMPS or set locally.
The state information for a given key includes:
Flow ID
Copied from GIMPS. Several entries are possible in case of
mobility events.
QSM ID
32 bit identification of the QSM.
SII for each upstream and downstream peer
The SII is a large identifier (minimum 128 bits) generated by the
QoS NSLP and passed over the API.
RSN from each upstream peer
The RSN is a 32 bit counter.
Current own RSN
A 32 bit random number.
List of RII for outstanding responses with processing information
the RII is a 32 bit number.
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State lifetime
The state lifetime indicates how long the state that is being
signalled for remains valid.
BOUND_SESSION_ID
The BOUND_SESSION_ID is a 128 bit random number.
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 an
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
behaviour depends on the object type value.
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
NSIS signalling session (i.e. with a particular GIMPS SESSION_ID).
It MUST be incremented for each new RESERVE message where the
reservation for the session changes. Once the RSN has reached its
maximum value, the next value it takes is zero.
When receiving a RESERVE message a QNE uses the RSN given in the
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message to determine whether the state being requested is different
to that already stored. If the RSN is the same as 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.
5.3.2 Request Identification Information (RII)
A QNE sending some types of 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 sender MUST select the value for the
RII such that it is probabilistically unique within the given
session.
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 is selected by
another QNE then RESPONSE messages may be incorrectly terminated, and
not passed back to the node that requested them.
When sending a message containing an RII object the sending node MUST
remember the value used in the RII to match back any RESPONSE
received. It 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.
When receiving a message containing an RII object the node MUST send
a RESPONSE if either
o The SCOPING flag is set to one ('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.
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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 SHOULD 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.
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:
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 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.
6. To improve robustness, a node may temporarily send refreshes
more often than R after a state change (including initial state
establishment).
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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 ERROR_SPEC
ERROR_SPEC processing rules are still to be defined in more detail.
5.3.6 QSPEC
The contents of the QSPEC depends on the QSM being used. It may be
that parts of the QSPEC are standardised across multiple QSMs. This
topic is currently under further study.
Upon reception, the complete QSPEC is passed to the Resource
Management Function (RMF).
A QNE that receives a QSPEC stack MUST only look at the top QSPEC in
the stack. If this QSPEC is not understood by the RMF, the QNE MUST
send an RESPONSE containing an ERROR_SPEC and MUST NOT attempt to
recover by inspecting the rest of the stack.
Parameters of the QSM that is being signalled 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 QSMs. The QoS NSLP supports this by allowing QSPEC objects
to be stacked.
When a domain wants to apply a certain QSM 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. the first QSPEC that is found 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) SHOULD
remove the topmost QSPEC object from the stack. It SHOULD update the
underlying QSM parameters if needed.
A QNE that receives a message with a QSPEC object stack of which the
topmost object is not understood MUST NOT forward the message and
MUST send an error indication to its upstream neighbour. It MUST NOT
attempt local recovery by inspecting the stack for a QSPEC object it
understands.
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If the RMF indicates it cannot process the QSPEC, e.g. because the
QSM is not supported the QNE sends a RESPONSE with the appropriate
ERROR_SPEC.
5.4 Message Processing Rules
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. The format of a RESERVE message is repeated here for
convenience:
RESERVE = COMMON_HEADER
RSN [ RII ] [ REFRESH_PERIOD ] [ BOUND_SESSION_ID ]
[ POLICY_DATA ] [ *QSPEC ]
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 sends a RESPONSE message with the
appropriate ERROR_SPEC.
Before performing any state changing actions a QNE MUST determine
whether the request is authorized. It SHOULD exercise its local
policy in conjunction with the POLICY_DATA object to do this.
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 GIMPS (over the API) that reverse path state for this reservation
is no longer required. 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 ERROR_SPEC. The QNE
MAY elect to send RESERVE messages with the TEAR flag set for these
reservations.
The default behaviour 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).
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In some cases, this may not be the desired behaviour. 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 update the flow ID and indicate REPLACE=0
to the RMF (where it will be used for the resource handling). If the
SII is different, this means that the QNE is a merge point. In that
case, the REPLACE=0 also indicates that a tearing RESERVE SHOULD NOT
be sent on the old branch.
When a QNE receives a (refreshing) RESERVE message with an unknown
SESSION_ID, it MAY send a NOTIFY message to its upstream peer,
indicating the unknown SESSION_ID. This indicates a downstream route
change to the upstream peer. The upstream peer SHOULD send a
complete RESERVE on the new path (new SII). It identifies the old
signalling association (old SII) and MAY start sending complete
RESERVE messages for other SESSION_IDs linked to this association.
At a QNE, resource handling is performed by the RMF. For sessions
with the REPLACE flag set to zero, we assume that the QSP 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 QSM 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 QSM 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 summary 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 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. 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 GIMPS 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
ERROR_SPEC value of 0x02000003, indicating that the reservation is
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installed at the QNE.
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 top of
the stack. If there are one or more QSPECs in the received RESERVE
message, the last 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 3.2.3. 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, GIMPS is informed, over the QoS NSLP/GIMPS API, to pass
the message upstream, i.e., by setting GIMPS "D" flag, see GIMPS
[I-D.ietf-nsis-ntlp].
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.
The format of a QUERY message is as follows:
QUERY = COMMON_HEADER
[ RII ] [ BOUND_SESSION_ID ]
[ POLICY_DATA ] [ *QSPEC ]
On receiving a QUERY message, a QNE checks whether an RII object is
present. If not, the QUERY is an empty QUERY which is used to
install reverse path state. In this case, if the QNE is not the QNR,
it creates a new QUERY message to send downstream. If the QUERY
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contained a QSPEC, this MUST be passed to the RMF where it MAY be
modified by QSM specific QUERY processing. If the QNE is the QNR,
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.
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.
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
impotent, it does not cause any state to be installed or modified.
The format of a RESPONSE message is repeated here for convenience:
RESPONSE = COMMON_HEADER
[ RII / RSN ] ERROR_SPEC
[ *QSPEC ]
A RESPONSE message MUST be sent where 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 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, this object
MUST be put in the RESPONSE, as described above. If the RESPONSE is
sent as a result of the receipt of a RESERVE message without an RII
object, then the RSN of the received RESERVE message MUST be copied
into the RESPONSE message.
On receipt of a RESPONSE message containing an RII object, the QNE
MUST attempt to match it to the outstanding response requests for
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that signalling session. If the match succeeds, then the RESPONSE
MUST NOT be forwarded further along the path. If the match fails,
then the QNE MUST attempt to forward the RESPONSE to the next peer
QNE.
On receipt of a RESPONSE message containing an RSN object, the QNE
MUST compare the RSN to that of the appropriate signalling session.
If the match succeeds then the ERROR_SPEC MUST be processed. The
RESPONSE message MUST NOT be forwarded further along the path whether
or not the match succeeds.
5.4.4 NOTIFY Messages
NOTIFY messages are used to convey information to a QNE
asynchronously. The format of a NOTIFY message is as follows:
NOTIFY = COMMON_HEADER
ERROR_SPEC [ QSPEC ]
NOTIFY messages are impotent. They do not cause any state to be
installed or modified and they do 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).
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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 two new registries. One for QoS
NSLP Message Types, the other for QoS Signaling Policy Identifiers.
The QoS NSLP Message Type is a 16 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.
The QoS Signaling Policy Identifier (QSP ID) is a 32 bit value
carried in a QSPEC object. The allocation policy for new QSP IDs is
TBD.
This specification defines a NSLP for use with GIMPS. Consequently,
a new identifier must be assigned for it from GIMPS NSLP Identifier
registry.
This document also defines six new objects for the QoS NSLP: RII,
RSN, REFRESH_PERIOD, BOUND_SESSION_ID, QSPEC and POLICY_DATA. Values
are to be assigned for them from GIMPS Object Type registry.
In addition it defines a number of Error Codes for the QoS NSLP.
These can be found in section Section 5.1.3 and are to be assigned
values from GIMPS Error Code registry.
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7. QoS use of GIMPS service interface
This section describes the use of GIMPS service interface to
implement QoS NSLP requirements on GIMPS.
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
GIMPS service interface in this case is explained on Figure 33. Note
that we assume the SII handling in GIMPS [I-D.ietf-nsis-ntlp] is
extended to distinguish between own and peer SII.
GIMPS QoS NSLP
| |
|<=====================================|
| SendMessage{ |
| NSLP-Data=RESERVE, |
| Retain-State=TRUE, |
| Size=X bytes, |
| Message-Handle=NULL, |
| NSLP-ID=QoS, |
| Session-ID=SID_X, |
| MRI=MRI, |
| Direction=downstream, |
| Own-SII-Handle=Own_SII_X, |
| Peer-SII-Handle=empty |
| Transfer-attributes=default, |
| Timeout=default, |
| IP-TTL=default} |
| |
Figure 33: GIMPS 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
interface parameters (e.g. Transfer-attributes=unreliable).
The message is received by the peer QNE. The use of GIMPS service
interface when receiving a RESERVE message for a sender-initiated
reservation is explained on Figure 34.
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GIMPS QoS NSLP
| |
|=====================================>|
| RecvMessage{ |
| NSLP-Data=RESERVE, |
| Size=X bytes, |
| Message-Handle=GIMPS_X, |
| NSLP-ID=QoS, |
| Session-ID=SID_X, |
| MRI=MRI, |
| Direction=downstream, |
| Peer-SII-Handle=UP_SII_X, |
| Transfer-attributes=default, |
| IP-TTL=TTL_X, |
| Original-TTL=TTL_Y} |
| |
|<=====================================|
| MessageReceived{ |
| Message-Handle=GIMPS_X, |
| Retain-State=TRUE |
| |
Figure 34: GIMPS 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 33, QoS NSLP picks a value SID_X
for Session-ID. This value is subsequently used by GIMPS 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 GIMPS level (which
can be invoked by the QoS NSLP) to bypass intermediates nodes between
the edges of the domain.
As a suggestion, we identified two ways for bypassing intermediate
nodes. One solution is for the end-to-end session to carry a
different protocol ID (QoS NSLP-E2E-IGNORE protocol ID, similar to
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the RSVP-E2E-IGNORE that is used for RSVP aggregation (RFC 3175
[RFC3175]). Another solution is based on the use of multiple levels
of the router alert option. In that case, internal routers are
configured to handle only certain levels of router alerts. The
choice between both approaches or another approach that fulfills the
requirement is left to GIMPS design.
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 signalling
application message; for example, 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 GIMPS 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 GIMPS service interface when the peer's
SII which is stored on message reception is passed to GIMPS 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 GIMPS level
as well. Such nodes should not worry about keeping reverse state,
message fragmentation and reassembly (at GIMPS), congestion control
or security associations. A stateless or reduced state QNE will be
able to inform the underlying GIMPS of this situation. GIMPS 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:
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o the QNE may be the flow destination
o the QNE have some other prior knowledge that it should act as the
QNR
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 GIMPS.
We rely on GIMPS 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. GIMPS 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 GIMPS layer or the information may
be obtained by GIMPS through local interaction with or notification
from routing protocols or modules. GIMPS 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 signalling messages
The QoS NSLP will generate messages with a range of performance
requirements for GIMPS. These requirements may result from a
prioritization at the QoS NSLP (Section 3.2.8) or from the
responsiveness expected by certain applications supported by the QoS
NSLP.
GIMPS design should be able to ensure that performance for one class
of messages was not degraded by aggregation with other classes of
messages. GIMPS 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.
GIMPS 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.
GIMPS service interface supports this by keeping track of IP-TTL and
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Original-TTL in the RecvMessage primitive. A difference between the
two indiactes the number of QoS NSLP unaware nodes.
7.10 NSLP Data Size
When GIMPS 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 GIMPS 'D' flag value
When GIMPS 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 GIMPS for NAT traversal.
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8. Assumptions on the QSM
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 QSM may elect to implement a more general behaviour of
supporting relative operations on existing reservations, such as
ADDING or SUBTRACTING a certain amount of resources from the current
reservation. A QSM 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 behaviour 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 QSM.
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9. Open issues
9.1 Peering agreements on interdomain links
This specification proposes ways to carry AAA information that may be
used at the edges of a domain to check whether the requestor is
allowed to use the requested resources. It is less likely that the
AAA information will be used inside a domain. In practice, there may
be peering relations between domains that allow for a certain amount
of traffic to be sent on an interdomain link without the need to
check the authorization of each individual session (effectively
making the peering domain the requestor of the resources). The
per-session authorization check may be avoided by setting up an
aggregate reservation on the inter-domain link for a specified amount
of resources and relating the end-to-end sessions to it using the
BOUND_SESSION_ID. In this way, the aggregate session is authorized
once (and infrequently updated). An alternative is for the edge node
of a domain to insert a token that authorizes the flow for the next
domain.
9.2 Protocol Operating Environment Assumptions
The NSIS protocol is not used alone. Rather, it is used in
conjunction with a variety of applications. For receiver initiated
and bidirectional reservations the question arises of what the
interactions are between the NSIS protocols and the end-to-end
applications. An assumption needs to be made about what information
should be determined outside the NSIS protocols, and what should be
carried end-to-end in NSLP messages in order to initiate signalling.
For a receiver initiated reservation, the we have the questions: How
do the sender and receiver determine that a receiver initiated
reservation is to be performed? And, how does information needed by
the receiver to perform the reservation, but only available at the
sender, be made transferred to the receiver so that the RESERVE
message can be sent?
In the bi-directional reservation case, we can either perform this as
a pair of two sender-initiated reservations or as a combination of
sender-initiated and receiver-initiated reservations. The latter
case has the same issues as for the general receiver initiated
reservation problem. The former raises similar questions: How does
the remote end know that a reservation is needed? And, how does it
know what resources to request?
Is it reasonable to assume that the decision that an end should
initiate a reservation is made totally outside the QoS NSLP itself
(e.g. through prior configuration, or application end-to-end
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signalling such as SIP) or, should the QoS NSLP messages include some
method to trigger the other end to perform a reservation (whether
that be a receiver initiated reservation, or a sender initiated
reservation for the first bidirectional reservation case)?
In addition, should the QoS NSLP messages be able to carry extra data
(e.g. a QSPEC object for the reverse direction) end-to-end that is
needed by the remote end to perform its reservation? (And, should
this be in the QoS NSLP, or through individual QoS models?) The
alternative to providing support in the QoS NSLP for this is to leave
it to application signalling to transfer any required information.
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10. Security Considerations
10.1 Introduction and Threat Overview
The security requirement for the QoS NSLP is to protect the
signalling exchange for establishing QoS reservations against
identified security threats. For the signalling problem as a whole,
these threats have been outlined in NSIS threats
[I-D.ietf-nsis-threats]; the NSIS framework [I-D.ietf-nsis-fw]
assigns a subset of the responsibility to GIMPS and the remaining
threats need to be addressed by NSLPs. The main issues to be handled
can be summarised as:
Authorization:
The QoS NSLP must assure that the network is protected against
theft-of-service by offering mechanisms to authorize the QoS
reservation requestor. 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:
Signalling 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
neccessary to protect messages between NSLP nodes which includes
end-to-middle, middle-to-middle and even end-to-end protection.
In addition to the above-raised issues we see the following
functionality provided at the NSLP layer:
Prevention of Denial of Service Attacks:
GIMPS and QoS NSLP nodes have finite resources (state storage,
processing power, bandwidth). The protocol mechanisms suggested
in this document should try to minimise exhaustion attacks against
these resources when performing authentication and authorization
for QoS resources.
To some extent the QoS NSLP relies on the security mechanisms
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provided by GIMPS which by itself relies on existing authentication
and key exchange protocols. Some signalling messages cannot be
protected by GIMPS 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 GIMPS peers. If a
level of security protection for QoS NSLP messages is required which
goes beyond the security offered by GIMPS 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.
10.2 Trust Model
For this version of the document we will rely on a model which
requires trust between neighboring NSLP nodes to establish a
chain-of-trust along the QoS signalling path. This 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 'New Jersey Turnpike'
model.
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 signalling 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 35: New Jersey Turnpike Model
The model shown in Figure 35 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 This model allows authorization on a request basis or on a
per-session basis. Authorization mechanisms will be 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 not
covered in this version of the document. This 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 and left for a future version of this
document.
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o This architecture seems to be simple enough to allow a scalable
solution (ignoring reverse charging, multicast issues and price
distribution).
Charging the data sender as performed in this model simplifies
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 signalling messages. The
identity used during the authentication and key establishment phase
would be used by Network X (see Figure 35) 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. Signalling 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.
10.3 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 will be left for
a future version of this document. The authors assume that the QoS
NSLP needs to provide a number of attributes to support the large
range of scenarios.
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11. Change History
Changes from -00
* Additional explanation of RSN versus Session ID differences.
(Session IDs still need to be present and aren't replaced by
RSNs. Explain how QoS NSLP could react once it notes that it
maintains stale state.)
* Additional explanation of message types - why we don't just
have RESERVE and RESPONSE.
* Clarified that figure 1 is not an implementation restriction.
Changes from -01
* Significant restructuring.
* Added more concrete details of message formats and processing.
* Added description of layering/aggregation concepts.
* Added details of authentication/authorisation aspects.
Changes from -02
* Addressed comments from early review.
* Added text on receiver-initiated and bi-directional
reservations.
* Extended description of session binding. Added support for
fate sharing.
* Restructured message formats and processing section.
* Clarified refresh reduction mechanism.
* Added assumptions on QSM.
* Added assumptions on operating environment.
Changes from -03
* Removed overlaps between sections.
* Clarified document does not specify how to aggregate individual
end-to-end flow from a resource point of view but rather how
such an aggregate can be signalled for.
* Made session binding purely informational.
* Clarified QSPEC stacking.
* Added object format for ERROR_SPEC object.
* Made RII a separate object from RESPONSE_REQUEST and outside of
the SCOPING object. Then removed RESPONSE_REQUEST and made
SCOPING a flag rather than an object.
* Closed open issue of "PATH" message functionality. An empty
QUERY is used to install reverse state along the path.
* Made all flag names positive. Removed NO_FATE_SHARING flag:
fate sharing is not supported by the signalling.
* Removed the open issue on one-sided bidirectional reservation.
Clarified how it can be done, even for stateless or reduced
state domains in an example.
* Removed open issue on priority. Message priority will be
handled over GIMPS API, reservation priority is an issue for
the RMF.
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Changes from -04
* Resolved a number of outstanding comments on clarifications
(likelihood of transport type, bidirectional reservations,
handle of RESERVE messages inside a domain in case of
aggregation or reduced state operation) from the mailing list.
* Introduced a default value for REFRESH_PERIOD.
* Introduced explicit feedback mechanism in case of route
changes.
* State acknowledgment is now supported by means of an
ACKNOWLEDGE flag. This is made the default case.
* Changed section 7 to reflect the use of GIMPS service
interface.
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12. Acknowledgements
The authors would like to thank Eleanor Hepworth, Ruediger Geib,
Roland Bless and Nemeth Krisztian for their useful comments.
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13. 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).
Yacine El Mghazli (Alcatel) contributed text on AAA.
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14. References
14.1 Normative References
[I-D.ietf-nsis-ntlp]
Schulzrinne, H., "GIMPS: General Internet Messaging
Protocol for Signaling", draft-ietf-nsis-ntlp-03 (work in
progress), July 2004.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
14.2 Informative References
[I-D.ash-nsis-nslp-qos-sig-proof-of-concept]
Ash, J., "NSIS Network Service Layer Protocol QoS
Signaling Proof-of-Concept",
draft-ash-nsis-nslp-qos-sig-proof-of-concept-01 (work in
progress), February 2004.
[I-D.bader-nsis-rmd-diffserv-qsm]
Bader, A., Westberg, L., Karagiannis, G., Kappler, C. and
T. Phelan, "Resource Management in Diffserv (RMD)
Framework", draft-bader-nsis-rmd-diffserv-qsm-00.txt,
work in progress, July 2004.
[I-D.bader-rmd-qos-model]
Bader, A., "RMD (Resource Management in Diffserv) QoS-NSLP
model", draft-bader-rmd-qos-model-00 (work in progress),
February 2004.
[I-D.ietf-nsis-fw]
Hancock, R., "Next Steps in Signaling: Framework",
draft-ietf-nsis-fw-06 (work in progress), July 2004.
[I-D.ietf-nsis-threats]
Tschofenig, H. and D. Kroeselberg, "Security Threats for
NSIS", draft-ietf-nsis-threats-05 (work in progress), June
2004.
[I-D.kappler-nsis-qosmodel-controlledload]
Kappler, C., "A QoS Model for Signaling IntServ
Controlled-Load Service with NSIS",
draft-kappler-nsis-qosmodel-controlledload-00 (work in
progress), February 2004.
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[I-D.manner-lrsvp]
Manner, J., Suihko, T., Kojo, M., Liljeberg, M. and K.
Raatikainen, "Localized RSVP", draft-manner-lrsvp-03.txt,
work in progress, January 2004.
[I-D.tschofenig-nsis-aaa-issues]
Tschofenig, H., "NSIS Authentication, Authorization and
Accounting Issues", draft-tschofenig-nsis-aaa-issues-01
(work in progress), March 2003.
[I-D.tschofenig-nsis-qos-authz-issues]
Tschofenig, H., "QoS NSLP Authorization Issues",
draft-tschofenig-nsis-qos-authz-issues-00 (work in
progress), June 2003.
[I-D.westberg-rmd-framework]
Westberg, L., "Resource Management In Diffserv: An NSIS
QoS Signalling Model for Diffserv Networks",
draft-westberg-rmd-framework-04.txt, work in progress,
September 2003.
[MEF.EthernetServicesModel]
Metro Ethernet Forum, "Ethernet Services Model", letter
ballot document , August 2003.
[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.
[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
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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.
[_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.
[shenker-pricing]
Shenker, S., Clark, D., Estrin, D. and S. Herzog, "Pricing
in computer networks: Reshaping the research agenda",
Proc. of TPRC 1995, 1995.
Authors' Addresses
Sven Van den Bosch
Alcatel
Francis Wellesplein 1
Antwerpen B-2018
Belgium
EMail: sven.van_den_bosch@alcatel.be
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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
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Appendix A. POLICY_DATA Class
This section presents a set of specifications for supporting generic
authorization in QoS NSLP. These specs include the standard format
of POLICY_DATA objects, and a description of QoS NSLP handling of
authorization events. This section does not advocate a particular
authorization approach (2-party, 3-party, token-based 3-party).
The traffic control block is responsible for controlling and
enforcing access and usage policies.
A.1 Base Format
POLICY_DATA object: Class=7, C-Type=1
+-------------------------------------------------------+
| |
// Option List //
| |
+-------------------------------------------------------+
| |
// Policy Element List //
| |
+-------------------------------------------------------+
Option List: Variable length. See more details in Appendix A.2.
Policy Element List: Variable length. See more details in Appendix
A.3.
A.2 Options
This section describes a set of options that may appear in
POLICY_DATA objects. Some policy options appear as QoS NSLP objects
but their semantic is modified when used as policy data options.
Policy Refresh TIME_VALUES (PRT) object:
The Policy Refresh TIME_VALUES (PRT) option is used to slow policy
refresh frequency for policies that have looser timing constraints
relative to QoS NSLP. If the PRT option is present, policy
refreshes can be withheld as long as at least one refresh is sent
before the policy refresh timer expires. A minimal value for PRT
is the NSLP session refresh period R; lower values are assumed to
be R (neither error nor warning should be triggered). This option
is especially useful to combine strong (high overhead) and weak
(low overhead) authentication certificates as policy data. In
such schemes the weak certificate can support admitting a
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reservation only for a limited time, after which the strong
certificate is required. This approach may reduce the overhead of
POLICY_DATA processing. Strong certificates could be transmitted
less frequently, while weak certificates are included in every QoS
NSLP refresh.
Policy Source Identification Information (PSII) object:
The Policy SII object identifies the neighbor/peer policy-capable
QN that constructed the policy object. When policy is enforced at
border QNEs, peer policy nodes may be several NSLP hops away from
each other and the SII is the basis for the mechanism that allows
them to recognize each other and communicate safely and directly.
As stated above, we assume such an (P)SII to be available from a
service from GIMPS. If no PSII object is present, the policy data
is implicitly assumed to have been constructed by the QoS NSLP HOP
indicated in the SII (i.e., the neighboring QoS NSLP node is
policy-capable).
A.3 Policy Elements
There are no requirements for all nodes to process this container.
Policy data is opaque to NSLP, which simply passes it to policy
control when required.
The content of policy elements is opaque to the QoS NSLP layer. Only
policy peers understand their internal format and NSLP layer simply
passes it to policy control when required.
Policy Elements have the following format:
+-------------+-------------+-------------+-------------+
| Length | P-Type |
+---------------------------+---------------------------+
| |
// Policy information (Opaque to QoS NSLP) //
| |
+-------------------------------------------------------+
A.3.1 Authorization token Policy Element
The AUTHZ_TOKEN policy element contains a list of fields, which
describe the session, along with other attributes.
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+-------------+-------------+-------------+-------------+
| Length | P-Type = AUTHZ_TOKEN |
+-------------+-------------+-------------+-------------+
// Session Authorization Attribute List //
+-------------------------------------------------------+
Session Authorization Attribute List: variable length. The
session authorization attribute list is a collection of objects
which describes the session and provides other information
necessary to verify the resource reservation request. See
[RFC3520] for a details.
Session Authorization Attributes. A session authorization
attribute may contain a variety of information and has both an
attribute type and subtype. The attribute itself MUST be a
multiple of 4 octets in length, and any attributes that are not a
multiple of 4 octets long MUST be padded to a 4-octet boundary.
All padding bytes MUST have a value of zero.
+--------+--------+--------+--------+
| Length | X-Type |SubType |
+--------+--------+--------+--------+
| Value ... |
+--------+--------+--------+--------+
Length: 16 bits
The length field is two octets and indicates the actual length of
the attribute (including Length, X-Type and SubType fields) in
number of octets. The length does NOT include any bytes padding
to the value field to make the attribute a multiple of 4 octets
long.
X-Type: 8 bits
Session authorization attribute type (X-Type) field is one octet.
IANA acts as a registry for X-Types as described in Section 6.
Initially, the registry contains the following X-Types:
1 AUTH_ENT_ID: The unique identifier of the entity which
authorized the session.
2 SESSION_ID: Unique identifier for this session.
3 SOURCE_ADDR: Address specification for the session originator.
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4 DEST_ADDR: Address specification for the session end-point.
5 START_TIME: The starting time for the session.
6 END_TIME: The end time for the session.
7 RESOURCES: The resources which the user is authorized to
request.
8 AUTHENTICATION_DATA: Authentication data of the session
authorization policy element.
SubType: 8 bits
Session authorization attribute sub-type is one octet in length.
The value of the SubType depends on the X-Type.
Value: variable length
The attribute specific information is defined in [RFC3520].
A.3.2 OSP Token Policy Element
To be completed.
A.3.3 User Identity Policy element
To be completed.
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