Next Steps in Signaling S. Van den Bosch
Internet-Draft Alcatel
Expires: August 16, 2004 G. Karagiannis
University of Twente/Ericsson
A. McDonald
Siemens/Roke Manor Research
February 16, 2004
NSLP for Quality-of-Service signaling
draft-ietf-nsis-qos-nslp-02.txt
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This draft describes an NSIS Signaling Layer Protocol (NSLP) for
signaling QoS reservations in the Internet. It is in accordance with
the framework and requirements developed in NSIS.
Together with the NTLP, 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.
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This version of the draft focuses on the basic protocol structure. It
identifies the different message types and describes the basic
operation of the protocol to create, refresh, modify and teardown a
reservation or to obtain information on the characteristics of the
associated data path.
Conventions used in this document
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Scope and background . . . . . . . . . . . . . . . . . . . . 5
1.2 Model of operation . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . 9
3.1 QoS Models . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 NTLP Interactions . . . . . . . . . . . . . . . . . . . . . 10
3.3 Authentication and authorization . . . . . . . . . . . . . . 10
3.4 Aggregation . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5 Examples of QoS NSLP Operation . . . . . . . . . . . . . . . 11
3.5.1 Simple Resource Reservation . . . . . . . . . . . . . . . . 12
3.5.2 Sending a Query . . . . . . . . . . . . . . . . . . . . . . 13
3.5.3 Use of Local QoS Models . . . . . . . . . . . . . . . . . . 14
3.5.4 Aggregate Reservations . . . . . . . . . . . . . . . . . . . 15
3.5.5 Reduced State or stateless Interior Nodes . . . . . . . . . 16
4. Design decisions . . . . . . . . . . . . . . . . . . . . . . 18
4.1 Message types . . . . . . . . . . . . . . . . . . . . . . . 18
4.1.1 RESERVE . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1.2 QUERY . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.1.3 RESPONSE . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.1.4 NOTIFY . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2 Control information . . . . . . . . . . . . . . . . . . . . 20
4.2.1 Message sequencing . . . . . . . . . . . . . . . . . . . . . 20
4.2.2 Requesting responses . . . . . . . . . . . . . . . . . . . . 21
4.2.3 Message scoping . . . . . . . . . . . . . . . . . . . . . . 22
4.2.4 State timers . . . . . . . . . . . . . . . . . . . . . . . . 22
4.2.5 Session binding . . . . . . . . . . . . . . . . . . . . . . 23
4.3 Layering . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.3.1 Local QoS models . . . . . . . . . . . . . . . . . . . . . . 23
4.3.2 Local control plane properties . . . . . . . . . . . . . . . 24
4.3.3 Aggregate reservations . . . . . . . . . . . . . . . . . . . 25
4.4 Extensibility . . . . . . . . . . . . . . . . . . . . . . . 25
4.5 Priority . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.6 Rerouting . . . . . . . . . . . . . . . . . . . . . . . . . 26
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4.7 State storage . . . . . . . . . . . . . . . . . . . . . . . 28
4.8 Authentication and authorization . . . . . . . . . . . . . . 29
4.8.1 Policy Ignorant Nodes . . . . . . . . . . . . . . . . . . . 29
4.8.2 Policy Data . . . . . . . . . . . . . . . . . . . . . . . . 30
5. QoS-NSLP Functional specification . . . . . . . . . . . . . 31
5.1 QoS-NSLP Message Formats . . . . . . . . . . . . . . . . . . 31
5.1.1 Common header . . . . . . . . . . . . . . . . . . . . . . . 31
5.1.2 Object Formats . . . . . . . . . . . . . . . . . . . . . . . 32
5.1.3 RESERVE Messages . . . . . . . . . . . . . . . . . . . . . . 34
5.1.4 QUERY Messages . . . . . . . . . . . . . . . . . . . . . . . 37
5.1.5 RESPONSE Messages . . . . . . . . . . . . . . . . . . . . . 38
5.1.6 NOTIFY Messages . . . . . . . . . . . . . . . . . . . . . . 40
6. IANA considerations . . . . . . . . . . . . . . . . . . . . 40
7. Requirements for the NSIS Transport Layer Protocol (NTLP) . 42
7.1 Session identification . . . . . . . . . . . . . . . . . . . 42
7.2 Support for bypassing intermediate nodes . . . . . . . . . . 42
7.3 Support for peer change identification . . . . . . . . . . . 42
7.4 Support for stateless operation . . . . . . . . . . . . . . 43
7.5 Last node detection . . . . . . . . . . . . . . . . . . . . 43
7.6 Re-routing detection . . . . . . . . . . . . . . . . . . . . 44
7.7 Priority of signalling messages . . . . . . . . . . . . . . 44
7.8 Knowledge of intermediate QoS NSLP unaware nodes . . . . . . 44
7.9 NSLP Data Size . . . . . . . . . . . . . . . . . . . . . . . 44
7.10 NAT Traversal . . . . . . . . . . . . . . . . . . . . . . . 45
8. Open issues . . . . . . . . . . . . . . . . . . . . . . . . 45
8.1 Aggregation error handling . . . . . . . . . . . . . . . . . 45
8.2 Region scoping . . . . . . . . . . . . . . . . . . . . . . . 45
8.3 Priority of reservations . . . . . . . . . . . . . . . . . . 45
9. Security Considerations . . . . . . . . . . . . . . . . . . 46
9.1 Introduction and Threat Overview . . . . . . . . . . . . . . 46
9.2 Trust Model . . . . . . . . . . . . . . . . . . . . . . . . 47
9.3 QoS Authorization . . . . . . . . . . . . . . . . . . . . . 49
9.3.1 Authorization for the two party approach . . . . . . . . . . 49
9.3.2 Token based three party approach . . . . . . . . . . . . . . 50
9.3.3 Generic three party approach . . . . . . . . . . . . . . . . 52
9.3.4 Computing the authorization decision . . . . . . . . . . . . 54
10. Change History . . . . . . . . . . . . . . . . . . . . . . . 55
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 55
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 55
Normative References . . . . . . . . . . . . . . . . . . . . 55
Informative References . . . . . . . . . . . . . . . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 57
A. Object Definitions . . . . . . . . . . . . . . . . . . . . . 58
A.1 RESPONSE_REQUEST Class . . . . . . . . . . . . . . . . . . . 58
A.2 RSN Class . . . . . . . . . . . . . . . . . . . . . . . . . 59
A.3 REFRESH_PERIOD Class . . . . . . . . . . . . . . . . . . . . 59
A.4 SESSION_ID Class . . . . . . . . . . . . . . . . . . . . . . 60
A.5 SCOPING Class . . . . . . . . . . . . . . . . . . . . . . . 60
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A.6 ERROR_SPEC Class . . . . . . . . . . . . . . . . . . . . . . 61
A.7 POLICY_DATA Class . . . . . . . . . . . . . . . . . . . . . 62
A.7.1 Base Format . . . . . . . . . . . . . . . . . . . . . . . . 62
A.7.2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . 63
A.7.3 Policy Elements . . . . . . . . . . . . . . . . . . . . . . 64
A.8 QSPEC Class . . . . . . . . . . . . . . . . . . . . . . . . 66
Intellectual Property and Copyright Statements . . . . . . . 67
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1. Introduction
1.1 Scope and background
This document defines a Quality of Service (QoS) NSIS Signaling Layer
Protocol (NSLP), henceforth referred to as the "QoS-NSLP". This
protocol establishes and maintains state at nodes along the path of a
data flow for the purpose of providing some forwarding resources for
that flow. It is intended to satisfy the QoS-related requirements of
[15]. This QoS-NSLP is part of a larger suite of signaling protocols,
whose structure is outlined in [3]; this defines a common NSIS
Transport Layer Protocol (NTLP) which QoS-NSLP uses to carry out many
aspects of signaling message delivery. The specification of the NTLP
is done in another document [4].
The design of QoS-NSLP is conceptually similar to RSVP [6], 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 signaling application gateway would be
possible in some circumstances. QoS-NSLP extends the set of
reservation mechanisms to meet the requirements of [15], 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 Model', 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 [5]. It should be able to carry information for various
QoS models; the specification of Integrated Services for use with
RSVP given in [7] could form the basis of one QoS model.
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. It
is adapted from the discussion in section 1 of [6]. The model is
shown in Figure 1.
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+---------------+
| Local |
|Applications or|
|Management (e.g|
|for aggregates)|
+---------------+
^
^
V
V
+----------+ +----------+ +---------+
| QoS-NSLP | | Resource | | Policy |
|Processing|<<<<<<>>>>>>>|Management|<<<>>>| Control |
+----------+ +----------+ +---------+
. ^ | * ^
| V . * ^
+----------+ * ^
| NTLP | * ^
|Processing| * V
+----------+ * V
| | * V
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
. . * V
| | * .............................
. . * . Traffic Control .
| | * . +---------+.
. . * . |Admission|.
| | * . | Control |.
+----------+ +------------+ . +---------+.
<-.-| Input | | Outgoing |-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.->
| Packet | | Interface | .+----------+ +---------+.
===>|Processing|====| Selection |===.| Packet |====| Packet |.==>
| | |(Forwarding)| .|Classifier| Scheduler|.
+----------+ +------------+ .+----------+ +---------+.
.............................
<.-.-> = signaling flow
=====> = data flow (sender --> receiver)
<<<>>> = control and configuration operations
****** = routing table manipulation
Figure 1: QoS-NSLP in a Node
This diagram shows an example implementation scenario where QoS
conditioning is performed on the output interface. However, this does
not limit the possible implementations. For example, in some cases
traffic conditioning may be performed on the incoming interface, or
it may be split over the input and output interfaces.
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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). 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 the NTLP. Only
messages related to QoS are passed to the QoS-NSLP. The NTLP 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.
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 [16] and [17]. More
generally, the processing of policy and resource management functions
may be outsourced to an external node leaving only 'stubs' co-located
with the NSLP; this is not visible to the protocol operation,
although it may have some influence on the detailed design of
protocol messages to allow the stub to be minimally complex.
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; we refer to this as a QoS
model. Our assumption is that the QoS-NSLP is independent of the QoS
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model, that is, QoS parameters (e.g. IntServ service elements) are
interpreted only by the resource management and associated functions,
and are opaque to the QoS-NSLP itself. QoS Models are discussed
further in Section 3.1.
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 the NTLP
module. Note that while Figure 1 shows a unidirectional data flow,
the signaling messages can pass in both directions through the node,
depending on the particular message and orientation of the
reservation.
2. Terminology
The terminology defined in [3] 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.
QNR: the last node in the sequence of QNEs that receives a
reservation request.
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.
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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 | +--------+
| | | | | |
+------+ +------+ +------+
=====================>
<=====================
Signaling
Flow
3. Protocol Overview
The QoS NSLP uses four message types: RESERVE, QUERY, RESPONSE and
NOTIFY. These contain three types of objects: Control Information
(CI), QSpecs, and Policy objects. The set of objects permissible
depends on the message type.
Messages are passed to the NTLP to be delivered to neighbouring NSIS
nodes. Similarly, QoS NSLP data from NTLP messages is passed to the
QoS NSLP component for processing. Additional meta-data (e.g. session
identifier, NSLP identifier) can also be sent in both directions.
The QoS NSLP separates the actual description of resources from the
QoS signalling protocol used to transport them. It uses
interchangeable QoS Models that allow the resource specification to
be performed in various ways, and to provide different processing
models (including reserve/commit models, measurement based models,
etc).
Control information objects carry general information for the QoS
NSLP processing, such as sequence numbers or whether a response is
required.
QSpec objects describe the actual resources that are required and are
specific to the QoS Model being used. Besides any resource
description they may also contain QoS Model specific control
information used by the QoS Model's processing.
The Policy objects contain data used to authorise the reservation of
resources.
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3.1 QoS Models
A QoS model is a defined mechanism for achieving QoS as a whole. The
specification of a QoS model 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 QoS model
goes beyond the QoS-NSLP protocol level in that it could also
describe underlying assumptions, conditions and/or specific
provisioning mechanisms appropriate for it.
A QoS model provides a specific set of parameters to be carried in
the QSpec, or restricts the values these parameters can take.
Integrated Services [5], Differentiated Services [9] and RMD [22] are
all examples that could provide the basis of an NSIS QoS model. There
is no restriction on the number of QoS models. QoS models may be
local (private to one network), implementation/vendor specific, or
global (implementable by different networks and vendors). The authors
are currently aware of three efforts related to QoS model
specification: [18], [19] and [20]. This specification will not
attempt to select between the moppling number of possible QoS models.
The QSpec contains a set of parameters and values describing the
requested resources. It is opaque to the QoS-NSLP and similar in
purpose to the TSpec, RSpec and AdSpec specified in [6][7]. At each
QNE, its content is interpreted by the resource management function
for the purposes of policy control and traffic control (including
admission control and configuration of the packet classifier and
scheduler).
3.2 NTLP Interactions
The QoS NSLP uses the NTLP for delivery of all its messages. Messages
are normally passed from the NSLP to the NTLP via an API, which also
specifies additional information, including an identifier for the
signaling application (e.g. 'QoS-NSLP'), the flow/session identifier,
and an indication of the intended direction - towards data sender or
receiver. On reception, the NTLP provides the same information to the
QoS-NSLP.
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 NTLP (as described in
the requirement given in Section 7.10).
3.3 Authentication and authorization
The QoS signaling protocol needs to exchange information which is
subsequently used as input to the AAA infrastructure. The response
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from the AAA infrastructure must also returned and processed by the
respective entities.
+-------------+
| Entity |
| authorizing |
| resource |
| request |
+-----+-------+
|
|
/-\----+-----/\
//// \\\\
|| ||
| AAA Cloud |
|| ||
\\\\ ////
\-------+-----/
|
+-------------+ QoS signaling +---+--+
| Entity |<=================>| |<=========>
| requesting | Data Flow | QNE |
| resource |-------------------|------|---------->
+-------------+ +------+
3.4 Aggregation
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 facilities to provide similar
aggregation facilities to [11]. However, the aggregation scenarios
supported are wider than that proposed there.
3.5 Examples of QoS NSLP Operation
The QoS NSLP can be used in a number 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.
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3.5.1 Simple Resource Reservation
NI NF NF NR
| | | |
| RESERVE | | |
+--------->| | |
| | RESERVE | |
| +--------->| |
| | | RESERVE |
| | +--------->|
| | | |
| | | RESPONSE |
| | |<---------+
| | RESPONSE | |
| |<---------+ |
| RESPONSE | | |
|<---------+ | |
| | | |
| | | |
Figure 4: Basic Sender Initiated Reservation
To make a new reservation, the QNI constructs a RESERVE message
containing a QSpec object, from its chosen QoS model, which describes
the required QoS parameters.
The RESERVE message is passed to the NTLP which transports it to the
next QoS NSLP node. There it is delivered to the QoS NSLP processing
which examines the message. Policy control and admission control
decisions are made. The exact processing also takes into account the
QoS Model being used. The node performs appropriate actions (e.g.
installing reservation) based on the QSpec object in the message.
The QoS NSLP then generates a new RESERVE message (usually based on
the one received). This is passed to the NTLP, 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 NTLP functionality to determine that there are no more
QNEs between this node and the data flow destination.
Any node may include a request for a RESPONSE in its RESERVE
messages. One such use is to confirm the installation of state, which
allows the use of summary refreshes that later refer to that state.
The RESPONSE is forwarded peer-to-peer along the reverse of the path
that the RESERVE message took (using NTLP path state), and so is seen
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by all the QNEs on the reverse-path. It is only forwarded as far as
the node which requested the RESPONSE. A RESPONSE message can also
indicate an error when, for example, a reservation has failed to be
installed.
The reservation can subsquently 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 QoS model 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 [10]. 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.
3.5.2 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 QoS model specific objects containing
the actual query to be performed at QoS NSLP nodes 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 the NTLP to forward it along the path.
The NTLP may use datagram mode or connection mode for forwarding the
QUERY message.
A QNE (including the QNR) receiving a QUERY message should inspect it
and create a new message, based on that received with the query
objects modified as required. For example, the query may request
information on whether a flow can be admitted, and so a node
processing the query might record the available bandwidth. The new
message is then passed to the NTLP 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 is generated. Into this is copied
various objects from the received QUERY message. It is then passed to
the NTLP to be forwarded peer-to-peer back along the path. This makes
use of the neighbour state retained by the NTLP, and may use datagram
or connection mode.
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Each QNE receiving the RESPONSE message should inspect the
ResponseRequest 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 the NTLP to be forwarded back down the path.
3.5.3 Use of Local QoS Models
In some cases it may be required to use a different QoS Model 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).
+--------+ +----+----+ +--------+ +----+----+ +--------+
| QM1 | |QM1 | QM2| | QM2 | |QM2 | QM1| | QM1 |
+--------+ +----+----+ +--------+ +----+----+ +--------+
|QoS-NSLP| |QoS-NSLP | |QoS-NSLP| |QoS-NSLP | |QoS-NSLP|
+--------+ +---------+ +--------+ +---------+ +--------+
| NTLP |===| NTLP |===| NTLP |===| NTLP |===| NTLP |
+--------+ +---------+ +--------+ +---------+ +--------+
<-------> <--------------------> <------->
RESV{QSpec1} RESV{QSpec1,QSpec2} RESV{QSpec1}
Figure 5: 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 QoS Model needs to be used. At the edge of this region
the QNEs support both the end-to-end and local QoS models. When the
RESERVE message reaches the QNE at the ingress, the initial
processing of the RESERVE proceeds as normal. However, the QNE also
determines the appropriate description using the second QoS model.
The RESERVE message to be sent out is constructed mostly as usual but
with a second QSpec object added, which becomes the 'current' one.
When this RESERVE message is received at the next node 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.
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3.5.4 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.
NI NF NF/NI' NF' NR'/NF NR
aggregator deaggregator
| | | | | |
| RESERVE | | | | |
+--------->| | | | |
| | RESERVE | | | |
| +--------->| | | |
| | | RESERVE | | |
| | +-------------------->| |
| | | RESERVE' | | |
| | +=========>| RESERVE' | |
| | | +=========>| RESERVE |
| | | | +--------->|
| | | | RESPONSE'| |
| | | RESPONSE'|<=========+ |
| | |<=========+ | |
| | | | | RESPONSE |
| | | | RESPONSE |<---------+
| | |<--------------------+ |
| | RESPONSE | | | |
| |<---------+ | | |
| RESPONSE | | | | |
|<---------+ | | | |
| | | | | |
| | | | | |
Figure 6: Sender Initiated Reservation with Aggregation
An end-to-end per-flow reservation is initiated as normal (with
messages shown in Figure 6 as "RESERVE").
At the aggregator a reservation for the aggregated flow is initiated
(shown in Figure 6 as "RESERVE'"). This may use the same QoS model as
the end-to-end reservation but has a flow identifier for the
aggregated flow (e.g. tunnel) instead of for the individual flows.
Markings are used so that intermediate routers do not need to inspect
the individual flow reservations. This might be done by creating an
NTLP connection mode association between the aggregator and
deaggregator for the end-to-end 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. For example, this is necessary so that the size of the
aggregate reservation can be reduced when the end-to-end reservation
is removed.
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.
3.5.5 Reduced State or stateless Interior Nodes
This example uses a different QoS model within a domain, in
conjunction with NTLP and NSLP functionality which allows the
interior nodes to avoid storing NTLP and QoS NSLP state. As a result
the interior nodes only store the QoS model specific reservation
state, or even no state at all. This allows the QoS model to use a
form of "reduced-state" operation, where reservation states with a
coarser granularity (e.g. per-class) are used, or a "stateless"
operation where no reservation state is needed (or created).
The key difference between this example and the use of different QoS
Models in Section 3.5.3 is that the transport characteristics for the
'local' reservation can be different from that of the end-to-end
reservation, i.e. the NTLP 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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NF NF NF NF
ingress interior interior egress
NTLP stateful NTLP stateless NTLP stateless NTLP stateful
| | | |
RESERVE | | | |
-------->| RESERVE | | |
+--------------------------------------------->|
| RESERVE' | | |
+-------------->| | |
| | RESERVE' | |
| +-------------->| |
| | | RESERVE' |
| | +------------->|
| | | | RESERVE
| | | +-------->
| | | | RESPONSE
| | | |<--------
| | | RESPONSE |
|<---------------------------------------------+
RESPONSE| | | |
<--------| | | |
Figure 8: 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 the NTLP 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 using
facilities provided by the NTLP to bypass the stateless or
reduced-state nodes. After the initial discovery phase using datagram
mode, connection mode between the ingress and egress can be used. At
the egress node the RESERVE message is then forwarded normally.
At the ingress a second RESERVE' message is also built. This makes
use of a QoS model suitable for a reduced state or stateless form of
operation (such as the RMD per hop reservation). When processed by
interior (stateless) nodes the QoS NSLP processing excercises its
options to not keep state wherever possible, so that no QoS NSLP
state is stored. Some state, e.g. per class, for the QoS model
related data may be held at these interior nodes. The QoS NSLP also
requests that the NTLP use different transport characteristics (i.e.
sending of messages in datagram mode, and not retaining optional path
state).
Nodes, such as those in the interior of the stateless or
reduced-state domain, that do not retain reservation state (and so
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cannot use summary refreshes) cannot send back RESPONSE messages.
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 NTLP neighbour relations are not maintained in the
reduced-state region, only sender initiated signalling can be
supported. If a bi-directional reservation is required then the
interior QoS model must provide an object that requests the egress
node to generate a sender initiated session in the reverse direction.
4. Design decisions
4.1 Message types
The QoS-NSLP specifies four message types: RESERVE, QUERY, RESPONSE
and NOTIFY.
The fundamental properties of each message determine how it is
analyzed from the perspective of re-ordering, loss, end-to-end
reliability and so on. It is important for applications to know
whether NSLP messages can be repeated, discarded or merged and so on
(e.g. for edge mobility support, rerouting, etc). Indeed, the
ordering of messages that do not manipulate state at QNEs matters
little, whereas the way that messages that manipulate state are
interleaved matters very much. Therefore NSLP is designed such that
the message type identifies whether a message is manipulating state
(in which case it is idempotent) or not (it is impotent).
4.1.1 RESERVE
The RESERVE message is the only message that manipulates QoS
reservation state. It is used to create, refresh, modify and remove
such state. The common message header contains a TEAR flag that
indicates complete QoS NSLP state removal (as opposed to a
reservation of zero resources). The TEAR flag indicates to the NTLP
that the corresponding NTLP (reverse) state is not required. The NTLP
the autonomously decides whether to keep such state or not.
The RESERVE message opaquely transports one or more QSPEC objects,
describing the desired service level and a POLICY_DATA object,
authorizing the requestor of the service. It carries the lifetime of
the reservation in the Common Control Information.
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RESERVE messages are sent peer-to-peer. This means that a QNE
considers its adjacent upstream or downstream peer to be the source
of the RESERVE message.
The RESERVE message is idempotent; the resultant effect is the same
whether a message is received once or many times. In addition, the
ordering of RESERVE messages matters - an old RESERVE message should
not replace a newer one. Both of these features are required for
protocol robustness - messages may be re-ordered on route (e.g.
because of mobility, or at intermediate NTLP nodes) or spuriously
retransmitted. Message re-ordering is supported by the inclusion of
the Reservation Sequence Number (RSN) in the RESERVE message.
The sender of a RESERVE message may want to receive confirmation of
successful state installation from a downstream node. Therefore, a
RESERVE message optionally contains a RESPONSE_REQUEST object
(Section 4.2.2).
4.1.2 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 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, nor does it cause state to be
installed in nodes other than the one that generated the QUERY.
A QUERY message contains 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.
A QUERY message may be scoped if a RESPONSE message from some other
node than the QNR is desired.
A QUERY message must contain a RESPONSE_REQUEST object (Section
4.2.2), the contents of which allow matching back RESPONSE messages
to the QUERY request. The RESPONSE_REQUEST object is transported
unchanged along the data path and may be used to scope the RESPONSE
to a QUERY message (Section 4.2.3).
4.1.3 RESPONSE
The REPONSE 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
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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. For this purpose, the RESPONSE message carries one or more
QSPEC objects.
The RESPONSE message is impotent, it does not cause any state to be
installed or modified.
The forwarding of the RESPONSE message along the path does not
necessarily imply the existence of NTLP reverse-path state at every
node. For example, the NTLP may have a mechanism to pass a message
directly from the egress to the ingress of a region of QNEs that do
not store per-flow reverse-path state.
4.1.4 NOTIFY
NOTIFY messages are used to convey information to a QNE. NOTIFY
messages are impotent (they do not cause a change in state directly).
They may carry one or more QSPEC objects. An example use of NOTIFY
would be to indicate when a reservation has been pre-empted.
NOTIFY messages differ from RESPONSE messages in that they need not
refer to any particular state or previously received message. They
are sent asynchronously. The NOTIFY message itself does not trigger
or mandate any action in the receiving QNE.
The information conveyed by a NOTIFY message is typically related to
error conditions. One example would be notification to an upstream
peer about state being torn down.
4.2 Control information
Control information conveys information on how specific messages
should be handled by a QNE, e.g. sequencing of messages. This may
include some mechanisms that are useful for many QoS models (Common
Control Information) and some that are for a particular QoS model
only (QoS-model specific Control Information). QoS-model specific
Control Information is specified together with a QoS model. 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.
4.2.1 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
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will be stored at a QNE. Therefore, a QNE may need to detect
re-ordered or duplicated RESERVE messages.
Detection of RESERVE message re-ordering or duplication is supported
by the Reservation Sequence Number (RSN). The RSN is a counter,
locally chosen to be unique (on a hop-by-hop basis) within a session.
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, this means that we can make the Reservation Sequence
Number unique just between a pair of neighboring stateful QNEs. By
managing the sequence numbers in this manner, the source of the
RESERVE does not need to determine how the next NSLP node will
process the message.
The RSN refers to a particular instance of the RESERVE state. This
allows explicit acknowledgment of state installation actions (by
including the RSN in a RESPONSE). It also allows 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, ...). Note that 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
RESPONSE_REQUEST to decide whether it wants to accept summary
refreshes and provide this explicit acknowledgment.
4.2.2 Requesting responses
Some QNEs may require explicit responses to messages they send. A QNE
which sends a QUERY message (Section 4.1), for instance, will require
a response with the requested information to be sent to it. A QNE
which sends a RESERVE message may want explicit confirmation that the
requested reservation state was installed.
A QNE that desires an explicit response includes a RESPONSE_REQUEST
object in its message. RESPONSE_REQUEST objects are used in RESERVE
and QUERY messages. The RESPONSE_REQUEST object may be used in
combination with message scoping (Section 4.2.3) to influence which
QNE will respond.
A message contains at most one RESPONSE_REQUEST object. The
RESPONSE_REQUEST object contains Request Identification Information
(RII) that is unique within a session and different for each message,
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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.
A message containing a RESPONSE_REQUEST object causes a RESPONSE
message to be sent back. The RESPONSE message contains the original
RESPONSE_REQUEST object and may be scoped, e.g. using the RII
(Section 4.2.3), to influence which (upstream) QNEs will receive the
RESPONSE.
4.2.3 Message scoping
For some messages, QNEs may want to restrict message propagation. For
a RESERVE message, this may be the case when state installation is
required on part of the path towards the destination only. For a
QUERY message, it allows limiting the nodes that can respond to the
QUERY. For a RESPONSE message, it allows limiting the nodes that
receive the RESPONSE.
Message scoping is supported by a SCOPING object. Different scopes
are supported. By default, no SCOPING object is present which
indicates that the scope is either "whole path" or limited by
configuration (and therefore not signalled). Other supported scopes
are "single hop" and "back to me". The latter is supported by copying
the RII from the RESPONSE_REQUEST object into the SCOPING object that
is put in the RESPONSE message, so that its forwarding can be
terminated by the node that requested the RESPONSE.
It is currently an open issue whether a "region" should be supported
as a separate scope or whether its application is sufficiently
supported by configuration and/or aggregation.
4.2.4 State timers
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 seconds 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.
The REFRESH_PERIOD 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
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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 given in Section 5.
4.2.5 Session binding
Some QNEs may need to have knowledge of session binding. With session
binding we mean that a relation exists between signalled sessions
with potentially different SESSION_IDs and/or flow IDs. The
SESSION_ID is defined in [4] This situation can occur in case of
layering or aggregation where multiple reservations are aggregated
together (and the flow ID changes) or when some local properties
(e.g. connection mode) for the session change.
Layering or aggregation may cause loss of information. If the edge
QNEs of the aggregation domain want to maintain some end-to-end
properties, they may establish a peering relation by sending the
end-to-end message transparantly over the domain. 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, a session (e.g., end to end session), may contain a
BOUND_SESSION_ID (the SESSION_ID of another session (e.g., the
aggregate one) in addition to its own SESSION_ID to indicate session
binding. This BOUND_SESSION_ID is called the session binding object.
4.3 Layering
The 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. datagram mode instead of connection
mode). They may also occur when several per-flow reservations are
locally combined into an aggregate reservation.
4.3.1 Local QoS models
Parameters of the QoS model 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 QoS models. The QoS NSLP supports this by allowing
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QSPEC objects to be stacked.
When a domain wants to apply a certain QoS model to an incoming
per-flow reservation request, each edge of the domain is configured
to map the incoming QSPEC object to a local QSPEC object and push
that object onto the stack of QSPEC objects (typically immediately
following the Common Control Information, i.e. 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 QoS model to apply for the
reservation.
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.
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 QoS model parameters if needed.
A QNE that receives a message with a QSPEC object stack of which the
topmost object is not understood SHOULD send an error indication to
its upstream neighbour. It is currently an open issue whether this
QNE MAY search the stack for a QSPEC object it understands to recover
from this situation. It is also an open issue if such a message can
be forwarded and if and how the QSPEC object stack should be updated.
4.3.2 Local control plane properties
The way signalling messages are handled is mainly determined by the
parameters that are sent over the NTLP-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 datagram
mode locally in the domain while still keeping e2e 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.
The local session and the end-to-end session are bound at the egress
QNE by means of the BOUND_SESSION_ID object. One approach could be
that the end-to-end session carries the SESSION_ID of the local
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session in its session binding object. Another approach could be that
the local session carries the SESSION_ID of the end-to-end session in
its BOUND_SESSION_ID object. This allows the QNE that performs
session binding to maintain end-to-end connection mode.
4.3.3 Aggregate reservations
For scalability reasons, a domain MAY want to combine two or more
end-to-end reservations into a single local aggregate reservation.
The domain over which the aggregation is done is limited by
configuration.
The essential difference with the layering approaches described in
Section 4.3.1 and Section 4.3.2 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 4.3.2 and to the RSVP aggregation
solution (reference to 3175). In addition to the different FlowID,
the aggregate session may specify a local QoS model and local control
plane parameters as explained above.
The aggregate reservation may or may not change source and
destination IP addresses, i.e. either the end-to-end adresses may be
used (if possible) or the IP address of ingress and egress of the
domain may be used as source and destination IP address. In some
cases, the latter option may cause data plane divergence between both
sessions. RSVP solves this by using tunnelling between the edges of
the domain.
In any case, session binding and a solution for intermediate node
bypass (as explained before) are required in this case as well.
4.4 Extensibility
The QoS NSLP specification foresees future specification of new error
codes and new Common Control Information objects. Specification of
new messages is not foreseen but not explicitly precluded.
Specification of new error codes and Common Control Information
objects is subject to IANA approval and assignment of ClassNum and
CType. ClassNum and CType of currently existing objects and error
codes are described in Section 6. New Common Control Information
objects need to specify whether they are mandatory or optional to
implement. Mandatory CCI that is not understood by a QNE needs to
generate an error. Optional CCI that is not understood by a QNE needs
to be passed transparantly.
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The QoS NSLP specification allows future QoS model specific
extensions, including the definition of new QoS models, the
specification of new objects for existing QoS models, the
specification of new processing rules for new or existing objects and
the specification of new QoS model specific error codes.
Different types of QoS models are foreseen: standardized QoS models,
well-known QoS models and QoS models for private use. We assume the
IANA registry of QoS models to distinguish between those. Apart from
the QoS model ID, all QoS model specific extensions are opaque to the
QoS NSLP (and have no impact on its IANA considerations section).
4.5 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 the
GIMPS or QoS NSLP processing is the congested part or scarce
resource. This specification requests the NTLP design to foresee a
mechanism to support a number of levels of message priority that can
be requested over the NSLP-NTLP API.
Priority of certain reservations over others may be required when QoS
resources are oversubscribed. In that case, existing reservations may
be preempted in other 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 resource 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 QoS model specific issue and
therefore outside the scope of this specification. However, the
concepts of setup and holding priority are widely accepted and we
expect the specification of a Priority object in the QSPEC template
to be useful for a wide range of QoS models.
4.6 Rerouting
The QoS NSLP needs to adapt to route changes in the data path. This
assumes the capability to detect rerouting events, perform QoS
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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 NTLP implementations may interact
with local routing module to receive quick notification of route
changes. This is largely implementation-specific and outside of the
scope of NSIS. Second, route changes may be detected at the NTLP
layer. This specification requests the NTLP 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 [6]. 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 automatically happens when a refreshing
RESERVE message arrives at the QNE where the old and the new path
diverge. 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 the NTLP
peering relations (e.g. by TTL counting the number of NTLP hops
between NSLP peers or the observing changes in the outgoing interface
towards the NTLP peer). These mechanisms are outside the scope of
this specification.
When the QoS NSLP is aware of the route change, it needs to set up
the reservation on the new path. This is done by sending a RESERVE
message with RSN+2. 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 the NTLP 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. Then, a RESERVE message with the TEAR
flag set (tearing RESERVE) and RSN+1 can be sent over the old branch
of the path. Setting the RSN+1 ensures that the reservation will not
be torn down if the neighbouring QNE has not, in fact, changed.
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4.7 State storage
For each flow, the QoS NSLP stores QoS reservation state. This state
includes QoS model specific state which is different for each QoS
model 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 the NTLP.
The state information for a given key includes:
Flow ID
Copied from the NTLP. Several entries are possible in case of
mobility events.
QoS model ID
8 bit identification of the QoS model.
SII for each upstream and downstream peer
The SII is a 128 bit identifier generated by the NTLP 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.
State lifetime
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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.
4.8 Authentication and authorization
QoS NSLP requests allow particular user(s) to obtain preferential
access to network resources. To prevent abuse, some form of an access
control (or 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.
4.8.1 Policy Ignorant Nodes
It is generally assumed that policy enforcement is likely to
concentrate on border nodes between autonomous systems. Figure 9
below illustrates a simple autonomous domain with:
o two boundary nodes (A, C), which represent QNEs authorized by AAA
entities.
o A core node (B) represents an Policy Ignorant QN (PIN) with
capabilities limited to default admission control handling.
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Authorizing Entity 1 Authorizing Entity 2
| |
| |
+---+ +---+ +---+
| A +---------+ B +---------+ C |
+---+ +---+ +---+
QN1 PIN QN2
Figure 9: Autonomous Domain scenario
Here, policy objects transmitted across the domain traverse an
intermediate PIN node (B) that is allowed to process QoS NSLP message
but considered non-trusted for handling policy information.
4.8.2 Policy Data
The input to policy control is referred to as "Policy data", which
QoS NSLP carries in the Policy 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 NSIS, which simply passes it to
policy control when required. The policy data is independent from the
QoS model 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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5. QoS-NSLP Functional specification
5.1 QoS-NSLP Message Formats
An QoS-NSLP message consists of a common header, followed by a body
consisting of a variable number of variable-length, typed "objects".
The following subsections define the formats of the common header,
the standard object header, and each of the QoS-NSLP message types.
For each QoS-NSLP message type, there is a set of rules for the
permissible choice of object types. These rules are specified using
Backus-Naur Form (BNF) augmented (see [2]). with square brackets
surrounding optional sub-sequences. The BNF implies an order for the
objects in a message. However, in many (but not all) cases, object
order makes no logical difference. An implementation should create
messages with the objects in the order shown here, but accept the
objects in any permissible order.
5.1.1 Common header
0 1
+---------------------------+---------------------------+
| Msg Type | Flags |
+---------------------------+---------------------------+
The fields in the common header are as follows:
Msg Type: 8 bits
1 = RESERVE
2 = QUERY
3 = RESPONSE
4 = NOTIFY
Flags: 8 bits
1 = TEAR flag
2 = BIDIRECTIONAL flag
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Other flags have to be defined.
5.1.2 Object Formats
Every object consists of one or more 32-bit words with a one-word
header, with the following format:
0 1 2 3
+-------------+-------------+-------------+-------------+
| Length (bytes) | Class-Num | C-Type |
+-------------+-------------+-------------+-------------+
| |
// (Object contents) //
| |
+-------------+-------------+-------------+-------------+
An object header has the following fields:
Length:
A 16-bit field containing the total object length in bytes. Must
always be a multiple of 4, and at least 4.
Class-Num:
Identifies the object class; values of this field are defined in
Appendix A. Each object class has a name, which is always
capitalized in this document. An QoS-NSLP implementation must
recognize the following classes:
RESPONSE_REQUEST:
Contains the request for the generation of a response message
and the Request Identification Information (RII).
RSN:
The Reservation Sequence Number (RSN) contains 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. RSN is a common control information object.
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REFRESH_PERIOD
Contains the value for the refresh period R used by the creator
of the message. Required in every RESERVE message.
REFRESH_PERIOD is a common control information object.
SESSION_ID
It represents the SESSION_ID as specified in [3] of the session
that must be bound to the session associated to the message
carrying this object.
SCOPING
contains information that limits the scope of the message
carrying this object. When no SCOPING object is available in a
message it means that its scoping is either the whole path or
it is defined by configuration. SCOPING is a common control
information object.
ERROR_SPEC
Contains an error code and can be carried by a Response or a
NOTIFY message. ERROR_SPEC is a common control information
object.
POLICY_DATA
Carries authentication, authorization and accounting
information.
QSPEC
Carries the information that is QoS model specific. This
information consists of the QoS model specific control
information and the QoS specification parameters.
C-Type:
Object type, unique within Class-Num. Values are defined in
Appendix A.
The maximum object content length is 65528 bytes. The Class- Num and
C-Type fields may be used together as a 16-bit number to define a
unique type for each object.
The high-order two bits of the Class-Num are used to determine what
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action a node should take if it does not recognize the Class-Num of
an object;
5.1.3 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 as follows:
RESERVE = COMMON_HEADER
RSN [ SCOPING ] [ RESPONSE_REQUEST ]
REFRESH_PERIOD [ BOUND_SESSION_ID ]
POLICY_DATA QSPEC [ *QSpec ]
The QSPEC object(s) must occur at the end of the message. There are
no other requirements on transmission order, although the above order
is recommended.
The SESSION_ID object must be included in the RESERVE message only if
the session associated to this message has to be bound to another
session. The content of the SESSION_ID object represents the
SESSION_ID of the session that must be bound to the session
associated to the RESERVE message carrying this object. The binding
of these two sessions is only possible in stateful QNEs.
The RESERVE message opaquely must transport a QSPEC object,
describing the desired service level and a POLICY_DATA object,
authorizing the requestor of the service. Based on configured local
policy, a node may ignore the content of the POLICY_DATA object.
Refresh timer management values are carried by the TIMER_VALUES
object. The details of timer management and timer changes (slew
handling and so on) are identical to the ones specified in Section
3.7 of [6]. 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
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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 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 [25] 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.
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6. To improve robustness, a node may temporarily send refreshes more
often than R after a state change (including initial state
establishment).
7. The values of Rdef, K, and Slew.Max used in an implementation
should be easily modifiable per interface, as experience may lead
to different values. The possibility of dynamically adapting K
and/or Slew.Max in response to measured loss rates is for future
study.
Each node may insert a local QSPEC object provided it has a way of
scoping this information (e.g. at the boundary of a domain or by
using the SCOPING object).
In some cases, a QNE needs to be able to distinguish between newly
created, modified state or refreshed state based on the RESERVE
message alone (not in combination with state information obtained
from previous messages). Therefore, one or more additional flags that
provide this differentiation may be needed. The specifictaion of
these flags are QoS model specific. Therefore, the contents and
encoding rules for this object are given in those QoS model
specifications.
In order to clearly distinguish between a RESERVE message that sets
the reserved resources to zero and a RESERVE message that tears down
QoS-NSLP state completely, a TEAR flag is foreseen that is carried in
the common header. Note that the potential initiation of (reverse
path) state removal at the NTLP is a separate issue. This will be
signaled over the API between NTLP and QoS-NSLP.
RESERVE messages are sent peer-to-peer. This means that a QNE
considers its adjacent upstream or downstream peer to be the source
of the RESERVE message. Note that two nodes that are adjacent at the
QoS-NSLP layer may in fact be separated by several NTLP hops. A QoS-
NSLP node may want to be able to detect changes in its QoS-NSLP
peers, or send a message to an explicitly identified node, e.g. for
tearing down a reservation on an old path. This functionality can be
provided by keeping track of a Source Identification Information
(SII) object that is similar in nature to the RSVP_HOP object
described in [6]. We assume such an SII (section 7.2) to be available
as a service from the NTLP.
The RESERVE message is idempotent; the resultant effect is the same
whether a message is received once or many times. In addition, the
ordering of RESERVE messages matters - an old RESERVE message does
not replace a newer one. Both of these features are required for
protocol robustness - messages may be re-ordered on route (e.g.
because of mobility, or at intermediate NTLP nodes) or spuriously
retransmitted.
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In order to tackle these issues, the RESERVE message contains a
Reservation Sequence Number (RSN) object. An RSN is 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 QNEs. Attempting to make an identifier that was unique
in the context of a session identifier 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, this means
that we can make the Reservation Sequence Number unique just between
a pair of neighboring stateful QNEs. Note that an alternative might
be for the NTLP to guarantee in-order delivery between the NSLP
peers.
A Flow identifier groups together state items for a single flow. The
RSN is one of these state items, and is used to identify reordering
of messages and to allow the use of partial refresh messages. The
state items for a number of flows can be linked together and
identified as part of a single reservation using a Session
Identifier. The identifiers play complementary roles in the
management of QoS NSLP state. The flow identifier is carried by the
NTLP and it is augmented by additional flow identifying information
in the QSPEC, which is QoS model specific.
The sender of a RESERVE message may want to receive some confirmation
from a downstream node. In this case the RESERVE message must contain
a RESPONSE_REQUEST object. The RESPONSE_REQUEST object contains the
Request Identification Information (RII) value used to match back a
RESPONSE to a request in a RESERVE message.
5.1.4 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 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, nor does it cause state to be
installed in nodes other than the one that generated the QUERY.
The format of a QUERY message is as follows:
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QUERY = COMMON_HEADER
[ SCOPING ] RESPONSE_REQUEST
[ REFRESH_PERIOD ] [ BOUND_SESSION_ID ]
POLICY_DATA QSPEC [ *QSPEC ]
The QSPEC object(s) must occur at the end of the message. There are
no other requirements on transmission order, although the above order
is recommended.
A QUERY message may be scoped using the SCOPING object.
A QUERY message must contain a RESPONSE_REQUEST object, that carries
the Request Identification Information (RII) that allows matching
back RESPONSE to the QUERY request. It is transported unchanged along
the data path and should be used in combination with the SCOPING
object to scope the RESPONSE to a QUERY message.
The QUERY message can gather information along the data path in a
number of objects. Some of these objects may be part of the QoS
model. Others may be generic to the QoS-NSLP protocol.
The QUERY message opaquely must transport a QSPEC object, describing
the desired service level and a POLICY_DATA object, authorizing the
requestor of the service. Based on configured local policy, a node
may ignore the content of the POLICY_DATA object.
The QUERY message may carry the REFRESH_PERIOD object. It is
RECOMMENDED that in case of a receiver initiated reservation, the
QUERY message carries the REFRESH_PERIOD object.
The SESSION_ID object must be included in the QUERY message only if
the session associated to this message has to be bound to another
session. The content of the SESSION_ID object represents the
SESSION_ID of the session that must be bound to the session
associated to the QUERY message carrying this object. The binding of
these two sessions is only possible in stateful QNEs.
5.1.5 RESPONSE Messages
The RESPONSE message is used to provide information about the result
of a previous QoS-NSLP message, e.g. confirmation, error or
information resulting from a query. The RESPONSE message is impotent,
it does not cause any state to be installed or modified.
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The format of a RESPONSE message is as follows:
RESPONSE = COMMON_HEADER
[ RSN ] [ SCOPING ] [ ERROR_SPEC ]
QSPEC [ *QSPEC]
The QSPEC object(s) must occur at the end of the message. There are
no other requirements on transmission order, although the above order
is recommended.
A QNE may want to receive a RESPONSE message to inform it that the
reservation has been successfully installed. A RESERVE or a QUERY
message may contain a RESPONSE_REQUEST object for this purpose. Such
a RESPONSE_REQUEST object can be used to request an explicit
confirmation of the state manipulation signaled in the RESERVE
message.
The forwarding of the RESPONSE message along the path does not
necessarily imply the existence of NTLP reverse-path state at every
node. For example, the NTLP may have a mechanism to pass a message
directly from the egress to the ingress of a region of QNEs that do
not store per-flow reverse-path state.
A RESPONSE message may be scoped using the SCOPING object. A QUERY
always causes a RESPONSE to be sent. Therefore, a QUERY message will
always contain a RESPONSE_REQUEST object. A RESERVE may cause a
RESPONSE to be sent if this is explicitly requested, by using a
RESPONSE_REQUEST object or when an error occurs. The RESPONSE
Identification Information (RII) included in the RESPONSE_REQUEST
object should be included in the SCOPING object of a RESPONSE
message.
A RESPONSE message may carry an RSN object. The content of this
object must be identical to the content of the RSN object contained
in the RESERVE message that generated this RESPONSE message.
If a QNE or the QNR is unable to provide the requested information or
if the response is negative, the RESPONSE message must carry an
ERROR_SPEC object.
The RESPONSE message opaquely must transport a QSPEC object(s),
describing the desired service level.
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5.1.6 NOTIFY Messages
NOTIFY messages are used to convey information to a QNE. NOTIFY
messages are impotent (they do not cause a change in state directly).
NOTIFY messages differ from RESPONSE messagess in that they need not
refer to any particular state or previously received message. They
are sent asynchronously. The NOTIFY message itself does not trigger
or mandate any action in the receiving QNE.
The format of a NOTIFY message is as follows:
NOTIFY = COMMON_HEADER
[ ERROR_SPEC ] QSPEC
The QSPEC object must occur at the end of the message. There are no
other requirements on transmission order, although the above order is
recommended.
The information conveyed by a NOTIFY message may be related to error
conditions. In this case the ERROR_SPEC object must be carried by the
NOTIFY message.
The NOTIFY message opaquely must transport a QSPEC object, describing
the desired service level.
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 [8].
The QoS NSLP requires IANA to create two registries. One for QoS NSLP
message types, the other for QoS NSLP objects.
This specification defines four message types: RESERVE=1, QUERY=2,
RESPONSE=3 and NOTIFY=4. Values are taken from the Message type name
space (8 bits). New Message types may be defined and assigned values
by IANA. For this, standards action is required.
Common Control Information has a Class and C-type assigned by IANA.
This specification defines the following Common Control Information
objects
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RESPONSE_REQUEST: Class=1
C-type=1: empty
C-type=2: Request Identification Information
RSN: Class=2
C-type=1: RSN
REFRESH_PERIOD: Class=3
C-type=1: REFRESH_PERIOD
SESSION_ID: Class=4
C-type=1: SESSION_ID
SCOPING: Class=5
C-type=1: single hop
C-type=2: Region scoping
C-type=3: RII scoping
ERROR_SPEC: Class=6
C-type=1: empty
IANA will assign new ClassNum values and/or C-type for Common Control
Information upon specification. The required specification needs to
indicate what the correct behaviour is in case the new ClassNum or
C-type is not understood.
This specification defines a QSPEC object with assigned class = 8.
The C-type identifies the QoS model, which can be standardized,
well-known or private.
Standardized
Standardized QoS models have a C-type value in the range of 1-64.
C-type values for standardized QoS models are assigned by IANA and
require standards action.
Well-known
Well-known QoS models have a C-type value in the range of 65-128.
They are assigned by IANA and require IETF consensus.
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Private
C-type values from the range 129-256 are for private use.
7. Requirements for the NSIS Transport Layer Protocol (NTLP)
For the moment this section will merely describe what we assume and/
or request to be available from the NTLP. This section will later be
updated to describe the eventual interface when NTLP work gets
finalized.
7.1 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. We rely on the NTLP to pick a value for the
Session ID and pass it over the API.
7.2 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 4.3), when only the edge QNEs of a domain
process the message. This requires a mechanism at the NTLP 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
the RSVP-E2E-IGNORE that is used for RSVP aggregation ([11]). 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 the NTLP
design.
7.3 Support for peer change identification
There are several circumstances where it is necessary for a QNE to
identify the adjacent QNE peer, which is the source of a signaling
application message; 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.
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We rely on the NTLP to provide this functionality and suggest it be
implemented as an opaque identifier (Source Identification
Information (SII)) which, by default, all outgoing QoS-NSLP messages
are tagged with at the NTLP layer. This identifier is propagated to
the next QNE, where it can be used to identify the state associated
with the message; The SII is logically similar to the RSVP_HOP object
of [6]; however, any IP (and possibly higher level) addressing
information is not interpreted in the QoS-NSLP. Indeed, the
intermediate NTLP nodes could enforce topology hiding by masking the
content of the SII (provided this is done in a stable way).
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 send initiate a teardown along the old section of the path. This
functionality would require the NTLP to be able to route based on the
SII. We would like this functionality to be available as a service
from the NTLP.
7.4 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 the NTLP
level as well. Such nodes should not worry about keeping reverse
state, message fragmentation and reassembly (at the NTLP), congestion
control or security associations. A stateless or reduced state QNE
will be able to inform the underlying NTLP of this situation. We rely
on the NTLP design to allow for a mode of operation that can take
advantage of this information.
7.5 Last node detection
There are situations in which a QNE needs to determine whether it is
the last QNE on the data path (QNR), e.g. to construct and send a
RESPONSE message.
A number of conditions may result in a QNE determining that it is the
QNR:
o the QNE may be the flow destination
o the QNE have some other prior knowledge that it should act as the
QNR
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 the
NTLP. We rely on the NTLP to inform the QoS-NSLP about these cases by
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providing a trigger to the QoS-NSLP when it determines that it is the
last NE on the path, which supports the QoS-NSLP. It requires the
NTLP to have an error message indicating that no more NSLPs of a
particular type are available on the path.
7.6 Re-routing detection
Route changes may be detected at the NTLP layer or the information
may be obtained by the NTLP through local interaction with or
notification from routing protocols or modules. This specification
requests the NTLP design to foresee notification of this information
over the API.
7.7 Priority of signalling messages
The QoS-NSLP will generate messages with a range of performance
requirements for the NTLP. These requirements may result from a
prioritization at the QoS-NSLP (Section 4.3) or from the
responsiveness expected by certain applications supported by the
QoS-NSLP.
The NTLP design should be able to ensure that performance for one
class of messages was not degraded by aggregation with other classes
of messages. It is currently an open issue how many priority levels
are required.
7.8 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.
The NTLP 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.
This might be realised by the NTLP by a mixture of NTLP node
counting, and examination of the IP TTL or Hop Limit. The QoS NSLP,
however, does not need to know the number of intermediate nodes, only
that one or more exists.
7.9 NSLP Data Size
When the NTLP passes the QoS NSLP data to the NSLP for processing, it
must also indicate the size of that data. (It is assumed that the
NTLP message structure will indicate how long this part of the NTLP
message is.)
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7.10 NAT Traversal
The QoS NSLP relies on the NTLP for NAT traversal.
8. Open issues
8.1 Aggregation error handling
QSPEC objects may be stacked to allow aggregation and layering. In
error-free conditions, the top of the QSPEC stack has the QSPEC
object that is locally valid.
A QNE may receive a QoS NSLP message with a QSPEC stack of which the
top object is not recognised. This can occur under error conditions,
e.g. when a domain boundary is misconfigured, or it me be the result
from a policy to detect domain boundaries by encountering
unrecognised QSPEC objects.
In some situations, a QNE may be able to recover from the error
condition by inspecting a larger portion of the stack.It is currently
an open question whether
o A QNE should be allowed to do that instead of or in addition to
sending an error.
o How far the stack can be inspected.
o If and how the QNE should update the stack in case it finds a
QSPEC it recognises.
8.2 Region scoping
This specification allows QNEs to scope their messages, i.e. to
restrict the extent to which messages may travel along and be
interpreted on the path. For this, the scopes of whole path, single
hop and back to me (RII) are defined. Also, a region can be
configured administratively or it can be derived from some other
means (e.g. RAO levels) in case of aggregation.
It is currently an open question whether this specification should
define and support a more generic notion of region (e.g. to implement
region policies independent from aggregation regions,...).
8.3 Priority of reservations
Priority of certain reservations over others may be required when QoS
resources are oversubscribed. In that case, existing reservations may
be preempted in other 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
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then keeps track of the resource consumption at each priority level.
Reservations are established when resource 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 QoS model specific issue and
therefore outside the scope of this specification. However, the
concepts of setup and holding priority are widely accept and we
expect the specification of a Priority object in the QSPEC template
to be useful for a wide range of QoS models.
It is an open question to the NSIS community whether the concepts of
setup and holding priority are useful enough to define a priority
object in this specification. Alternatively, this could be left as
QoS model specific.
9. Security Considerations
9.1 Introduction and Threat Overview
The security requirement for the QoS NSLP is to protect the signaling
exchange for establishing QoS reservations against identified
security threats. For the signaling problem as a whole, these threats
have been outlined in [21]; the NSIS framework [3] assigns a subset
of the responsibility to the NTLP 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:
Signaling message content should be protected against
modification, replay, injection and eavesdropping while in
transit. Authorization information, such as authorization tokens,
need protection. This type of protection at the NSLP layer is
neccessary to protect messages between NSLP nodes which includes
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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
provided by GIMPS which by itself relies on existing authentication
and key exchange protocols. Some signaling 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.
9.2 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 signaling 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 signaling in the Internet this procedure is roughly
similar. In most cases the data sender is charged for transmitted
data traffic whereby 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 16: New Jersey Turnpike Model
The model shown in Figure 16 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 9.3. 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 signaling messages. The identity
used during the authentication and key establishment phase would be
used by Network X (see Figure 16) to perform the so-called
policy-based admission control procedure. In our context this user
identifier would be used to establish the necessary infrastructure to
provide authorization and charging. Signaling messages later
exchanged between the different networks are then also subject to
authentication and authorization. The authenticated entity thereby
is, however, the neighboring network and not the end host.
The New Jersey Turnpike model is attractive because of its
simplicity. S. Schenker et. al. [23] discuss various accounting
implications and introduced the edge pricing model. The edge pricing
model shows similarity to the model described in this section with
the exception that mobility and the security implications itself are
not addressed.
9.3 QoS Authorization
Authorization is a necessary function in order to prevent
theft-of-service and to enable charging. With regard to authorization
a few issues still need to be resolved to specify the protocol
interaction for a QoS NSLP with regard to authorization of resource
requests.
This section provides a description of the different approaches for
providing authorization for QoS resource requests. Three different
approaches are shown, whereby one is a two-party and two others
describe a three party approach.
9.3.1 Authorization for the two party approach
This section starts with the conceptually simpler two party approach.
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+-------------+ QoS request +--------------+
| Entity |----------------->| Entity |
| requesting | | authorizing |
| resource |granted / rejected| resource |
| |<-----------------| request |
+-------------+ +--------------+
^ ^
+...........................+
financial establishment
Figure 17: Two party approach
Figure 17 describes the simple and basic approach where
the authorization decision is purely executed between the two
entities only or
where previous (out-of-band) mechanisms separated the signaling
protocol from executing other entities during NSIS protocol
execution.
The entity authorizing the resource request and the entity actually
performing the QoS reservation are in the same administrative domain.
Hence they are treated as a single logical entity.
Examples for this type of model can be found between two neighboring
networks (inter-domain signaling) where a long-term contract (or
other out-of-band mechanisms) exists and allows both networks to know
how to charge the other entity (i.e. how the authorizing entity
finally gets paid for the consumed resources) and
how to authorize the resource requesting entity (i.e. associating
the identifier of the protected signaling message to the identity
used in the authentication and key exchange protocol run and
finally this identity to the user identity of the contract for the
purpose of charging).
No additional message signaling for authorization is required. In
this scenario the identity used during the authentication and key
exchange process is used for authorizing the same entity. The QoS
NSLP needs to have access to this authenticated identity via an API.
9.3.2 Token based three party approach
This section describes an approach which uses authorization tokens
such as those introduced with [12] and [13] or with the Open
Settlement protocol [26]. The former only associates two different
signaling protocols and their authorization with each other whereas
the latter is a form of digital money. In this text we refer to the
former as the 'authorization tokens' and in the latter case as 'OSP
tokens'. In case of authorization tokens the entity which requests
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authorization wants to run, for example, SIP with an entity in the
local network and wants to experience quality of service for the
media traffic. Some form of authorization will be provided at the SIP
proxy, which acts as the resource authorizing entity in Figure 18. In
case of a successful verification of the request SIP signaling
returns an authorization token which is subsequently included in the
QoS signaling protocol to refer to the previous authorization
decision. The authorization decision can be passed by value or by
reference. The advantage of the latter is that the token is smaller
(i.e., effectively only a pointer to installed state in the network)
with the disadvantage that the entity performing the QoS reservation
has to query the state, possibly from a central entity.
The token based approach assumes that the entity which authorizes the
QoS request (and which also creates the token) is trusted by the
entity which performs the QoS reservation. These two entities do not
necessarily need to be in the same administrative domain. Security
mechanisms must ensure that
the token cannot be modified
the token questing entity is authenticated and authorized at the
token granting entity
the token cannot be stolen and reused by an adversary
Hence, to prevent an adversary from eavesdropping and stealing the
authorization token it is necessary to establish at least a
unilateral authenticated secure channel between entity A and B. As a
side-effect it is possible to provide anonymous authorization since
the authorization decision based on the received token by entity B
does not need to be based on the identity of A. This assumes that
entity C does not provide entity B with the identity.
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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 18: Token based three party approach
The token is only an attribute in the QoS NSLP message. The token
acts as a form of voucher and is therefore a one-shot message. For
the OSP token (or digital money) alike approach, as soon as the
credits are consumed a new token needs to be requested in order.
Refresh messages can therefore be used to trigger the transmission of
new tokens. A trigger message from the network is necessary to
request a new token. Tokens provide a good mechanism for the client
to restrict the amount of spend resources and to quickly learn about
the cost of a QoS reservation if tokens represent only a small value
(such as those used in hash-chain based approaches). The refresh
interval is therefore, in some sense, bound to the "charging"
interval.
Please note that OSP tokens only serve as an example here. The
content of the OSP token is tailored towards its usage in the
telephony environment. Therefore, we see OSP tokens as a prominent
representative of authorization token usage.
Since authorization tokens or OSP tokens can be fairly large
fragmentation is possible or even likely.
9.3.3 Generic three party approach
This section covers a generic three party approach. Figure 19 shows
the intra-domain variant of the exchange.
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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 19: Three party approach (intra-domain)
The main difference between the scenario in Figure 19 and Figure 20
is the trust relationship between the participating entities. In
Figure 20 the home AAA server is responsible for authoring the QoS
request. This might be on a per-request basis, periodically, or on a
per-session basis. In both cases the EAP authentication runs between
the EAP Peer (entity A in Figure 19) and between the EAP Server
(entity C in Figure 19). For the EAP method protocol run the
Authenticator (entity B in Figure 19) is not actively involved. To
fulfill the requirements of the EAP keying framework it is necessary
to execute a protocol exchange between entity A and entity B
subsequently to successful EAP authentication. This exchange should
lead to a secure channel between these two entities.
The main advantage of this exchange is that
a number of authentication and key exchange protocols can be used
in a very flexible fashion; these protocols can be tailed exactly
to the needs of the architecture and the environment
a secure channel can be established
the protocol exchange is effectively a three party protocol
authorization can be incorporated in a very flexible way which
allows the home network (or some other entity) to give tight
control over the sessions
The disadvantage of this approach is that there is no out-of-the-box
solution available. Further investigation is required here.
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+-----------------------------+ +-----------------+
| Local Network | | |
| |QoS | |
| +------------+ authz. req. +---------+ |
| | Local |-----+----+--->| Home | |
| | AAA | |QoS | | AAA | |
| | Server |<----+----+----| Server | |
| +---------+--+ authz. res. +---------+ |
| ^ | | | |
| | | <...financial...> |
| QoS | QoS | settlement |
| authz| authz| | | |
| req.| res.| | | |
| | | | | |
| | v | | |
+----------+ QoS +----+---------+ | | Users |
|Entity | request | Entity | | | Home Network |
|requesting|--+------->| performing | | +-----------------+
|resource |<-+--------| QoS | |
+----------+ granted/ | reservation | |
rejected +--------------+ |
| |
+-----------------------------+
Figure 20: Three party approach (inter-domain)
9.3.4 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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10. 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.
11. Acknowledgements
The authors would like to thank Eleanor Hepworth for her useful
comments.
12. 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.
Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[3] Hancock, R., "Next Steps in Signaling: Framework",
draft-ietf-nsis-fw-05 (work in progress), October 2003.
[4] Schulzrinne, H., "GIMPS: General Internet Messaging Protocol for
Signaling", draft-ietf-nsis-ntlp-00 (work in progress), October
2003.
Informative References
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[5] Braden, B., Clark, D. and S. Shenker, "Integrated Services in
the Internet Architecture: an Overview", RFC 1633, June 1994.
[6] Braden, B., Zhang, L., Berson, S., Herzog, S. and S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification", RFC 2205, September 1997.
[7] Wroclawski, J., "The Use of RSVP with IETF Integrated
Services", RFC 2210, September 1997.
[8] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
1998.
[9] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z. and W.
Weiss, "An Architecture for Differentiated Services", RFC 2475,
December 1998.
[10] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F. and S.
Molendini, "RSVP Refresh Overhead Reduction Extensions", RFC
2961, April 2001.
[11] Baker, F., Iturralde, C., Le Faucheur, F. and B. Davie,
"Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC 3175,
September 2001.
[12] Hamer, L-N., Gage, B., Kosinski, B. and H. Shieh, "Session
Authorization Policy Element", RFC 3520, April 2003.
[13] Hamer, L-N., Gage, B. and H. Shieh, "Framework for Session
Set-up with Media Authorization", RFC 3521, April 2003.
[14] Chaskar, H., "Requirements of a Quality of Service (QoS)
Solution for Mobile IP", RFC 3583, September 2003.
[15] Brunner, M., "Requirements for Signaling Protocols",
draft-ietf-nsis-req-09 (work in progress), August 2003.
[16] Tschofenig, H., "NSIS Authentication, Authorization and
Accounting Issues", draft-tschofenig-nsis-aaa-issues-01 (work
in progress), March 2003.
[17] Tschofenig, H., "QoS NSLP Authorization Issues",
draft-tschofenig-nsis-qos-authz-issues-00 (work in progress),
June 2003.
[18] Ash, J., "NSIS Network Service Layer Protocol QoS Signaling
Proof-of-Concept",
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draft-ash-nsis-nslp-qos-sig-proof-of-concept-01 (work in
progress), February 2004.
[19] Kappler, C., "A QoS Model for Signaling IntServ Controlled-Load
Service with NSIS",
draft-kappler-nsis-qosmodel-controlledload-00 (work in
progress), February 2004.
[20] Bader, A., "RMD (Resource Management in Diffserv) QoS-NSLP
model", draft-bader-rmd-qos-model-00 (work in progress),
February 2004.
[21] Tschofenig, H. and D. Kroeselberg, "Security Threats for NSIS",
draft-ietf-nsis-threats-03 (work in progress), October 2003.
[22] Westberg, L., "Resource Management in Diffserv (RMD)
Framework", draft-westberg-rmd-framework-04.txt, work in
progress, September 2003.
[23] Shenker, S., Clark, D., Estrin, D. and S. Herzog, "Pricing in
computer networks: Reshaping the research agenda", Proc. of
TPRC 1995, 1995.
[24] Metro Ethernet Forum, "Ethernet Services Model", letter ballot
document , August 2003.
[25] Jacobson, V., "Synchronization of Periodic Routing Messages",
IEEE/ACM Transactions on Networking , Vol. 2 , No. 2 , April
1994.
[26] 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.
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
Appendix A. Object Definitions
The currentlly specified C-Types definitions are contained in this
Appendix. To accommodate other address families, additional C-Types
could easily be defined.
All unused fields should be sent as zero and ignored on receipt.
A.1 RESPONSE_REQUEST Class
RESPONSE_REQUEST Class = 1.
RESPONSE_REQUEST object: Class = 1, C-Type = 1
The object content is empty
RESPONSE_REQUEST object: Class = 1, C-Type = 2
+-------------+-------------+-------------+-------------+
| Request Identification Information (RII)(4 bytes) |
+-------------+-------------+-------------+-------------+
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Request Identification Information (RII) (4 bytes)
An identifier which must be (probabilistically) unique
within the context of a SESSION_ID, and SHOULD be different
for each response request. Used by a node to match back a
RESPONSE to a request in a RESERVE or QUERY message.
A.2 RSN Class
RSN class = 2.
RSN object: Class = 2, C-Type = 1
+-------------+-------------+-------------+-------------+
| Reservation Sequence Number (RSN) (4 bytes) |
+-------------+-------------+-------------+-------------+
Reservation Sequence Number (RSN) (4 bytes)
An incrementing sequence number that indicates the order in
which state modifying actions are performed by a QNE. It has
local significance only, i.e. between a pair of neighbouring
stateful QNEs.
A.3 REFRESH_PERIOD Class
REFRESH_PERIOD class = 3.
REFRESH_PERIOD Object: Class = 3, C-Type = 1
+-------------+-------------+-------------+-------------+
| Refresh Period R (4 bytes) |
+-------------+-------------+-------------+-------------+
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Refresh Period R (4 bytes)
The refresh timeout period R used to generate this message;
in milliseconds.
A.4 SESSION_ID Class
SESSION_ID class = 4.
SESSION_ID Object: Class = 4, C-Type = 1
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ SESSION_ID (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
SESSION_ID (16 bytes)
It represents the SESSION_ID as specified in [3] of the
session that must be bound to the session associated to the
message carrying this object.
A.5 SCOPING Class
SCOPING class = 5.
SCOPING Object: Class = 5, C-Type = 1
No content value. Selection of a single hop message scoping.
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SCOPING Object: Class = 5, C-Type = 2
+-------------+-------------+-------------+-------------+
| Region scoping (4 bytes) |
+-------------+-------------+-------------+-------------+
Region scoping (4 bytes)
Ordered number, forwarded by routers belonging to region
with same or higher number;
SCOPING Object: Class = 5, C-Type = 3
+-------------+-------------+-------------+-------------+
| RII scoping (4 bytes) |
+-------------+-------------+-------------+-------------+
RII (back to me) scoping (4 bytes)
An identifier which must be (probabilistically) unique
within the context of a SESSION_ID, and SHOULD be different
for each response request. Used by a node to match back a
RESPONSE to a request in a RESERVE or QUERY message.
A.6 ERROR_SPEC Class
ERROR_SPEC class = 6.
ERROR_SPEC object: Class = 6, C-Type = 1
+-------------+-------------+-------------+-------------+
| Error (4 bytes) |
+-------------+-------------+-------------+-------------+
| Flags | Error Code | Error Value |
+-------------+-------------+-------------+-------------+
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Error (4 bytes)
To be done
Flags (1 byte)
To be done
Error Code (1 byte)
A one-octet error description.
Error Value (2 bytes)
A two-octet field containing additional information about
the error. Its contents depend upon the Error Type.
The values for Error Code and Error Value are defined in
Appendix B (to be done).
A.7 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.7.1 Base Format
POLICY_DATA object: Class=7, C-Type=1
+-------------------------------------------------------+
| |
// Option List //
| |
+-------------------------------------------------------+
| |
// Policy Element List //
| |
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+-------------------------------------------------------+
Option List: Variable length. See more details in Appendix A.7.2.
Policy Element List: Variable length. See more details in Appendix
A.7.3.
A.7.2 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 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 the NTLP. 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).
Integrity object:
The INTEGRITY object option inside POLICY_DATA object creates
direct secure communications between non-neighboring policy aware
nodes without involving PIN nodes.
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A.7.3 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.7.3.1 Authorization token Policy Element
The AUTHZ_TOKEN policy element contains a list of fields, which
describe the session, along with other attributes.
+-------------+-------------+-------------+-------------+
| 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 [12] 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.
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+--------+--------+--------+--------+
| 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.
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 [12].
A.7.3.2 OSP Token Policy Element
To be completed.
A.7.3.3 User Identity Policy element
To be completed.
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A.8 QSPEC Class
QSPEC class = 8.
QSPEC object: Class = 8, C-Type = (QoS model ID)
This object contains the QSPEC (QoS specification) information.
Its content has a variable length and it is QoS model specific.
Such a QoS model can be a standardized one, a private one, or a
well-known one. The C-Type contains the QoS model ID that
identifies the used QSPEC.
The contents and encoding rules for this object are specified
in other documents, prepared by QoS model designers.
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