draft-ietf-mpls-cr-ldp-00.txt   draft-ietf-mpls-cr-ldp-01.txt 
MPLS Working Group L. Andersson, A. Fredette, B. Jamoussi MPLS Working Group Bilel Jamoussi, Editor
Internet Draft Nortel Networks Internet Draft Nortel Networks
Expiration Date: July 1999 Expiration Date: August 1999
R. Callon
IronBridge Networks
P. Doolan
Ennovate Networks
N. Feldman
IBM Corp
E. Gray
Lucent Technologies
J. Halpern
Newbridge Networks
J. Heinanen
Telia Finland
T. E. Kilty
Northchurch Communications
A. G. Malis
Ascend Communications, Inc.
M. Girish
SBC Technology Resources, Inc.
K. Sundell
Ericsson
P. Vaananen
Nokia Telecommunications
T. Worster
General DataComm, Inc.
L. Wu, R. Dantu
Alcatel
January 1998 February 1999
Constraint-Based LSP Setup using LDP Constraint-Based LSP Setup using LDP
draft-ietf-mpls-cr-ldp-00.txt draft-ietf-mpls-cr-ldp-01.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
CR-LDP Specification - 2 - Exp. Apr 1999
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Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract Abstract
Label Distribution Protocol (LDP) is defined in [LDP] for Label Distribution Protocol (LDP) is defined in [LDP] for
distribution of labels inside one MPLS domain. One of the most distribution of labels inside one MPLS domain. One of the most
important services that may be offered using MPLS in general and LDP important services that may be offered using MPLS in general and LDP
in particular is support for constraint-based routing of traffic in particular is support for constraint-based routing of traffic
across the routed network. Constraint-based routing offers the across the routed network. Constraint-based routing offers the
opportunity to extend the information used to setup paths beyond what opportunity to extend the information used to setup paths beyond what
is available for the routing protocol. For instance, an LSP can be is available for the routing protocol. For instance, an LSP can be
setup based on an explicit route constraint, a Service Class (SC) setup based on explicit route constraints, QoS constraints, and
constraint, or both. Constraint-based routing (CR) and Traffic others. Constraint-based routing (CR) is a mechanism used to meet
Engineering requirements have been proposed by [FRAME], [ARCH] and Traffic Engineering requirements that have been proposed by [FRAME],
[TER]. These requirements may be met by extending LDP for support of [ARCH] and [TER]. These requirements may be met by extending LDP for
constraint-based routed label switched paths (CRLSPs). Other uses support of constraint-based routed label switched paths (CRLSPs).
exist for CRLSPs as well ([VPN1] and [VPN2]).
CR-LDP Specification - 2 - Exp. August 1999
Other uses exist for CRLSPs as well ([VPN1], [VPN2] and [VPN3]).
This draft specifies mechanisms and TLVs for support of CRLSPs using This draft specifies mechanisms and TLVs for support of CRLSPs using
LDP. The Explicit Route object and procedures are extracted from LDP. The Explicit Route object and procedures are extracted from
[ER]. [ER].
Table of Contents
1. Introduction ......................................... 3
2. Constraint-based Routing Overview .................... 3
2.1 Strict and Loose Explicit Routes ..................... 4
2.2 Traffic Characteristics .............................. 4
2.3 Pre-emption .......................................... 5
2.4 Route Pinning ........................................ 5
2.5 Resource Class ....................................... 5
3. Solution Overview .................................... 5
3.1 Required Messages and TLVs ........................... 7
3.2 Label Request Message ................................ 7
3.3 Label Mapping Message ................................ 8
3.4 Notification Message ................................. 9
3.5 Release & Withdraw Messages .......................... 9
4. Protocol Specification .............................. 9
4.1 Explicit Route TLV (ER-TLV) ......................... 10
4.2 Explicit Route Hop TLV .............................. 10
4.3 Traffic Parameters TLV .............................. 12
4.3.1 Semantics ........................................... 13
4.3.1.1 Frequency ........................................... 13
4.3.1.2 Peak Rate ........................................... 14
4.3.1.3 Committed Rate ...................................... 14
4.3.1.4 Excess Burst Size .................................... 14
4.3.1.5 Peak Rate Token Bucket................................ 14
4.3.1.6 Committed Data Rate Token Bucket ..................... 15
4.3.1.7 Weight ......................... ..................... 16
4.3.2 Procedures ........................................... 16
4.3.2.1 Label Request Message ................................ 16
4.3.2.2 Label Mapping Message ................................ 16
4.3.2.3 Notification Message ................................. 17
4.4 Preemption TLV ....................................... 18
4.5 LSPID TLV ........................................... 18
4.6 Resource Class TLV .................................. 19
4.7 ER-Hop Semantics ..................................... 19
4.7.1 ER-Hop 1 TLV IPv4 Prefix ............................. 20
4.7.2 ER-Hop 2 TLV IPv6 Prefix ............................. 20
4.7.3 ER-Hop 3 TLV AS Number ............................... 21
4.7.4 ER-Hop 4 TLV LSPID ................................... 21
4.8 Processing of the ER-TLV ............................. 22
4.8.1 Selection of the next hop ............................ 22
4.8.2 Adding the Label Request Message to the next hop ..... 24
4.9 Route Pinning TLV ................................... 24
4.10 CR-LSP FEC Element ................................... 24
4.11 Error Subcodes ...................................... 25
CR-LDP Specification - 3 - Exp. August 1999
5. Security Considerations .............................. 26
6. Acknowledgement ...................................... 26
7. References ........................................... 26
8. Author Information ................................... 28
Appendix A CRLSP Establishment Examples ......................... 30
A.1 Strict Explicit Route Example ........................ 30
A.2 Node Groups and Specific Nodes Example ............... 31
Appendix B QoS Service Examples ................................. 34
B.1 Service Examples ..................................... 34
B.2 Establishing CR-LSP Supporting Real-Time Applications. 35
B.3 Establishing CR-LSP Delay Insensitive Applications ... 36
1. Introduction 1. Introduction
The need for constraint-based routing (CR) in MPLS has been explored The need for constraint-based routing (CR) in MPLS has been explored
elsewhere [ARCH], [FRAME], and [TER]. Explicit routing is a subset elsewhere [ARCH], [FRAME], and [TER]. Explicit routing is a subset
of the more general constraint-based routing function. At the MPLS WG of the more general constraint-based routing function. At the MPLS WG
meeting held during the Washington IETF there was consensus that LDP meeting held during the Washington IETF there was consensus that LDP
should support explicit routing of LSPs with provision for indication should support explicit routing of LSPs with provision for indication
of associated (forwarding) priority. In the Chicago meeting, the of associated (forwarding) priority. In the Chicago meeting, a
decision was made that support for explicit path setup in LDP will be decision was made that support for explicit path setup in LDP will be
moved to a separate document. This document provides that support. We moved to a separate document. This document provides that support and
propose an end-to-end setup mechanism of a constraint-based routed it has been accepted as a working document in the Orlando meeting.
LSP (CRLSP) initiated by the ingress LSR. We also specify mechanisms This specification proposes an end-to-end setup mechanism of a
to provide means for reservation of resources for the explicitly constraint-based routed LSP (CRLSP) initiated by the ingress LSR. We
routed LSP. also specify mechanisms to provide means for reservation of resources
using LDP.
We introduce TLVs and procedures that provide support for:
CR-LDP Specification - 3 - Exp. Apr 1999 This document introduce TLVs and procedures that provide support for:
- Strict and Loose Explicit Routing - Strict and Loose Explicit Routing
- Specification of Service Class
- Specification of Traffic Parameters - Specification of Traffic Parameters
- Route Pinning - Route Pinning
- CRLSP bumping though setup/holding priority - CRLSP Pre-emption though setup/holding priorities
- Handling Failures - Handling Failures
- LSPID
- Resource Class
2. CRLSP Overview Section 2 introduces the various constraints defined in this
specification. Section 3 outlines the CR-LDP solution. Section 4
defines the TLVs and procedures used to setup constraint-based routed
label switched paths. Appendix A provides several examples of CR-LSP
path setup. Appendix B provides Service Definition Examples.
CRLSP over LDP Specification is designed with several goals in mind: 2. Constraint-based Routing Overview
Constraint-based routing is a mechanism that supports the Traffic
Engineering requirements defined in [TER]. Explicit Routing is a
subset of the more general constraint-based routing where the
CR-LDP Specification - 4 - Exp. August 1999
constraint is the explicit route (ER). Other constraints are defined
to provide a network operator with control over the path taken by an
LSP. This section is an overview of the various constraints supported
by this specification.
2.1 Strict and Loose Explicit Routes
Like any other LSP an CRLSP is a path through an MPLS network. The
difference is that while other paths are setup solely based on
information in routing tables or from a management system, the
constraint-based route is calculated at one point at the edge of
network based on criteria, including but not limited to routing
information. The intention is that this functionality shall give
desired special characteristics to the LSP in order to better support
the traffic sent over the LSP. The reason for setting up CRLSPs,
might be that one wants to assign certain bandwidth or other Service
Class characteristics to the LSP, or that one wants to make sure that
alternative routes use physically separate paths through the network.
An explicit route is represented in a Label Request Message as a
list of nodes or groups of nodes along the constraint-based route.
When the CRLSP is established, all or a subset of the nodes in a
group may be traversed by the LSP. Certain operations to be
performed along the path can also be encoded in the constraint-based
route.
The capability to specify, in addition to specified nodes, groups of
nodes, of which a subset will be traversed by the CRLSP, allows the
system a significant amount of local flexibility in fulfilling a
request for a constraint-based route. This allows the generator of
the constraint-based route to have some degree of imperfect
information about the details of the path.
The constraint-based route is encoded as a series of ER-Hops
contained in a constraint-based route TLV. Each ER-Hop may identify
a group of nodes in the constraint-based route. A constraint-based
route is then a path including all of the identified groups of nodes.
To simplify the discussion, we call each group of nodes an abstract
node. Thus, we can also say that a constraint-based route is a path
including all of the abstract nodes, with the specified operations
occurring along that path.
2.2 Traffic Characteristics
The traffic characteristics of a path are described in the Traffic
Parameters TLV in terms of a peak rate, committed rate, and service
granularity. The peak and committed rates describe the bandwidth
constraints of a path while the service granularity can be used to
specify a constraint on the delay variation that the CRLDP MPLS
domain may introduce to a path's traffic.
CR-LDP Specification - 5 - Exp. August 1999
2.3 Pre-emption
CR-LDP signals the resources required by a path on each hop of the
route. If a route with sufficient resources can not be found,
existing paths may be rerouted to reallocate resources to the new
path. This is the process of path pre-emption. Setup and holding
priorities are used to rank existing paths (holding priority) and the
new path (setup priority) to determine if the new path can pre-empt
an existing path.
The setupPriority of a new CRLSP and the holdingPriority attributes
of the existing CRLSP are used to specify priorities. Signaling a
higher holding priority expresses that the path, once it has been
established, should have a lower chance of being pre-empted.
Signaling a higher setup priority expresses the expectation that, in
the case that resource are unavailable, the path is more likely to
pre-empt other paths. The exact rules determining bumping are an
aspect of network policy.
The allocation of setup and holding priority values to paths is an
aspect of network policy.
The setup and holding priority values range from zero (0) to seven
(7). The value zero (0) is the priority assigned to the most
important path. It is referred to as the highest priority. Seven (7)
is the priority for the least important path. The use of default
priority values is an aspect of network policy.
The setupPriority of a CRLSP should not be higher (numerically less)
than its holdingPriority since it might bump an LSP and be bumped by
next "equivalent" request.
2.4 Route Pinning
Route pinning is applicable to segments of an LSP that are loosely
routed - i.e. those segments which are specified with a next hop with
the 'L' bit set or where the next hop is an "abstract node". A CRLSP
may be setup using route pinning if it is undesirable to change the
path used by an LSP because a better next hop becomes available at
some LSR along the loosely routed portion of the LSP.
2.5 Resource Class
Network resources may be classified in various ways by the network
operator. These classes are also known as "colors" or "administrative
groups". When an CR-LSP is being established, it's necessary to
indicate which resource classes the CR-LSP can draw from.
3. Solution Overview
CRLSP over LDP Specification is designed with the following goals:
CR-LDP Specification - 6 - Exp. August 1999
1. Meet the requirements outlined in [TER] for performing traffic 1. Meet the requirements outlined in [TER] for performing traffic
engineering and provide a solid foundation for performing more engineering and provide a solid foundation for performing more
general constrain-based routing. general constraint-based routing.
2. Build on already specified functionality that meets the 2. Build on already specified functionality that meets the
requirements whenever possible. Hence, this specifications is requirements whenever possible. Hence, this specifications is
based on [LDP] and the Explicit Route object and procedures based on [LDP] and the Explicit Route object and procedures
defined in [ER]. defined in [ER].
3. Keep the solution simple and tractable. 3. Keep the solution simple.
In this document, support for unidirectional point-to-point CRLSPs is In this document, support for unidirectional point-to-point CRLSPs is
specified. Support for point-to-multipoint, multipoint-to-point, is specified. Support for point-to-multipoint, multipoint-to-point, is
for further study (FFS). for further study (FFS).
Support for explicitly routed LSPs in this specification depends on Support for constraint-based routed LSPs in this specification
the following minimal LDP behaviors as specified in [LDP]: depends on the following minimal LDP behaviors as specified in [LDP]:
- Basic and/or Extended Discovery Mechanisms. - Basic and/or Extended Discovery Mechanisms.
- Use the Label Request Message defined in [LDP] in downstream on - Use the Label Request Message defined in [LDP] in downstream on
demand label advertisement mode with ordered control. demand label advertisement mode with ordered control.
- Use the Label Mapping Message defined in [LDP] in downstream on - Use the Label Mapping Message defined in [LDP] in downstream on
demand mode with ordered control. demand mode with ordered control.
- Use the Notification Message defined in [LDP]. - Use the Notification Message defined in [LDP].
- Use the Withdraw and Release Messages defined in [LDP]. - Use the Withdraw and Release Messages defined in [LDP].
- Loop detection (in the case of loosely routed segments of a - Use the Loop Detection (in the case of loosely routed segments
CRLSP) mechanisms. of a CRLSP) mechanisms defined in [LDP].
In addition, the following functionality is added to what's defined In addition, the following functionality is added to what's defined
in [LDP]: in [LDP]:
- The Label Request Message used to setup a CRLSP includes a CR- - The Label Request Message used to setup a CRLSP includes one or
TLV based on the path vector defined in [ER] and specified in more CR-TLVs defined in Section 4. For instance, the Label Request
Section 4 of this document. Message may include the ER-TLV.
CR-LDP Specification - 4 - Exp. Apr 1999
- An LSR implicitly infers ordered control from the existence of a
CR-TLV in the Label Request Message. This means that the LSR can
still be configured for independent control for LSPs established
as a result of dynamic routing. However, when a Label Request
Message includes a CR TLV, then ordered control is used to setup
the CRLSP. Note that this is also true for the loosely routed
parts of a CRLSP.
- Traffic Parameters TLVs may optionally be carried in the Label - An LSR implicitly infers ordered control from the existence of
Request Message to specify the CRLSP traffic characteristics. one or more CR-TLVs in the Label Request Message. This means that
the LSR can still be configured for independent control for LSPs
established as a result of dynamic routing. However, when a Label
Request Message includes one or more of the CR-TLVs, then ordered
control is used to setup the CRLSP. Note that this is also true
for the loosely routed parts of a CRLSP.
- New status codes are defined to handle error notification for - New status codes are defined to handle error notification for
failure of established paths specified in the CR-TLV. failure of established paths specified in the CR-TLV.
CR-LDP Specification - 7 - Exp. August 1999
Examples of CRLSP establishment are given in Appendix A to illustrate Examples of CRLSP establishment are given in Appendix A to illustrate
how the mechanisms described in this draft work. how the mechanisms described in this draft work.
3. Required Messages and TLVs 3.1 Required Messages and TLVs
Any Messages, TLVs, and procedures not defined explicitly in this Any Messages, TLVs, and procedures not defined explicitly in this
document are defined in the [LDP] Specification. The following document are defined in the [LDP] Specification. The state
subsections are meant as a cross reference to the [LDP] document and transitions which relate to CR-LDP messages can be found in [LDP-
indication of additional functionality beyond what's defined in [LDP] STATE].
where necessary.
3.1 Label Request Message The following subsections are meant as a cross reference to the [LDP]
document and indication of additional functionality beyond what's
defined in [LDP] where necessary.
3.2 Label Request Message
The Label Request Message is as defined in 3.5.8 of [LDP] with the The Label Request Message is as defined in 3.5.8 of [LDP] with the
following modifications (required only if the CR-TLV is included in following modifications (required only if any of the CR-TLVs is
the Label Request Message): included in the Label Request Message):
- Only a single FEC-TLV may be included in the Label Request - Only a single FEC-TLV may be included in the Label Request
Message. Message. The CR-LSP FEC TLV should be used.
- The Optional Parameters TLV includes the definition of the - The Return Message ID TLV is MANDATORY.
Constraint-based TLV specified in Section 4 and the Traffic
Parameters TLV specified in Section 5.
- The Procedures to handle the Label Request are augmented by the - The Optional Parameters TLV includes the definition of any of
procedures for processing of the CR-TLV as defined in Section 4. the Constraint-based TLVs specified in Section 4.
- The Procedures to handle Service Classes are defined in Section - The Procedures to handle the Label Request Message are augmented
5. by the procedures for processing of the CR-TLVs as defined in
Section 4.
3.2 Label Mapping Message The encoding for the CR-LDP Label Request Message is as follows:
CR-LDP Specification - 8 - Exp. August 1999
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Message ID TLV (mandatory) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSPID TLV (CR-LDP, mandatory) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER-TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pinning TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Resource Class TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pre-emption TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.3 Label Mapping Message
The Label Mapping Message is as defined in 3.5.7 of [LDP] with the The Label Mapping Message is as defined in 3.5.7 of [LDP] with the
following modifications: following modifications:
- Only a single Label-TLV may be included in the Label Mapping - Only a single Label-TLV may be included in the Label Mapping
Message. Message.
CR-LDP Specification - 5 - Exp. Apr 1999 - The Label Mapping Message MUST include Label Request Message ID
TLV.
- The FEC-Label Mapping TLV does not include any of the optional - The Label Mapping Message MUST include LSPID TLV.
TLVs.
- The Label Mapping Message Procedures are limited to downstream - The Label Mapping Message Procedures are limited to downstream
on demand ordered control mode of mapping. on demand ordered control mode.
A Mapping message is transmitted by a downstream LSR to an upstream A Mapping message is transmitted by a downstream LSR to an upstream
LSR under one of the following conditions: LSR under one of the following conditions:
1. The LSR is the egress end of the CRLSP and an upstream mapping 1. The LSR is the egress end of the CRLSP and an upstream mapping
has been requested. has been requested.
2. The LSR received a mapping from its downstream next hop LSR for 2. The LSR received a mapping from its downstream next hop LSR for
an CRLSP for which an upstream request is still pending. an CRLSP for which an upstream request is still pending.
3.3. Notification Message The encoding for the CR-LDP Label Mapping Message is as follows:
The Notification message is as defined in Section 3.5.1 of [LDP] and CR-LDP Specification - 9 - Exp. August 1999
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Request Message ID TLV (mandatory) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSPID TLV (CR-LDP, mandatory) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.4 Notification Message
The Notification Message is as defined in Section 3.5.1 of [LDP] and
the Status TLV encoding is as defined in Section 3.4.7 of [LDP]. the Status TLV encoding is as defined in Section 3.4.7 of [LDP].
Establishment of an Explicitly Routed LSP may fail for a variety of Establishment of an Explicitly Routed LSP may fail for a variety of
reasons. All such failures are considered advisory conditions and reasons. All such failures are considered advisory conditions and
they are signaled by the Notification Message. they are signaled by the Notification Message.
Notification messages carry Status TLVs to specify events being Notification Messages carry Status TLVs to specify events being
signaled. New status codes are defined in Section 4.8.3 to signal signaled. New status codes are defined in Section 4.11 to signal
error notifications associated with the establishment of a CRLSP and error notifications associated with the establishment of a CRLSP and
the processing of the CR-TLV. the processing of the CR-TLV.
4. Constraint-based Routing TLV The Notification Message must carry the LSPID TLV of the
corresponding CRLSP.
Label Request Messages defined in [LDP] optionally carry the 3.5 Release and Withdraw Messages
Constraint-based Routing TLV (CR-TLV) based on the path vector
defined in [ER] and described in this section of the specification.
The inclusion of the CR TLV in the Label Request Message indicates
the path to be taken in the network even if normal routing indicates
otherwise.
The format of the CR-TLV is described below. The Label Release and Label Withdraw Messages are used as specified
in [LDP] to clear CR-LSPs. These message may also carry the LSPID
TLV.
4.1 CR-TLV 4. Protocol Specification
The CR-TLV is an object that specifies the path to be taken by the The Label Request Messages defined in [LDP] optionally carries one or
LSP being established. In addition, the CR-TLV may also include the more of the optional Constraint-based Routing TLVs (CR-TLVs) defined
the Service Class (SC) constraints associated with the LSP, a setup in this section. If needed, other constraints can be supported later
and a holding priority used for path bumping, and an LSP pinning through the definition of new TLVs. In this specification, the
request flag. Reserved bits in the CR-TLV allow for the following TLVs are defined:
specification of other LSP attributes in the future. If the reserved
bits are exhausted, additional TLVs may be specified to allow for the
indication of other LSP attributes during the CRLSP setup.
CR-LDP Specification - 6 - Exp. Apr 1999 - Explicit Route TLV
CR-LDP Specification - 10 - Exp. August 1999
- Explicit Route Hop TLV
- Traffic Parameters TLV
- Preemption TLV
- LSPID TLV
- Route Pinning TLV
- Resource Class TLV
- CRLSP FEC TLV
4.1 Explicit Route TLV (ER-TLV)
The ER-TLV is an object that specifies the path to be taken by the
LSP being established. It is composed of one or more Explicit Route
Hop TLVs (ER-Hop TLVs) defined in Section 4.2.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| CR-TLV (0x0800) | Length | |U|F| ER-TLV (0x0800) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Reserved | SC |P| Hp | Sp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER-Hop TLV 1 | | ER-Hop TLV 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER-Hop TLV 2 | | ER-Hop TLV 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ............ ~ ~ ............ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER-Hop TLV n | | ER-Hop TLV n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit U bit
Unknown TLV bit. As defined in [LDP].
Unknown TLV bit. Upon receipt of an unknown TLV, if clear (=0), a
notification must be returned to the message originator and the
entire message must be ignored; if set (=1), the unknown TLV is
silently ignored and the rest of the message is processed as if the
unknown TLV did not exist.
F bit F bit
Forward unknown TLV bit. As defined in [LDP].
Forward unknown TLV bit. This bit only applies when the U bit is set
and the LDP message containing the unknown TLV is to be forwarded.
If clear (=0), the unknown TLV is not forwarded with the containing
message; if set (=1), the unknown TLV is forwarded with the
containing message.
Type Type
A two byte field carrying the value of the ER-TLV type which
is 0x800.
A two byte field carrying the value of the CR-TLV type which is Length
0x800. Specifies the length of the value field in bytes.
ER-Hop TLVs
One or more ER-Hop TLVs defined in Section 4.2.
4.2 Explicit Route Hop TLV (ER-Hop TLV)
The contents of an ER-TLV are a series of variable length ER-Hop
TLVs. Each ER-Hop TLV has the form:
CR-LDP Specification - 11 - Exp. August 1999
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| ER-Hop-Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Content // |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown TLV bit. As defined in [LDP].
F bit
Forward unknown TLV bit. As defined in [LDP].
ER-Hop Type
A fourteen-bit field indicating the type of contents of
the ER-Hop. Currently defined values are:
Value Type
----- ------------------------
0x801 IPv4 prefix
0x802 IPv6 prefix
0x803 Autonomous system number
0x804 LSPID
Length Length
Specifies the length of the value field in bytes.
L bit
The L bit is an attribute of the ER-Hop. The L bit is set if the
ER-Hop represents a loose hop in the explicit route. If the bit is
not set, the ER-Hop represents a strict hop in the explicit route.
The L bit in the ER-Hop is a one-bit attribute. If the L bit is
set, then the value of the attribute is "loose." Otherwise, the
value of the attribute is "strict." For brevity, we say that if
the value of the ER-Hop attribute is loose then it is a "loose
ER-Hop." Otherwise, it's a "strict ER-Hop." Further, we say that
the abstract node of a strict or loose ER-Hop is a strict or a
loose node, respectively. Loose and strict nodes are always
interpreted relative to their prior abstract nodes.
The path between a strict node and its prior node MUST include
only network nodes from the strict node and its prior abstract
node.
The path between a loose node and its prior node MAY include other
network nodes which are not part of the strict node or its prior
abstract node.
CR-LDP Specification - 12 - Exp. August 1999
Contents
A variable length field containing the node or abstract node that
is the consecutive nodes that make up the explicit routed LSP.
4.3 Traffic Parameters TLV
The following sections describe the CRLSP Traffic Parameters. The
required characteristics of a CRLSP are expressed by the Traffic
Parameter values.
A Traffic Parameters TLV, is used to signal the Traffic Parameter
values. The Traffic Parameters are defined in the subsequent
sections.
The Traffic Parameters TLV contains a Flags field, a Frequency, a
Weight, and the five Traffic Parameters PDR, PBS, CDR, CBS, EBS. The
Traffic Parameters TLV is shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Traf. Param. TLV (0x0810)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Frequency | Reserved | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Peak Data Rate (PDR) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Peak Burst Size (PBS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Committed Data Rate (CDR) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Committed Burst Size (CBS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Excess Burst Size (EBS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown TLV bit. As defined in [LDP].
F bit
Forward unknown TLV bit. As defined in [LDP].
Type
A fourteen-bit field carrying the value of the ER-TLV type which
is 0x810.
Length
Specifies the length of the value field in bytes. Specifies the length of the value field in bytes.
Flags
The Flags field is shown below:
CR-LDP Specification - 13 - Exp. August 1999
+--+--+--+--+--+--+--+--+
| Res |F6|F5|F4|F3|F2|F1|
+--+--+--+--+--+--+--+--+
Res - These bits are reserved.
Zero on transmission.
Ignored on receipt.
F1 - Corresponds to the PDR.
F2 - Corresponds to the PBS.
F3 - Corresponds to the CDR.
F4 - Corresponds to the CBS.
F5 - Corresponds to the EBS.
F6 - Corresponds to the Weight.
Each flag Fi is a Negotiable Flag corresponding to a Traffic
Parameter. The Negotiable Flag value zero denotes NotNegotiable
and value one denotes Negotiable.
Frequency
The Frequency field is coded as an 8 bit unsigned integer with
the following code points defined:
0 - Unspecified
1 - Frequent
2 - VeryFrequest
3-255 - Reserved
Reserved Reserved
Zero on transmission. Ignored on receipt.
This field is reserved. It must be set to zero on transmission and Weight
must be ignored on receipt. We expect to use these fields for An 8 bit unsigned integer indicating the weight of the CRLSP.
carrying information that support other constrain-based routing Valid weight values are from 1 to 255. The value 0 means
information. that weight is not applicable for the CRLSP.
P bit Traffic Parameters
Each Traffic Parameter is encoded as a 32 bit IEEE single-
precision floating point number. A value of positive infinity is
represented as an IEEE single-precision floating-point number with
an exponent of all ones (255) and a sign and mantissa of all
zeros. The values PDR and CDR are in units of bytes per second.
The values PBS, CBS and EBS are in units of bytes.
CR-LDP Specification - 7 - Exp. Apr 1999 The value of PDR MUST be greater than or equal to the value of CDR
in a correctly encoded Traffic Parameters TLV.
When set indicates that the loosely routed segments must remain 4.3.1 Semantics
pinned-down. CRLSP must be rerouted only when adjacency is lost
along the segment. When not set, it indicates that the loose segment
is not pinned down and must be changed to match the underlying hop-
by-hop path.
SC 4.3.1.1 Frequency
The SC Field is used to specify the Service Class of the CRLSP. This CR-LDP Specification - 14 - Exp. August 1999
field allows for the definition of up to 8 different Service Classes.
Currently, Three Service Classes are defined: Best Effort (0),
Throughput Sensitive (1), and Delay Sensitive (2) Service Classes.
These SCs are further defined in Section 5.
Sp The Frequency specifies at what granularity the CDR allocated to the
CRLSP is made available. The value VeryFrequently means that the
available rate should average at least the CDR when measured over any
time interval equal to or longer than the shortest packet time at the
CDR. The value Frequently means that the available rate should
average at least the CDR when measured over any time interval equal
to or longer than a small number of shortest packet times at the CDR.
The value Unspecified means that the CDR MAY be provided at any
granularity.
A SetupPriority of value zero (0) is the priority assigned to the 4.3.1.2 Peak Rate
most important path. It is referred to as the highest priority. Four
(4) is the priority for the least important path. The higher the
setup priority, the more paths CR-LDP can bump to set up the path.
The default value is 2. Values 5, 6, and 7 are reserved.
Hp The Peak Rate defines the maximum rate at which traffic SHOULD be
sent to the CRLSP. The Peak Rate is useful for the purpose of
resource allocation. If resource allocation within the MPLS domain
depends on the Peak Rate value then it should be enforced at the
ingress to the MPLS domain.
A HoldingPriority of value zero (0) is the priority assigned to the The Peak Rate is defined in terms of the two Traffic Parameters PDR
most important path. It is referred to as the highest priority. Four and PBS, see section 4.3.1.5 below.
(4) is the priority for the least important path. The higher the
holding priority, the less likely it is for CR-LDP to reallocate its
bandwidth to a new path. The default value is 2. Values 5, 6, and 7
are reserved.
4.1.1 Setup and holding priorities 4.3.1.3 Committed Rate
CR-LDP signals the resources required by a path on each hop of the The Committed Rate defines the rate that the MPLS domain commits to
route. If a route with sufficient resources can not be found, be available to the CRLSP.
existing paths may be rerouted to reallocate resources to the new
path. This is the process of bumping paths. Setup and holding
priorities are used to rank existing paths (holding priority) and the
new path (setup priority) to determine if the new path can bump an
existing path.
The setupPriority of a new CRLSP and the holdingPriority attributes The Committed Rate is defined in terms of the two Traffic Parameters
of the existing CRLSP are used to specify these priorities. The CDR and CBS, see section 4.3.1.6 below.
higher the holding priority, the less likely it is for CR-LDP to
reallocate its bandwidth to a new path. Similarly, the higher the
setup priority, the more paths CR-LDP can bump to set up the path.
The setup and holding priority values range from zero (0) to four 4.3.1.4 Excess Burst Size
(4). The value zero (0) is the priority assigned to the most
important path. It is referred to as the highest priority. Four (4)
is the priority for the least important path. The default values for
CR-LDP Specification - 8 - Exp. Apr 1999 The Excess Burst Size may be used at the edge of an MPLS domain for
the purpose of traffic conditioning. The EBS MAY be used to measure
the extent by which the traffic sent on a CRLSP exceeds the committed
rate.
both setup and holding priority should be 2. By setting the default The possible traffic conditioning actions, such as passing, marking
value of both setup and holding priorities at the middle of the or dropping, are specific to the MPLS domain.
range, all connections are initially treated the same. However, when
network operators see a need for the use of path bumping, the values
of setup and holding priorities can be gracefully adjusted up or down
from the middle of the range.
An existing path can be bumped if and only if the setupPriority of The Excess Burst Size is defined together with the Committed Rate,
the new path is numerically less than the holdingPriority of the see section 4.3.1.6 below.
existing path.
To illustrate the use of the setup and holding priority, consider a 4.3.1.5 Peak Rate Token Bucket
network which supports two service types (e.g., video and data
services). The video traffic is given a low setup priority because
new video paths can use an alternate public network if the primary
network cannot accommodate the new path. However, the video traffic
is given a high holding priority since it is undesirable for the path
to be rerouted during an active LSP. For data traffic, high setup and
holding priorities are desirable since data paths cannot be
established on an alternate network.
The setup and holding priorities can be different to allow setup at The Peak Rate of a CRLSP is specified in terms of a token bucket P
one priority and holding at an independent priority. This would allow with token rate PDR and maximum token bucket size PBS.
some calls not to invoke bumping and not to be bumped at the same
time.
The setupPriority of a CRLSP should not be higher (numerically less) The token bucket P is initially (at time 0) full, i.e., the token
than its holdingPriority since it might bump an LSP and be bumped by count Tp(0) = PBS. Thereafter, the token count Tp, if less than PBS,
next "equivalent" request. is incremented by one PDR times per second. When a packet of size B
bytes arrives at time t, the following happens:
Bumping by default only happens as a last resort when there are no CR-LDP Specification - 15 - Exp. August 1999
routes available for a given path.
During the instantiation of a path that must bump other paths, lower o If Tp(t)-B >= 0, the packet is not in excess of the peak
holding priority paths are bumped before higher priority paths. The rate and Tp is decremented by B down to the minimum value
decision as to which of the available paths are bumped at each of 0, else
intermediate node by the new path is arbitrary.
4.2 ER-Hop TLV o the packet is in excess of the peak rate and Tp is
not decremented.
The contents of a constraint-based route TLV are a series of variable Note that according to the above definition, a positive infinite
length ER-Hop TLVs. Each ER-Hop TLV has the form: value of either PDR or PBS implies that arriving packets are never in
excess of the peak rate.
0 1 The actual implementation of a LSR doesn't need to be modeled
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 according to the above formal token bucket specification.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------//--------------+
|L| Type | Length | Contents |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------//--------------+
L 4.3.1.6 Committed Data Rate Token Bucket
CR-LDP Specification - 9 - Exp. Apr 1999 The committed rate of a CRLSP is specified in terms of a token bucket
C with rate CDR. The extent by which the offered rate exceeds the
committed rate MAY be measured in terms of another token bucket E,
which also operates at rate CDR. The maximum size of the token
bucket C is CBS and the maximum size of the token bucket E is EBS.
The L bit is an attribute of the ER-Hop. The L bit is set if the The token buckets C and E are initially (at time 0) full, i.e., the
ER-Hop represents a loose hop in the explicit route. If the bit is token count Tc(0) = CBS and the token count Te(0) = EBS. Thereafter,
not set, the ER-Hop represents a strict hop in the explicit route. the token counts Tc and Te are updated CDR times per second as
follows:
Type o If Tc is less than CBS, Tc is incremented by one, else
A seven-bit field indicating the type of contents of the ER-Hop. o if Te is less then EBS, Te is incremented by one, else
Currently defined values are:
Value Type o neither Tc nor Te is incremented.
----- ------------------------
0 Reserved
1 IPv4 prefix
2 IPv6 prefix
32 Autonomous system number
Length When a packet of size B bytes arrives at time t, the following
happens:
The Length field contains the total length of the ER-Hop in bytes. It o If Tc(t)-B >= 0, the packet is not in excess of the Committed
includes the L bit, Type and Length fields. The length must always be Rate and Tc is decremented
a multiple of 4, and at least 4. by B down to the minimum value of 0, else
Contents o if Te(t)-B >= 0, the packet is in excess of the Committed Rate
but is not in excess of the EBS and Te is
decremented by B down to the minimum value of 0, else
A variable length field containing the node or abstract node that is o the packet is in excess of both the Committed Rate and the EBS
the consecutive nodes that make up the explicit routed LSP. and neither Tc nor Tc is decremented.
4.3 Applicability Note that according to the above specification, a CDR value of
positive infinity implies that arriving packets are never in excess
of either the Committed Rate or EBS. A positive infinite value of
either CBS or EBS implies that the respective limit cannot be
The CR-TLV in this version of the specification is intended for CR-LDP Specification - 16 - Exp. August 1999
unicast only. CRLSPs for multicast are FFS.
4.4 Semantics of the CR-TLV exceeded.
Like any other LSP an CRLSP is a path through a network. The The actual implementation of a LSR doesn't need to be modeled
difference is that while other paths are setup solely based on according to the above formal specification.
information in routing tables or from a management system, the
constraint-based route is calculated at one point at the edge of
network based on criteria, including but not limited to routing
information. The intention is that this functionality shall give
desired special characteristics to the LSP in order to better support
the traffic sent over the LSP. The reason for setting up CRLSPs,
might be that one wants to assign certain bandwidth or other Service
Class characteristics to the LSP, or that one wants to make sure that
alternative routes use physically separate paths through the network.
A CRLSP is represented in a Label Request Message as a list of nodes 4.3.1.7 Weight
or groups of nodes along the constraint-based route. When the CRLSP
is established, all or a subset of the nodes in a group may be
CR-LDP Specification - 10 - Exp. Apr 1999 The weight determines the CRLSP's relative share of the possible
excess bandwidth above its committed rate. The definition of
"relative share" is MPLS domain specific.
traversed by the LSP. Certain operations to be performed along the 4.3.2 Procedures
path can also be encoded in the constraint-based route.
The capability to specify, in addition to specified nodes, groups of 4.3.2.1 Label Request Message
nodes, of which a subset will be traversed by the CRLSP, allows the
system a significant amount of local flexibility in fulfilling a
request for a constraint-based route. This allows the generator of
the constraint-based route to have some degree of imperfect
information about the details of the path.
The constraint-based route is encoded as a series of ER-Hops If an LSR receives an incorrectly encoded Traffic Parameters TLV in
contained in a constraint-based route TLV. Each ER-Hop may identify which the value of PDR is less than the value of CDR then it MUST
a group of nodes in the constraint-based route. A constraint-based send a Notification Message including the Status code Traffic
route is then a path including all of the identified groups of nodes. Parameters Unavailable to the upstream LSR from which it received the
erroneous message.
To simplify the discussion, we call each group of nodes an abstract If a Traffic Parameter is indicated as Negotiable in the Label
node. Thus, we can also say that a constraint-based route is a path Request Message by the corresponding Negotiable Flag then an LSR MAY
including all of the abstract nodes, with the specified operations replace the Traffic Parameter value with a smaller value.
occurring along that path.
4.5 Strict and Loose ER-Hops If the Weight is indicated as Negotiable in the Label Request Message
by the corresponding Negotiable Flag then an LSR may adjust replace
the Weight value with a lower value (down to 1).
The L bit in the ER-Hop is a one-bit attribute. If the L bit is set, If, after possible Traffic Parameter negotiation, an LSR can support
then the value of the attribute is "loose." Otherwise, the value of the CRLSP Traffic Parameters then the LSR MUST reserve the
the attribute is "strict." For brevity, we say that if the value of corresponding resources for the CRLSP.
the ER-Hop attribute is loose then it is a "loose ER-Hop."
Otherwise, it's a "strict ER-Hop." Further, we say that the abstract
node of a strict or loose ER-Hop is a strict or a loose node,
respectively. Loose and strict nodes are always interpreted relative
to their prior abstract nodes.
The path between a strict node and its prior node MUST include only If, after possible Traffic Parameter negotiation, an LSR cannot
network nodes from the strict node and its prior abstract node. support the CRLSP Traffic Parameters then the LSR MUST send a
notification message that contains the Resource Unavailable status
code.
The path between a loose node and its prior node MAY include other 4.3.2.2 Label Mapping Message
network nodes which are not part of the strict node or its prior
abstract node.
4.6 Loops If an LSR receives an incorrectly encoded Traffic Parameters TLV in
which the value of PDR is less than the value of CDR then it MUST
send a Label Release message containing the Status code Traffic
Parameters Unavailable to the LSR from which it received the
erroneous message.
While the constraint-based route TLV is of finite length, the The egress LSR MUST include the (possibly negotiated) Traffic
existence of loose nodes implies that it is possible to construct Parameters and Weight in the Label Mapping message.
forwarding loops during transients in the underlying routing
protocol. This may be detected by the originator of the constraint-
based route through the use a path vector object as defined in [LDP].
4.7 ER-Hop semantics The Traffic Parameters and the Weight in a Label Mapping message MUST
be forwarded unchanged.
4.7.1. ER-Hop 1: The IPv4 prefix CR-LDP Specification - 17 - Exp. August 1999
The contents of an IPv4 prefix ER-Hop are a 4 byte IPv4 address, 1 An LSR SHOULD adjust the resources that it reserved for a CRLSP when
it receives a Label Mapping Message if the Traffic Parameters differ
from those in the corresponding Label Request Message.
CR-LDP Specification - 11 - Exp. Apr 1999 4.3.2.3 Notification Message
byte of prefix length, and 1 byte of padding. The abstract node If an LSR receives a Notification Message for a CRLSP, it SHOULD
represented by this ER-Hop is the set of nodes which have an IP release any resources that it possibly had reserved for the CRLSP.
address which lies within this prefix. Note that a prefix length of
32 indicates a single IPv4 node.
The length of the IPv4 prefix ER-Hop is 8 bytes. The contents of the In addition, on receiving a Notification Message from a Downstream
1 byte of padding must be zero on transmission and must not be LSR that is associated with a Label Request from an upstream LSR, the
checked on receipt. local LSR MUST propagate the Notification message using the
procedures in [LDP].
4.4 Preemption TLV
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | IPv4 Address (4 bytes) | |U|F| Preemption-TLV (0x0820) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address (Continued) | Prefix |0 0 0 0 0 0 0 0| | SetPrio | HoldPrio | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown TLV bit. As defined in [LDP].
F bit
Forward unknown TLV bit. As defined in [LDP].
Type Type
A fourteen-bit field carrying the value of the Preemption-TLV
type which is 0x810.
IPv4 Address 0x01 Length
Specifies the length of the value field in bytes.
Reserved
Zero on transmission. Ignored on receipt.
SetPrio
A SetupPriority of value zero (0) is the priority assigned to the
most important path. It is referred to as the highest priority.
Seven (7) is the priority for the least important path. The higher
the setup priority, the more paths CR-LDP can bump to set up the
path.
HoldPrio
A HoldingPriority of value zero (0) is the priority assigned to
the most important path. It is referred to as the highest
priority. Seven (7) is the priority for the least important path.
CR-LDP Specification - 18 - Exp. August 1999
The higher the holding priority, the less likely it is for CR-LDP
to reallocate its bandwidth to a new path.
4.5 LSPID TLV
LSPID is a unique identifier of a CRLSP within an MPLS network.
The LSPID is composed of the ingress LSR Router ID and a Locally
unique CRLSP ID to that LSR.
The LSPID is useful in network management, in CR-LSP repair, and in
using an already established CR-LSP as a hop in an ER-TLV.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| LSPID-TLV (0x0821) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Local CRLSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress LSR Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown TLV bit. As defined in [LDP].
F bit
Forward unknown TLV bit. As defined in [LDP].
Type
A fourteen-bit field carrying the value of the LSPID-TLV
type which is 0x821.
Length Length
Specifies the length of the value field in bytes.
A one byte field indicating the total length of the TLV in bytes. It Reserved
includes the L-bit, the Type, Length, the IP Address, and the Prefix Zero on transmission. Ignored on receipt.
fields. The length is always 8 bytes.
IP Address Local CRLSP ID
The Local LSP ID is an identifier of the CRLSP locally unique
within the Ingress LSR originating the CRLDP.
A four byte field indicating the IP Address. Ingress LSR Router ID
A 4 byte field indicating the Ingress LSR ID.
Prefix Length 4.6 Resource Class (Color) TLV
1-32 The Resource Class as defined in [TER] is used to specify which links
are acceptable by this CRLSP. This information allows for the
Padding CR-LDP Specification - 19 - Exp. August 1999
networks topology to be pruned.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| ResCls-TLV (0x0822) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RsCls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown TLV bit. As defined in [LDP].
F bit
Forward unknown TLV bit. As defined in [LDP].
Type
A fourteen-bit field carrying the value of the ResCls-TLV
type which is 0x822.
Length
Specifies the length of the value field in bytes.
RsCls
The Resource Class bit mask indicating which of the
32 "administrative groups" or "colors" of links
the CRLSP can traverse.
4.7 ER-Hop semantics
4.7.1. ER-Hop 1: The IPv4 prefix
The abstract node represented by this ER-Hop is the set of nodes
which have an IP address which lies within this prefix. Note that a
prefix length of 32 indicates a single IPv4 node.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| 0x801 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Reserved | PreLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown TLV bit. As defined in [LDP].
F bit
Forward unknown TLV bit. As defined in [LDP].
CR-LDP Specification - 20 - Exp. August 1999
Type
IPv4 Address 0x801
Length
Specifies the length of the value field in bytes.
L Bit
Set to indicate Loose hop.
Cleared to indicate a strict hop.
Reserved
Zero on transmission. Ignored on receipt. Zero on transmission. Ignored on receipt.
4.7.2. ER-Hop 2: The IPv6 address PreLen
Prefix Length 1-32
CR-LDP Specification - 12 - Exp. Apr 1999 IP Address
A four byte field indicating the IP Address.
4.7.2. ER-Hop 2: The IPv6 address
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | IPV6 address (16 bytes) | |U|F| 0x802 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) | |L| Reserved | PreLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) | | IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) | | IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) | Prefix |0 0 0 0 0 0 0 0| | IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type U bit
Unknown TLV bit. As defined in [LDP].
0x02 IPv6 address F bit
Forward unknown TLV bit. As defined in [LDP].
Type
0x802 IPv6 address
Length Length
Specifies the length of the value field in bytes.
The Length contains the total length of the ER-Hop TLV in bytes, L Bit
including the Type and Length fields. The Length is always 20. Set to indicate Loose hop.
IPv6 address CR-LDP Specification - 21 - Exp. August 1999
Cleared to indicate a strict hop.
Reserved
Zero on transmission. Ignored on receipt.
PreLen
Prefix Length 1-128
IPv6 address
A 128-bit unicast host address. A 128-bit unicast host address.
Prefix Length 4.7.3. ER-Hop 32: The autonomous system number
1-128 The abstract node represented by this ER-Hop is the set of nodes
belonging to the autonomous system.
Padding 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| 0x803 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Reserved | AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown TLV bit. As defined in [LDP].
F bit
Forward unknown TLV bit. As defined in [LDP].
Type
AS Number 0x803
Length
Specifies the length of the value field in bytes.
L Bit
Set to indicate Loose hop.
Cleared to indicate a strict hop.
Reserved
Zero on transmission. Ignored on receipt. Zero on transmission. Ignored on receipt.
4.7.3. ER-Hop 32: The autonomous system number AS Number
Autonomous System number
The contents of an autonomous system (AS) number ER-Hop are a 2 byte 4.7.4. ER-Hop 4: LSPID
autonomous system number. The abstract node represented by this ER-
Hop is the set of nodes belonging to the autonomous system.
The length of the AS number ER-Hop is 4 bytes. The LSPID is used to identify the tunnel ingress point as the next
hop in the ER. This ER-Hop allows for stacking new CR-LSPs within an
already established CR-LSP. It also allows for splicing the CR-LSP
CR-LDP Specification - 22 - Exp. August 1999
being established with an existing CR-LSP.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Autonomous System number | |U|F| 0x804 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Reserved | Local LSPID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress LSR Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type U bit
Unknown TLV bit. As defined in [LDP].
CR-LDP Specification - 13 - Exp. Apr 1999 F bit
Forward unknown TLV bit. As defined in [LDP].
AS Number 0x20 Type
LSPID 0x804
Length Length
Specifies the length of the value field in bytes.
A one byte field indicating the total length of the TLV in bytes. It L Bit
includes the L-bit, the Type, and Length, and the AS number fields. Set to indicate Loose hop.
The length is always 4 bytes. Cleared to indicate a strict hop.
AS number Reserved
Zero on transmission. Ignored on receipt.
A two byte field indicating the AS number. Local LSPID
A 2 byte field indicating the LSPID which is unique
with reference to the its Ingress LSR.
4.8. Processing of the Constraint-Based Route TLV Ingress LSR Router ID
A 4 byte field indicating the Ingress LSR ID.
4.8. Processing of the Explicit Route TLV
4.8.1. Selection of the next hop 4.8.1. Selection of the next hop
A Label Request message containing a constraint-based route TLV must A Label Request Message containing a explicit route TLV must
determine the next hop for this path. Selection of this next hop may determine the next hop for this path. Selection of this next hop may
involve a selection from a set of possible alternatives. The involve a selection from a set of possible alternatives. The
mechanism for making a selection from this set is implementation mechanism for making a selection from this set is implementation
dependent and is outside of the scope of this specification. dependent and is outside of the scope of this specification.
Selection of particular paths is also outside of the scope of this Selection of particular paths is also outside of the scope of this
specification, but it is assumed that each node will make a best specification, but it is assumed that each node will make a best
effort attempt to determine a loop-free path. Note that such best effort attempt to determine a loop-free path. Note that such best
CR-LDP Specification - 23 - Exp. August 1999
efforts may be overridden by local policy. efforts may be overridden by local policy.
To determine the next hop for the path, a node performs the following To determine the next hop for the path, a node performs the following
steps: steps:
1) The node receiving the Label Request message must first 1) The node receiving the Label Request Message must first
evaluate the first ER-Hop. If the L bit is not set in the first evaluate the first ER-Hop. If the L bit is not set in the first
ER-Hop and if the node is not part of the abstract node described ER-Hop and if the node is not part of the abstract node described
by the first ER-Hop, it has received the message in error, and by the first ER-Hop, it has received the message in error, and
should return a "Bad initial ER-Hop" error. If the L bit is set should return a "Bad initial ER-Hop" error. If the L bit is set
and the local node is not part of the abstract node described by and the local node is not part of the abstract node described by
the first ER-Hop, the node selects a next hop that is along the the first ER-Hop, the node selects a next hop that is along the
path to the abstract node described by the first ER-Hop. If there path to the abstract node described by the first ER-Hop. If there
is no first ER-Hop, the message is also in error and the system is no first ER-Hop, the message is also in error and the system
should return a "Bad Constraint-Based Routing TLV" error. should return a "Bad Explicit Routing TLV" error.
2) If there is no second ER-Hop, this indicates the end of the 2) If there is no second ER-Hop, this indicates the end of the
constraint-based route. The constraint-based route TLV should be explicit route. The explicit route TLV should be removed from the
removed from the Label Request message. This node may or may not Label Request Message. This node may or may not be the end of the
be the end of the LSP. Processing continues with section 4.8.2, LSP. Processing continues with section 4.8.2, where a new
where a new constraint-based route TLV may be added to the Label explicit route TLV may be added to the Label Request Message.
Request message.
3) If the node is also a part of the abstract node described by 3) If the node is also a part of the abstract node described by
the second ER-Hop, then the node deletes the first ER-Hop and the second ER-Hop, then the node deletes the first ER-Hop and
continues processing with step 2, above. Note that this makes the continues processing with step 2, above. Note that this makes the
second ER-Hop into the first ER-Hop of the next iteration. second ER-Hop into the first ER-Hop of the next iteration.
CR-LDP Specification - 14 - Exp. Apr 1999
4) The node determines if it is topologically adjacent to the 4) The node determines if it is topologically adjacent to the
abstract node described by the second ER-Hop. If so, the node abstract node described by the second ER-Hop. If so, the node
selects a particular next hop which is a member of the abstract selects a particular next hop which is a member of the abstract
node. The node then deletes the first ER-Hop and continues node. The node then deletes the first ER-Hop and continues
processing with section 4.8.2. processing with section 4.8.2.
5) Next, the node selects a next hop within the abstract node of 5) Next, the node selects a next hop within the abstract node of
the first ER-Hop that is along the path to the abstract node of the first ER-Hop that is along the path to the abstract node of
the second ER-Hop. If no such path exists then there are two the second ER-Hop. If no such path exists then there are two
cases: cases:
5a) If the second ER-Hop is a strict ER-Hop, then there is an 5a) If the second ER-Hop is a strict ER-Hop, then there is an
error and the node should return a "Bad strict node" error. error and the node should return a "Bad strict node" error.
5b) Otherwise, if the second ER-Hop is a loose ER-Hop, then the 5b) Otherwise, if the second ER-Hop is a loose ER-Hop, then the
node selects any next hop that is along the path to the next node selects any next hop that is along the path to the next
abstract node. If no path exists, then there is an error, and the abstract node. If no path exists within the MPLS domain, then
node should return a "Bad loose node" error. there is an error, and the node should return a "Bad loose node"
error.
6) Finally, the node replaces the first ER-Hop with any ER-Hop 6) Finally, the node replaces the first ER-Hop with any ER-Hop
that denotes an abstract node containing the next hop. This is that denotes an abstract node containing the next hop. This is
necessary so that when the constraint-based route is received by necessary so that when the explicit route is received by the next
the next hop, it will be accepted. hop, it will be accepted.
CR-LDP Specification - 24 - Exp. August 1999
7) Progress the Label Request Message to the next hop. 7) Progress the Label Request Message to the next hop.
4.8.2. Adding ER-Hops to the constraint-based route TLV 4.8.2. Adding ER-Hops to the explicit route TLV
After selecting a next hop, the node may alter the constraint-based After selecting a next hop, the node may alter the explicit route in
route in the following ways. the following ways.
If, as part of executing the algorithm in section 4.8.1, the If, as part of executing the algorithm in section 4.8.1, the explicit
constraint-based route TLV is removed, the node may add a new route TLV is removed, the node may add a new explicit route TLV.
constraint-based route TLV.
Otherwise, if the node is a member of the abstract node for the first Otherwise, if the node is a member of the abstract node for the first
ER-Hop, then a series of ER-Hops may be inserted before the first ER-Hop, then a series of ER-Hops may be inserted before the first
ER-Hop or may replace the first ER-Hop. Each ER-Hop in this series ER-Hop or may replace the first ER-Hop. Each ER-Hop in this series
must denote an abstract node that is a subset of the current abstract must denote an abstract node that is a subset of the current abstract
node. node.
Alternately, if the first ER-Hop is a loose ER-Hop, an arbitrary Alternately, if the first ER-Hop is a loose ER-Hop, an arbitrary
series of ER-Hops may be inserted prior to the first ER-Hop. series of ER-Hops may be inserted prior to the first ER-Hop.
4.8.3. Error subcodes 4.9 Route Pinning TLV
In the processing described above, certain errors need to be reported
as part of the Notification message. This section defines the status
codes for the errors described above.
CR-LDP Specification - 15 - Exp. Apr 1999
Status Code Type
-------------------------------------- ----------
Bad Constraint-Based Routing TLV Error 0x04000001
Bad Strict Node Error 0x04000002
Bad Loose Node Error 0x04000003
Bad Initial ER-Hop Error 0x04000004
Resource Unavailable 0x04000005
Service Class Unavailable 0x04000006
Traffic Parameters Unavailable 0x04000007
5.0 CRLSP Service Classes and Traffic Parameters
The following sections describe the CRLSP Service Classes (SCs), and
their associated traffic parameters.
The CRLSP Service Class is signaled in the SC Field of the CR-TLV
defined in Section 4.1.
Three Service Classes are currently supported by CR-LDP:
Service Class Value
-------------------------- -----
Best Effort (BE) 0x0
Throughput Sensitive (TS) 0x1
Delay Sensitive (DS) 0x2
These service classes are specified in the following sections.
5.1 Best Effort (BE)
The request of the BE SC implies that there are no expected service
guarantees from the network. The service provided by the network is
the familiar best effort service.
The Peak Date Rate (PDR) is the only traffic parameter that may be
specified with the BE SC. The specification of the PDR allows the
network to perform traffic shaping and policing functions.
5.2 Throughput Sensitive (TS)
In the service model for the Throughput Sensitive SC, the network
commits to deliver with high probability user datagrams at a rate of
at least CDR (Committed Data Rate). The user may transmit at a rate
higher than CDR but datagrams in excess of CDR would have a lower
probability of being delivered. If the user sends at a rate of CDR or
lower the network commits to deliver with high probability all the
user datagrams.
The TS SC has an associated tolerance to the burstiness of arriving
CR-LDP Specification - 16 - Exp. Apr 1999
user datagrams. This tolerance is defined by the traffic parameter
Committed Burst Tolerance (CBT).
Ideally, a TS CRLSP request carries with it a rich set of three
traffic parameters (PDR, CDR, and CBT) that accurately describe its
traffic characteristics. This allows the network to perform resource
reservation, traffic shaping, and traffic policing.
However, for the sake of simplicity of the service definition, the
CDR is the only parameter that MUST always be specified for a TS
CRLSP. A peak data rate parameter (PDR) and a CBT are optional
traffic parameters for the TS SC.
The network should make every effort to preserve ordering of the
delivered datagrams of a TS CRLSP.
Network traffic that requires a low packet loss ratio at a given CDR
but is not particularly sensitive to delay and jitter (e.g., network
control traffic) is suited to the TS SC. The selection of the TS SC
is used to signal to the various nodes along the path that the
queuing and scheduling mechanisms used to handle the CRLSP should
provide a low packet loss ratio.
5.3 Delay Sensitive (DS)
In the service model for the Delay Sensitive SC, the network commits
to deliver with high probability user datagrams at a rate of CDR
(Committed Data Rate) with minimum delay and delay variation. The
user MUST transmit data at a rate of CDR or lower in order to be
eligible for DS service. Datagrams in excess of CDR may be discarded
by the network. If the user sends at a rate of CDR or lower the
network commits to deliver with high probability all user datagrams
with low delay and delay variation. If the user sends at a rate
higher than CDR the network does not provide any guarantees on the
excess traffic.
The Delay Sensitive SC has an associated tolerance to the burstiness
of arriving user datagrams. This tolerance is defined by the traffic
parameter Committed Burst Tolerance (CBT).
Ideally, a DS CRLSP request carries with it a rich set of three
traffic parameters (PDR, CDR, and CBT) that accurately describe its
traffic characteristics. This allows the network to perform resource
reservation, traffic shaping and policing.
However, for the sake of simplicity of the service definition, the
CDR is the only parameter that MUST always be specified for a DS
CRLSP. A peak data rate parameter (PDR) and a CBT are optional
traffic parameters for the DS SC.
The network should make every effort to preserve ordering of the
CR-LDP Specification - 17 - Exp. Apr 1999
delivered datagrams of a DS CRLSP.
Network traffic that requires a low delay and delay variation at a
given CDR (e.g., voice traffic) is suited to the DS SC. The selection
of the DS SC is used to signal to the various nodes along the path
that the queuing and scheduling mechanisms used to handle the CRLSP
should provide low delay and delay variation.
5.4 Traffic Parameters
The CRLSP traffic parameters are defined in this section.
The traffic parameters CDR, CBT and PDR are defined in terms of a
TOKEN_BUCKET_TSPEC as specified in [RFC2215]. The following mapping
of parameters in the TOKEN_BUCKET_TSPEC is used:
Token rate, r = CDR
Bucket depth, b = CBT
Peak traffic rate, p = PDR
Minimum policed unit, m = 1
Maximum packet size, M = MTU
The Traffic Parameters TLV is used to signal the traffic
characteristics of the CRLSP. These traffic parameters are used to
perform functions such as resource reservation, Shaping, and
Policing. See [SIN] for more details. The encoding for the Traffic
Parameters TLV is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Traffic TLV (0x0810) | Length | |U|F| 0x823 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDR TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CDR TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CBT TLV | |P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.4.1 Peak data rate (PDR) TLV U bit
Unknown TLV bit. As defined in [LDP].
The value of traffic parameter PDR is given as a positive integer in F bit
bytes per second. Zero is not a valid value of PDR. Forward unknown TLV bit. As defined in [LDP].
The user may specify the value of PDR depending the SC of the CRLSP. Type
Specifying the PDR allows the network to use traffic management Pinning-TLV type 0x823
functions such as shaping.
CR-LDP Specification - 18 - Exp. Apr 1999 Length
Specifies the length of the value field in bytes.
0 1 2 3 P Bit
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 The P bit is set to 1 to indicate that route pinning is requested.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The P bit is set to 0 to indicate that route pinning is not
|U|F| PDR TLV (0x0811) | Length | requested
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDR in Bytes/sec |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.4.2. Committed Data Rate (CDR) Reserved
Zero on transmission. Ignored on receipt.
The value of traffic parameter CDR is given as a positive integer in 4.10 CRLSP FEC Element
bytes per second. Zero is not a valid value of CDR.
The user may provide a requested value of CDR in the CRLSP request CR-LDP Specification - 25 - Exp. August 1999
depending on the SC of the CRLSP.
0 1 2 3 A new FEC element is introduced in this specification to support CR-
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 LSPs. The CRLDP FEC Element is an opaque FEC.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| CDR TLV (0x0812) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CDR in Bytes/sec |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.4.3. Committed Burst Tolerance (CBT) FEC Element Type Value
type name
The value of traffic parameter CBT is given in bytes. Zero is not a CRLSP 0x04 No value; i.e., 0 value octets;
valid value of CBT. see below.
The requested value of CBT MUST be no smaller than the MTU of the CRLSP FEC Element
originating interface. To be used only in Messages of CR-LSPs.
The user may provide a requested value of CBT in the CRLSP request. The CR-LSP FEC TLV encoding is as follows:
If the user chooses not to specify a requested value of CBT and the
network is policing the traffic, then any excess traffic will be
dropped by the network.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| CBT TLV (0x0813) | Length | |U|F| FEC(0x0100) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CBT in Bytes | | CR-LSP (4) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6. Open Issues U bit
Unknown TLV bit. As defined in [LDP].
This section captures the issues that need further study.
CR-LDP Specification - 19 - Exp. Apr 1999
1) Review the FSM described in Appendix B and extend it by the CR-TLV
processing defined in Sections 4.8.1 and 4.8.2.
2) Consider if all three traffic parameters have to be signaled at
all times and if the network should supply default values for the
missing parameters.
3) Consider the following extensions to the CR-TLV:
3.1) Changing the 'P' bit to "next hop flag" and making it a 2-bit
wide field with the following values:
- 00 "local repair", which means if it belongs to a loosely
routed segment, and the LSR detects a next hop change, the LSR
will try to establish a new LSP from this point on and switch
it over to the new LSP when it is setup.
- 01 "global repair", which means when the LSR detects a next
hop change, the LSR will tear down the LSP, the ingress LSR
will try to reestablish another LSP through the new path.
- 10 "pinned", which means that the loosely routed segments
must remain pinned down.
- 11 Reserved. F bit
Forward unknown TLV bit. As defined in [LDP].
3.2) Adding one more field "LSPID" before ER-Hop TLV. LSPID can Type
be used to identify a network wide unique CRLSP. FEC TLV type 0x0100
- The first 4 bytes carrying the ingress LSR IP address Length
Specifies the length of the value field in bytes.
- The second 4 bytes carrying the unique ID value assigned by CR-LSP FEC Element Type
the ingress LSR. 0x04
4) Consider the following extension to the ER-Hop TLV: Reserved
Zero on transmission. Ignored on receipt.
For Type field, add one more type, LSPID, which means the current 4.11 Error subcodes
CRLSP will go through another CRLSP which is identified with this
LSPID value:
Value Type In the processing described above, certain errors need to be reported
----- ----- as part of the Notification Message. This section defines the status
4 LSPID codes for the errors described in this specification.
Extend processing the LSPID ER-Hop as follows: If the type of ER- CR-LDP Specification - 26 - Exp. August 1999
Hop is LSPID, and the other end of this CRLSP is not part of the
constraint-based route TLV, add it to the constraint-based TLV
with L bit turned off.
5) Consider traffic parameter negotiation and the ability to change Status Code Type
the traffic parameters associated with an already established path -------------------------------------- ----------
Bad Explicit Routing TLV Error 0x04000001
Bad Strict Node Error 0x04000002
Bad Loose Node Error 0x04000003
Bad Initial ER-Hop Error 0x04000004
Resource Unavailable 0x04000005
Traffic Parameters Unavailable 0x04000006
Setup abort 0x04000007
CR-LDP Specification - 20 - Exp. Apr 1999 5. Security
without tearing the old path down. Pre-emption has to be controlled by the MPLS domain.
7. Security Resource reservation requires the LSRs to have an LSP admission
control function.
No security issues are discussed in this version of the draft. Normal routing can be bypassed by Traffic Engineered LSPs.
8. Acknowledgments 6. Acknowledgments
The messages used to signal the CRLSP setup are based on the work The messages used to signal the CRLSP setup are based on the work
done by the [LDP] team. The Explicit Route object and procedures used done by the [LDP] team. The Explicit Route object and procedures used
in this specification are based on [ER]. in this specification are based on [ER].
The authors would also like to acknowledge the careful review and The authors would also like to acknowledge the careful review and
comments of Osama Aboul-Magd, Ken Hayward, Greg Wright, Geetha Brown, comments of Ken Hayward, Greg Wright, Geetha Brown, Brian Williams,
Brian Williams, Peter Ashwood-smith, Paul Beaubien, Matthew Yuen, Paul Beaubien, Matthew Yuen, Liam Casey, and Ankur Anand.
Liam Casey, and Ankur Anand.
9. References 7. References
[FRAME] Callon et al, "Framework for Multiprotocol Label Switching", [LDP] Andersson et al, "Label Distribution Protocol Specification"
work in progress (draft-ietf-mpls-framework-02), November 1997. work in progress (draft-ietf-mpls-ldp-03), Feb. 1999.
[ARCH] Rosen et al, "Multiprotocol Label Switching Architecture", [ARCH] Rosen et al, "Multiprotocol Label Switching Architecture",
work in progress (draft-ietf-mpls-arch-02), July 1998. work in progress (draft-ietf-mpls-arch-04), Feb. 1999.
[LDP] Andersson et al, "Label Distribution Protocol Specification"
work in progress (draft-ietf-mpls-ldp-02.txt), November 1998.
[ER] Guerin et al, "Setting up Reservations on Explicit Paths using [FRAME] Callon et al, "Framework for Multiprotocol Label Switching",
RSVP", work in progress (draft-guerin-expl-path-rsvp-01.txt, November work in progress (draft-ietf-mpls-framework-02), November
1997. 1997.
[TER] Awduche et al, "Requirements for Traffic Engineering Over [TER] Awduche et al, "Requirements for Traffic Engineering Over
MPLS", work in progress (draft-awduche-mpls-traffic-eng-00), April MPLS", work in progress (draft-ietf-mpls-traffic-eng-00),
1998. August 1998.
[ER] Guerin et al, "Setting up Reservations on Explicit Paths
using RSVP", work in progress (draft-guerin-expl-path-rsvp-
01)
November 1997.
CR-LDP Specification - 27 - Exp. August 1999
[VPN1] Heinanen et al, "MPLS Mappings of Generic VPN Mechanisms", [VPN1] Heinanen et al, "MPLS Mappings of Generic VPN Mechanisms",
work in progress (draft-heinanen-generic-vpn-mpls-00), August 1998. work in progress (draft-heinanen-generic-vpn-mpls-00),
August 1998.
[VPN2] Jamieson et al, "MPLS VPN Architecture" work in progress [VPN2] Jamieson et al, "MPLS VPN Architecture" work in progress
(draft-jamieson-mpls-vpn-00), August 1998. (draft-jamieson-mpls-vpn-00), August 1998.
[RFC2215] S. Shenker and J. Wroclawski, General Characterization [VPN3] T. Li, "CPE based VPNs using MPLS", work in progress (draft-
Parameters for Integrated Service Network Elements, RFC 2215, Sep li-mpls-vpn-00.txt), October 1998.
1997.
[SIN] B. Jamoussi, N. Feldman, and L. Andersson, "MPLS Ships in the [LDP-STATE] L. Wu, et. al., "LDP State Machine" work in progress
Night with ATM", (draft-jamoussi-mpls-sin-00.txt), August 1998. (draft-ietf-mpls-ldp-state-00), Feb 1999.
CR-LDP Specification - 21 - Exp. Apr 1999 CR-LDP Specification - 28 - Exp. August 1999
10. Author Information 8. Author Information
Loa Andersson Osama S. Aboul-Magd Loa Andersson
Director Bay Architecture Lab, EMEA Nortel Networks Director Bay Architecture Lab,EMEA
Kungsgatan 34, PO Box 1788 P O Box 3511 Station C Kungsgatan 34, PO Box 1788
111 97 Stockholm, Sweden Ottawa, ON K1Y 4H7 111 97 Stockholm, Sweden
phone: +46 8 441 78 34 Canada phone: +46 8 441 78 34
mobile +46 70 522 78 34 phone: +1 613 763-5827 mobile +46 70 522 78 34
e-mail: loa_andersson@baynetworks.com osama@NortelNetworks.com loa_andersson@baynetworks.com
Ross Callon Peter Ashwood-Smith Ross Callon
IronBridge Networks Nortel Networks IronBridge Networks
55 Hayden Avenue, P O Box 3511 Station C 55 Hayden Avenue,
Lexington, MA 02173 Ottawa, ON K1Y 4H7 Lexington, MA 02173
Phone: +1-781-402-8017 Canada Phone: +1-781-402-8017
Email: rcallon@ironbridgenetworks.com phone: +1 613 763-4534 rcallon@ironbridgenetworks.com
petera@NortelNetworks.com
Ram Dantu Ram Dantu Paul Doolan
Alcatel USA Inc. Alcatel USA Inc. Ennovate Networks
IP Competence Center IP Competence Center 330 Codman Hill Rd
1201 E. Campbell Road.,446-315 1201 E. Campbell Road.,446-315 Marlborough MA 01719
Richadson, TX USA., 75081-2206 Richadson, TX USA., 75081-2206 Phone: 978-263-2002
Phone: 972 996 2938 Phone: 972 996 2938 pdoolan@ennovatenetworks.com
Fax: 972 996 5902 Fax: 972 996 5902
Email: ram.dantu@aud.alcatel.com ram.dantu@aud.alcatel.com
Paul Doolan
Ennovate Networks
330 Codman Hill Rd
Marlborough MA 01719
Phone: 978-263-2002
email: pdoolan@ennovatenetworks.com
Nancy Feldman
IBM Corp.
17 Skyline Drive
Hawthorne NY 10532
Phone: 914-784-3254
email: nkf@us.ibm.com
Andre Fredette
Nortel Networks
3 Federal Street
Billerica, MA 01821
email: fredette@baynetworks.com
Eric Gray
Lucent Technologies, Inc
1600 Osgood St.
North Andover, MA 01847
email: ewgray@lucent.com
CR-LDP Specification - 22 - Exp. Apr 1999
Joel M. Halpern
Newbridge Networks Inc.
593 Herndon Parkway
Herndon, VA 20170
email: jhalpern@newbridge.com
phone: 1-703-736-5954
fax: 1-703-736-5959
Juha Heinanen
Telia Finland, Inc.
Myyrmaentie 2
01600 VANTAA
Finland
Tel: +358 303 944 808
Email: jh@telia.fi
Bilel Jamoussi
Nortel Networks
P O Box 3511 Station C
Ottawa, ON K1Y 4H7
Canada
phone: +1 613 765-4814
email: jamoussi@NortelNetworks.com
Timothy E. Kilty
Northchurch Communications
5 Corporate Drive,
Andover, MA 018110
phone: 978 691-4656
Email: tkilty@northc.com
Andrew G. Malis Nancy Feldman Andre Fredette
Ascend Communications, Inc. IBM Corp. Nortel Networks
1 Robbins Road 17 Skyline Drive 3 Federal Street
Westford, MA 01886 Hawthorne NY 10532 Billerica, MA 01821
phone: 978 952-7414 Phone: 914-784-3254 fredette@baynetworks.com
fax: 978 392-2074 nkf@us.ibm.com
Email: malis@ascend.com
Muckai K Girish Eric Gray Joel M. Halpern
SBC Technology Resources, Inc. Lucent Technologies, Inc Newbridge Networks Inc.
4698 Willow Road 1600 Osgood St. 593 Herndon Parkway
Pleasanton, CA 94588 North Andover, MA 01847 Herndon, VA 20170
Phone: (925) 598-1263 Phone: 603-659-3386 phone: 1-703-736-5954
Fax: (925) 598-1321 ewgray@lucent.com jhalpern@newbridge.com
Email: mgirish@tri.sbc.com
Kenneth Sundell Juha Heinanen Fiffi Hellstrand
Ericsson Telia Finland, Inc. Ericsson Telecom AB
SE-126 25 Stockholm Myyrmaentie 2 S-126 25 STOCKHOLM
Sweden 01600 VANTAA Sweden
Finland Tel: +46 8 719 4933
Tel: +358 41 500 4808 etxfiff@etxb.ericsson.se
jh@telia.fi
CR-LDP Specification - 23 - Exp. Apr 1999 CR-LDP Specification - 29 - Exp. August 1999
email: kenneth.sundell@etx.ericsson.se Bilel Jamoussi Timothy E. Kilty
Nortel Networks Northchurch Communications
P O Box 3511 Station C 5 Corporate Drive,
Ottawa, ON K1Y 4H7 Andover, MA 018110
Canada phone: 978 691-4656
phone: +1 613 765-4814 tkilty@northc.com
jamoussi@NortelNetworks.com
Pasi Vaananen Andrew G. Malis Muckai K Girish
Nokia Telecommunications Ascend Communications, Inc. SBC Technology Resources, Inc.
3 Burlington Woods Drive, Suite 250 1 Robbins Road 4698 Willow Road
Burlington, MA 01803 Westford, MA 01886 Pleasanton, CA 94588
Phone: +1-781-238-4981 phone: 978 952-7414 Phone: (925) 598-1263
Email: pasi.vaananen@ntc.nokia.com fax: 978 392-2074 Fax: (925) 598-1321
malis@ascend.com mgirish@tri.sbc.com
Tom Worster Kenneth Sundell Pasi Vaananen
General DataComm, Inc. Ericsson Nokia Telecommunications
5 Mount Royal Ave. SE-126 25 Stockholm 3 Burlington Woods Drive, Suite 250
Marlboro MA 01752 Sweden Burlington, MA 01803
Email: tom.worster@gdc.com kenneth.sundell@etx.ericsson.se Phone: +1-781-238-4981
pasi.vaananen@ntc.nokia.com
Liwen Wu Tom Worster Liwen Wu
Alcatel U.S.A General DataComm, Inc. Alcatel U.S.A
44983 Knoll Square 5 Mount Royal Ave. 44983 Knoll Square
Ashburn, Va. 20147 Marlboro MA 01752 Ashburn, Va. 20147
USA tom.worster@gdc.com USA
Phone: (703) 724-2619 Phone: (703) 724-2619
FAX: (703) 724-2005 FAX: (703) 724-2005
Inet: liwen.wu@adn.alcatel.com liwen.wu@adn.alcatel.com
CR-LDP Specification - 30 - Exp. August 1999
Appendix A: CRLSP Establishment Examples Appendix A: CRLSP Establishment Examples
A.1 Strict Constraint-Based Route Example A.1 Strict Explicit Route Example
This appendix provides an example for the setup of a strictly routed This appendix provides an example for the setup of a strictly routed
CRLSP. In this example, each abstract node is represented by a CRLSP. In this example, each abstract node is represented by a
specific node. specific node.
The sample network used here is a four node network with two edge The sample network used here is a four node network with two edge
LSRs and two core LSRs as follows: LSRs and two core LSRs as follows:
a b c a b c
LSR1------LSR2------LSR3------LSR4 LSR1------LSR2------LSR3------LSR4
LSR1 generates a Label Request Message as described in Section 3.1 of LSR1 generates a Label Request Message as described in Section 3.1 of
this draft and sends it to LSR2. This message includes the CR-TLV. this draft and sends it to LSR2. This message includes the CR-TLV.
The CR-TLV is composed by a vector of three ER-Hop TLVs <a, b, c>. The ER-TLV is composed by a vector of three ER-Hop TLVs <a, b, c>.
The ER-Hop TLVs used in this example are of type 0x01 (IPv4 prefix) The ER-Hop TLVs used in this example are of type 0x0801 (IPv4 prefix)
with a prefix length of 32. Hence, each ER-Hop TLV identifies a with a prefix length of 32. Hence, each ER-Hop TLV identifies a
specific node as opposed to a group of nodes. specific node as opposed to a group of nodes.
At LSR2, the following processing of the CR-TLV per Section 4.8.1 of At LSR2, the following processing of the ER-TLV per Section 4.8.1 of
this draft takes place: this draft takes place:
1) The first hop <a> is part of the abstract node LSR2. Therefore, 1) The first hop <a> is part of the abstract node LSR2. Therefore,
the first step passes the test. Go to step 2. the first step passes the test. Go to step 2.
CR-LDP Specification - 24 - Exp. Apr 1999
2) There is a second ER-Hop, <b>. Go to step 3. 2) There is a second ER-Hop, <b>. Go to step 3.
3) LSR2 is not part of the abstract node described by the second 3) LSR2 is not part of the abstract node described by the second
ER-Hop <b>. Go to Step 4. ER-Hop <b>. Go to Step 4.
4) LSR2 determines that it is topologically adjacent to the 4) LSR2 determines that it is topologically adjacent to the
abstract node described by the second ER-Hop <b>. LSR2 selects a abstract node described by the second ER-Hop <b>. LSR2 selects a
next hop (LSR3) which is the abstract node. LSR2 deletes the first next hop (LSR3) which is the abstract node. LSR2 deletes the first
ER-Hop <a> from the CR-TLV which now becomes <b , c>. Go to ER-Hop <a> from the ER-TLV which now becomes <b , c>. Go to
Section 4.8.2. Section 4.8.2.
At LSR2, the following processing of Section 4.8.2 takes place: At LSR2, the following processing of Section 4.8.2 takes place:
Executing algorithm 4.8.1 did not result in the removal of the Executing algorithm 4.8.1 did not result in the removal of the
CR-TLV. ER-TLV.
Also, LSR2 is not a member of the abstract node described by the Also, LSR2 is not a member of the abstract node described by the
first ER-Hop <b>. first ER-Hop <b>.
Finally, the first ER-Hop <b> is a strict hop. Finally, the first ER-Hop <b> is a strict hop.
Therefore, processing section 4.8.2 does not result in the Therefore, processing section 4.8.2 does not result in the
insertion of new ER-Hops. The selection of the next hop has been insertion of new ER-Hops. The selection of the next hop has been
CR-LDP Specification - 31 - Exp. August 1999
already done is step 4 of Section 4.8.1 and the processing of the already done is step 4 of Section 4.8.1 and the processing of the
CR-TLV is completed at LSR2. In this case, the Label Request ER-TLV is completed at LSR2. In this case, the Label Request
Message including the CR-TLV <b, c> is progressed by LSR2 to LSR3. Message including the ER-TLV <b, c> is progressed by LSR2 to LSR3.
At LSR3, a similar processing to the CR-TLV takes place except that At LSR3, a similar processing to the ER-TLV takes place except that
the incoming CR-TLV = <b, c> and the outgoing CR-TLV is <c>. the incoming ER-TLV = <b, c> and the outgoing ER-TLV is <c>.
At LSR4, the following processing of section 4.8.1 takes place: At LSR4, the following processing of section 4.8.1 takes place:
1) The first hop <c> is part of the abstract node LSR4. Therefore, 1) The first hop <c> is part of the abstract node LSR4. Therefore,
the first step passes the test. Go to step 2. the first step passes the test. Go to step 2.
2) There is no second ER-Hop, this indicates the end of the CRLSP. 2) There is no second ER-Hop, this indicates the end of the CRLSP.
The CR-TLV is removed from the Label Request Message. Processing The ER-TLV is removed from the Label Request Message. Processing
continues with Section 4.8.2. continues with Section 4.8.2.
At LSR4, the following processing of Section 4.8.2 takes place: At LSR4, the following processing of Section 4.8.2 takes place:
Executing algorithm 4.8.1 resulted in the removal of the CR-TLV. Executing algorithm 4.8.1 resulted in the removal of the ER-TLV.
LSR4 does not add a new CR-TLV. LSR4 does not add a new ER-TLV.
Therefore, processing section 4.8.2 does not result in the Therefore, processing section 4.8.2 does not result in the
insertion of new ER-Hops. This indicates the end of the CRLSP and insertion of new ER-Hops. This indicates the end of the CRLSP and
the processing of the CR-TLV is completed at LSR4. the processing of the ER-TLV is completed at LSR4.
At LSR4, processing of Section 3.2 is invoked. The first condition is At LSR4, processing of Section 3.2 is invoked. The first condition is
satisfied (LSR4 is the egress end of the CRLSP and upstream mapping satisfied (LSR4 is the egress end of the CRLSP and upstream mapping
has been requested). Therefore, a Label Mapping Message is generated has been requested). Therefore, a Label Mapping Message is generated
CR-LDP Specification - 25 - Exp. Apr 1999
by LSR4 and sent to LSR3. by LSR4 and sent to LSR3.
At LSR3, the processing of Section 3.2 is invoked. The second At LSR3, the processing of Section 3.2 is invoked. The second
condition is satisfied (LSR3 received a mapping from its downstream condition is satisfied (LSR3 received a mapping from its downstream
next hop LSR4 for a CRLSP for which an upstream request is still next hop LSR4 for a CRLSP for which an upstream request is still
pending). Therefore, a Label Mapping Message is generated by LSR3 and pending). Therefore, a Label Mapping Message is generated by LSR3 and
sent to LSR2. sent to LSR2.
At LSR2, a similar processing to LSR 3 takes place and a Label At LSR2, a similar processing to LSR 3 takes place and a Label
Mapping Message is sent back to LSR1 which completes the end-to-end Mapping Message is sent back to LSR1 which completes the end-to-end
CRLSP setup. CRLSP setup.
A.2. Node Groups and Specific Nodes Example A.2. Node Groups and Specific Nodes Example
A request at an ingress LSR to setup a CRLSP might originate from a A request at an ingress LSR to setup a CRLSP might originate from a
management system or an application, the details are implementation management system or an application, the details are implementation
specific. specific.
The ingress LSR uses information provided by the management system or The ingress LSR uses information provided by the management system or
the application and possibly also information from the routing the application and possibly also information from the routing
database to calculated the constraint-based route and to create the database to calculated the explicit route and to create the Label
Label Request Message. Request Message.
CR-LDP Specification - 32 - Exp. August 1999
The Label request message carries together with other necessary The Label request message carries together with other necessary
information a CR-TLV defining the constraint-based routed path. In information a ER-TLV defining the explicitly routed path. In our
our example the list of hops in the ER-Hop TLV is supposed to contain example the list of hops in the ER-Hop TLV is supposed to contain an
an abstract node representing a group of nodes, an abstract node abstract node representing a group of nodes, an abstract node
representing a specific node, another abstract node representing a representing a specific node, another abstract node representing a
group of nodes, and an abstract node representing a specific egress group of nodes, and an abstract node representing a specific egress
point. point.
In--{Group 1}--{Specific A}--{Group 2}--{Specific Out: B} In--{Group 1}--{Specific A}--{Group 2}--{Specific Out: B}
The CR-TLV contains four ER-Hop TLVs: The ER-TLV contains four ER-Hop TLVs:
1. An ER-Hop TLV that specifies a group of LSR valid for the first 1. An ER-Hop TLV that specifies a group of LSR valid for the first
abstract node representing a group of nodes (Group 1). abstract node representing a group of nodes (Group 1).
2. An ER-Hop TLV that indicates the specific node (Node A). 2. An ER-Hop TLV that indicates the specific node (Node A).
3. An ER-Hop TLV that specifies a group of LSRs valid for the 3. An ER-Hop TLV that specifies a group of LSRs valid for the
second abstract node representing a group of nodes (Group 2). second abstract node representing a group of nodes (Group 2).
4. An ER-Hop TLV that indicates the specific egress point for the 4. An ER-Hop TLV that indicates the specific egress point for the
CRLSP (Node B). CRLSP (Node B).
All the ER-Hop TLVs are strictly routed nodes. All the ER-Hop TLVs are strictly routed nodes.
The setup procedure for this CRLSP works as follows: The setup procedure for this CRLSP works as follows:
CR-LDP Specification - 26 - Exp. Apr 1999 1. The ingress node sends the Label Request Message to a node that
is a member the group of nodes indicated in the first ER-Hop TLV,
1. The ingress node sends the Label Request to a node that is a
member the group of nodes indicated in the first ER-Hop TLV,
following normal routing for the specific node (A). following normal routing for the specific node (A).
2. The node that receives the message identifies itself as part of 2. The node that receives the message identifies itself as part of
the group indicated in the first ER-Hop TLV, and that it is not the group indicated in the first ER-Hop TLV, and that it is not
the specific node (A) in the second. Further it realizes that the the specific node (A) in the second. Further it realizes that the
specific node (A) is not one of its next hops. specific node (A) is not one of its next hops.
3. It keeps the ER-Hop TLVs intact and sends a Label Request 3. It keeps the ER-Hop TLVs intact and sends a Label Request
Message to a node that is part of the group indicated in the first Message to a node that is part of the group indicated in the first
ER-Hop TLV (Group 1), following normal routing for the specific ER-Hop TLV (Group 1), following normal routing for the specific
skipping to change at page 26, line 32 skipping to change at page 33, line 5
the group indicated in the first ER-Hop TLV, and that it is not the group indicated in the first ER-Hop TLV, and that it is not
the specific node (A) in the second ER-Hop TLV. Further it the specific node (A) in the second ER-Hop TLV. Further it
realizes that the specific node (A) is one of its next hops. realizes that the specific node (A) is one of its next hops.
5. It removes the first ER-Hop TLVs and sends a Label Request 5. It removes the first ER-Hop TLVs and sends a Label Request
Message to the specific node (A). Message to the specific node (A).
6. The specific node (A) recognizes itself in the first ER-Hop 6. The specific node (A) recognizes itself in the first ER-Hop
TLV. Removes the specific ER-Hop TLV. TLV. Removes the specific ER-Hop TLV.
7. It sends a Label Request message to a node that is a member of CR-LDP Specification - 33 - Exp. August 1999
7. It sends a Label Request Message to a node that is a member of
the group (Group 2) indicated in the ER-Hop TLV. the group (Group 2) indicated in the ER-Hop TLV.
8. The node that receives the message identifies itself as part of 8. The node that receives the message identifies itself as part of
the group indicated in the first ER-Hop TLV, further it realizes the group indicated in the first ER-Hop TLV, further it realizes
that the specific egress node (B) is one of its next hops. that the specific egress node (B) is one of its next hops.
9. It sends a Label Request message to the specific egress node 9. It sends a Label Request Message to the specific egress node
(B). (B).
10. The specific egress node (B) recognizes itself as the egress 10. The specific egress node (B) recognizes itself as the egress
for the CRLSP, it returns a Label Mapping Message, that will for the CRLSP, it returns a Label Mapping Message, that will
traverse the same path as the Label Request Message in the traverse the same path as the Label Request Message in the
opposite direction. opposite direction.
CR-LDP Specification - 27 - Exp. Apr 1999 CR-LDP Specification - 34 - Exp. August 1999
Appendix B. CR-LDP Finite State Machine
In this description of the CR-LDP FSM, behavior relating to the
state of LDP messages is assumed to be defined (implicitly or
explicitly) in [LDP]. In particular, LDP is assumed to retain
state information relating a Label Request made of a downstream
neighbor to the Label Request message(s) of upstream neighbors
(downstream-on-demand mode) which the (downstream) Label Request
is meant to satisfy. This will be true of many potential
applications of LDP, of which CR-LDP is an example. Minimally,
this state should include message IDs of Label Requests (both sent
and received) and the LSR(s) from which pending Label Request(s)
were received.
The FSM describes CR-LDP behavior in the following operations:
- Start of CRLSP setup (in which a Label Request is sent);
- Processing the CR-TLV portion of Label Requests;
- Completion of CRLSP setup (via Label Mapping messages);
- Notification of originator when:
- a loop is detected in a loose constraint-based route segment,
- an ER-Hop is not reachable from a previous ER-Hop,
- a next ER-Hop is strict and not directly connected to the
current LSR or
- the current LSR is strict and is not (part of the abstract
node in) the first ER-Hop in the CR-TLV;
- Withdrawing a CRLSP.
For the description, the following pictorial representations may be
used as an aid to understanding:
LSR 1 LSR 2 ... LSR n
.-----. .-----. .-----.
| ER | | ER | | ER |
`-----' `-----' `-----'
| CR-TLV CR-TLV ^ | CR-TLV CR-TLV ^
| Next | | Next |
| Hop | | Hop |
V | V |
.-----. Label .-----. Label Label .-----.
| LDP |----------->| LDP |-------> ... ------->| LDP |
`-----' Request `-----' Request Request `-----'
CR-LDP Specification - 28 - Exp. Apr 1999
CRLSP Setup propagation
LSR 1 LSR 2 ... LSR n
.-----. .-----. .-----.
| ER | | ER | | ER |
`-----' `-----' `-----'
^ Status Status |
| Previous |
| Hop |
| V
.-----. Label .-----. Label Label .-----.
| LDP |<-----------| LDP |<------- ... <-------| LDP |
`-----' Mapping `-----' Mapping Mapping `-----'
CRLSP Status propagation
.---------------.
| ER | .---------------.
| Link/Call | | LDP |
| Admission | | |
| Control | | Label |
`---------------' | Allocation |
`---------------'
Related Tasks
B.1. CR-LDP Primitives
The following sections describe the logical interactions between
Constrain-based Route and LDP state machines in terms of
primitives that describe the minimal information exchange
required. These assume an asynchronous exchange model involving
locally significant IDs that is used to tie status of a request to
the initial setup and to allow LDP to relate incoming/outgoing
Label Request messages. A synchronous model - possibly based on
multiple threads - is also possible and would eliminate the need
for IDs.
B.1.1. CR to LDP Primitives
LDP_SEND_REQ( TLV_List, To_LSR, Identifier )
TLV_List
TLVs to be sent to a neighboring LSR; includes at least an
CR-LDP Specification - 29 - Exp. Apr 1999
CR-TLV and may contain additional TLVs (i.e. QoS TLVs).
To_LSR
The neighbor LSR to which a Label Request is to be sent.
Identifier
Locally significant unique identifier. May be used to
associate the Label Request to be sent either with a Label
Request that was previously received (e.g. - LSR 2 above)
or a subsequent CRLSP Status (e.g. - LSR 1 above).
LDP_SEND_RSP( Status, Identifier )
Status Appendix B. QoS Service Examples
Status of a specific CRLSP Setup Request. A Status of zero B.1 Service Examples
indicates success; other Status values are given in Error
Subcodes section. This Status is carried in Label Mapping or
Notification messages to the originator of the CRLSP setup.
Identifier Construction of an end-to-end service is the result of the rules
enforced at the edge and the treatment that packets receive at the
network nodes. The rules define the traffic conditioning actions that
are implemented at the edge and they include policing with pass,
mark, and drop capabilities. The edge rules are expected to be
defined by the mutual agreements between the service providers and
their customers and they will constitute an essential part of the
SLA. Therefore edge rules are not included in the signaling protocol.
Locally significant unique identifier used to associate the Packets treatment at a network node is usually referred to as the
Label Mapping to be sent with a Label Request received (e.g. local behavior. Local behavior could be specified in many ways. One
LSR n above). example for local behavior specification is the service frequency
introduced in section 4.3.2.1., together with the resource
reservation rules implemented at the nodes.
B.1.2. LDP to CR Primitives Edge rules and local behaviors can be viewed as the main building
blocks for the end-to-end service construction. The following table
illustrates the applicability of the building block approach for
constructing different services including those defined for ATM.
CR_RECEIVED_REQ( TLV_List, Identifier ) Service PDR PBS CDR CBS EBS Service Conditioning
Examples Frequency Action
---------------------------------------------------------------------------
TLV_List DS S S =PDR =PBS 0 Frequent drop>PDR
TLVs to be processed by the local constraint-based route TS S S S S 0 Unspecified drop>PDR,PBS
function. mark>CDR,CBS
Identifier BE inf inf inf inf 0 Unspecified -
Locally significant unique identifier used to associate the FRS S S CIR ~B_C ~B_E Unspecified drop>PDR,PBS
received request either with a subsequent further request mark>CDR,CBS,EBS
or a response. For example, the identifier provided here
would be used in a subsequent LDP_SEND_REQ or LDP_SEND_RSP.
CR_LSP_STATUS( Status, Identifier ) ATM-CBR PCR CDVT =PCR =CDVT 0 VeryFrequent drop>PCR
Status ATM-VBR.3(rt) PCR CDVT SCR MBS 0 Frequent drop>PCR
mark>SCR,MBS
Status of a specific CRLSP Setup Request. A Status of zero ATM-VBR.3(nrt) PCR CDVT SCR MBS 0 Unspecified drop>PCR
indicates success; other Status values are given in section mark>SCR,MBS
Error Subcodes. This Status originated at the remote LSR
CR-LDP Specification - 30 - Exp. Apr 1999 ATM-UBR PCR CDVT - - 0 Unspecified drop>PCR
which either completed the CRLSP setup or determined that ATM-GFR.1 PCR CDVT MCR MBS 0 Unspecified drop>PCR
CRLSP setup could not be done.
Identifier CR-LDP Specification - 35 - Exp. August 1999
Locally significant unique identifier used to associate the ATM-GFR.2 PCR CDVT MCR MBS 0 Unspecified drop>PCR
received response with the original request. For example, mark>MCR,MFS
this identifier would be the same as was used in the initial
LDP_SEND_REQ.
B.2. CR-LDP States int-serv-CL p m r b 0 Frequent drop>p
drop>r,b
This document defines 3 states relative to any one specific CRLSP. S= User specified
They are:
CR_Non_Existant - no state information exists relative to this In the above table, the DS refers to a delay sensitive service where
CRLSP; the network commits to deliver with high probability user datagrams
at a rate of PDR with minimum delay and delay requirements. Datagrams
in excess of PDR will be discarded.
CR_In_Progress - LDP_SEND_REQ has been called in result The TS refers to a generic throughput sensitive service where the
of external input (e.g. - management); network commit to deliver with high probability user datagrams at a
rate of at least CDR. The user may transmit at a rate higher than CDR
but datagrams in excess of CDR would have a lower probability of
being delivered.
CR_Established - a successful status has been received from The BE is the best effort service and it implies that there are no
an earlier setup. expected service guarantees from the network.
These states are defined such that no additional state is required B.2. Establishing CR-LSP Supporting Real-Time Applications
to support CRLSPs using LDP at intermediate LSRs than is already
required in LDP.
B.3. CR-LDP Events In this scenario the customer needs to establish an LSP for
supporting real-time applications such voice and video. The Delay-
sensitive (DS) service is requested in this case.
This document defines 4 events impacting any one specific CRLSP. The first step is the specification of the traffic parameters in the
They are: signaling message. The two parameters of interest to the DS service
are the PDR and the PBS and their values are specified by the user
based on his requirements. Since all the traffic parameters are
included in the signaling message, appropriate values must be
assigned to all of them. For DS service, the CDR and the CBS values
are set equal to the PDR and the PBS respectively. An indication of
whether the parameter values are subject to negotiation is flagged.
CR_Start - a CRLSP is required based on an external stimulus The transport characteristics of the DS service requires that
(e.g. - management); Frequent frequency to be requested to reflect the real-time delay
requirements of the service.
CR_Req_Received - further CRLSP setup processing is required In addition to the transport characteristics, both the network
based on CR_RECEIVED_REQ (i.e. - from an upstream LSR's CRLSP provider and the customer need to agree on the actions enforced at
Label Request); the edge. The specification of those actions is expected to be a part
of the service level agreement (SLA) negotiation and is not included
in the signaling protocol. For DS service, the edge action is to drop
packets that exceed the PDR and the PBS specifications.
CR_Setup_Complete - CRLSP setup has been successfully completed The signaling message will be sent in the direction of the ER path
based on CR_LSP_STATUS (with success status); and the LSP is established following the normal LDP procedures. Each
CR_LSP_Failure - Either a CRLSP could not be established as CR-LDP Specification - 36 - Exp. August 1999
requested, or a setup CRLSP has dropped; based on CR_LSP_STATUS
(with error status).
B.4. CR-LDP Transitions LSR applies its admission control rules. If sufficient resources are
not available and the parameter values are subject to negotiation,
then the LSR could negotiate down either the PDR, the PBS, or both.
The new parameters values are echoed back in the Label Mapping
Message. LSRs might need to re-adjust their resource reservations
based on the new traffic parameter values.
State transitions are defined as follows: B.3. Establishing CR-LSP Supporting Delay Insensitive Applications
CR-LDP Specification - 31 - Exp. Apr 1999 In this example we assume that a throughput sensitive (TS) service is
requested. For resource allocation the user assigns values for PDR,
PBS, CDR, and CBS. The negotiation flag is set if the traffic
parameters are subject to negotiation.
State Event Action New State Since the service is delay insensitive by definition, the Unspecified
==================== ================= ====== =============== frequency is signaled to indicate that the service frequency is not
CR_Non_Existant CR_Start 1 CR_In_Progress an issue.
CR_Non_Existant CR_Req_Rec 2 CR_Non_Existant
CR_In_Progress CR_Setup_Complete CR_Established
CR_In_Progress CR_LSP_Failure 3 CR_Non_Existant
CR_Established CR_LSP_Failure 3 CR_Non_Existant
Actions: Similar to the previous example, the edge actions are not subject for
signaling and are specified in the service level agreement between
the user and the network provider.
1) Establish CRLSP state, create CR-TLV information, For TS service, the edge rules might include marking to indicate high
LDP_SEND_REQ. discard precedence values for all packets that exceed CDR and the
2) Process CR-TLV (as described in "Processing of CBS. The edge rules will also include dropping of packets that are do
the Constraint-Based Route TLV" section) and either not conform to either PDR and PBS.
LDP_SEND_REQ or LDP_SEND_RSP.
3) Remove state information relative to this CRLSP (may notify
management, other external source initially requiring
setup).
For the purposes of this transition table, illegal transitions Each LSR of the LSP is expected to run its admission control rules
(not included in the table) are ignored. and negotiate traffic parameters down if sufficient resources do not
exist. The new parameters values are echoed back in the Label Mapping
Message. LSRs might need to re-adjust their resources based on the
new traffic parameter values.
 End of changes. 

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