PCE Working Group D. Dhody
Internet-Draft Q. Wu
Intended status: Standards Track Huawei Technologies
Expires: January 22, 2015 July 21, 2014

Path Computation Element communication Protocol extension for relationship between LSPs and Attributes


The Path Computation Element (PCE) provides functions of path computation in support of traffic engineering in networks controlled by Multi-Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS).

This document defines a mechanism to create associations between a set of LSPs and a set of attributes (such as configuration parameters, policy or behaviors).

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Table of Contents

1. Introduction

[RFC5440] describes the Path Computation Element communication Protocol (PCEP) which enables the communication between a Path Computation Client (PCC) and a Path Control Element (PCE), or between two PCEs based on the PCE architecture [RFC4655].

[I-D.minei-pce-association-group] introduces a generic mechanism to create a grouping of LSPs which can then be used to define associations between a set of LSPs and a set of attributes (such as configuration parameters or behaviors).

This document specifies a PCEP extension to associate one or more LSPs with a set of attributes, which includes, but not limited to -

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

2. Terminology

The following terminology is used in this document.

Association Group ID.
Label Switch Router.
Multiprotocol Label Switching.
Path Computation Client. Any client application requesting a path computation to be performed by a Path Computation Element.
Path Computation Element. An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints.
Path Computation Element Communication Protocol.

3. Motivation

This section discusses in more detail the motivation and use cases for such an association including but not limited to -

3.1. Opaque Identifier

An opaque identifier may represent attributes such as configured parameters or constraints that a PCEP speaker may invoke on a peer. Thus a PCEP speaker may only need an opaque identifier to invoke these attributes (parameters or constraints).

3.2. Policy based Constraints

In the context of policy-enabled path computation [RFC5394], path computation policies may be applied at both a PCC and a PCE. Consider an Label Switch Router (LSR) with a policy enabled PCC, it receives a service request via signaling, including over a Network-Network Interface (NNI) or User Network Interface (UNI) reference point, or receives a configuration request over a management interface to establish a service. The PCC may also apply user- or service-specific policies to decide how the path selection process should be constrained, that is, which constraints, diversities, optimization criterion, and constraint relaxation strategies should be applied in order for the service LSP(s) to have a likelihood to be successfully established and provide necessary QoS and resilience against network failures. The user- or service-specific policies applied to PCC and are then passed to the PCE along with the Path computation request, in the form of constraints [RFC5394].

PCEP speaker can use the generic mechanism as per [I-D.minei-pce-association-group] to associate a set of LSPs with policy and its resulting path computation constraints. This way simplifying the path computation message exchanges.

3.3. Bundled requests

In some scenarios(e.g.,the topology example described in Section 4.6 of [RFC6805]), there is a need to send multiple requests with the same constraints and attributes to the PCE. Currently these requests are either sent in a separate path computation request (PCReq) messages or bundled together in one (or more) PCReq messages. In either case, the constraints and attributes need to be encoded separately for each request even though they are exactly identical.

If a association is used to identify these constraints and attributes shared by multiple requests, thus simplifying the path computation message exchanges.

4. Overview

As per [I-D.minei-pce-association-group], LSPs are associated with other LSPs with which they interact by adding them to a common association group. This document uses the same association for attributes, called Attribute Association Group (AAG) based on the generic Association object. This document defines a new association type called "Attribute Association Type" of value TBD. An AAG can have one or more LSPs and its associated attributes. The scope and handling of AAG identifier is similar to the generic association identifier defined in [I-D.minei-pce-association-group].

One or more LSP are grouped via a common group identifier in the same way as [I-D.minei-pce-association-group]. The attributes that may be associated with this set of LSPs may either are -

Error handling would be taken up in future revision.

5. Attribute Association Group

The format of the Association object used for AAG is shown in Figure 1:

 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
|Type   |  Generic flags    |R| Type-specific flags             |
|             Association group id                              |
//            Optional TLVs                                    //

Figure 1: The Association Object format

Type - TBD for the Attribute Association Type.

This document does not have any new type-specific flags.

AAG may carry optional TLVs including but not limited to -


The ATTRIBUTE-OBJECT-TLV maybe included in AAG object to associate attributes encoded in PCEP objects.

The format of the ATTRIBUTE-OBJECT-TLV is shown in the following figure:

 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
|           Type=[TBD]          |           Length              |
| Object-Class  |   OT  |Res|P|I|   Object Length (bytes)       |
| Object-Class  |   OT  |Res|P|I|   Object Length (bytes)       |
~                              ...                              ~
| Object-Class  |   OT  |Res|P|I|   Object Length (bytes)       |


The type of the TLV is [TBD] and it has a variable length. The value part consist of the PCEP object header [RFC5440] identifying the objects that are associated with this AAG. Thus this TLV identify the attributes present in the PCEP message that are associated with this group. Future PCEP messages may only carry the AAG.

6. Security Considerations


7. IANA Considerations


8. Acknowledgments

A special thanks to author of [I-D.minei-pce-association-group], this document borrow some of the text from it.

9. References

9.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4655] Farrel, A., Vasseur, J. and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009.
[I-D.minei-pce-association-group] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H., Zhang, X. and Y. Tanaka, "PCEP Extensions for establishing relationships between sets of LSPs", Internet-Draft draft-minei-pce-association-group-00, June 2014.

9.2. Informative References

[RFC5394] Bryskin, I., Papadimitriou, D., Berger, L. and J. Ash, "Policy-Enabled Path Computation Framework", RFC 5394, December 2008.
[RFC6805] King, D. and A. Farrel, "The Application of the Path Computation Element Architecture to the Determination of a Sequence of Domains in MPLS and GMPLS", RFC 6805, November 2012.
[RFC7150] Zhang, F. and A. Farrel, "Conveying Vendor-Specific Constraints in the Path Computation Element Communication Protocol", RFC 7150, March 2014.

Appendix A. Contributor Addresses

Xian Zhang
Huawei Technologies
Bantian, Longgang District
Shenzhen  518129

EMail: zhang.xian@huawei.com
Udayasree Palle
Huawei Technologies
Leela Palace
Bangalore, Karnataka  560008

EMail: udayasree.palle@huawei.com


Authors' Addresses

Dhruv Dhody Huawei Technologies Leela Palace Bangalore, Karnataka 560008 INDIA EMail: dhruv.ietf@gmail.com
Qin Wu Huawei Technologies 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China EMail: sunseawq@huawei.com