Network Working Group                                  S. Sivabalan, Ed.
Internet Draft                                                 J. Parker
Intended status: Standards Track                              S. Boutros
Expires: May 2, 2009                                 Cisco Systems, Inc.

                                                               K. Kumaki
                                                        KDDI Corporation

                                                        November 3, 2008

                   Diff-Serv Aware Class Type Object for
              Path Computation Element Communication Protocol

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

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   This document specifies a CLASSTYPE object to support Diff-Serve
   Aware Traffic Engineering (DS-TE) where path computation is performed
   with an aid of Path Computation Element (PCE).

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 Error!
   Reference source not found..

Table of Contents

   1. Introduction...................................................2
   2. Terminology....................................................3
   3. CLASSTYPE Object...............................................4
      3.1. Object Definition.........................................4
      3.2. Path Computation Request message with CLASSTYPE Object....4
      3.3. Processing CLASSTYPE Object...............................5
      3.4. Determination of Traffic Engineering Class (TE-Class).....6
      3.5. Significance of Class-Type and TE-Class...................6
      3.6. Error Codes for CLASSTYPE Object..........................6
   4. Security Considerations........................................7
   5. IANA Considerations............................................7
   6. Acknowledgments................................................7
      6.1. Normative References......................................8
      6.2. Informative References....................................8
   Author's Addresses................................................8
   Intellectual Property Statement...................................9
   Disclaimer of Validity............................................9

1. Introduction

   The Internet Draft [PCEP-ID] specifies the Path Computation Element
   communication Protocol (PCEP) for communications between a Path
   Computation Client (PCC) and a Path Computation Element (PCE), or
   between two PCEs, in compliance with [RFC4657].

   Differentiated Service aware MPLS Traffic Engineering (DS-TE)
   addresses the fundamental requirement to be able to enforce different
   bandwidth constraints for different classes of traffic. It describes
   mechanisms to achieve per-class traffic engineering, rather than on
   an aggregate basis across all classes by enforcing Bandwidth
   Constraints (BCs) on different classes. Requirements for DS-TE and

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   the associated protocol extensions are specified in [RFC3564] and
   [RFC4124] respectively.

   As per [RFC4657], PCEP must support traffic class-type as an MPLS TE
   specific constraint. However, in the present form, PCEP [PCEP-ID]
   does not have the capability to specify the class-type in the path
   computation request.

   In this document, we define a new PCEP object called CLASSTYPE which
   carries the class-type of the TE LSP in the path computation request.
   During path computation, a PCE uses the class-type to identify the
   bandwidth constraint of the TE-LSP.

2. Terminology

   CT: Class type: A set of Traffic Trunks governed by a set of
   bandwidth constraints. Used for the purpose of link bandwidth
   allocation, constraint based routing and admission control. A given
   Traffic Trunk belongs to the same CT on all links.

   DS-TE: Diff-Serv Aware Traffic Engineering.

   LSR: Label Switching Router.

   LSP: Label Switched Path.

   PCC: Path Computation Client: any client application requesting a
   path computation to be performed by a Path Computation Element.

   PCE: 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.

   PCEP Peer: an element involved in a PCEP session (i.e. a PCC or the

   TE-Class: A pair consisting of a class-type and a preemption priority
   allowed for that class type. An LSP transporting a Traffic Trunk from
   that class type can use that preemption priority as the setup
   priority, the holding priority, or both.

   TE LSP: Traffic Engineering Label Switched Path.

   Traffic Trunk: An aggregation of traffic flows of the same class
   (i.e. treated equivalently from the DS-TE perspective) which is
   placed inside a TE LSP.

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   The CLASSTYPE object is optional and is used to specify the class-
   type of a TE LSP. This object is meaningful only within the path
   computation request, and is ignored in the path reply message. If the
   TE LSP for which the path is to be computed belongs to Class 0, the
   path computation request MUST NOT contain the CLASSTYPE object. This
   allows backward compatibility with PCE that does not support the
   CLASSTYPE object.

3.1. Object Definition

   The CLASSTYPE object contains a 32-bit word PCEP common object header
   defined in [PCEP-ID] followed by another 32-bit word object body as
   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
  |                       PCEP common header                      |
  |            Reserved                                     | CT  |

                   Figure 1 CLASSTYPE object format.

   The fields in the object common header are processed as specified in
   [PCEP-ID]. The values of object class and object type are 22 and 1
   respectively. If included, CLASSTYPE object must be taken into
   account by PCE. As such, the P flag MUST be set. I flag is ignored.

   The CLASSTYPE object body contains the following fields:

   CT: 3-bit field that indicates the class-type. Values allowed are 1,
   2, ... , 7. Value of 0 is Reserved.

   Reserved: 29-bit reserved field. It MUST be set to zero on
   transmission and MUST be ignored on receipt.

3.2. Path Computation Request message with CLASSTYPE Object

   [PCEP-ID] specifies the object orders in which objects must be
   inserted in the PCEP messages. This document specifies that the
   CLASSTYPE object be inserted after the END-POINT objects as shown

   The format of a PCReq message is as follows:

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      <PCReq Message>::= <Common Header>
         <request>::= <RP>

   Note that an implementation MUST form the PCEP messages using the
   object ordering rules specified using Backus-Naur Form. Please refer
   [OBJ-ORD] for more details.

3.3. Processing CLASSTYPE Object

   If the LSP is associated with Class-Type N (1 <= N <= 7), the PCC
   originating the path computation request MUST include the CLASSTYPE
   object in the Path computation request message with the Class-Type
   (CT) field set to N.

   If a path computation request contains multiple CLASSTYPE objects,
   only the first one is meaningful; subsequent CLASSTYPE object(s) MUST
   be ignored and MUST NOT be forwarded.

   If the CLASSTYPE object is not present in the path computation
   request message, the LSR MUST associate the Class-Type 0 to the LSP.

   Path computation reply message MUST NOT include a CLASSTYPE object.
   If a PCE needs to forward a path computation request containing the
   CLASSTYPE object to another PCE, it MUST store the class-type of the
   TE LSP in order to complete the path computation when the path
   computation reply arrives.

   A PCE that does not recognize the CLASSTYPE object MUST reject the
   entire PCEP message and MUST send a PCE error message with Error-
   Type="Unknown Object" or "Not supported Object" defined in [PCEP-ID].

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   A PCE that recognizes the CLASSTYPE object finds that P flag is not
   set in the CLASSTYPE object, it MUST send PCE error message towards
   the sender with the with the error type and error value specified in

   A PCE that recognizes the CLASSTYPE object, but does not support the
   particular Class-Type, MUST send a PCE error message towards the
   sender with the error type  "Diff-Serv aware TE Error" and the error
   value of "Unsupported Class-Type" (new error code provided below).

   A PCE that recognizes the CLASSTYPE object, but determines that the
   Class-Type value is not valid (i.e., Class Type value 0), MUST send a
   PCE error towards the sender with the error type "Diff-Serve aware TE
   Error" and an error value of "Invalid Class-Type value" (new error
   code provided below).

3.4. Determination of Traffic Engineering Class (TE-Class)

   As specified in RFC4124, a CT and a Preemption priority map to a
   Traffic Engineering Class (TE-Class), and there can be up to 8 TE-
   classes. The TE-class value is used to determine the unreserved
   bandwidth on the links during path computation. In the case of a PCE,
   the CT value carried in the CLASSTYPE object and the setup priority
   in the LSP Attribute (LSPA) object are used to determine the TE-class
   corresponding to the path computation request. If LSPA object is
   absent, the setup priority is assumed to be 0.

3.5. Significance of Class-Type and TE-Class

   To ensure coherent DS-TE operation, a PCE and a PCC should have a
   common understanding of a particular DS-TE classtype and TE-Class.
   If a path computation request crosses an AS boundary, these should
   have global significance in all domains.  Enforcement of this global
   significance is outside the scope of this document.

3.6. Error Codes for CLASSTYPE Object

   This document defines the following error type and values:

   Error-Type    Meaning

      12         Diff-Serve aware TE Error
                 Error-value=1: unsupported class-type.
                 Error-value=2: invalid class-type.
                 Error-value=3: class-type and setup priority does not
                 form a configured TE class.

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4. Security Considerations

   This document does not introduce new security issues.  The security
   considerations pertaining to PCEP [PCEP-ID] remain relevant.

5. IANA Considerations

   IANA maintains a registry of parameters for PCEP. This contains a
   sub-registry for PCEP objects. IANA is requested to make new
   allocation from this registry as follows:

   Object-Class     Name                  Reference

       22           CLASSTYPE             draft-ietf-pce-dste-02.txt


                      1: Class Type       draft-ietf-pce-dste-02.txt

   IANA is requested to make new allocation for error types and values
   as follows:

   Error-Type  Meaning                    Reference

       12      Diff-Serv aware TE error   draft-ietf-pce-dste-02.txt

               Error-value = 1:           draft-ietf-pce-dste-02.txt

                 Unsupported class-type

               Error-value = 2:           draft-ietf-pce-dste-02.txt

                 Invalid class-type

               Error-value = 3:           draft-ietf-pce-dste-02.txt

                 Class type and setup priority

                 does not form a configured TE class

6. Acknowledgments

   The authors would like to thank Jean Philippe Vasseur, Adrian
   Farrel and Zafar Ali for their valuable comments.


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6.1. Normative References

   [RFC4124] Le Faucheur, F. and W. Lai, "Protocol Extensions for
             Support of Diffserv-aware MPLS Traffic Engineering", RFC
             4124, June 2005.

   [PCEP-ID] Path Computation Element (PCE) communication  Protocol
             (PCEP)", draft-ietf-pce-pcep-18.txt (work in progress),
             November 2008.

6.2. Informative References

   [RFC4657] Ash, J. and J. Le Roux, "Path Computation Element   (PCE)
             Communication Protocol Generic Requirements", RFC 4657,
             September 2006.

   [RFC3564] Le Faucheur, F. and W. Lai, "Requirements for Support of
             Differentiated Services-aware MPLS Traffic Engineering",
             RFC 3564, July 2003.

   [OBJ-ORD] Farrel, A., "Reduced Backus-Naur Form (RBNF) A Syntax Used
             in Various Protocol Specifications", draft-farrel-rtg-
             common-bnf-07.txt, November 2008.

Author's Addresses

   Siva Sivabalan
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario, K2K 3E8


   Jon Parker
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario, K2K 3E8


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   Sami Boutros
   Cisco Systems, Inc.
   3750 Cisco Way
   San Jose, California 95134


   Kenji Kumaki
   KDDI Corporation
   Garden Air Tower Iidabashi, Chiyoda-ku
   Tokyo, 102-8460

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   This document and the information contained herein are provided on an

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