Encoding of Objective Functions in the Path Computation Element Communication Protocol (PCEP)
RFC 5541

Network Working Group                                        JL. Le Roux
Request for Comments: 5541                                France Telecom
Category: Standards Track                                    JP. Vasseur
                                                       Cisco System Inc.
                                                                  Y. Lee
                                                                  Huawei
                                                               June 2009

                Encoding of Objective Functions in the
         Path Computation Element Communication Protocol (PCEP)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

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Le Roux, et al.             Standards Track                     [Page 1]
RFC 5541              Objective Functions in PCEP              June 2009

Abstract

   The computation of one or a set of Traffic Engineering Label Switched
   Paths (TE LSPs) in MultiProtocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) networks is subject to a set of one or more
   specific optimization criteria, referred to as objective functions
   (e.g., minimum cost path, widest path, etc.).

   In the Path Computation Element (PCE) architecture, a Path
   Computation Client (PCC) may want a path to be computed for one or
   more TE LSPs according to a specific objective function.  Thus, the
   PCC needs to instruct the PCE to use the correct objective function.
   Furthermore, it is possible that not all PCEs support the same set of
   objective functions; therefore, it is useful for the PCC to be able
   to automatically discover the set of objective functions supported by
   each PCE.

   This document defines extensions to the PCE communication Protocol
   (PCEP) to allow a PCE to indicate the set of objective functions it
   supports.  Extensions are also defined so that a PCC can indicate in
   a path computation request the required objective function, and a PCE
   can report in a path computation reply the objective function that
   was used for path computation.

   This document defines objective function code types for six objective
   functions previously listed in the PCE requirements work, and
   provides the definition of four new metric types that apply to a set
   of synchronized requests.

Le Roux, et al.             Standards Track                     [Page 2]
RFC 5541              Objective Functions in PCEP              June 2009

Table of Contents

   1. Introduction ....................................................3
      1.1. Conventions Used in This Document ..........................5
      1.2. Terminology ................................................5
      1.3. Message Formats ............................................6
   2. Discovery of PCE Objective Functions ............................6
      2.1. OF-List TLV ................................................6
      2.2. Elements of Procedure ......................................7
   3. Objective Function in PCEP Path Computation Request and Reply
      Messages ........................................................7
      3.1. OF Object ..................................................7
           3.1.1. Elements of Procedure ...............................8
      3.2. Carrying The OF Object In a PCEP Message ...................9