Applicability Statement for CR-LDP
RFC 3213

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Network Working Group                                             J. Ash
Request for Comments: 3213                                          AT&T
Category: Informational                                        M. Girish
                                                           Atoga Systems
                                                                 E. Gray
                                                               Sandburst
                                                             B. Jamoussi
                                                               G. Wright
                                                   Nortel Networks Corp.
                                                            January 2002

                   Applicability Statement for CR-LDP

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document discusses the applicability of Constraint-Based LSP
   Setup using LDP.  It discusses possible network applications,
   extensions to Label Distribution Protocol (LDP) required to implement
   constraint-based routing, guidelines for deployment and known
   limitations of the protocol.  This document is a prerequisite to
   advancing CR-LDP on the standards track.

1. Introduction

   As the Internet evolves, additional capabilities are required to
   ensure proper treatment of data [3], voice, video and other delay
   sensitive traffic [4].  MPLS enhances source routing and allows for
   certain techniques, used in circuit switching, in IP networks.  This
   permits a scalable approach to handling these diverse transmission
   requirements.  CR-LDP [1] is a simple, scalable, open, non-
   proprietary, traffic engineering signaling protocol for MPLS IP
   networks.

   CR-LDP provides mechanisms for establishing explicitly routed Label
   Switched Paths (LSPs).  These mechanisms are defined as extensions to
   LDP [2].  Because LDP is a peer-to-peer protocol based on the

Ash, et al                   Informational                      [Page 1]
RFC 3213           Applicability Statement for CR-LDP       January 2002

   establishment and maintenance of TCP sessions, the following natural
   benefits exist:

      CR-LDP messages are reliably delivered by the underlying TCP, and
      State information associated with explicitly routed LSPs does not
      require periodic refresh.

      CR-LDP messages are flow controlled (throttled) through TCP.

   CR-LDP is defined for the specific purpose of establishing and
   maintaining explicitly routed LSPs.  Additional optional capabilities
   included have minimal impact on system performance and requirements
   when not in use for a specific explicitly routed LSP.  Optional
   capabilities provide for negotiation of LSP services and traffic
   management parameters over and above best-effort packet delivery
   including bandwidth allocation, setup and holding priorities.  CR-LDP
   optionally allows these parameters to be dynamically modified without
   disruption of the operational (in-service) LSP [4].

   CR-LDP allows the specification of a set of parameters to be signaled
   along with the LSP setup request.  Moreover, the network can be
   provisioned with a set of edge traffic conditioning functions (which
   could include marking, metering, policing and shaping).  This set of
   parameters along with the specification of edge conditioning
   functions can be shown to be adequate and powerful enough to
   describe, characterize and parameterize a wide variety of QoS
   scenarios and services including IP differentiated services [5],
   integrated services [6], ATM service classes [7], and frame relay
   [8].

   CR-LDP is designed to adequately support the various media types that
   MPLS was designed to support (ATM, FR, Ethernet, PPP, etc.).  Hence,
   it will work equally well for Multi-service switched networks, router
   networks, or hybrid networks.

   This applicability statement does not preclude the use of other
   signaling and label distribution protocols for the traffic
   engineering application in MPLS based networks.  Service providers
   are free to deploy whatever signaling protocol meets their needs.

   In particular CR-LDP and RSVP-TE [9] are two signaling protocols that
   perform similar functions in MPLS networks.  There is currently no
   consensus on which protocol is technically superior.  Therefore,
   network administrators should make a choice between the two based
   upon their needs and particular situation.  Applicability of RSVP-TE
   is described in [10].

Ash, et al                   Informational                      [Page 2]
RFC 3213           Applicability Statement for CR-LDP       January 2002

2. Applicability of extensions to LDP