Network Working Group J. Ash
Request for Comments: 3213 AT&T
Category: Informational M. Girish
Nortel Networks Corp.
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 (C) The Internet Society (2002). All Rights Reserved.
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.
As the Internet evolves, additional capabilities are required to
ensure proper treatment of data , voice, video and other delay
sensitive traffic . 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  is a simple, scalable, open, non-
proprietary, traffic engineering signaling protocol for MPLS IP
CR-LDP provides mechanisms for establishing explicitly routed Label
Switched Paths (LSPs). These mechanisms are defined as extensions to
LDP . 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
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 .
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 ,
integrated services , ATM service classes , and frame relay
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  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 .
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