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Versions: 00                                                            
MPLS WG                                                        Jerry Ash
Internet Draft                                                      AT&T
Expiration Date: February 2000                             Muckai Girish
                                           SBC Technology Resources Inc.
                                                               Eric Gray
                                                     Lucent Technologies
                                                          Bilel Jamoussi
                                                          Gregory Wright
                                                   Nortel Networks Corp.

                                                             August 1999

                   Applicability Statement for CR-LDP


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at


   This Internet-Draft discusses the applicability of Constraint-Based
   LSP Setup using LDP [1]. It discusses possible network applications,
   extensions to Label Distribution Protocol (LDP) [2] 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.

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Internet Draft    Applicability Statement for CR-LDP      August, 1999

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 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 [1].  Because LDP is a peer-to-peer protocol based on the
   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

   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, a router networks, or hybrid networks.

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Internet Draft    Applicability Statement for CR-LDP      August, 1999

2. Applicability of extensions to LDP

   To provide for support of additional LSP services, CR-LDP extensions
   are defined in such a way as to be directly translatable to objects
   and messages used in other protocols defined to provide similar
   services [9]. Implementations can take advantage of this fact to:

   Setup LSPs for provision of an aggregate service associated with the
   services being provided via these other protocols;

   Directly translate protocol messages to provide services defined in
   a non-CR-LDP portion of the network.

   Describe, characterize and parameterize a wide variety of QoS
   scenarios and services including IP differentiated services,
   integrated services, ATM service classes, and frame relay.

   Steady state information required for proper maintenance of an LSP
   may be as little as 200 bytes or less.  It is not unreasonable to
   anticipate that CR-LDP implementations may support in excess of one
   hundred thousand or one million LSPs switched through a single Label
   Switching Router (LSR) under fairly stable conditions.

   Because CR-LDP provides for low overhead per LSP - both in terms of
   needed state information and control traffic - CR-LDP is applicable
   in those portions of the Internet where very large numbers of LSPs
   may need to be switched at each LSR.  An example of this would be
   large backbone networks using MPLS exclusively to transport very
   large numbers of traffic streams between a moderately large number
   of MPLS edge nodes.

   CR-LDP may also be applicable as a mediating service between
   networks providing similar service extensions using widely varying
   signaling models.

3. Implementation and deployment considerations in relation to LDP

   LDP specifies the following label distribution and management modes
   (which can be combined in various logical ways described in LDP):

      . Downstream On Demand label distribution
      . Downstream Unsolicited label distribution
      . Independent Label Distribution Control
      . Ordered Label Distribution Control
      . Conservative Label Retention Mode
      . Liberal Label Retention Mode

   In networks where only Traffic Engineered LSPs are required, the CR-
   LDP implementation and deployment does NOT require all the
   functionality defined in the LDP specification. The basic Discovery,

Jamoussi, et. al.           February 2000                     [Page 3]

Internet Draft    Applicability Statement for CR-LDP      August, 1999

   Session, and Notification messages are required. However, CR-LDP
   requires one specific combination of the label distribution modes:

        . Downstream On Demand Ordered label distribution and
        conservative Label Retention Mode

   Although CR-LDP is defined as an extension to LDP, support for
   Downstream Unsolicited Label Advertisement and Independent Control
   modes is not required for support of Strict Explicit Routes.  In
   addition, implementations of CR-LDP MAY be able to support Loose
   Explicit Routes via the use of `Abstract Nodes' and/or `Hierarchical
   Explicit Routing', without using LDP for hop-by-hop LSP setup.

   CR-LDP also includes support for loose explicit routes. Use of this
   capability allows the network operator to define an 'explicit path'
   through portions of their network with imperfect knowledge of the
   entire network topology.  Proper use of this capability may also
   allow CR-LDP implementations to inter-operate with 'vanilla' LDP
   implementations - particularly if it is desired to set up an
   explicitly routed LSP for best-effort packet delivery via a loosely
   defined path.

   Finally, in networks where both Routing Protocol-driven LSPs (a.k.a.
   hop-by-hop LSPs) and Traffic Engineered LSPs are required, asingle
   protocol (LDP, with the extensions defined in CR-LDP) can be used
   for both TE and Hop-by-Hop LSPs. New protocols do not have to be
   introduced in the network to provide TE-LSP signaling.

4. Limitations

   CR-LDP specification only supports point-to-point LSPs. Multi-point-
   to-point and point-to-multi-point are FFS.

   CR-LDP specification only supports unidirectional LSP setup. Bi-
   directional LSP setup is FFS.

   CR-LDP specification only supports a unique label allocation per LSP
   setup. Multiple label allocations per LSP setup are FFS.

5. Security Considerations

   No additional security issues are introduced in this draft. As an
   extension to LDP, CR-LDP shares the security concerns associated
   with LDP.

6. Acknowledgements

   The authors would like to thank the following people for their
   careful review of the draft and their comments: Loa Andersson, Peter
   Ashwood-Smith, Anoop Ghanwani, Juha Heinanen, and Jon Weil.

Jamoussi, et. al.           February 2000                     [Page 4]

Internet Draft    Applicability Statement for CR-LDP      August, 1999

7. References

   1  B. Jamoussi, et., al., _Constraint-based LSP Setup Using LDP_,
      work in progress, March 1999.

   2  L. Andersson, et., al., _LDP Specification_, work in progress,
      June 1999.

   3  D. Awduche et., al., "Requirements for Traffic Engineering Over
      MPLS", work in progress, June 1999.

   4  G. Ash, Y. Lee, B. Jamoussi, P. Ashwood-Smith, L. Li, D.
      Skalecki, D. Fedyk, "LSP Modification using CR-LDP," work in
      progress, July 1999.

   5  S. Blake et., al., "An Architecture for Differentiated Services",
      RFC-2495, December 1998.

   6  S. Shenker, J. Wroclawski, "General Characterization Parameters
      for Integrated Service Network Elements" RFC-2215

   7  ATM Forum Traffic Management Specification Version 4.1 (AF-TM-
      0121.000), March 1999.

      SERVICE, ITU (CCITT) Recommendation I.370, 1991.

   9  D. Awduche, L. Berger, D. Gan, T. Li, G. Swallow, V. Srinivasan,
      "Extensions to RSVP for LSP Tunnels," work in progress, March

8. Author's Addresses

   Gerald R. Ash                     M. K. Girish
   AT&T                              SBC Technology Resources, Inc.
   Room MT E3-3C37                   4698 Willow Road,
   200 Laurel Avenue                 Pleasanton, CA 94588
   Middletown, NJ 07748              USA
   USA                               Phone: +1 925 598-1263
   Phone: 732-420-4578               Fax:   +1 925 598-1322
   Fax:   732-440-6687               mgirish@tri.sbc.com
   Email: gash@att.com

   Eric W Gray                       Bilel Jamoussi
   Lucent Technologies, Inc.         Nortel Networks Corp.
   PO Box 0710                       3 Federal Street
   Durham, NH, 03824-0710            Billerica, MA 01821
   USA                               USA
   Phone: +1 603 659 3386            phone: +1 978-288-4506
   Ewgray@lucent.com                 Jamoussi@nortelnetworks.com

Jamoussi, et. al.           February 2000                     [Page 5]

Internet Draft    Applicability Statement for CR-LDP      August, 1999

   Gregory Wright
   Nortel Networks Corp.
   P O Box 3511 Station C
   Ottawa, ON K1Y 4H7
   Phone: +1 613 765-7912

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