rfc3270.txt

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Network Working Group                             F. Le Faucheur, Editor
Request for Comments: 3270                                         L. Wu
Category: Standards Track                                       B. Davie
                                                           Cisco Systems
                                                               S. Davari
                                                         PMC-Sierra Inc.
                                                             P. Vaananen
                                                                   Nokia
                                                             R. Krishnan
                                                       Axiowave Networks
                                                               P. Cheval
                                                                 Alcatel
                                                             J. Heinanen
                                                           Song Networks
                                                                May 2002


                 Multi-Protocol Label Switching (MPLS)
                   Support of Differentiated Services

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.

Copyright Notice

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

Abstract

   This document defines a flexible solution for support of
   Differentiated Services (Diff-Serv) over Multi-Protocol Label
   Switching (MPLS) networks.

   This solution allows the MPLS network administrator to select how
   Diff-Serv Behavior Aggregates (BAs) are mapped onto Label Switched
   Paths (LSPs) so that he/she can best match the Diff-Serv, Traffic
   Engineering and protection objectives within his/her particular
   network.  For instance, this solution allows the network
   administrator to decide whether different sets of BAs are to be
   mapped onto the same LSP or mapped onto separate LSPs.






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Table of Contents

   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   1.1  Terminology. . . . . . . . . . . . . . . . . . . . . . . . . . 5
   1.2 EXP-Inferred-PSC LSPs (E-LSP) . . . . . . . . . . . . . . . . . 6
   1.3 Label-Only-Inferred-PSC LSPs (L-LSP). . . . . . . . . . . . . . 7
   1.4 Overall Operations. . . . . . . . . . . . . . . . . . . . . . . 7
   1.5 Relationship between Label and FEC. . . . . . . . . . . . . . . 8
   1.6 Bandwidth Reservation for E-LSPs and L-LSPs . . . . . . . . . . 8
   2. Label Forwarding Model for Diff-Serv LSRs and Tunneling Models . 9
   2.1 Label Forwarding Model for Diff-Serv LSRs . . . . . . . . . . . 9
   2.2 Incoming PHB Determination. . . . . . . . . . . . . . . . . . .10
   2.3 Outgoing PHB Determination With Optional Traffic Conditioning .11
   2.4 Label Forwarding. . . . . . . . . . . . . . . . . . . . . . . .11
   2.5 Encoding Diff-Serv Information Into Encapsulation Layer . . . .13
   2.6 Diff-Serv Tunneling Models over MPLS. . . . . . . . . . . . . .13
   3. Detailed Operations of E-LSPs. . . . . . . . . . . . . . . . . .22
   3.1 E-LSP Definition. . . . . . . . . . . . . . . . . . . . . . . .22
   3.2 Populating the `Encaps-->PHB mapping' for an incoming E-LSP . .23
   3.3 Incoming PHB Determination On Incoming E-LSP. . . . . . . . . .23
   3.4 Populating the `Set of PHB-->Encaps mappings' for an outgoing
       E-LSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
   3.5 Encoding Diff-Serv information into Encapsulation Layer On
       Outgoing E-LSP. . . . . . . . . . . . . . . . . . . . . . . . .26
   3.6 E-LSP Merging . . . . . . . . . . . . . . . . . . . . . . . . .27
   4.  Detailed Operation of L-LSPs. . . . . . . . . . . . . . . . . .28
   4.1 L-LSP Definition. . . . . . . . . . . . . . . . . . . . . . . .28
   4.2 Populating the `Encaps-->PHB mapping' for an incoming L-LSP . .28
   4.3 Incoming PHB Determination On Incoming L-LSP. . . . . . . . . .30
   4.4 Populating the `Set of PHB-->Encaps mappings' for an outgoing
       L-LSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
   4.5 Encoding Diff-Serv Information into Encapsulation Layer on
       Outgoing L-LSP. . . . . . . . . . . . . . . . . . . . . . . . .33
   4.6 L-LSP Merging . . . . . . . . . . . . . . . . . . . . . . . . .34
   5. RSVP Extension for Diff-Serv Support . . . . . . . . . . . . . .34
   5.1 Diff-Serv related RSVP Messages Format. . . . . . . . . . . . .34
   5.2 DIFFSERV Object . . . . . . . . . . . . . . . . . . . . . . . .35
   5.3 Handling DIFFSERV Object. . . . . . . . . . . . . . . . . . . .37
   5.4 Non-support of the DIFFSERV Object. . . . . . . . . . . . . . .40
   5.5 Error Codes For Diff-Serv . . . . . . . . . . . . . . . . . . .40
   5.6 Intserv Service Type. . . . . . . . . . . . . . . . . . . . . .41
   6. LDP Extensions for Diff-Serv Support . . . . . . . . . . . . . .41
   6.1 Diff-Serv TLV . . . . . . . . . . . . . . . . . . . . . . . . .42
   6.2 Diff-Serv Status Code Values. . . . . . . . . . . . . . . . . .44
   6.3 Diff-Serv Related LDP Messages. . . . . . . . . . . . . . . . .44
   6.4 Handling of the Diff-Serv TLV . . . . . . . . . . . . . . . . .46
   6.5 Non-Handling of the Diff-Serv TLV . . . . . . . . . . . . . . .49
   6.6 Bandwidth Information . . . . . . . . . . . . . . . . . . . . .49



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   7. MPLS Support of Diff-Serv over PPP, LAN, Non-LC-ATM and
      Non-LC-FR Interfaces . . . . . . . . . . . . . . . . . . . . . .49
   8. MPLS Support of Diff-Serv over LC-ATM Interfaces . . . . . . . .50
   8.1 Use of ATM Traffic Classes and Traffic Management mechanisms. .50
   8.2 LSR Implementation With LC-ATM Interfaces . . . . . . . . . . .50
   9. MPLS Support of Diff-Serv over LC-FR Interfaces. . . . . . . . .51
   9.1 Use of Frame Relay Traffic parameters and Traffic Management
       mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . .51
   9.2 LSR Implementation With LC-FR Interfaces. . . . . . . . . . . .51
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .52
   11. Security Considerations . . . . . . . . . . . . . . . . . . . .52
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .52
   APPENDIX A. Example Deployment Scenarios. . . . . . . . . . . . . .53
   APPENDIX B. Example Bandwidth Reservation Scenarios . . . . . . . .58
   References. . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
   Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . .62
   Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . .64

1. Introduction

   In an MPLS domain [MPLS_ARCH], when a stream of data traverses a
   common path, a Label Switched Path (LSP) can be established using
   MPLS signaling protocols.  At the ingress Label Switch Router (LSR),
   each packet is assigned a label and is transmitted downstream.  At
   each LSR along the LSP, the label is used to forward the packet to
   the next hop.

   In a Differentiated Service (Diff-Serv) domain [DIFF_ARCH] all the IP
   packets crossing a link and requiring the same Diff-Serv behavior are
   said to constitute a Behavior Aggregate (BA).  At the ingress node of
   the Diff-Serv domain, the packets are classified and marked with a
   Diff-Serv Code Point (DSCP) which corresponds to their Behavior
   Aggregate.  At each transit node, the DSCP is used to select the Per
   Hop Behavior (PHB) that determines the scheduling treatment and, in
   some cases, drop probability for each packet.

   This document specifies a solution for supporting the Diff-Serv
   Behavior Aggregates whose corresponding PHBs are currently defined
   (in [DIFF_HEADER], [DIFF_AF], [DIFF_EF]) over an MPLS network.  This
   solution also offers flexibility for easy support of PHBs that may be
   defined in the future.

   This solution relies on the combined use of two types of LSPs:

   -  LSPs which can transport multiple Ordered Aggregates, so that the
      EXP field of the MPLS Shim Header conveys to the LSR the PHB to be
      applied to the packet (covering both information about the
      packet's scheduling treatment and its drop precedence).



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   -  LSPs which only transport a single Ordered Aggregate, so that the
      packet's scheduling treatment is inferred by the LSR exclusively
      from the packet's label value while the packet's drop precedence
      is conveyed in the EXP field of the MPLS Shim Header or in the
      encapsulating link layer specific selective drop mechanism (ATM,
      Frame Relay, 802.1).

   As mentioned in [DIFF_HEADER], "Service providers are not required to
   use the same node mechanisms or configurations to enable service
   differentiation within their networks, and are free to configure the
   node parameters in whatever way that is appropriate for their service
   offerings and traffic engineering objectives".  Thus, the solution
   defined in this document gives Service Providers flexibility in
   selecting how Diff-Serv classes of service are Routed or Traffic
   Engineered within their domain (e.g., separate classes of services
   supported via separate LSPs and Routed separately, all classes of
   service supported on the same LSP and Routed together).

   Because MPLS is path-oriented it can potentially provide faster and
   more predictable protection and restoration capabilities in the face
   of topology changes than conventional hop by hop routed IP systems.
   In this document we refer to such capabilities as "MPLS protection".
   Although such capabilities and associated mechanisms are outside the
   scope of this specification, we note that they may offer different
   levels of protection to different LSPs.  Since the solution presented
   here allow Service Providers to choose how Diff-Serv classes of
   services are mapped onto LSPs, the solution also gives Service
   Providers flexibility in the level of protection provided to
   different Diff-Serv classes of service (e.g., some classes of service
   can be supported by LSPs which are protected while some other classes
   of service are supported by LSPs which are not protected).

   Furthermore, the solution specified in this document achieves label
   space conservation and reduces the volume of label set-up/tear-down
   signaling where possible by only resorting to multiple LSPs for a
   given Forwarding Equivalent Class (FEC) [MPLS_ARCH] when useful or
   required.

   This specification allows support of Differentiated Services for both
   IPv4 and IPv6 traffic transported over an MPLS network.  This
   document only describes operations for unicast.  Multicast support is
   for future study.

   The solution described in this document does not preclude the
   signaled or configured use of the EXP bits to support Explicit
   Congestion Notification [ECN] simultaneously with Diff-Serv over
   MPLS.  However, techniques for supporting ECN in an MPLS environment
   are outside the scope of this document.



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1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

   The reader is assumed to be familiar with the terminology of
   [MPLS_ARCH], [MPLS_ENCAPS], [MPLS_ATM], [MPLS_FR], including the
   following:

      FEC        Forwarding Equivalency Class

      FTN        FEC-To-NHLFE Map

      ILM        Incoming Label Map

      LC-ATM     Label Switching Controlled-ATM (interface)

      LC-FR      Label Switching Controlled-Frame Relay (interface)

      LSP        Label Switched Path

      LSR        Label Switch Router

      MPLS       Multi-Protocol Label Switching

      NHLFE      Next Hop Label Forwarding Entry

   The reader is assumed to be familiar with the terminology of
   [DIFF_ARCH], [DIFF_HEADER], [DIFF_AF], [DIFF_EF], including the
   following:

      AF         Assured Forwarding

      BA         Behavior Aggregate

      CS         Class Selector

      DF         Default Forwarding

      DSCP       Differentiated Services Code Point

      EF         Expedited Forwarding

      PHB        Per Hop Behavior






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   The reader is assumed to be familiar with the terminology of
   [DIFF_NEW], including the following:

      OA        Ordered Aggregate.  The set of Behavior Aggregates which
                share an ordering constraint.

      PSC       PHB Scheduling Class.  The set of one or more PHB(s)
                that are applied to the Behavior Aggregate(s) belonging
                to a given OA.  For example, AF1x is a PSC comprising
                the AF11, AF12 and AF13 PHBs.  EF is an example of PSC
                comprising a single PHB, the EF PHB.

   The following acronyms are also used:

      CLP        Cell Loss Priority

      DE         Discard Eligibility

      SNMP       Simple Network Management Protocol

   Finally, the following acronyms are defined in this specification:

      E-LSP      EXP-Inferred-PSC LSP

      L-LSP      Label-Only-Inferred-PSC LSP