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RFC 3496

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Protocol Extension for Support of Asynchronous Transfer Mode (ATM) Service Class-aware Multiprotocol Label Switching (MPLS) Traffic Engineering


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Network Working Group                                        A. G. Malis
Request for Comments: 3496                                      T. Hsiao
Category: Informational                                  Vivace Networks
                                                              March 2003

  Protocol Extension for Support of Asynchronous Transfer Mode (ATM)
        Service Class-aware Multiprotocol Label Switching (MPLS)
                          Traffic Engineering

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 (2003).  All Rights Reserved.


   This document specifies a Resource ReSerVation Protocol-Traffic
   Engineering (RSVP-TE) signaling extension for support of Asynchronous
   Transfer Mode (ATM) Service Class-aware Multiprotocol Label Switching
   (MPLS) Traffic Engineering.

Table of Contents

   1.  Overview......................................................2
   2.  Extended RSVP-TE Path Message Format..........................2
       2.1 PATH Message Format.......................................3
   3.  ATM_SERVICECLASS Object.......................................3
   4.  Handling the ATM_SERVICECLASS Object..........................4
   5.  Non-support of the ATM_SERVICECLASS Object....................4
   6.  Security Considerations.......................................4
   7.  IANA Considerations...........................................5
   8.  References....................................................5
   9.  Authors' Addresses............................................5
   10. Full Copyright Statement......................................6

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1. Overview

   This document defines a Resource ReSerVation Protocol-Traffic
   Engineering (RSVP-TE) protocol addition to support ATM (Asynchronous
   Transfer Mode) Service Class-aware MPLS (MultiProtocol Label
   Switching) Traffic Engineering.

   This protocol addition is used with all MPLS Label Switched Routers
   (LSRs) and link types (including, but not restricted to, Packet over
   SONET, Ethernet, and ATM links) to signal traffic engineered paths
   that can support the ATM service classes as defined by the ATM Forum
   [TM].  This document does not specify HOW to actually implement the
   functionality in the MPLS LSRs to emulate the ATM Forum service
   classes (such as necessary queuing and scheduling mechanisms), only
   how to signal that the TE path must support the ATM Forum service
   classes.  A useful application for such paths is the carriage of ATM
   cells encapsulated in IP or MPLS packets in order to use MPLS
   networks as functional replacements for ATM networks.

2. Extended RSVP-TE Path Message Format

   One new RSVP-TE Object is defined in this document: the
   ATM_SERVICECLASS Object.  Detailed description of this Object is
   provided below.  This new Object is applicable to PATH messages.
   This specification only defines the use of the ATM_SERVICECLASS
   Object in PATH messages used to establish LSP (Label Switched Path)
   Tunnels in accordance with [RSVP-TE].  Such PATH messages contain a
   Session Object with a C-Type equal to LSP_TUNNEL_IPv4 and a
   LABEL_REQUEST object.

   Restrictions defined in [RSVP-TE] for support of establishment of LSP
   Tunnels via RSVP-TE are also applicable to the establishment of LSP
   Tunnels supporting ATM Service Class-aware traffic engineering.  For
   instance, only unicast LSPs are supported and Multicast LSPs are for
   further study.

   This new ATM_SERVICECLASS object is optional with respect to RSVP-TE
   so that general RSVP-TE implementations not concerned with ATM
   Service Class-aware traffic engineering MPLS LSP setup do not have to
   support this object.

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2.1 PATH Message Format

   The format of the extended PATH message is as follows:

   <PATH Message> ::=      <Common Header> [ <INTEGRITY> ]
                                <SESSION> <RSVP_HOP>
                            [ <EXPLICIT_ROUTE> ]
                            [ <SESSION_ATTRIBUTE> ]
                            [ <DIFFSERV> ]
                            [ <ATM_SERVICECLASS> ]
                            [ <POLICY_DATA> ... ]
                            [ <sender descriptor> ]

   <sender descriptor> ::=  <SENDER_TEMPLATE> [ <SENDER_TSPEC> ]
                            [ <ADSPEC> ]
                            [ <RECORD_ROUTE> ]


   The ATM_SERVICECLASS object format is as follows:

   Class Number = 227, C_Type = 1

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                       Reserved                          | SC  |

   Reserved : 29 bits
        This field is reserved. It must be set to zero on transmission
        and must be ignored on receipt.

   SC : 3 bits
        Indicates the ATM Service Class. Values currently allowed are:
        0: UBR (Unspecified Bit Rate)
        1: VBR-NRT (Variable Bit Rate, Non-Real Time)
        2: VBR-RT (Variable Bit Rate, Real Time)
        3: CBR (Constant Bit Rate)
        4-7: reserved

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4. Handling the ATM_SERVICECLASS Object

   To establish an LSP tunnel with RSVP-TE, the sender LSR creates a
   PATH message with a session type of LSP_Tunnel_IPv4 and with a
   LABEL_REQUEST object as per [RSVP-TE].  The sender LSR may also
   include the DIFFSERV object as per [DIFF-MPLS].

   If the LSP is associated with an ATM Service Class, the sender LSR
   must include the ATM_SERVICECLASS object in the PATH message with the
   Service-Class (SC) field set to signify the desired ATM Service

   If a path message contains multiple ATM_SERVICECLASS objects, only
   the first one is meaningful; subsequent ATM_SERVICECLASS object(s)
   must be ignored and must not be forwarded.

   Each LSR along the path that is ATM_SERVICECLASS-aware records the
   ATM_SERVICECLASS object, when present, in its path state block.

   The destination LSR responds to the PATH message by sending a RESV
   message without an ATM_SERVICECLASS object (whether the PATH message
   contained an ATM_SERVICECLASS object or not).

5. Non-support of the ATM_SERVICECLASS Object

   An LSR that does not recognize the ATM_SERVICECLASS object Class
   Number must behave in accordance with the procedures specified in
   [RSVP] for an unknown Class Number with the binary format 11bbbbbb,
   where b=0 or 1 (i.e., RSVP will ignore the object but forward it
   unexamined and unmodified).

   An LSR that recognizes the ATM_SERVICECLASS object Class Number but
   does not recognize the ATM_SERVICECLASS object C-Type, must behave in
   accordance with the procedures specified in [RSVP] for an unknown
   C-type (i.e., it must send a PathErr with the error code 'Unknown
   object C-Type' toward the sender).

   In both situations, this causes the path setup to fail.  The sender
   should notify management that a LSP cannot be established and
   possibly might take action to retry reservation establishment without
   the ATM_SERVICECLASS object.

6. Security Considerations

   The solution is not expected to add specific security requirements
   beyond those of Diff-Serv and existing TE.  The security mechanisms
   currently used with Diff-Serv and existing TE can be used with this

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7. IANA Considerations

   The IANA has registered a new RSVP Class Number for ATM_SERVICECLASS
   (227).  (See

8. References

   [DIFF-MPLS] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
               P., Krishnan, R., Cheval, P. and J. Heinanen, "Multi-
               Protocol Label Switching (MPLS) Support of Differentiated
               Services", RFC 3270, May 2002.

   [RSVP]      Braden, R., Ed., Zhang, L., Berson, S., Herzog, S. and S.
               Jazmin , "Resource ReSerVation Protocol (RSVP) -- Version
               1 Functional Specification", RFC 2205, September 1997.

   [RSVP-TE]   Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.
               and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
               Tunnels", RFC 3209, December 2001.

   [TM]        ATM Forum Traffic Management Specification Version 4.0,
               af-tm-0056.000, April 1996.

9. Authors' Addresses

   Andrew G. Malis
   Vivace Networks, Inc.
   2730 Orchard Parkway
   San Jose, CA 95134


   Tony Hsiao
   Vivace Networks, Inc.
   2730 Orchard Parkway
   San Jose, CA 95134


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10.  Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an


   Funding for the RFC Editor function is currently provided by the
   Internet Society.