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Versions: 00 01 02 03                                                   
PPP Working Group                                          Pat R. Calhoun
INTERNET DRAFT                                     Sun Microsystems, Inc.
Category: Informational                                        Ken Peirce
Title: draft-ietf-pppext-l2tp-ds-02.txt                  3Com Corporation
Date: July 1998

                  Layer Two Tunneling Protocol "L2TP"
                   IP Differential Services Extension

Status of this Memo

   This document is an Internet-Draft. 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-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months.  Internet-Drafts may be updated, replaced, or obsoleted by
   other documents at any time.  It is not appropriate to use Internet-
   Drafts as reference material or to cite them other than as a
   ``working draft'' or ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   1id-abstracts.txt listing contained in the Internet-Drafts Shadow
   Directories on ftp.ietf.org, nic.nordu.net, ftp.nisc.sri.com, or


   The L2TP document [1] defines the base protocol which describes the
   method of tunneling PPP [2] data. The L2TP base protocol does not
   address any Differential Services extensions.

   Since the market is reluctant to outsource dial access without any
   Quality of Service assurances, this draft addresses this problem by
   allowing each L2TP Data Session to be assigned an appropriate
   differential services indicator.

Table of Contents

      1.0 Introduction
      1.1 Conventions
      2.0 Quality of Service/Diferential Services Negotiation

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      2.1 Differential Sevices Indicator Exchange
      2.2 Error Reporting
      3.0 References
      4.0 Authors' Addresses

1.0 Introduction

   The L2TP protocol specification does not discuss Quality of
   Service/Differential Services in any way. The current state of the
   market has shown that many customers are reluctant to adopt L2TP
   without any quality of service assurances.

   This document will describe how two L2TP peers can negotiate a
   differential services indicator for a dial-in user. Note that each
   individual session within a tunnel can have its own Diff Serv

   The mechanism defined in this document assumes that the Tunnel
   Initiator determines what the user's appropriate service level is and
   sends the value in either the ICRQ or OCRQ messages. The Tunnel
   Terminator can respond to the message by stating what it believes is
   the user's appropriate service level. The values of the indicator
   supplied by the Tunnel Terminator will supercede those provided by
   the Tunnel Initiator if a difference is found.  However, the Tunnel
   Terminator MUST NOT propose a higher differential service level than
   was proposed by the Tunnel Initiator.

   In the case where the Tunnel Terminator does not propose ANY
   indicator (which is infered by the absence of the QOS AVPs in either
   the ICRP or OCRP) the Tunnel Initiator will assume no QOS is assigned
   to the session.

   A tunnel peer which violates the negotiated differential service
   level is liable to have it's tunnel shutdown.

1.1 Conventions

   The following language conventions are used in the items of specifi-
   cation in this document:

         o  MUST, SHALL, or MANDATORY -- This item is an absolute
            requirement of the specification.

         o  SHOULD or RECOMMEND -- This item should generally be followed
            for all but exceptional circumstances.

         o  MAY or OPTIONAL -- This item is truly optional and may be

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INTERNET DRAFT                                                 July 1998

            followed or ignored according to the needs of the

2.0 Quality of Service/Diferential Services Negotiation

   This section will define the new AVPs which are required for the
   Quality of Service extension of the L2TP protocol. The AVPs allow
   designation of a Quality of Service level for a specific data

2.1 Differential Services Indicator AVP

   The Differential Services indicator AVP is found in the IPv4 header's
   Type of Service octet. This is the second octet in the header. The
   actual bit interpretation of the IP Precedence and Type of Service
   bit fields is left to the appropriate documentation[2][3][4]. This
   document is concerned with defining a uniform exchange mechanism for
   the indicator only.

   The Differential Services Indicator AVP MAY be present in ICRQ, ICRP,
   OCRQ and OCRP. This message is used to inform the tunnel peer that a
   set of differential service indicator value SHOULD be used for all
   packets related to the data channel associated with the Tunnel and
   Call Identifiers in the L2TP header [1].

   The presence of this AVP in the ICRQ or OCRQ indicates that the
   tunnel initiator wishes to use a specific differential service
   indicator value on all data packets. However, the value found in the
   ICRP or OCRP indicate the value which the Tunnel Terminator is
   willing to accept.  However, the Tunnel Terminator MUST NOT propose a
   higher differential service level than was proposed by the Tunnel

   A tunnel peer which violates the negotiated indicator value is liable
   to have it's tunnel shutdown.

       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
      |1|1|0|0|        Length         |              43               |
      |                1              |  Diff Serv Indicator Value    |

      This AVP MAY be present in the messages shown above. It is encoded

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INTERNET DRAFT                                                 July 1998

      with a Vendor ID of 43 (3Com Corporation) with the attribute set
      to 1, marked as optional, with the indicator value as data. This
      AVP SHOULD NOT be hidden and is optional. When present, the L2TP
      peer is indicating that differential services are to be used on IP
      packets within the session's data channel.

2.2 Error Reporting

   In the event that the peer did not accept the Diff Serv Indicator
   provided, or is unable to support Differential Services a Call-
   Disconnect-Notify is returned to the peer.

   If the indicator provided cannot be used by the peer, the Call-
   Disconnect-Notify message will include the Diff Serv Indicator AVP as
   provided in the message that caused the Call-Disconnect-Notify.

3.0 References

   [1] K. Hamzeh, T. Kolar, M. Littlewood, G. Singh Pall, J. Taarud,
       A. J. Valencia, W. Verthein, W.M. Townsley, B. Palter,
       A. Rubens "Layer Two Tunneling Protocol (L2TP)",
       Internet draft, October 1997

   [2] D. Clark, J. Wroclawski, "An Approach to Service Allocation in
       the Internet", draft-clark-diff-svc-alloc-00.txt, July 1997.

   [3] P. Ferguson, "Simple Differential Services: IP TOS and
       Precedence, Delay Indication, and Drop Preference,",
       draft-ferguson-delay-drop-00.txt, November 1997

   [4] J. Heinanen, "Use of the IPv4 TOS Octet to Support Differential
       Services", draft-heinanen-diff-tos-octet-01.txt, November 1997

4.0 Authors' Addresses

   Questions about this memo can be directed to:

      Pat R. Calhoun
      Technology Development
      Sun Microsystems, Inc.
      15 Network Circle
      Menlo Park, California, 94025

       Phone:  1-650-786-7733

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INTERNET DRAFT                                                 July 1998

         Fax:  1-650-786-6445
      E-mail:  pcalhoun@eng.sun.comt

      Ken Peirce
      3Com Corporation
      1800 Central Ave.
      Mount Prospect, Il, 60056

       Phone:  1-847-342-6794
         Fax:  1-847-222-2424
      E-mail:  Ken_Peirce@mw.3com.com

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