Layer Two Tunnelling Protocol (L2TP): ATM access network extensions
RFC 3301

Network Working Group                                         Y. T'Joens
Request for Comments: 3301                                      B. Sales
Category: Standards Track                                        Alcatel
                                                           P. Crivellari
                                                                Belgacom
                                                               June 2002

                 Layer Two Tunnelling Protocol (L2TP):
                     ATM access network extensions

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 augments the procedures described in RFC 2661 to
   further support ATM SVC (Switched Virtual Circuits) or PVC (Permanent
   Virtual Circuits) based access networks.  L2TP (Layer 2 Tunneling
   Protocol) specifies a protocol for tunnelling PPP packets over packet
   based networks and over IP networks in particular.  L2TP supports
   remote access by ISDN and PSTN networks.  The extensions defined
   within this document allow for asymmetric bi-directional call
   establishment and service selection in the ATM access network.

Table Of Contents

   1. Introduction ..................................................  2
   1.1 Conventions ..................................................  2
   2. Assumptions ...................................................  3
   2.1 Topology .....................................................  3
   2.2 Connection Establishment .....................................  3
   2.3 LCP Negotiation ..............................................  3
   3. ATM access enhanced procedures ................................  3
   3.1 ATM connectivity .............................................  4
   3.2 Tunnel establishment .........................................  4
   3.3 Call establishment ...........................................  5
   3.3.1 Incoming Call Establishment ................................  5
   3.3.2 Outgoing Call Establishment ................................  6

T'Joens, et al.             Standards Track                     [Page 1]
RFC 3301          L2TP: ATM access network extensions          June 2002

   3.4 Framing ......................................................  6
   4. Service model issues ..........................................  7
   4.1 Authentication ...............................................  7
   4.2 Authorization ................................................  7
   5. New and extended AVPs .........................................  7
   5.1 New AVP Summary ..............................................  7
   5.2 New AVP definition ...........................................  8
   5.3 Changed AVP Definition ....................................... 12
   6. IANA considerations ........................................... 16
   7. Security considerations ....................................... 17
   8. Acknowledgements .............................................. 17
   9. References .................................................... 17
   10. Authors Addresses ............................................ 18
   11. Full Copyright Statement ..................................... 19

1. Introduction

   L2TP [RFC2661] defines the procedures for tunneling PPP sessions
   between a so called L2TP Access Concentrator (LAC) and an L2TP
   Network Server (LNS).  The main focus of [RFC2661] is on supporting
   HDLC based ISDN/PSTN access networks.

   This document augments the procedures described in [RFC2661] to
   further support ATM SVC or PVC based access networks.  Support for
   ATM access networks requires extensions to the present L2TP
   procedures so as to cope with :

   (a) the traffic management aspects of ATM connections (e.g.
       asymmetric bandwidth allocation and service category selection
       capabilities),

   (b) the addressing format to be used in switched ATM networks [AESA]
       and

   (c) the limitations imposed on LCP negotiation by transporting PPP
       over AAL5 over the access network segment of the PPP connection
       [RFC2364].

   Within this document, the necessary extensions to [RFC2661] are
   defined to cope with issues (a) and (b), issue (c) which is not
   specific to ATM may be solved as described in [L2TP_link].

1.1 Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",