RFC 3573 (rfc3573) - Page 2 of 13

Signalling of Modem-On-Hold status in Layer 2 Tunneling Protocol (L2TP)

RFC 3573       Signaling of Modem-On-Hold status in L2TP       July 2003


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
       1.1.  Specification of Requirements. . . . . . . . . . . . . .  3
       1.2.  Terminology. . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Protocol Operation . . . . . . . . . . . . . . . . . . . . . .  3
       2.1.  Typical Modem on Hold Usage Scenario . . . . . . . . . .  4
       2.2.  Capability Negotiation . . . . . . . . . . . . . . . . .  4
       2.3.  Modem On-Hold. . . . . . . . . . . . . . . . . . . . . .  5
       2.4.  Modem Online . . . . . . . . . . . . . . . . . . . . . .  5
   3.  New Control Messages . . . . . . . . . . . . . . . . . . . . .  5
       3.1.  Modem-Status (MDMST) . . . . . . . . . . . . . . . . . .  5
   4.  New Attribute Value Pairs. . . . . . . . . . . . . . . . . . .  6
       4.1.  Modem On-Hold Capable AVP. . . . . . . . . . . . . . . .  6
       4.2.  Modem On-Hold Status AVP . . . . . . . . . . . . . . . .  6
   5.  Sample LNS Actions . . . . . . . . . . . . . . . . . . . . . .  7
   6.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations. . . . . . . . . . . . . . . . . . . .  9
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
       8.1.  Normative References . . . . . . . . . . . . . . . . . .  9
       8.2.  Informative References . . . . . . . . . . . . . . . . .  9
   9.  Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 10
   Appendix A: Vendor Specific Assignments. . . . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 13

1.  Introduction

   The Layer 2 Tunneling Protocol (L2TP) [RFC 2661] defines a general
   purpose mechanism for tunneling Point-to-Point Protocol (PPP) [STD51]
   sessions over various media.  By design, the operation of L2TP is
   insulated from the details of the media from which the PPP session
   originated.

   It is common for PPP sessions to be established using modems
   connected over the public switched telephone network.  The ITU-T
   Recommendation V.92 [V92] is one of the standards governing modem
   operation and it defines procedures that enable a client modem to put
   the call on hold and later, re-establish the modem link without
   having to redial.  While the modem call is on hold, the client phone
   line can be used for another phone call.

   The L2TP base protocol does not provide any means to signal these
   events from the L2TP Access Controller (LAC), where the modem is
   physically connected, to the L2TP Network Server (LNS), where the PPP
   session is handled.  It may be desirable for this information (which
   is available only on the LAC) to be provided to the LNS.




Goyret                      Standards Track