IFX Mail Archive: IFX> I-D Realtime Internet Fax via SIP

IFX Mail Archive: IFX> I-D Realtime Internet Fax via SIP

IFX> I-D Realtime Internet Fax via SIP

From: McDonald, Ira (imcdonald@sharplabs.com)
Date: Fri Jun 14 2002 - 15:52:20 EDT

  • Next message: Gail Songer: "IFX> Portland topics"

    Hi folks,

    You may find this interesting. It's called "SIP Support for Real-time Fax:
    Call Flow Examples And Best Current Practices". See the Abstract below.


    This is a recent draft from the IETF SIPPING (Session Initiation Proposal
    Investigation) Working Group - their charter is at:


    - Ira McDonald
      High North Inc

    PS - Note that SIPPING is chartered to do realtime Internet Fax. If IPPFAX
    is to be useful, we should probably try to reach closure on minimum required
    document formats (TIFF-FX, PDF, or whatever) and bring the PWG IPPFAX WG
    to the attention of the IETF SIPPING WG (as a _complement_, not a


    1. Abstract

       The Session Initiation Protocol (SIP) allows the establishment of
       real-time Internet fax communications. Real-time facsimile
       communications over IP may follow 2 modes of operation: T.38 fax
       relay as defined by the ITU-T T.38 recommendation or fax pass-
       This document clarifies the options available to Internet telephony
       gateway vendors to handle real-time fax calls using SIP. While our
       primary focus is to address the more reliable real-time T.38 Group 3
       fax mode, we briefly cover the fax pass-through mode to enable
       fallback operations and super G3 fax communications using SIP. We
       also give examples of SIP call flows for real-time Internet fax
       gateways or SIP proxy redirect servers. Elements in these call
       flows include SIP User Agents, SIP Proxy Servers, and Gateways to
       the PSTN (Public Switch Telephone Network).
       This document introduces best current practices for SIP T.38 fax and
       SIP fax pass-through sessions. A session starts with audio
       capabilities, and, upon fax tone detection, T.38 fax capabilities
       are negotiated; upon successful negotiation, the session continues
       with fax capabilities and the media termination hosts exchange T.38
       Internet fax packets. The T.38 fax call scenarios include various
       aspects of the call sequence: the detection of fax transmission, the
       usage of the T.38 session description attributes, the optional
       fallback into fax pass-through mode and the session termination. The
       fax pass-through call scenarios involve some specific SDP media
       attributes to enable proper fax transmission.
       Fax transmission can be detected by the receiving side, the emitting
       side or both (in the latter case, a 'glare' effect may appear).
       This document only covers the case when the fax transmission is
       detected by the receiving side: it is the most common practice and
       the other cases do not represent any particular challenges and are
       therefore left for future discussions). Call flow diagrams and
       message details are shown. A list of IANA defined SDP attribute
       names for T.38 is summarized in section 7.

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