Subject: I-D ACTION:draft-ietf-sipping-realtimefax-01.txt

From: [email-masked]
Date: Thu, 06 Mar 2003 06:29:03 -0500

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Session Initiation Proposal Investigation Working Group of the IETF.

	Title		: SIP Support for Real-time Fax: Call Flow Examples And 
                          Best Current Practices
	Author(s)	: J. Mule, J. Li
	Filename	: draft-ietf-sipping-realtimefax-01.txt
	Pages		: 56
	Date		: 2003-3-5
	
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-
through.  
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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