Internet Engineering Task Force (IETF) D. Hanes
Request for Comments: 6913 G. Salgueiro
Category: Standards Track Cisco Systems
ISSN: 2070-1721 K. Fleming
Digium, Inc.
March 2013
Indicating Fax over IP Capability
in the Session Initiation Protocol (SIP)
Abstract
This document defines and registers with IANA the new "fax" media
feature tag for use with the Session Initiation Protocol (SIP).
Currently, fax calls are indistinguishable from voice calls at call
initiation. Consequently, fax calls can be routed to SIP user agents
that are not fax capable. A "fax" media feature tag implemented in
conjunction with caller preferences allows for more accurate fax call
routing.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6913.
Hanes, et al. Standards Track [Page 1]RFC 6913 Fax Media Feature Tag March 2013Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Usage of the "sip.fax" Parameter . . . . . . . . . . . . . . . 4
5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
1. Introduction
Fax communications in the Session Initiation Protocol (SIP) [RFC3261]
are handled in a "voice first" manner. Indications that a user
desires to use a fax transport protocol, such as ITU-T T.38 [T38], to
send a fax are not known when the initial INVITE message is sent.
The call is set up as a voice call first, and then, only after it is
connected, does a switchover to the T.38 [T38] protocol occur. This
is problematic in that fax calls can be routed inadvertently to SIP
user agents (UAs) that are not fax capable.
To ensure that fax calls are routed to fax-capable SIP UAs, an
implementation of caller preferences defined in RFC 3841 [RFC3841]
can be used. Feature preferences are a part of RFC 3841 [RFC3841]
that would allow UAs to express their preference for receiving fax
communications. Subsequently, SIP servers take these preferences
into account to increase the likelihood that fax calls are routed to
fax-capable SIP UAs.
Hanes, et al. Standards Track [Page 2]RFC 6913 Fax Media Feature Tag March 2013
This document defines the "fax" media feature tag for use in the SIP
tree, as per Section 12.1 of RFC 3840 [RFC3840]. This feature tag
will be applied per RFC 3841 [RFC3841] as a feature preference for
fax-capable UAs.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
datatracker.ietf.org