Internet Engineering Task Force Steven R. Donovan
INTERNET DRAFT MCI Worldcom
February 8, 1999 Expires August 8, 1999
<draft-ietf-mmusic-sip-info-method-00.txt>
The SIP INFO Method
Status of this document
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026.
Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other groups
may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference material
or to cite them other than as "work in progress."
To view the entire list of current Internet-Drafts, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe),
ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim),
ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).
Abstract
This document proposes an extension to the Session Initiation Protocol.
This extension adds the INFO method to the SIP protocol. The intent
of the INFO method is to allow for the carrying of session related
control information that is generated during a session. Examples of
such session control information are ISUP/ISDN signaling messages
and DTMF digits used to control telephony services.
Donovan [Page 1]
Internet draft The SIP INFO Method February 8, 1999
1.0 Introduction
There are situations where session related control information needs to
be sent during a session. This information is separate from the media
that is being exchanged as part of the session.
Two examples of this are motivated by telephony related services:
1 - Mid Call Telephony Signaling Messages
2 - DTMF Digit/Dial Plus Control of Telephony Services
It can also be envisioned that there will be non telephony inspired
uses of a mechanism for relaying mid session information between
participants of the session and to Proxy Servers interested in the
session.
This document proposes the addition of the INFO Request method to the
SIP specification.
1.1 Mid Call Telephony Signaling Messages
The first use for the INFO method is the need to carry mid call
signaling information resulting from the interworking between an ISUP
or ISDN network/device and a SIP controlled network.
One specific example of this interworking is when the SIP controlled
network is used for transport between two PSTN locations. For this
call, there will be a PSTN leg from the calling party to the SIP
network, a SIP leg through the SIP network and a PSTN leg from the SIP
network to the called party. There needs to be a method to carry mid-
call PSTN signaling that is originated by the calling party through the
SIP network to the called party.
1.2 DTMF Digit/Dial Plus Control of Telephony Services
The second type of telephony session control information that needs to
be carried during a session is DTMF or dial plus (refered to from here
on as DTMF) generated information. There are various telephony services
implemented today which require the use of DTMF digits. Due to the
design of these features, the DTMF information needs to be carried both
as part of the media stream (in the RTP flow) and as part of the
signaling or control path. This is due to the fact that there is an
implicit separation of the media and control path in the SIP protocol.
Thus, SIP Proxy Servers that implement services that require DTMF
control and that are not in the media path require a mechanism to be
notified of the DTMF digits.
Donovan [Page 2]
Internet draft The SIP INFO Method February 8, 1999
2.0 INFO Method
The INFO method is used for communicating mid-session control
information along the signaling path for the session. The signaling
path for the INFO method is the signaling path established as a
result of the session setup.
The mid-session control information can be communicated in either
an INFO message header or as part of an attachment.
If the control information is telephony signaling information than the
signaling message would be carried as part of an ISUP attachment to the
INFO message as described in draft-ietf-sigtran-mime-isup-00.txt.
The method for carrying the DTMF information in the INFO message has
not yet been defined and is outside the scope of this document.
2.1 Header Field Support for INFO Method
The following table is an extension of tables 4 and 5 in the SIP
specification. Refer to the SIP Specification for a description of
the content of the table.
Header Where INFO
------ ----- ----
Accept R -
Accept-Encoding R -
Accept-Language R o
Allow 200 -
Allow 405 o
Authorization R o
Call-ID gc m
Contact R -
Contact 1xx -
Contact 2xx -
Contact 3xx -
Contact 485 -
Content-Encoding e o
Content-Length e o
Content-Type e *
CSeq gc m
Date g o
Encryption g o
Expires g -
>From gc m
Hide R o
Max-Forwards R o
Organization g o
Donovan [Page 3]
Internet draft The SIP INFO Method February 8, 1999
Header Where INFO
------ ----- ----
Priority R o
Proxy-Authenticate 407 o
Proxy-Authorization R o
Proxy-Require R o
Require R o
Retry-After R -
Retry-After 404,480,486 o
Retry-After 503 o
Retry-After 600,603 o
Response-Key R o
Record-Route R o
Record-Route 2xx o
Route R o
Server r o
Subject R -
Timestamp g o
To gc(1) m
Unsupported 420 o
User-Agent g o
Via gc(2) m
Warning r o
WWW-Authenticate 401 o
2.2 Responses to the INFO Request Method
A 200 OK response shall be sent if the INFO request was successful.
Request Failure (4xx), Server Failure (5xx) and Global Failure (6xx)
responses can also be sent for the INFO Request.
2.3 Message Body Inclusion
The INFO request may contain a message body.
2.4 Behavior of SIP User Agents
The protocol rules applied by the SIP User Agent shall be similar to
those applied used for the BYE request. However, the INFO message shall
shall not change the state of the session.
2.5 Behavior of SIP Proxy and Redirect Servers
2.5.1 Proxy Server
The protocol rules applied by the SIP Proxy Server shall be similar to
those applied used for the BYE request. However, the INFO message shall
shall not change the state of the session.
Donovan [Page 4]
Internet draft The SIP INFO Method February 8, 1999
2.5.2 Forking Proxy Server
The protocol rules applied by the SIP Forking Proxy Server shall be
similar to those applied used for the BYE request. However, the INFO
message shall shall not change the state of the session.
2.5.3 Redirection Server
A redirection server should not receive the INFO method as it is a part
of the signaling path only at the initiation of the session. As
such, a redirection server should send a 403 Forbidden response.
2.6 Security Considerations
There are no security issues specific to the INFO method. The security
requirements specified in the SIP specification apply to the INFO
method.
3.0 References
[1] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg,
"SIP: Session Initiation Protocol", Internet Draft, Internet
Engineering Task Force, January 15, 1999. Work in progress.
[2] C. Huitema, "The multipart/sip-id media type", Internet Draft,
Internet Engineering Task Force, February 5, 1999. Work in
Progress
4.0 Author's Address
Steve Donovan
MCI Worldcom
1493/678
901 International Parkway
Richardson, Texas 75081
Email: steven.r.donovan@mci.com
Donovan [Page 5]
