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Versions: 00 01 draft-ietf-sip-info-method

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.

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and may be updated, replaced, or obsoleted by other documents at any
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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.






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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]


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