SIPPING Working Group S. Loreto
Internet-Draft G. Camarillo
Expires: December 27, 2006 Ericsson
June 25, 2006
The Session Initiation Protocol (SIP) Dialog Correlation
draft-loreto-sipping-dialog-correlation-01.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document defines a new header field for use with SIP. The Same-
Session header field is used to logically correlate an existing SIP
dialog with a new SIP dialog when the media sessions established by
both dialogs can be considered a single logical session. This
mechanism can be used to share the user interface and other resources
between all the media streams from both sessions.
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Use case . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Same-Session Header Field Syntax . . . . . . . . . . . . . . . 4
6. User Agent Server Behavior . . . . . . . . . . . . . . . . . . 4
7. User Agent Client Behavior . . . . . . . . . . . . . . . . . . 6
8. New Same-Session Option Tag . . . . . . . . . . . . . . . . . 6
9. Usage Example . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Correlate a Dialog . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
11.1. Registration of Same-Session SIP header field . . . . . . 9
11.2. Registration of Same-Session SIP Option-tag . . . . . . . 9
12. Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 9
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
13.1. Normative References . . . . . . . . . . . . . . . . . . . 9
13.2. Informational References . . . . . . . . . . . . . . . . . 9
Appendix A. Same Session header AND Third Party Call Controll . 11
Appendix A.1. Example: preconditions using the Same-Session
Header . . . . . . . . . . . . . . . . . . . . . . . 11
Appendix A.2. Example: preconditions using the 3pcc . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [3].
2. Overview
This document defines a new SIP [5] header field: Same-Session. The
Same-Session header field is used to logically correlate an existing
SIP dialog with a new SIP dialog when the media sessions established
by both dialogs can be considered a single logical session. This is
especially useful in peer-to-peer call control environments.
While is possible insert a new participant into a multimedia
conversation with the Join header field [6], the Join operation is
normally used to create or join a conference. It adds a dialog to
the conversation space associated with the matched dialog and
performs a media mixing or media combining.
Instead, the Same-Session operation inserts a new dialog into a
multimedia conversation. It enables a dialog to share all the
resources and the user interface with the matched dialog.
Obviously it is also possible to achive the Same-Session operetion
effect using Third Party Call Controll (3pcc) [18] and the SIP
Session Mobility [20]. However there are various disadvantages in
the use of 3pcc.
Appendix A provides some concrete examples regarding the different
complexity level using the 3pcc or the Same-Session header.
3. Requirements
This specification was created in order to meet the following
requirement:
It should be possible for a user agent to correlate two dialogs so
that all the media streams associated to them are treated as a single
media session.
4. Use case
Alice establishes a voice session with Bob. Alice wants add video to
the session using her SIP-enabled camera. Alice sends a REFER to her
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camera, which has SIP user agent on it, so that her camera sends an
INVITE request to Bob in order to establish a video stream. Alice
wants Bob to treat the video stream from her camera and the voice
stream from her voice-only user agent as part of the same media
session. That is, Alice wants Bob to treat both streams as if both
had been established using a single SIP dialog.
5. Same-Session Header Field Syntax
The following is the augmented Backus-Naur Form (BNF) syntax [2] of
the Same-Session header field:
Same-Session = "Same-Session" HCOLON callid * (SEMI same-session-param)
same-session-param = to-tag / form-tag / strictly-flag / generic-param
to-tag = "to-tag" EQUAL token
from-tag = "from-tag" EQUAL token
Examples:
Same-Session: 98732@sip.example.com
;from-tag=r33th4x0r
;to-tag=ff87ff
Same-Session: 12adf2f34456gs5;to-tag=12345;from-tag=54321;strictly
Same-Session: 87134@171.161.34.23;to-tag=24796;from-tag=0
6. User Agent Server Behavior
The Same-Session header field contains information used to match an
existing SIP dialog (Call-ID, to-tag, and from-tag). Upon receiving
an INVITE with a Same-Session header field, the UA (User Agent)
attempts to match this information with a confirmed or early dialog.
The to-tag and from-tag parameters are matched as if they were tags
present in an incoming request. In other words the to-tag parameter
is compared to the local tag, and the from-tag parameter is compared
to the remote tag.
If more than one Same-Session header field is present in an INVITE,
or if a Same-Session header field is present in a request other than
INVITE, the UAS (User Agent Server) MUST reject the request with a
400 (Bad Request) response.
The Same-Session header has specific call control semantics. If both
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a Same-Session header field and another header field with
contradictory semantics (for example a Replaces [7] header field) are
present in a request, the request MUST be rejected with a 400 (Bad
Request) response.
If the Same-Session header field matches more than one dialog, the UA
MUST act as if no match is found.
If no match is found, the UAS rejects the INVITE and returns a 481
(Call/Transaction Does Not Exist) response. Likewise, if the Same-
Session header field matches a dialog which was not created with an
INVITE, the UAS MUST reject the request with a 481 (Call/Transaction
Does Not Exist) response.
If the Same-Session header field matches a dialog which has already
terminated, the UA SHOULD decline the request with a 603 (Decline)
response.
If the Same-Session header field matches an active dialog, the UA
MUST verifies that the initiator of the new INVITE is authorized to
be part of the session previously established by the matched dialog.
If the initiator of the new INVITE has authenticated successfully as
equivalent to the user who established the matched dialog, then the
merging of both session is authorized. For example, if the user who
established the initial dialog and the initiator of the new INVITE
request share the same credentials for Digest authentication [8], or
they sign the correlation request with S/MIME [11] with the same
private key and present the (same) corresponding certificate used in
the original dialog, then the merging of the session is authorized.
Alternatively, the Referred-By mechanism [9] defines a mechanism that
the UAS can use to verify that an INVITE request with a Same-Session
header field was sent on behalf of the other participant in the
matched dialog (in this case, triggered by a REFER request). If the
INVITE request contains a Referred-By header which corresponds to the
user that established the matched dialog, the UA SHOULD authorize the
merging of the sessions. The Referred-By header field MUST reference
a corresponding, valid Referred-By Authenticated Identity Body [10].
The UA MAY apply other local policy to authorize the remainder of the
request. In other words, the UAS may apply different policy to the
new dialog than was applied to the matched dialog.
If authorization is successful, the UA attempts to accept the new
INVITE and treats the session newly-established and the previously
established session as if they were one. It SHOULD return in the
response the Contact header filled in the same way as it returned
during the original dialog establishment phase; in this way,
subsequent users joining the session will be able to use the same
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URL.
If the authorization is successful, but the UA cannot accept the new
INVITE (for example: it cannot establish required QoS or keying, or
it has incompatible media), the UA MUST return an appropriate error
response and MUST leave the matched dialog unchanged.
If the UAS is incapable of satisfying the Same-Session request, it
MUST return a 488 (Not Acceptable Here) response.
7. User Agent Client Behavior
A User Agent that wishes to add a new dialog of its own to a single
existing early or confirmed dialog sends the target User Agent an
INVITE request containing a Same-Session header field. The UAC (User
Agent Client) places the Call-ID, to-tag, and from-tag information
for the target dialog in a single Same-Session header field and sends
the new INVITE to the target.
If the User Agent receives a 300-class response, and acts on this
response by sending an INVITE to a Contact in the response, this
redirected INVITE MUST contain the same Same-Session header which was
present in the original request. Although this is unusual, this
allows INVITE requests with a Same-Session header to be redirected
before reaching the target UAS.
Note that use of the Same-Session mechanism does not provide a way to
match multiple dialogs, nor does it provide a way to match an entire
call, an entire transaction, or to follow a chain of proxy forking
logic.
8. New Same-Session Option Tag
This specification defines a new Require/Supported header option tag
"Same-Session". UAs which support the Same-Session header field MUST
include the "Same-Session" option tag in a Supported header field.
UAs that want explicit failure notification if Same-Session is not
supported MAY include the "Same-Session" option in a Require header
field.
The following is an example of a Require header field with the "Same-
Session" option tag:
Require: Same-Session
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9. Usage Example
The following non-normative examples are not intended to enumerate
all the possibilities for the usage of this extension, but rather to
provide examples or ideas only.
9.1. Correlate a Dialog
Alice's phone Alice's video Bob
| | |
| | |
|(1) INVITE | |
|---------------------------->|
|(2) 200 Ok | |
|<----------------------------|
|(3) ACK | |
|---------------------------->|
|dialog 1 | |
|.............................|
|(4) REFER (Target-Dialog: 1) |
|------------->| |
|(5) 202 Accepted |
|<-------------| |
|(6) NOTIFY (100 Trying) |
|<-------------| |
|(7) 200 Ok | |
|------------->| |
| |(8) INVITE |
| |------------->|
| |(9) 200 Ok |
| |<-------------|
| |(10) ACK |
| |------------->|
| |dialog 2 (correlated to dialog 1)
| |..............|
|(11) NOTIFY (200 Ok) |
|<-------------| |
|(12) 200 Ok | |
|------------->| |
| | |
| | |
In this example, Alice starts a phone call with Bob (messages 1,2,3).
At a later point, Alice wants to add video to the session using a
different user agent that supports video. Alice wants Bob to treat
media stream (i.e., audio and video)as if they had been established
using a single INVITE-initiated dialog. Consequently, Alice's user
agent generates the following REFER request.
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REFER sip:aliceVideo@b.example.org SIP/2.0
To: <sip:aliceVideo@example.org>
From: <sip:alicePhone@example.org>;tag=iii
Call-Id: 7@a.example.org
CSeq: 1 REFER
Contact: <sip:alicePhone@example.org>
Refer-to: <sip:Bob@example.com?Same-Session=98732@example.com
%3Bfrom-tag=r33th4x0r%3Bto-tag=ff87ff>
Referred-By: < sip:alicePhone@example.org>
When Alice video-enabled user agent receives the REFER request, it
establish a new dialog (message 8,9,10) with Bob using the
information received in the REFER request.
INVITE sip:bob@b.example.org SIP/2.0
To: <sip:bob@example.org>
From: <sip:aliceVideo@example.org>;tag=iii
Call-Id: 777@a.example.org
CSeq: 1 INVITE
Contact: <sip:aliceVideo@example.org>
Same-Session: 425928@phone.example.org;to-tag=xyz;from-tag=pdq
SIP/2.0 200 OK
To: <sip:bob@example.org>
From: <sip:aliceVideo@example.org>;tag=iii
Call-Id: 777@a.example.org
CSeq 1 INVITE
Contact: <sip:bob@b.example.org>
10. Security Considerations
The extension specified in this document significantly changes the
relative security of SIP devices. It has the same problems of both
"Join" and "Replace" header fields.
This extension can be used to insert a new dialog in a multimedia
conversation in order to monitor potentially sensitive content. As
such, invitations with the Same-Session header field MUST only be
accepted if the peer requesting a Same-Session has been properly
authenticated as a user already involved in the call.
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11. IANA Considerations
11.1. Registration of Same-Session SIP header field
Name of Header: Same-Session
Short form: none
Normative description: RFC xxxx
11.2. Registration of Same-Session SIP Option-tag
Name of option: Same-Session
Description: Support for the SIP Correlation header
SIP headers defined: Same-Session
Normative description: RFC xxxx
12. Acknowledges
Goeran Ericsson provided valuable ideas for this document.
13. References
13.1. Normative References
[1] Handley, M., "SDP: Session Description Protocol",
draft-ietf-mmusic-sdp-new-26 (work in progress), January 2006.
[2] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
13.2. Informational References
[5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
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Session Initiation Protocol", RFC 3261, June 2002.
[6] Mahy, R. and D. Petrie, "The Session Initiation Protocol (SIP)
"Join" Header", RFC 3911, October 2004.
[7] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation
Protocol (SIP) "Replaces" Header", RFC 3891, September 2004.
[8] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication:
Basic and Digest Access Authentication", RFC 2617, June 1999.
[9] Sparks, R., "The Session Initiation Protocol (SIP) Referred-By
Mechanism", RFC 3892, September 2004.
[10] Peterson, J., "Session Initiation Protocol (SIP) Authenticated
Identity Body (AIB) Format", RFC 3893, September 2004.
[11] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Message Specification", RFC 3851,
July 2004.
[12] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and
D. Gurle, "Session Initiation Protocol (SIP) Extension for
Instant Messaging", RFC 3428, December 2002.
[13] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[14] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[15] Donovan, S., "The SIP INFO Method", RFC 2976, October 2000.
[16] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE
Method", RFC 3311, October 2002.
[17] Rosenberg, J. and H. Schulzrinne, "Reliability of Provisional
Responses in Session Initiation Protocol (SIP)", RFC 3262,
June 2002.
[18] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo,
"Best Current Practices for Third Party Call Control (3pcc) in
the Session Initiation Protocol (SIP)", BCP 85, RFC 3725,
April 2004.
[19] Camarillo, G., Marshall, W., and J. Rosenberg, "Integration of
Resource Management and Session Initiation Protocol (SIP)",
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RFC 3312, October 2002.
[20] Shacham, R., "Session Initiation Protocol (SIP) Session
Mobility", draft-shacham-sipping-session-mobility-02 (work in
progress), March 2006.
Appendix A. Same Session header AND Third Party Call Controll
It is possible to achive the Same-Session operation effect using
Third Party Call Controll (3pcc) [18] and the SIP Session Mobility
[20]. However there are various cons in the use of 3pcc:
o complexity: some use cases that are quite complex implemented
using the Third Party Call Controll (3pcc) become more simpler
using the Same-Session Header.
o implementation: not many terminals are going to implement what is
needed to be a 3pcc controller. However, any terminal will
implement REFER.
o support of an extension at the remote end: the controller needs to
understand all the SIP extensions applied to both dialogs.
Moreover Same-Session Header solves the SIP lack, underlined in the
SIP Session Mobility [20], of a standard way to associate multiple
sessions as part of a single call in SIP.
The following examples show the different complexity, in term of
amount of messages, using the Same-Session header or the 3pcc, in the
scenario where the user A has an on-going session with the user agent
B and then A wants to add a new media to the session using a
different user agent C.
Appendix A.1. Example: preconditions using the Same-Session Header
A ------------------ B
|
C -------------------|
Figure 1: Same-Session architecture
Fig.1 shows the architecture achived using the Same-Sessione header
peer to peer call control model.
Using the same-session header, as showed in fig.2, A issues a REFER
transaction to C, then C send an INVITE to B following the basic
session establishment call flow showed in Figure 1 of [19]. The flow
if fig.2 has 17 messages.
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A C B
| | |
|............dialog 1............................|
|(1) REFER | |
|-------------->| |
|(2) 202 Accepted |
|<--------------| |
|(3) NOTIFY (100 Trying) |
|-------------->| |
|(4) 200 Ok | |
|<--------------| |
| | |
| |--------(5) INVITE SDP1-------->|
| | |
| |<-(6) 183 Session Progress SDP2-|
| | |
| |-----------(7) PRACK----------->|
| | |
| |<------(8) 200 OK (PRACK)-------|
| | |
| |--------(9) UPDATE SDP3-------->|
| | |
| |<---(10) 200 OK (UPDATE) SDP4---|
| | |
| |<--------(11) 180 Ringing-------|
| | |
| |------------(12) PRACK--------->|
| | |
| |<-------(13) 200 OK (PRACK)-----|
| | |
| |<------(15) 200 OK (INVITE)-----|
| | |
| |-------------(15) ACK---------->|
| | |
| |............dialog 2............|
|(16) NOTIFY (200 Ok) |
|<--------------| |
|(17) 200 Ok | |
|-------------->| |
Figure 2: Basic session establishment using Same-Session and
preconditions
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Appendix A.2. Example: preconditions using the 3pcc
A ------------------ B
|
C
Figure 3: 3pcc architecture
Fig.3 shows the architecture achived using the Third Party Call
Control (3pcc) model.
Using 3pcc, A behaves as the controller in Figure 11 of [18]. In
this scenario the flow contains 26 messages. We don't insert the
figure for the sake of space.
Alternatively, it is possible using 3pcc in a different way. A
issues a REFER to C and C send the INVITE towards A. The flow, as
showed in fig.4, without precondition already has 16 messages.
C A B
| | |
|(1)REFER | |
|<------------------| |
|(2) 202 Accepted | |
|------------------>| |
|(3) NOTIFY(100 Trying) |
|<------------------| |
|(4) 200 Ok | |
|------------------>| |
|(5) INVITE | |
|------------------>| |
| |(6) INVITE SDP C |
| |----------------->|
| |(7) 200 Ok SDP AB+AC
| |<-----------------|
| |(8) ACK |
| |----------------->|
|(9) 200 OK SDP AC | |
|<------------------| |
|(10) ACK SDP C | |
|------------------>| |
| |(11) INVITE |
| |----------------->|
| |(12) 200 OK SDP AB+AC
| |<-----------------|
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|(13) INVITE SDP AC | |
|<------------------| |
|(14) 200 OK SDP C | |
|------------------>| |
|(15) ACK | |
|<------------------| |
| |(16) ACK SDP A+C |
| |----------------->|
| |dialog 1 |
| |..................|
Figure 4
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Authors' Addresses
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Salvatore.Loreto@ericsson.com
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
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