[secdir] [New-work] WG Review: Call Control UUI for SIP (cuss)

IESG Secretary <iesg-secretary@ietf.org> Tue, 22 June 2010 17:00 UTC

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Subject: [secdir] [New-work] WG Review: Call Control UUI for SIP (cuss)
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A new IETF working group has been proposed in the Real-time Applications
and Infrastructure Area.  The IESG has not made any determination as yet.
The following draft charter was submitted, and is provided for
informational purposes only. Please send your comments to the IESG mailing
list (iesg@ietf.org) by Tuesday, June 29, 2010.  

Call Control UUI for SIP  (cuss)
Current Status: Proposed Working Group

Last modified: 2010-06-21


Real-time Applications and Infrastructure Area Director(s):
  Gonzalo Camarillo <Gonzalo.Camarillo@ericsson.com>
  Robert Sparks <rjsparks@nostrum.com>

Real-time Applications and Infrastructure Area Advisor:
  Gonzalo Camarillo <Gonzalo.Camarillo@ericsson.com>

Mailing Lists: TBD

Description of Working Group:

The Call Control UUI for SIP (CUSS) working group is chartered to
define a Session Initiation Protocol (SIP) mechanism for transporting
call-control related user-to-user information (UUI) between User
The mechanism developed in this working group is applicable in the
following situations:

1. The information is generated and consumed by an application using
   SIP during session setup but the application is not necessarily
   even SIP aware.
2. The behavior of SIP entities that support it is not significantly
   changed (as discussed in Section 4 of RFC 5727).
3. Generally only the User Agent Client (UAC) and User Agent Server
   (UAS) are interested in the information.
4. The information is expected to survive retargeting, redirection,
   and transfers.
5. SIP elements may need to apply policy about passing and screening
   the information.
6. Multi-vendor interoperability is important.

This mechanism is not applicable in the following situations:

1. The behavior of SIP entities that support it is significantly
   changed (as discussed in Section 4 of RFC 5727).
2. The information is generated and consumed at the SIP layer by SIP
3. SIP elements besides the UAC and UAS might be interested in
   consuming (beyond applying policy) the information.
4. There are specific privacy issues involved with the information
   being transported (e.g., geolocation or emergency-related

User data of the mechanism will be clearly marked with the
application, encoding, semantics, and content type, allowing policy to
be applied by UAs.  The working group will define the information that
each application must specify to utilize the mechanism. This type of
application-specific information will be specified in standards-track
One important application of this mechanism is interworking with the
ISDN User to User Information Service.  This application defined by
ITU-T Q.931 is extensively deployed in the PSTN today supporting such
applications as contact centers, call centers, and automatic call
distributors (ACDs).  A major barrier to the movement of these
applications to SIP is the lack of a standard mechanism to transport
this information in SIP.  For interworking with ISDN, minimal
information about the content of the UUI is available to the PSTN-SIP
gateways.  In this case only, the content will just indicate ISDN UUI
Service 1 interworking rather than the actual content.
Call control UUI is user information conveyed between user agents
during call control operations.  As a result, the information must be
conveyed with the INVITE transaction, and must survive proxy
retargeting, redirection, and transfers.  The mechanism must utilize a
minimum of SIP extensions since it will need to be supported by many
simple SIP user agents such as PSTN gateways.  The mechanism must
interwork with the existing ISDN service but should also be extensible
for use by other applications and non-ISDN protocols.

Even though interworking with the PSTN is an important requirement,
call control UUI can be exchanged between native SIP clients that do
not have any ISUP support. Therefore, existing SIP-T
encapsulation-based approaches defined in RFC3372 do not meet the
requirements to transport this type of information.

Mechanisms based on the SIP INFO method, RFC2976, will not be
considered by the working group since the UUI contents carry
information that must be conveyed during session setup at the user
agent - the information must be conveyed with the INVITE transaction.
The information must be passed with the session setup request
(INVITE), responses to that INVITE, or session termination requests.
As a result, it is not possible to use INFO in these cases.
The group will produce:

- A problem statement and requirements document for implementing a SIP
call control UUI mechanism
- A specification of the SIP extension to best meet those requirements.
Goals and Milestones
Sep 10 - Problem statement and requirements document to IESG
Mar 11 - SIP call control UUI specification to IESG (PS)
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