Call Control UUI Service for SIP
charter-ietf-cuss-01

Document Charter Call Control UUI Service for SIP WG (cuss)
Title Call Control UUI Service for SIP
Last updated 2010-08-31
State Approved
WG State Concluded
IESG Responsible AD Alissa Cooper
Charter Edit AD (None)
Send notices to (None)

Charter
charter-ietf-cuss-01

The Call control UUI Service 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) for
  applications using SIP to establish media sessions.  The information
  transported is essentially opaque to SIP, but is tagged with the
  application that generated it and the encoding method.
   
  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 special case, the application tag will indicate
  ISDN UUI Service 1 interworking.
  
  Call control UUI is a small piece of application information conveyed
  between user agents during call control operations.  As a result, the
  information must be conveyed with the INVITE transaction.  A goal is
  to avoid a dependency on multipart MIME support. 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 working group will define guidelines for other applications to
  utilize the mechanism and the information that each application must
  specify to utilize the mechanism. New applications of the mechanism
  will require a standards-track document.
  
  The mechanism developed in this working group is applicable in the
  following situations:
  
  1. The information is generated and consumed by an application during
     session setup using SIP, 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. User Agent Clients (UAC) and User Agent Servers (UAS) are the
     generator and consumer of the UUI data.  Proxies may route
     based on the application tag.
  
  4. Intermediary elements or proxies can remove or insert UUI
     information
  
  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 elements.
  
  3. SIP elements besides the UAC and UAS might be interested in
     consuming (beyond adding or removing) the information.
  
  4. There are specific privacy issues involved with the information
     being transported (e.g., geolocation or emergency-related
     information).
  
  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.
  
  - An application usage specification for the ISDN UUI Service.