Problem Statement and Requirements for Transporting User-to-User Call Control Information in SIP
RFC 6567

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Internet Engineering Task Force (IETF)                       A. Johnston
Request for Comments: 6567                                         Avaya
Category: Informational                                         L. Liess
ISSN: 2070-1721                                      Deutsche Telekom AG
                                                              April 2012

                 Problem Statement and Requirements for
       Transporting User-to-User Call Control Information in SIP

Abstract

   This document introduces the transport of call control User-to-User
   Information (UUI) using the Session Initiation Protocol (SIP) and
   develops several requirements for a new SIP mechanism.  Some SIP
   sessions are established by or related to a non-SIP application.
   This application may have information that needs to be transported
   between the SIP User Agents during session establishment.  In
   addition to interworking with the Integrated Services Digital Network
   (ISDN) UUI Service, this extension will also be used for native SIP
   endpoints requiring application UUI.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6567.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

Johnston & Liess              Informational                     [Page 1]
RFC 6567                      SIP UUI Reqs                    April 2012

   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Overview ........................................................2
   2. Use Cases .......................................................3
      2.1. User Agent to User Agent ...................................3
      2.2. Proxy Retargeting ..........................................4
      2.3. Redirection ................................................4
      2.4. Referral ...................................................5
   3. Requirements ....................................................6
   4. Security Considerations .........................................8
   5. Acknowledgements ...............................................10
   6. Informative References .........................................10

1.  Overview

   This document describes the transport of User-to-User Information
   (UUI) during SIP [RFC3261] session setup.  This section introduces
   UUI and explains how it relates to SIP.

   We define SIP UUI data as application-specific information that is
   related to a session being established using SIP.  It is assumed that
   the application is running in both endpoints in a two-party session.
   That is, the application interacts with both the User Agents in a SIP
   session.  In order to function properly, the application needs a
   small piece of information, the UUI, to be transported at the time of
   session establishment.  This information is essentially opaque data
   to SIP -- it is unrelated to SIP routing, authentication, or any
   other SIP function.  This application can be considered to be
   operating at a higher layer on the protocol stack.  As a result, SIP
   should not interpret, understand, or perform any operations on the
   UUI.  Should this not be the case, then the information being
   transported is not considered UUI, and another SIP-specific mechanism
   will be needed to transport the information (such as a new header
   field).  In particular, this mechanism creates no requirements on
   intermediaries such as proxies, Back-to-Back User Agents, and Session
   Border Controllers.

   UUI is defined this way for two reasons.  First, this definition
   supports a strict layering of protocols and data.  Providing
   information and understanding of the UUI to the transport layer (SIP
   in this case) would not provide any benefits and instead could create