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Network Working Group                                         C. Boulton
Internet-Draft                                                     Avaya
Intended status: Standards Track                       November 12, 2007
Expires: May 15, 2008


     A Session Description Protocol (SDP) Control Package Attribute
           draft-boulton-mmusic-sdp-control-package-attribute-00

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Copyright Notice

   Copyright (C) The IETF Trust (2007).














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Internet-Draft          Control Package Attribute          November 2007


Abstract

   This document defines a new Session Description Protocol (SDP) media-
   level attribute: "ctrl-package".  The "ctrl-package" attribute
   conveys details of the SIP Control Framework extension packages that
   are supported by a client participating in an offer/answer exchange.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions and Terminology  . . . . . . . . . . . . . . . . .  4
   3.  The Ctrl-Package Attribute . . . . . . . . . . . . . . . . . .  5
   4.  The Ctrl-Package Attribute in the Offer/Answer Model . . . . .  6
   5.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 13




























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1.  Introduction

   The MEDIACTRL work group of the IETF has defined a SIP Control
   Framework[I-D.boulton-sip-control-framework].  The SIP Control
   Framework introduces the concept of Control Packages which are
   extensions to the core connection framework.  The Control Package
   extension documents allow for the base mechanism to be extended for
   specific usages.  A good example is the Basic IVR Control
   Package[I-D.boulton-ivr-control-package] that is also defined by the
   MEDIACTRL work group for basic Interactive Voice Response.

   [Editors Note: Reference to change].

   Sip Control Packages are identified using a unique registered token
   in a similar mechanism to other IETF technologies such as RFC 3265
   [RFC3265].  The core SIP Control Framework provides a dynamic,
   session level negotiation mechanism to decide on a common set of SIP
   Control Packages that are supported by both clients participating in
   a session.  A mechanism does not exist for clients to identify SIP
   Control Packages supported before the control channel has been
   established.

   This specification defines the SDP 'ctrl-package' media-level
   attribute which provides an indication of SIP Control Package
   extensions that are supported.


























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2.  Conventions and Terminology

   In this document, BCP 14/RFC 2119 [RFC2119] defines the key words
   "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
   "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL".  In addition, BCP 15 indicates requirement levels for
   compliant implementations.












































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3.  The Ctrl-Package Attribute

   This specification defines a new media-level value attribute: 'ctrl-
   package'.  Its formatting in SDP is described by the following
   ABNF[RFC4234].


ctrl-package-attribute = "a=ctrl-package:" 1*(SP ctrl-package-name) CRLF

     ctrl-package-name = token

                 token = 1*(token-char)

            token-char = %x21 / %x23-27 / %x2A-2B / %x2D-2E / %x30-39
                         / %x41-5A / %x5E-7E


   The token-char and token elements are defined in RFC 4566 [RFC4566]
   but included here to provide support for the implementer of this SDP
   feature.

   The values of a 'ctrl-package' attribute consists of a token that has
   been appropriately defined by the Sip Control Framework extension
   procedures for Control packages.  This includes appropriate
   registration.  The 'ctrl-package' attribute serves as a complimentary
   mechanism to the Control Package extension negotiation mechanism that
   is defined in the SIP Control Framework.  It serves as an initial
   hint to the negotiating endpoints on exactly what Control Packages
   are supported in the initial offer/answer [RFC3264] exchange.  This
   can be beneficial both from a resource allocation perspective and it
   could also result in two clients identifying they are not capable of
   successful control channel interactions.  This would lead to early
   abandonment of control channel setup (for example, a client may
   choose to terminate the associated SIP dialog and not attempt to make
   the connection).

   It should be noted that the 'ctrl-package' attribute does not have
   any context outside the initial offer/answer exchange.  It is simply
   to provide two Control Framework clients an opportunity to convey
   supported Control Packages.  The SIP Control Framework has its own
   dynamic negotiation mechanism that is used to negotiate session level
   supported Control Packages.  Allowing such additional semantics
   during an active Control Framework session would result in confusing
   and conflicting operation.  For this reason, after the initial offer/
   answer exchange has taken place, the 'ctrl-package' attribute (and
   changes to it) has no impact on the Control Framework session and
   should be ignored.




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4.  The Ctrl-Package Attribute in the Offer/Answer Model

   This specification does not define a means to discover whether or not
   the peer endpoint understands the 'ctrl-package' attribute because
   values contained in the attribute are informative and only intended
   as a hint at the offer/answer level.

   At the offer/answer level, the fact that an offer does not contain a
   'ctrl-package' attribute does not imply that the answer should not
   contain one.  As a result, this also implies that an offer containing
   a 'ctrl-package' attribute does not imply that the answer should
   contain one.







































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5.  Example

   The following is an example of an SDP session description that uses
   the 'ctrl-package' attribute:


      v=0
      o=originator 2890844526 2890842808 IN IP4 controller.example,com
      s=-
      i=A demo of the ctrl-package attribute
      c=IN IP4 controller.example.com
      t=0 0
      m=application 7575 TCP/ESCS
      a=setup:active
      a=connection:new
      a=ctrl-package:basic-ivr



































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6.  Security Considerations

   Security Considerations to be included in later versions of this
   document.















































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7.  IANA Considerations


    Contact name:          Chris Boulton cboulton@avaya.com.

      Attribute name:        "ctrl-package".

      Type of attribute      Media level.

      Subject to charset:    Not.

      Purpose of attribute:  The 'ctrl-package' attribute indicates
      supported Sip Control Framework extension documents that are
      supported in an associatd media session.

      Allowed attribute values:  A token.



































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8.  Acknowledgments

   The authors would like to thank....
















































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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC4234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, October 2005.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

9.2.  Informative References

   [I-D.boulton-ivr-control-package]
              Boulton, C., Melanchuk, T., McGlashan, S., and A.
              Shiratzky, "A Basic Interactive Voice Response (IVR)
              Control Package for the Session  Initiation Protocol
              (SIP)", draft-boulton-ivr-control-package-04 (work in
              progress), November 2007.

   [I-D.boulton-sip-control-framework]
              Boulton, C., "A Control Framework for the Session
              Initiation Protocol (SIP)",
              draft-boulton-sip-control-framework-05 (work in progress),
              February 2007.

   [RFC3265]  Roach, A., "Session Initiation Protocol (SIP)-Specific
              Event Notification", RFC 3265, June 2002.

















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Author's Address

   Chris Boulton
   Avaya
   Building 3
   Wern Fawr Lane
   St Mellons
   Cardiff, South Wales  CF3 5EA

   Email: cboulton@avaya.com









































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