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 (C) The IETF Trust (2007).
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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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