[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 6230

Network Working Group                                         C. Boulton
Internet-Draft                                                     Avaya
Expires: June 6, 2009                                       T. Melanchuk
                                              Rain Willow Communications
                                                            S. McGlashan
                                                         Hewlett-Packard
                                                        December 3, 2008


                    Media Control Channel Framework
             draft-ietf-mediactrl-sip-control-framework-08

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on June 6, 2009.

Abstract

   This document describes a Framework and protocol for application
   deployment where the application programming logic and processing are
   distributed.  This implies that application programming logic can
   seamlessly gain access to appropriate resources that are not co-
   located on the same physical network entity.  The framework uses the
   Session Initiation Protocol (SIP) to establish an application-level
   control mechanism between application servers and associated external
   servers such as media servers.




Boulton, et al.           Expires June 6, 2009                  [Page 1]

Internet-Draft       Media Control Channel Framework       December 2008


   The motivation for the creation of this Framework is to provide an
   interface suitable to meet the requirements of a distributed,
   centralized conference system, as defined by the IETF.  It is not,
   however, limited to this scope and it is envisioned that this generic
   Framework will be used for a wide variety of de-coupled control
   architectures between network entities.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions and Terminology  . . . . . . . . . . . . . . . . .  4
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Control Channel Setup  . . . . . . . . . . . . . . . . . . . . 10
     4.1.   Control Client SIP UAC Behavior . . . . . . . . . . . . . 10
     4.2.   Control Server SIP UAS Behavior . . . . . . . . . . . . . 13
   5.  Establishing Media Streams - Control Client SIP UAC
       Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   6.  Control Framework Interactions . . . . . . . . . . . . . . . . 15
     6.1.   General Behaviour for Constructing Requests . . . . . . . 17
     6.2.   General Behaviour for Constructing Responses  . . . . . . 17
     6.3.   Transaction Processing  . . . . . . . . . . . . . . . . . 18
       6.3.1.  CONTROL Transactions . . . . . . . . . . . . . . . . . 19
       6.3.2.  REPORT Transactions  . . . . . . . . . . . . . . . . . 19
       6.3.3.  K-ALIVE Transactions . . . . . . . . . . . . . . . . . 21
       6.3.4.  SYNC Transactions  . . . . . . . . . . . . . . . . . . 22
   7.  Response Code Descriptions . . . . . . . . . . . . . . . . . . 24
     7.1.   200 Response Code . . . . . . . . . . . . . . . . . . . . 24
     7.2.   202 Response Code . . . . . . . . . . . . . . . . . . . . 25
     7.3.   400 Response Code . . . . . . . . . . . . . . . . . . . . 25
     7.4.   403 Response Code . . . . . . . . . . . . . . . . . . . . 25
     7.5.   405 Response Code . . . . . . . . . . . . . . . . . . . . 25
     7.6.   420 Response Code . . . . . . . . . . . . . . . . . . . . 25
     7.7.   421 Response Code . . . . . . . . . . . . . . . . . . . . 25
     7.8.   422 Response Code . . . . . . . . . . . . . . . . . . . . 25
     7.9.   423 Response Code . . . . . . . . . . . . . . . . . . . . 25
     7.10.  481 Response Code . . . . . . . . . . . . . . . . . . . . 25
     7.11.  500 Response Code . . . . . . . . . . . . . . . . . . . . 26
   8.  Control Packages . . . . . . . . . . . . . . . . . . . . . . . 26
     8.1.   Control Package Name  . . . . . . . . . . . . . . . . . . 26
     8.2.   Framework Message Usage . . . . . . . . . . . . . . . . . 26
     8.3.   Common XML Support  . . . . . . . . . . . . . . . . . . . 27
     8.4.   CONTROL Message Bodies  . . . . . . . . . . . . . . . . . 27
     8.5.   REPORT Message Bodies . . . . . . . . . . . . . . . . . . 27
     8.6.   Audit . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     8.7.   Examples  . . . . . . . . . . . . . . . . . . . . . . . . 28
   9.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . . 28
     9.1.   Control Framework Formal Syntax . . . . . . . . . . . . . 28



Boulton, et al.           Expires June 6, 2009                  [Page 2]

Internet-Draft       Media Control Channel Framework       December 2008


     9.2.   Control Framework Dialog Identifier SDP Attribute . . . . 31
   10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 36
     11.1.  Session Establishment . . . . . . . . . . . . . . . . . . 37
     11.2.  Transport Level Protection  . . . . . . . . . . . . . . . 37
     11.3.  Control Channel Policy Management . . . . . . . . . . . . 37
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 38
     12.1.  Control Packages Registration Information . . . . . . . . 38
       12.1.1. Control Package Registration Template  . . . . . . . . 39
     12.2.  Control Framework Method Names  . . . . . . . . . . . . . 39
     12.3.  Control Framework Status Codes  . . . . . . . . . . . . . 40
     12.4.  Control Framework Header Fields . . . . . . . . . . . . . 40
     12.5.  Control Framework Port  . . . . . . . . . . . . . . . . . 41
     12.6.  SDP Transport Protocol  . . . . . . . . . . . . . . . . . 41
     12.7.  'cfw-id' SDP Attribute  . . . . . . . . . . . . . . . . . 41
     12.8.  URN Sub-Namespace for
            urn:ietf:params:xml:ns:control:framework-attributes . . . 42
     12.9.  XML Schema Registration . . . . . . . . . . . . . . . . . 42
     12.10. MIME Media Type Registration for
            'application/framework-attributes+xml'  . . . . . . . . . 43
   13. Changes  . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
     13.1.  Changes from 07 Version . . . . . . . . . . . . . . . . . 43
     13.2.  Changes from 06 Version . . . . . . . . . . . . . . . . . 44
     13.3.  Changes from 05 Version . . . . . . . . . . . . . . . . . 44
     13.4.  Changes from 04 Version . . . . . . . . . . . . . . . . . 44
     13.5.  Changes from 03 Version . . . . . . . . . . . . . . . . . 44
     13.6.  Changes from 02 Version . . . . . . . . . . . . . . . . . 44
     13.7.  Changes from 01 Version . . . . . . . . . . . . . . . . . 45
     13.8.  Changes from 00 Version . . . . . . . . . . . . . . . . . 45
   14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 45
   15. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 46
   16. Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . 46
     16.1.  Common Dialog/Multiparty Reference Schema . . . . . . . . 46
   17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48
     17.1.  Normative References  . . . . . . . . . . . . . . . . . . 48
     17.2.  Informative References  . . . . . . . . . . . . . . . . . 49
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 50
   Intellectual Property and Copyright Statements . . . . . . . . . . 51













Boulton, et al.           Expires June 6, 2009                  [Page 3]

Internet-Draft       Media Control Channel Framework       December 2008


1.  Introduction

   Real-time media applications are often developed using an
   architecture where the application logic and processing activities
   are distributed.  Commonly, the application logic runs on
   "application servers" but the processing runs on external servers,
   such as "media servers".  This document focuses on the framework and
   protocol between the application server and external processing
   server.  The motivation for this framework comes from a set of
   requirements for Media Server Control, which can be found in the
   'Media Server Control Protocol Requirements' document[RFC5167].
   While the Framework is not media server control specific, it is the
   primary driver and use case for this work.  It is intended that the
   framework contained in this document can be used for a variety of
   device control scenarios (for example, conference control).

   This document does not define a SIP protocol driven extension that
   can be used directly for the control of external components.  The
   framework mechanism is extended by other documents that are known as
   "Control Packages".  A comprehensive set of guidelines for creating
   "Control Packages" is described in Section 8.

   Current IETF device control protocols, such as megaco [RFC3525],
   while excellent for controlling media gateways that bridge separate
   networks, are troublesome for supporting media-rich applications in
   SIP networks, because they duplicate many of the functions inherent
   in SIP.  Rather than relying on single protocol session
   establishment, application developers need to translate between two
   separate mechanisms.

   SIP [RFC3261] provides the ideal rendezvous mechanism for
   establishing and maintaining control connections to external server
   components.  The control connections can then be used to exchange
   explicit command/response interactions that allow for media control
   and associated command response results.


2.  Conventions and Terminology

   In this document, BCP 14 [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.

   The following additional terms are defined for use in this document:





Boulton, et al.           Expires June 6, 2009                  [Page 4]

Internet-Draft       Media Control Channel Framework       December 2008


   User Agent Client (UAC):  As specified in [RFC3261].
   User Agent Server (UAS):  As specified in [RFC3261].
   B2BUA:  A B2BUA is a Back-to-Back SIP User Agent.
   Control Server:  A Control Server is an entity that performs a
      service, such as media processing, on behalf of a Control Client.
      For example, a media server offers mixing, announcement, tone
      detection and generation, and play and record services.  The
      Control Server in this case, has a direct RTP [RFC3550]
      relationship with the source or sink of the media flow.  In this
      document, we often refer to the Control Server simply as "the
      Server".
   Control Client:  A Control Client is an entity that requests
      processing from a Control Server.  Note that the Control Client
      may not have any processing capabilities whatsoever.  For example,
      the Control Client may be an Application Server (B2BUA) or other
      endpoint requesting manipulation of a third-party's media stream,
      that terminates on a media server acting in the role of a Control
      Server.  In this document, we often refer to the Control Client
      simply as "the Client".
   Control Channel:  A Control Channel is a reliable connection between
      a Client and Server that is used to exchange Framework messages.
      The term "Connection" is used synonymously within this document.
   Framework Message:  A Framework Message is a message on a Control
      Channel that has a type corresponding to one of the Methods
      defined in this document.  A Framework message is often referred
      to by its method, such as a "CONTROL message".
   Method:  A Method is the type of a framework message.  Four Methods
      are defined in this document: SYNC, CONTROL, REPORT, and K-ALIVE.
   Control Command:  A Control Command is an application level request
      from a Client to a Server.  Control Commands are carried in the
      body of CONTROL messages.  Control Commands are defined in
      separate specifications known as "Control Packages".
   framework transaction:  A framework transaction is defined as a
      sequence composed of a control framework message originated by
      either a Control Client or Control Server and responded to with a
      control Framework response code message.  Note that the control
      framework has no "provisional" responses.  A control framework
      transaction MUST complete within 5 seconds and is referenced
      throughout the draft as 'Transaction-Timeout'.
   extended transaction lifetime:  An extended transaction lifetime is
      used to extend the lifetime of a CONTROL method transaction when
      the Control Command it carries cannot be completed within
      'Transaction-Timeout'.  A Server extends the lifetime of a CONTROL
      method transaction by sending a 202 response code followed by one
      or more REPORT transactions as specified in Section 6.3.2.
      Extended transaction lifetimes allow command failures to be
      discovered at the transaction layer.




Boulton, et al.           Expires June 6, 2009                  [Page 5]

Internet-Draft       Media Control Channel Framework       December 2008


   Transaction-Timeout:  the maximum allowed time between a control
      Client or Server issuing a framework message and receiving a
      corresponding response.  The value for the timeout should be based
      on a multiple of the network RTT plus an appropriate number
      milliseconds to allow for message parsing and processing.  The
      value for 'Transaction-Timeout' is 5 seconds.


3.  Overview

   This document details mechanisms for establishing, using, and
   terminating a reliable transport connection channel using SIP and the
   Session Description Protocol offer/answer [RFC3264] exchange.  The
   established connection is then used for controlling an external
   server.  The following text provides a non-normative overview of the
   mechanisms used.  Detailed, normative guidelines are provided later
   in the document.

   Control channels are negotiated using standard SIP mechanisms that
   would be used in a similar manner to creating a SIP multimedia
   session.  Figure 1 illustrates a simplified view of the mechanism.
   It highlights a separation of the SIP signaling traffic and the
   associated control channel that is established as a result of the SIP
   interactions.

   Initial analysis into the control framework, as documented in
   [I-D.burger-mscl-thoughts], established the following.  One might
   ask, "If all we are doing is establishing a TCP connection to control
   the media server, what do we need SIP for?"  This is a reasonable
   question.  The key is to be using SIP for media session
   establishment.  If we are using SIP for media session establishment,
   then we need to ensure the URI used for session establishment
   resolves to the same node as the node for session control.  Using the
   SIP routing mechanism, and having the server initiate the TCP
   connection back, ensures this works.  For example, the URI sip:
   myserver.example.com may resolve to sip:
   server21.farm12.northeast.example.net, whereas the URI
   http://myserver.example.com may resolve to
   http://server41.httpfarm.central.example.net.  That is, the host part
   is NOT NECESSARILY unambiguous.

   The use of SIP for to negotiate the control-channel provides many
   inherent capabilities which include:
   o  Service location - Use SIP Proxies or Back-to-Back User Agents for
      discovering Control Servers.
   o  Security mechanisms - Leverage established security mechanisms
      such as Transport Layer Security (TLS) and Client Authentication.




Boulton, et al.           Expires June 6, 2009                  [Page 6]

Internet-Draft       Media Control Channel Framework       December 2008


   o  Connection maintenance - The ability to re-negotiate a connection,
      ensure it is active, and so forth.
   o  Application agnostic - Generic protocol allows for easy extension.

   As mentioned in the previous list, one of the main benefits of using
   SIP as the session control protocol is the "Service Location"
   facilities provided.  This applies at both a routing level, where
   [RFC3263] provides the physical location of devices, and at the
   Service level, using Caller Preferences [RFC3840] and Callee
   Capabilities [RFC3841].  The ability to select a Control Server based
   on Service level capabilities is extremely powerful when considering
   a distributed, clustered architecture containing varying services
   (for example Voice, Video, IM).  More detail on locating Control
   Server resources using these techniques is outlined in Section 4.1 of
   this document.


          +--------------SIP Traffic--------------+
          |                                       |
          v                                       v
       +-----+                                 +--+--+
       | SIP |                                 | SIP |
       |Stack|                                 |Stack|
   +---+-----+---+                         +---+-----+---+
   |   Control   |                         |   Control   |
   |   Client    |<----Control Channel---->|   Server    |
   +-------------+                         +-------------+



                       Figure 1: Basic Architecture

   The example from Figure 1 conveys a 1:1 connection between the
   Control Client and the Control Server.  It is possible, if required,
   for multiple control channels using separate SIP dialogs to be
   established between the Control Client and the Control Server
   entities.  Any of the connections created between the two entities
   can then be used for Server control interactions.  The control
   connections are agnostic to any media sessions.  Specific media
   session information can be incorporated in control interaction
   commands (which themselves are defined in external packages) using
   the XML schema defined in Section 16.  The ability to have multiple
   control channels allows for stronger redundancy and the ability to
   manage high volumes of traffic in busy systems.

   Consider the following simple example for session establishment
   between a Client and a Server (Note: Some lines in the examples are
   removed for clarity and brevity).  Note that the roles discussed are



Boulton, et al.           Expires June 6, 2009                  [Page 7]

Internet-Draft       Media Control Channel Framework       December 2008


   logical and can change during a session, if the Control Package
   allows.

   The Client constructs and sends a standard SIP INVITE request, as
   defined in [RFC3261], to the external Server.  The SDP payload
   includes the required information for control channel negotiation and
   is the primary mechanism for conveying support for this specification
   (through the media type).  The COMEDIA [RFC4145] specification for
   setting up and maintaining reliable connections is used as part of
   the negotiation mechanism (more detail available in later sections).
   The Client will also include the 'cfw-id' SDP attribute, as defined
   in this specification which is used to correlate the underlying Media
   Control Channel with the offer/answer exchange.

   Client Sends to External Server:

   INVITE sip:External-Server@example.com SIP/2.0
   To: <sip:External-Server@example.com>
   From: <sip:Client@example.com>;tag=64823746
   Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK72dhjsU
   Call-ID: 7823987HJHG6
   CSeq: 1 INVITE
   Contact: <sip:Client@clientmachine.example.com>
   Content-Type: application/sdp
   Content-Length: [..]

   v=0
   o=originator 2890844526 2890842808 IN IP4 controller.example,com
   s=-
   c=IN IP4 controller.example.com
   m=application 7575 TCP/CFW *
   a=setup:active
   a=connection:new
   a=cfw-id:H839quwhjdhegvdga


   On receiving the INVITE request, an external Server supporting this
   mechanism generates a 200 OK response containing appropriate SDP.
   The 'cfw-id' SDP attribute is copied from the original offer.

   External Server Sends to Client:










Boulton, et al.           Expires June 6, 2009                  [Page 8]

Internet-Draft       Media Control Channel Framework       December 2008


   SIP/2.0 200 OK
   To: <sip:External-Server@example.com>;tag=28943879
   From: <sip:Client@example.com>;tag=64823746
   Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK72dhjsU
   Call-ID: 7823987HJHG6
   CSeq: 1 INVITE
   Contact: <sip:External-Server@servermachine.example.com>
   Content-Type: application/sdp
   Content-Length: [..]

   v=0
   o=originator 2890844526 2890842808 IN IP4 server.example.com
   s=-
   c=IN IP4 mserver.example.com
   m=application 7563 TCP/CFW *
   a=setup:passive
   a=connection:new
   a=cfw-id:H839quwhjdhegvdga


   The Control Client receives the SIP 200 OK response and extracts the
   relevant information (also sending a SIP ACK).  It creates an
   outgoing (as specified by the SDP 'setup:' attribute of 'active') TCP
   connection to the Control Server.  The connection address (taken from
   'c=') and port (taken from 'm=')are used to identify the remote port
   in the new connection.

   Once established, the newly created connection can be used to
   exchange requests and responses as defined in this document.  If
   required, after the control channel has been setup, media sessions
   can be established using standard SIP third party call control.

   Figure 2 provides a simplified example where the framework is used to
   control a User Agent's RTP session. (1) in brackets represents the
   SIP dialog and dedicated control channel previously described in this
   overview section.















Boulton, et al.           Expires June 6, 2009                  [Page 9]

Internet-Draft       Media Control Channel Framework       December 2008


                         +--------Control SIP Dialog(1)---------+
                         |                                      |
                         v                                      v
                      +-----+                                +--+--+
     +------(2)------>| SIP |---------------(2)------------->| SIP |
     |                |Stack|                                |Stack|
     |            +---+-----+---+                        +---+-----+---+
     |            |             |                        |             |
     |            |   Control   |<--Control Channel(1)-->|             |
     |            |   Client    |                        |   Control   |
     |            +-------------+                        |   Server    |
  +--+--+                                                |             |
  |User |                                                |             |
  |Agent|<=====================RTP(2)===================>|             |
  +-----+                                                +-------------+


                    Figure 2: Participant Architecture

   (2) from Figure 2 represents the User Agent SIP dialog interactions
   and associated media flow.  A User Agent would create a SIP dialog
   with the Control Client entity.  The Control Client entity will also
   create a related dialog to the Control Server (B2BUA type
   functionality).  Using the interaction illustrated by (2), the
   Control Client negotiates media capabilities with the Control Server,
   on behalf of the User Agent, using SIP Third Party Call Control
   [RFC3725].


4.  Control Channel Setup

   This section describes the setup, using SIP, of the dedicated
   control.  Once the control channel has been established commands can
   be exchanged (as discussed in Section 6).

4.1.  Control Client SIP UAC Behavior

   When a UAC wishes to establish a control channel, it MUST construct
   and transmit a new SIP INVITE request for control channel setup, a
   UAC MUST construct the protocol message as defined in [RFC3261].

   If a reliable response is received (as defined [RFC3261] and
   [RFC3262]), the mechanisms defined in this document are applicable to
   the newly created dialog.

   The UAC SHOULD include a valid session description (an 'offer' as
   defined in [RFC3264]) in an INVITE request using the Session
   Description Protocol defined in [RFC4566] (*note - SIP also allows an



Boulton, et al.           Expires June 6, 2009                 [Page 10]

Internet-Draft       Media Control Channel Framework       December 2008


   'offer-less' INVITE which is also maintained by this specification).
   The following information defines the composition of some specific
   elements of the SDP payload that MUST be adhered to for compliancy to
   this specification when used in an SIP SDP offer.

   The Connection Data line in the SDP payload is constructed as
   specified in [RFC4566]:

   c=<nettype> <addrtype> <connection-address>

   The first sub-field, <nettype>, MUST equal the value "IN".  The
   second sub-field, <addrtype>, MUST equal either "IP4" or "IP6".  The
   third sub-field for Connection Data is <connection-address>.  This
   supplies a representation of the SDP originators address, for example
   dns/IP representation.  The address will be the network address used
   for connections in this specification.

   Example:

   c=IN IP4 controller.example.com

   The SDP MUST contain a corresponding Media Description entry for
   compliance to this specification:

   m=<media> <port> <proto>

   The first "sub-field" <media> MUST equal the value "application".
   The second sub-field, <port>, MUST represent a port on which the
   constructing client can receive an incoming connection if required.
   The port is used in combination with the address specified in the
   'Connection Data line defined previously to supply connection
   details.  If the constructing client can't receive incoming
   connections it MUST still enter a valid port range entry.  The use of
   the port value '0' has the same meaning as defined in the SDP
   specification[RFC4566].  The Control Framework has an IANA-registered
   recommended port defined in Section 12.5.  This value is not a
   default as a client is free to choose explicit port numbers.
   However, SDP SHOULD be configured so that the recommended port is
   used whenever appropriate.  This makes life easier for network
   administrators who need to manage firewall policy for Control
   Framework interactions.  The third sub-field, <proto>, MUST equal a
   transport value defined in Section 12.6.  All implementations
   compliant to this specification MUST support the value "TCP/CFW",
   "TCP/TLS/CFW", "SCTP/CFW" and "SCTP/TLS/CFW" as defined in
   Section 12.6 of this document.  Implementations MUST support TLS as a
   transport-level security mechanism for the control channel, although
   use of TLS in specific deployments is optional.  Control Framework
   implementations MUST support TCP as a transport protocol.  Control



Boulton, et al.           Expires June 6, 2009                 [Page 11]

Internet-Draft       Media Control Channel Framework       December 2008


   Framework implementations MAY support SCTP as a transport protocol.
   When an entity identifies one of the transport values defined in
   Section 12.6 but is not willing to establish the session, it MUST
   respond using the appropriate SIP mechanism.

   The SDP MUST also contain a number of SDP media attributes(a=) that
   are specifically defined in the COMEDIA [RFC4145] specification.  The
   attributes provide connection negotiation and maintenance parameters.
   A client conforming to this specification SHOULD support all the
   possible values defined for media attributes from the COMEDIA
   [RFC4145] specification but MAY choose not to support values if it
   can definitely determine they will never be used (for example will
   only ever initiate outgoing connections).  It is RECOMMENDED that a
   Controlling UAC initiate a connection to an external Server but that
   an external Server MAY negotiate and initiate a connection using
   COMEDIA, if network topology prohibits initiating connections in a
   certain direction.  An example of the attributes is:


                           a=setup:active
                           a=connection:new


   This example demonstrates a new connection that will be initiated
   from the owner of the SDP payload.  The connection details are
   contained in the SDP answer received from the UAS.  A full example of
   an SDP payload compliant to this specification can be viewed in
   Section 3.  Once the SDP has been constructed along with the
   remainder of the SIP INVITE request (as defined in [RFC3261]), it can
   be sent to the appropriate location.  The SIP dialog and appropriate
   control connection is then established.

   A SIP UAC constructing an offer MUST include the 'cfw-id' SDP
   attribute as defined in Section 9.2.  The 'cfw-id' attribute
   indicates an identifier that can be used within the control channel
   to correlate the control channel with this SIP dialog.  This
   attribute MUST contain an appropriately random value of at least 64
   bits of randomness that will not clash with other offer/answer
   exchanges that will take place and is globally unique over space and
   time.  The value chosen for the 'cfw-id' attribute MUST be used for
   the entire duration of the associated SIP dialog and not be changed
   during updates to the offer/answer exchange.  This applies to
   specifically to the 'connection' attribute as defined in [RFC4145].
   If a SIP UAC wants to change some other parts of the SDP but reuse
   the already established connection it should use the value of
   'existing' in the 'connection' attribute (for example, a=connection:
   existing).  If it has noted that a connection has failed and wants to
   re-establish, it uses the value of 'new' in the 'connection'



Boulton, et al.           Expires June 6, 2009                 [Page 12]

Internet-Draft       Media Control Channel Framework       December 2008


   attribute (for example, a=connection:new).  Throughout this the
   connection identifier specified in the 'cfw-id' SDP parameter does
   not change.  You are simply negotiating the underlying TCP connection
   between endpoints but always using the same Control Framework
   session, which is 1:1 for the lifetime of the SIP dialog.

   A non-2xx class final response (4xx, 5xx and 6xx) SIP response
   received for the INVITE request indicates that no SIP dialog has been
   created and is treated as specified [RFC3261].  Specifically, support
   of this specification is negotiated through the presence of the media
   type defined in this specification.  The receipt of a SIP error
   response like "488" indicates that the offer contained in a request
   is not acceptable.  The inclusion of the media line associated with
   this specification in such a rejected offer should indicate to the
   client generating the offer that this could be due to the receiving
   client not supporting this specification.  The client generating the
   offer MUST act as it would normally on receiving this response, as
   per [RFC3261].  Media streams can also be rejected by setting the
   port to "0" in the "m=" line of the session description.  A client
   using this specification MUST be prepared to receive an answer where
   the "m=" line it inserted for using the Control Framework has been
   set to "0".  In this situation the client will act as it would for
   any other media type with a port set to "0".

4.2.  Control Server SIP UAS Behavior

   On receiving a SIP INVITE request, an external Server(SIP UAS)
   inspects the message for indications of support for the mechanisms
   defined in this specification.  This is achieved through inspection
   of the Sessions Description of the offer message and identifying
   support for the appropriate media type.  If the SIP UAS wishes to
   construct a reliable response that conveys support for the extension,
   it MUST follow the mechanisms defined in [RFC3261].  If support is
   conveyed in a reliable SIP provisional response, the mechanisms in
   [RFC3262] MUST also be used.  It should be noted that the SDP offer
   is not restricted to the initial INVITE request and may appear in any
   series of messages that are compliant to [RFC3261], [RFC3262], and
   [RFC3264].

   When constructing an answer, the SDP payload MUST be constructed
   using the semantic (Connection, Media and attribute) defined in
   Section 4.1 using valid local settings and also with full compliance
   to the COMEDIA[RFC4145] specification.  For example, the SDP
   attributes included in the answer constructed for the example offer
   provided in Section 4.1 would look as illustrated below:


                           a=setup:passive



Boulton, et al.           Expires June 6, 2009                 [Page 13]

Internet-Draft       Media Control Channel Framework       December 2008


                           a=connection:new


   A client constructing an answer MUST include the 'cfw-id' SDP
   attribute as defined in Section 9.2.  This attribute MUST exactly
   copy the value which appeared in the initial offer.

   Once the SDP answer has been constructed, it is sent using standard
   SIP mechanisms.  Depending on the contents of the SDP payloads that
   were negotiated using the Offer/Answer exchange, a reliable
   connection will be established between the Controlling UAC and
   external Server UAS entities.  The newly established connection is
   now available to exchange control command primitives.  The state of
   the SIP Dialog and the associated Control channel are now implicitly
   linked.  If either party wishes to terminate a Control channel it
   simply issues a SIP termination request (for example a SIP BYE
   request, or appropriate response in an early dialog).  The Control
   Channel therefore lives for the duration of the SIP dialog.

   If the SIP UAS does not support the extension defined in this
   document, as identified by the media contained in the Session
   Description, it should respond as detailed in [RFC3261] with a "SIP
   488" response code.  If multiple media descriptions exist it might
   choose to continue processing the request and mark the port field
   equal to "0".

   A SIP entity receiving a SIP OPTIONS request MUST respond
   appropriately as defined in [RFC3261].  This involves providing
   information relating to supported SIP extensions and media types in a
   200 OK response.  For this extension the media types supported MUST
   be included in the SIP 200 OK response in a SIP "Accept" header to
   indicate a valid media type.


5.  Establishing Media Streams - Control Client SIP UAC Behavior

   It is intended that the Control framework will be used within a
   variety of architectures for a wide range of functions.  One of the
   primary functions will be the use of the control channel to apply
   specific Control package commands to media sessions established by
   SIP dialogs (media dialogs) with the same remote server.  For
   example, to apply a command to generate audio media (such as an
   announcement) on an RTP session between a User Agent and a Media
   Server.

   SIP dialogs used to establish media sessions (see Figure 2) on behalf
   of User Agents may contain more than one Media Description (as
   defined by "m=" in the SDP).  The Control Client SHOULD include a



Boulton, et al.           Expires June 6, 2009                 [Page 14]

Internet-Draft       Media Control Channel Framework       December 2008


   media label attribute, as defined in [RFC4574], for each "m="
   definition received that is to be directed to an entity using the
   control framework.  This allows the Control Client to later
   explicitly direct commands on the control channel at a specific media
   line (m=).  A Control Client constructing the SDP MAY choose not to
   include the media label SDP attribute if it does not require direct
   control on a per media stream basis.

   This framework identifies the referencing of such associated media
   dialogs as extremely important.  A connection reference attribute has
   been specified that can optionally be imported into any Control
   Package.  It is intended that this will reduce repetitive specifying
   of dialog reference language.  The schema can be found in
   Section 16.1 in Appendix A.

   Similarly, the ability to identify and apply commands to a group of
   associated media dialogs (multiparty) is also identified as a common
   structure that could be defined and re-used, for example playing a
   prompt to all participants in a Conference.  The schema for such
   operations can also be found in Section 16.1 in Appendix A.

   Support for both the common attributes described here is specified as
   part of each Control Package definition, as detailed in Section 8.


6.  Control Framework Interactions

   The use of the COMEDIA specification in this document allows for a
   Control Channel to be set up in either direction as a result of a SIP
   INVITE transaction.  SIP provides a flexible negotiation mechanism to
   establish the control channel, but there needs to be a mechanism
   within the control channel to correlate the control channel with the
   SIP dialog used for its establishment.  A Control Client receiving an
   incoming connection (whether it be acting in the role of UAC or UAS)
   has no way of identifying the associated SIP dialog as it could be
   simply listening for all incoming connections on a specific port.
   The following steps, which implementations MUST support, allow a
   connecting UA (defined as 'active' role in COMEDIA) to identify the
   associated SIP dialog that triggered the connection.  These steps
   SHOULD be carried out before any other signaling on the newly created
   Control channel.  An alternative dialog association mechanism MAY be
   specified in extensions to this document.
   o  Once the connection has been established, the UA acting in the
      active role (active UA) to initiate the connection MUST
      immediately send a Control Framework SYNC request.  The SYNC
      request MUST be constructed as defined in Section 9.1 and MUST
      contain the message header, 'Dialog-ID', which contains the SIP
      dialog information.



Boulton, et al.           Expires June 6, 2009                 [Page 15]

Internet-Draft       Media Control Channel Framework       December 2008


   o  The 'Dialog-ID' message header value is the value contained in the
      'cfw-id' SDP media level attribute.  This allows for a correlation
      between the control channel and its associated SIP dialog.
   o  On creating the SYNC request the active UA MUST follow the
      procedures outlined in Section 6.3.3.  This provides details of
      connection keep alive messages.
   o  On creating the SYNC request the active UA MUST also follow the
      procedures outlined in Section 6.3.4.2.  This provides details of
      the negotiation mechanism used to determine the Protocol Data
      Units (PDUs) that can be exchanged on the established control
      channel connection.
   o  The active UA MUST then send the SYNC request.  It MUST then wait
      for a period of at least 'Transaction-Timeout' to receive a
      response.  It MAY choose a longer time to wait but it MUST not be
      shorter than 'Transaction-Timeout'.
   o  If no response is received for the SYNC control message, a timeout
      occurs and the control channel is terminated along with the
      associated SIP dialog (issue a BYE request).
   o  If the active UA receives a 481 response, this implies that the
      SYNC request was received but no associated SIP dialog exists.
      This also results in the control channel being terminated along
      with the associated SIP dialog (issue a BYE request).
   o  All other error responses received for the SYNC request are
      treated as detailed in this specification and also result in the
      termination of the control channel and the associated SIP dialog
      (issue a BYE request).
   o  The receipt of a 200 response to a SYNC message implies that the
      SIP dialog and control connection have been successfully
      correlated.  The control channel can now be used for further
      interactions.

   SYNC messages can be sent at any point while the Control Channel is
   open from either side, once the initial exchange is complete.  If
   present, the contents of the "Keep-Alive" and "Dialog-ID" headers
   MUST not change.  New values of the "Keep-Alive" and "Dialog-ID"
   headers have no relevance as they are negotiated for the lifetime of
   the Media Control Channel Framework session.

   Once a successful control channel has been established, as defined in
   Section 4.1 and Section 4.2, and the connection has been correlated,
   as described in previous paragraphs, the two entities are now in a
   position to exchange control framework messages.  The following sub-
   sections specify the general behaviour for constructing control
   framework requests and responses.  Section 6.3 specifies the core
   Control Framework methods and their transaction processing.






Boulton, et al.           Expires June 6, 2009                 [Page 16]

Internet-Draft       Media Control Channel Framework       December 2008


6.1.  General Behaviour for Constructing Requests

   An entity acting as a Control Client that constructs and sends
   requests on a control channel MUST adhere to the syntax defined in
   Section 9 (Note: either entity can act as a control client depending
   on individual package requirements).  Control Commands MUST also
   adhere to the syntax defined by the Control Packages negotiated in
   Section 4.1 and Section 4.2 of this document.  A Control Client MUST
   create a unique control message transaction and associated identifier
   for insertion in the request.  The transaction identifier is then
   included in the first line of a control framework message along with
   the method type (as defined in the ABNF in Section 9).  The first
   line starts with the "CFW" token for the purpose of easily extracting
   the transaction identifier.  The transaction identifier MUST be
   globally unique over space and time with at least 64 bits of
   randomness.  This unique property helps in the avoidance of clashes
   when multiple client entities could be creating transactions to be
   carried out on a single receiving server.  All required mandatory and
   optional control framework headers are then inserted into the control
   message with appropriate values (see relevant individual header
   information for explicit detail).  A "Control-Package" header MUST
   also be inserted with the value indicating the Control Package to
   which this specific request applies.  Multiple packages can be
   negotiated per control channel using the SYNC control message
   discussed in Section 6.3.4.2.

   Any framework message that contains an associated payload MUST also
   include a 'Content-Type' and 'Content-Length' message header which
   represents the size of the message body in decimal number of octets.
   The 'Content-Type' header represents the MIME payload to be used as
   specified by the individual control framework packages.  If no
   associated payload is to be added to the message, a 'Content-Length'
   header with a value of '0' is considered the same as one not being
   present.

   When all of the headers have been included in the framework message,
   it is sent down the control channel.

   A Server receiving such a request needs to respond quickly with an
   appropriate response (as defined in Section 6.2).  Control Clients
   MUST wait for a minimum of 'Transaction-Timeout' for a response
   before considering the transaction a failure and tidying state
   appropriately depending on the extension package being used.

6.2.  General Behaviour for Constructing Responses

   An entity acting as a Control Server, on receiving a request, MUST
   generate a response within the 'Transaction-Time'.  The response MUST



Boulton, et al.           Expires June 6, 2009                 [Page 17]

Internet-Draft       Media Control Channel Framework       December 2008


   conform to the ABNF defined in Section 9.  The first line of the
   response MUST contain the transaction identifier used in first line
   of the request, as defined in Section 6.1.  Responses MUST NOT
   include the 'Status' or 'Timeout' message headers, and these MUST be
   ignored if received by a Client in a response.

   A Control Server MUST then include a status code in the first line of
   the constructed response.  A Control Framework request (like CONTROL)
   that has been received, and either the actions specified by the
   request have completed or a control command error is detected, uses
   the 200 Control Framework status code as defined in Section 7.1 in
   the response.  A 200 response MAY include message bodies.  If a 200
   response does contain a payload it MUST include Content-Length and
   Content-Type headers.  A 200 is the only response defined in this
   specification that allows a message body to be included.  The
   'Content-Type' header represents the MIME payload to be used as
   specified by the individual control framework packages.  A client
   receiving a 200 class response then considers the control command
   transaction completed.  A Control Framework request (like CONTROL)
   that is received and understood but requires processing that extends
   beyond 'Transaction-Timeout' will result in a 202 status code in the
   response.  This will be followed by one or more REPORT messages as
   defined in Section 6.3.2.  A Control Package SHOULD explicitly define
   the circumstances under which either 200 or 202 with subsequent
   processing takes place.

   If a Control Server encounters problems with a Control Framework
   request (like REPORT or CONTROL), an appropriate error code should be
   used in the response, as listed in Section 7.  The generation of a
   non 2xx class response code to a Control Framework request (like
   CONTROL or REPORT) will indicate failure of the transaction, and all
   associated state and resources should be terminated.  The response
   code may provide an explicit indication of why the transaction
   failed, which might result in a re-submission of the request
   depending on the extension package being used.

6.3.  Transaction Processing

   The Control Framework defines four types of requests (methods):
   CONTROL, REPORT, K-ALIVE, and SYNC.  Implementations MUST support
   sending and receiving all four methods.  Future extensions to this
   document MAY define new methods and responses.

   The following sub-sections specify each Control Framework method and
   its associated transaction processing.






Boulton, et al.           Expires June 6, 2009                 [Page 18]

Internet-Draft       Media Control Channel Framework       December 2008


6.3.1.  CONTROL Transactions

   A 'CONTROL' message is used by the Control Client to pass control
   related information to a Control Server.  It is also used as the
   event reporting mechanism in the control framework.  Reporting events
   is simply another usage of the 'CONTROL' message which is permitted
   to be sent in either direction between two participants in a session,
   carrying the appropriate payload for an event.  The message is
   constructed in the same way as any standard Control Framework
   message, as discussed previously in Section 6.1 and defined in
   Section 9.  A CONTROL message MAY contain a message body.  The
   explicit control command(s) of the message payload contained in a
   CONTROL message are specified in separate Control Package
   specifications.  These specifications MUST conform to the format
   defined in Section 8.4.  A CONTROL message containing a payload MUST
   include a 'Content-Type' header indicating the payload type defined
   by the control package.  A CONTROL message that does not contain a
   payload should be dealt with in the individual package.  This could
   in fact be a valid message exchange within a specific package and if
   not an appropriate package level error message should be generated.

6.3.2.  REPORT Transactions

   A 'REPORT' message is used by a Control Server when processing of a
   CONTROL Command extends beyond a 'Transaction-Timeout'.  In this case
   a 202 response is returned.  Status updates and the final results of
   the command are then returned in subsequent REPORT messages.

   All REPORT messages MUST contain the same transaction ID in the
   request start line that was present in the original CONTROL
   transaction.  This allows extended transactions to be correlated with
   the original CONTROL transaction.  A REPORT message containing a
   payload MUST include a 'Content-Length and 'Content-Type' header
   indicating the payload MIME[RFC2045] type defined by the control
   package and its length.

6.3.2.1.  Reporting the Status of Extended Transactions

   On receiving a CONTROL message, a Control Server MUST respond within
   'Transaction-Timeout' with a status code for the request, as
   specified in Section 6.2.  If the command completed within that time,
   a 200 response code would have been sent.  If the command did not
   complete within that time, the response code 202 would have been sent
   indicating that the requested command is still being processed and
   the CONTROL transaction is being extended.  The REPORT method is then
   used to update and terminate the status of the extended transaction.

   A Control Server issuing a 202 response MUST contain a 'Timeout'



Boulton, et al.           Expires June 6, 2009                 [Page 19]

Internet-Draft       Media Control Channel Framework       December 2008


   message header.  This header will contain a value in seconds that
   represents the amount of time the recipient of the 202 message must
   wait before assuming that there has been a problem and terminating
   the extended transaction and associated state (no corresponding
   REPORT message arrived).

   The initial REPORT message MUST contain a 'Seq' (Sequence) message
   header with a value equal to '1' (It should be noted that the 'Seq'
   numbers at both Control Client and Control Server for framework
   messages are independent).

   All REPORT messages for an extended CONTROL transaction MUST contain
   a 'Timeout' message header.  This header will contain a value in
   seconds that represents the amount of time the recipient of the
   REPORT message must wait before assuming that there has been a
   problem and terminating the extended transaction and associated
   state.  On receiving a REPORT message with a 'Status' header of
   'update', the Control Client MUST reset the timer for the associated
   extended CONTROL transaction to the indicated timeout period.  If the
   timeout period approaches with no intended REPORT messages being
   generated, the entity acting as a Control Framework UAS for the
   interaction MUST generate a REPORT message containing, as defined in
   this paragraph, a 'Status' header of 'update' with no associated
   payload.  Such a message acts as a timeout refresh and in no way
   impacts the extended transaction, because no message body or
   semantics are permitted.  It is RECOMMENDED that a minimum value of
   10 and a maximum value of 15 seconds be used for the value of the
   'Timeout' message header.  It is also RECOMMENDED that a Control
   Server refresh the timeout period of the CONTROL transaction at an
   interval that is not too close to the expiry time.  A value of 80% of
   the timeout period could be used, for example a timeout period of 10
   seconds would be refreshed after 8 seconds.

   Subsequent REPORT messages that provide additional information
   relating to the extended CONTROL transaction MUST also include and
   increment by 1 the 'Seq' header value.  They MUST also include a
   'Status' header with a value of 'update'.  These REPORT messages sent
   to update the extended CONTROL transaction status MAY contain a
   message body, as defined by individual Control Packages and specified
   in Section 9.5.  A REPORT message sent updating the extended
   transaction also acts as a timeout refresh, as described earlier in
   this section.  This will result in a transaction timeout period at
   the initiator of the original CONTROL request being reset to the
   interval contained in the 'Timeout' message header.

   When all processing for an extended CONTROL transaction has taken
   place, the entity acting as a Control Server MUST send a terminating
   REPORT message.  The terminating REPORT message MUST increment the



Boulton, et al.           Expires June 6, 2009                 [Page 20]

Internet-Draft       Media Control Channel Framework       December 2008


   value in the 'Seq' message header by the value of '1' from the
   previous REPORT message.  It MUST also include a 'Status' header with
   a value of 'terminate' and MAY contain a message body.  A Control
   Framework UAC can then clean up any pending state associated with the
   original control transaction.

6.3.3.  K-ALIVE Transactions

   The protocol defined in this document may be used in various network
   architectures.  This will include a wide range of deployments where
   the clients could be co-located in a secured, private domain, or
   spread across disparate domains that require traversal of devices
   such as Network Address Translators (NAT) and Firewalls.  A keep
   alive mechanism enables the control channel to be kept active during
   times of inactivity (for example, most Firewalls have a timeout
   period after which connections are closed).  This mechanism also
   provides the ability for application level failure detection.  It
   should be noted that the following procedures apply explicitly to the
   control channel being created.  For details relating to a SIP keep
   alive mechanism, implementers should seek guidance from SIP Outbound
   [I-D.ietf-sip-outbound].

   The following keep alive procedures MUST be implemented.  Specific
   deployments MAY choose not to use the keep alive mechanism if both
   entities are in a co-located domain.  Note that choosing not to use
   the keep alive mechanism defined in this section, even when in a co-
   located architecture, will reduce the ability to detect application
   level errors - especially during long periods of in-activity.

   Once the SIP dialog has been established and the underlying control
   channel has been set-up (including the initial correlation handshake
   using SYNC as discussed in Section 6), both entities acting in the
   'active' and 'passive' roles (as defined in COMEDIA [RFC4145]) MUST
   start a keep alive timer equal to the value negotiated during the
   control channel SYNC request/response exchange (the value from the
   'Keep-Alive' header in seconds).

6.3.3.1.  Behaviour for an Entity in an Active Role

   When acting in an 'active' role, a 'K-ALIVE' Control Framework
   message MUST be generated before the local keep alive timer fires.
   An active entity is free to send the K-ALIVE Control Framework
   message whenever it chooses.  A guideline of 80% of the local keep
   alive timer is suggested.  On receiving a 200 OK Control Framework
   message for the K-ALIVE request, the 'active' entity MUST reset the
   local keep alive timer.  If no 200 OK response is received to the
   K-ALIVE Control Framework message (or a transport level problem is
   detected by some other means) before the local keep alive timer



Boulton, et al.           Expires June 6, 2009                 [Page 21]

Internet-Draft       Media Control Channel Framework       December 2008


   fires, the 'active' entity SHOULD tear down the SIP dialog and
   recover the associated control channel resources.  The 'active'
   entity MAY choose to try and recover the connection by renegotiation
   using COMEDIA.

6.3.3.2.  Behaviour for an Entity in an Passive Role

   When acting as a 'passive' entity, a 'K-ALIVE' Control Framework
   message must be received before the local keep alive timer fires.
   When a K-ALIVE request is received, the 'passive' entity MUST
   generate a 200 OK control framework response and reset the local keep
   alive timer.  No other Control Framework response is valid.  If no
   K-ALIVE message is received (or a transport level problem is detected
   by some other means) before the local keep alive timer fires, the
   'passive' entity SHOULD tear down the SIP dialog and recover the
   associated control channel resources.  The 'active' entity MAY try to
   and recover the connection by renegotiating using COMEDIA.

6.3.4.  SYNC Transactions

   The initial SYNC request on a control channel is used to negotiate
   the timeout period for the control-channel keep alive mechanism and
   to allow clients and servers to learn the Control Packages that each
   supports.  Subsequent SYNC requests may be used to change the set of
   Control Packages that can be used on the control-channel.

6.3.4.1.  Timeout Negotiation for the Initial SYNC Transaction

   The initial SYNC request allows the timeout period for the control-
   channel keep alive mechanism to be negotiated.  The following rules
   SHOULD be followed for the initial SYNC request:
   o  If the Client initiating the SDP "Offer" has a COMEDIA 'setup'
      attribute equal to 'active', the 'Keep-Alive' header MUST be
      included in the SYNC message generated by the offerer.  The value
      of the 'Keep-Alive' header SHOULD be in the range of 95 and 120
      seconds (this is consistent with SIP
      Outbound[I-D.ietf-sip-outbound]).  The client that generated the
      SDP "Answer" ('passive' client) MUST copy the 'Keep-Alive' header
      into the 200 response to the SYNC message with the same value.
   o  If the Client initiating the SDP "Offer" has a COMEDIA 'setup'
      attribute equal to 'passive', the 'Keep-Alive' header parameter
      MUST be included in the SYNC message generated by the answerer.
      The value of the 'Keep-Alive' header SHOULD be in the range of 95
      and 120 seconds.  The client that generated the SDP "Offer"
      ('passive' client) MUST copy the 'Keep-Alive' header into the 200
      response to the SYNC message with the same value.





Boulton, et al.           Expires June 6, 2009                 [Page 22]

Internet-Draft       Media Control Channel Framework       December 2008


   o  If the Client initiating the SDP "Offer" has a COMEDIA 'setup'
      attribute equal to 'actpass', the 'Keep-Alive' header parameter
      MUST be included in the SYNC message of the entity who is the
      'Active' participant in the SDP session.  If the client generating
      the subsequent SDP 'Answer' places a value of 'active' in the
      COMEDIA SDP 'setup' attribute, it will generate the SYNC request
      and include the 'Keep-Alive' header.  The value SHOULD be in the
      range 95 to 120 seconds.  If the client generating the subsequent
      SDP 'Answer' places a value of 'passive' in the COMDEDIA 'setup'
      attribute, the original 'Offerer' will generate the SYNC request
      and include the 'Keep-Alive' header.  The value SHOULD be in the
      range 95 to 120 seconds.
   o  If the initial negotiated offer/answer results in a COMEDIA
      'setup' attribute equal to 'holdconn', the initial SYNC mechanism
      will occur when the offer/answer exchange is updated and active/
      passive roles are delegated using COMEDIA.

   The previous steps ensures that the entity initiating the control
   channel connection is always the one specifying the keep alive
   timeout period.  It will always be the initiator of the connection
   who generates the 'K-ALIVE' Control Framework level messages.

   Once negotiated, the keep alive timeout applies for the remainder of
   the Control Framework session.  Any subsequent SYNC messages
   generated in the control channel do not impact the negotiated keep
   alive property of the session.  The "Keep-Alive" header MUST NOT be
   included in subsequent SYNC messages and if it is received it MUST be
   ignored.

6.3.4.2.  Package Negotiation

   As part of the SYNC message exchange a client generating the request
   MUST include a "Packages" header, as defined in Section 9.  The
   "Packages" header will contain a list of all Control Framework
   packages that can be supported within this control session (from the
   perspective of the client creating the SYNC message).  All tokens
   MUST be Channel Framework packages that adhere to the rules set out
   in Section 8.  The "Packages" header of the initial SYNC message MUST
   contain at least one value.

   A server receiving the initial SYNC request MUST examine the contents
   of the "Packages" header.  If the server supports at least one of the
   packages listed in the request, it MUST respond with a 200 response
   code.  The response MUST contain a "Packages" header that lists the
   supported packages that are in common with those from the "Packages"
   header of the request (either all or a subset).  This list forms a
   common set of Control Packages that are supported by both parties.
   Any Control Packages supported by the server that are not listed in



Boulton, et al.           Expires June 6, 2009                 [Page 23]

Internet-Draft       Media Control Channel Framework       December 2008


   the "Packages" header of the SYNC request, MAY be placed in the
   "Supported" header of the response.  This provides a hint to the
   client that generated the SYNC request of the additional packages
   supported by the server.

   If no common packages are supported by the server receiving the SYNC
   message, it MUST respond with a 422 error response code.  The error
   response MUST contain a "Supported" header indicating the packages
   that are supported.  The initiating client can then choose to either
   re-submit a new SYNC message based on the 422 response or consider
   the interaction as a failure.  This would lead to termination of the
   associated SIP dialog by sending a SIP BYE request, as per [RFC3261].

   Once the initial SYNC transaction is completed, either client MAY
   choose to send a subsequent new SYNC Control Framework message to re-
   negotiate the packages that are supported within the control channel.
   A new SYNC message whose Packages header has different values from
   the previous SYNC message can effectively add and delete the packages
   used in the control channel.  If a client receiving a subsequent SYNC
   message does not wish to change the set of packages, it MUST respond
   with a 421 Control Framework response code.  Subsequent SYNC messages
   MUST NOT change the value of the "Dialog-ID" and "Keep-Alive" Control
   Framework headers that appeared in the original SYNC negotiation.

   Any Control Framework commands relating to a Control Package that is
   no longer supported by the session which are received after package
   re-negotiation SHOULD be responded to with a 420 response.  An entity
   MAY choose to honor such commands for a limited period of time but
   this is implementation specific.


7.  Response Code Descriptions

   The following response codes are defined for transaction responses to
   methods defined in Section 6.1.  All response codes in this section
   MUST be supported and can be used in response to both CONTROL and
   REPORT messages except that a 202 MUST NOT be generated in response
   to a REPORT message.

   Note that these response codes apply to framework transactions only.
   Success or error indications for control commands MUST be treated as
   the result of a control command and returned in either a 200 response
   or REPORT message.

7.1.  200 Response Code

   The 200 code indicates the completion of a successful framework
   protocol transaction.



Boulton, et al.           Expires June 6, 2009                 [Page 24]

Internet-Draft       Media Control Channel Framework       December 2008


7.2.  202 Response Code

   The 202 response code indicates the completion of a successful
   framework protocol transaction with additional information to be
   provided at a later time through the REPORT mechanism defined in
   Section 6.3.2.

7.3.  400 Response Code

   The 400 response indicates that the request was syntactically
   incorrect.

7.4.  403 Response Code

   The server understood the request, but is refusing to fulfill it.
   The request SHOULD NOT be repeated.

7.5.  405 Response Code

   Method not allowed.  The primitive is not supported.

7.6.  420 Response Code

   Intended target of the request is for a Control Package that is not
   valid for the current session.

7.7.  421 Response Code

   Recipient does not wish to re-negotiate Control Packages at this
   moment in time.

7.8.  422 Response Code

   Recipient does not support any Control Packages listed in the SYNC
   message.

7.9.  423 Response Code

   Recipient has an existing transaction with the same transaction ID.

7.10.  481 Response Code

   The 481 response indicates that the transaction of the request does
   not exist.  In response to a SYNC request, it indicates that the
   corresponding SIP dialog does not exist.






Boulton, et al.           Expires June 6, 2009                 [Page 25]

Internet-Draft       Media Control Channel Framework       December 2008


7.11.  500 Response Code

   The 500 response indicates that the recipient does not understand the
   request


8.  Control Packages

   "Control Packages" are intended to specify behavior that extends the
   the capability defined in this document.  "Control Packages" are not
   allowed to weaken "MUST" and "SHOULD" strength statements that are
   detailed in this document.  A "Control Package" MAY strengthen
   "SHOULD" to "MUST" if justified by the specific usage of the
   framework.

   In addition to normal sections expected in a standards-track RFC and
   SIP extension documents, authors of "Control Packages" need to
   address each of the issues detailed in the following subsections.
   The following sections MUST be used as a template and included
   appropriately in all Control-Packages.  To reiterate, the following
   sections do not solely form the basis of all Control-Package
   structure but are included as a minimum to provide essential package
   level information.  A Control-Package can take any valid form it
   wishes as long as the following sections are additionally included.

8.1.  Control Package Name

   This section MUST be present in all extensions to this document and
   provides a token name for the Control Package.  The section MUST
   include information that appears in the IANA registration of the
   token.  Information on registering control package tokens is
   contained in Section 12.  The package name MUST also register a
   version number for the package which is separated with a '/' symbol
   e.g. package_name/1.0.  This enables updates to the package to be
   registered where appropriate.  An initial version of a package MUST
   start with the value '1.0'.  Subsequent versions MUST increment this
   number if the same package name is to be used.  The exact increment
   is left to the discretion of the package author.  It is RECOMMENDED
   that package authors make a clear statement on backwards
   compatibility with any new version.

8.2.  Framework Message Usage

   The Control Framework defines a number of message primitives that can
   be used to exchange commands and information.  There are no
   limitations restricting the directionality of messages passed down a
   control channel.  This section of a Control package document should
   explicitly detail the control messages that can be used as well as



Boulton, et al.           Expires June 6, 2009                 [Page 26]

Internet-Draft       Media Control Channel Framework       December 2008


   provide an indication of directionality between entities.  This will
   include which role type is allowed to initiate a request type.

8.3.  Common XML Support

   This optional section is only included in a Control Package if the
   attributes for media dialog or Conference reference are required, as
   defined and discussed in Section 16.1 in Appendix A.  The Control
   Package will make strong statements (using language from RFC 2119
   [RFC2119]) if the XML schema defined in Section 16.1 in Appendix A is
   to be supported.  If only part of the schema is required (for example
   just 'connectionid' or just conferenceid), the Control Package will
   make equally strong (using language from RFC 2119 [RFC2119])
   statements.

8.4.  CONTROL Message Bodies

   This mandatory section of a Control Package defines the control body
   that can be contained within a CONTROL command request, as defined in
   Section 6 (or that no control package body is required).  This
   section should indicate the location of detailed syntax definitions
   and semantics for the appropriate MIME[RFC2045] body type that apply
   to a CONTROL command request and optionally the associated 200
   response.

8.5.  REPORT Message Bodies

   This mandatory section of a Control Package defines the REPORT body
   that can be contained within a REPORT command request, as defined in
   Section 6 (or that no report package body is required).  This section
   should indicate the location of detailed syntax definitions and
   semantics for the appropriate MIME[RFC2045] body type.  It should be
   noted that the Control Framework specification does allow for
   payloads to exist in 200 responses to CONTROL messages (as defined in
   this document).  An entity that is prepared to receive a payload type
   in a REPORT message MUST also be prepared to receive the same payload
   in a 200 response to a CONTROL message.

8.6.  Audit

   Auditing of various control package properties such as capabilities
   and resources (meta package level information) is extremely useful.
   Such meta-data usually has no direct impact on control framework
   interactions but allows for contextual information to be learnt.
   Control Packages are encouraged to make use of Control Framework
   interactions to provide relevant package audit information.

   This section should include information including:



Boulton, et al.           Expires June 6, 2009                 [Page 27]

Internet-Draft       Media Control Channel Framework       December 2008


   o  If an auditing capability is available in this package.
   o  How auditing information is triggered (for example, using Control
      framework CONTROL message) and delivered (for example in a Control
      Framework 200 response).
   o  The location of the audit query and response format for the
      payload (for example, it could be a separate XML schema OR part of
      a larger XML schema).

8.7.  Examples

   It is strongly recommended that Control Packages provide a range of
   message flows that represent common flows using the package and this
   framework document.


9.  Formal Syntax

9.1.  Control Framework Formal Syntax

   The Control Framework interactions use the UTF-8 transformation
   format as defined in [RFC3629].  The syntax in this section uses the
   Augmented Backus-Naur Form (ABNF) as defined in [RFC2234].


control-req-or-resp = control-request / control-response
control-request = control-req-start *headers CRLF [control-content]
control-response = control-resp-start *headers CRLF [control-content]
control-req-start  = pCFW SP transact-id SP method CRLF
control-resp-start = pCFW SP transact-id SP status-code [SP comment] CRLF
comment = utf8text

pCFW = %x43.46.57; CFW in caps
transact-id = alpha-num-token
method = mCONTROL / mREPORT / mSYNC / mK-ALIVE / other-method
mCONTROL = %x43.4F.4E.54.52.4F.4C; CONTROL in caps
mREPORT = %x52.45.50.4F.52.54; REPORT in caps
mSYNC = %x53.59.4E.43; SYNC in caps
mK-ALIVE = %x4B.2D.41.4C.49.56.45;K-ALIVE in caps

other-method = 1*UPALPHA
status-code = 3*DIGIT ; any code defined in this and other documents

headers = header-name CRLF

header-name = (Content-Length
 /Content-Type
 /Control-Package
 /Status



Boulton, et al.           Expires June 6, 2009                 [Page 28]

Internet-Draft       Media Control Channel Framework       December 2008


 /Seq
 /Timeout
 /Dialog-id
 /Packages
 /Supported
 /Keep-alive
 /ext-header) CRLF

Content-Length = "Content-Length:" SP 1*DIGIT
Control-Package = "Control-Package:" SP 1*alpha-num-token
Status = "Status:" SP ("update" / "terminate" )
Timeout = "Timeout:" SP 1*DIGIT
Seq = "Seq:" SP 1*DIGIT
Dialog-id = "Dialog-ID:" SP dialog-id-string
Packages = "Packages:" SP package-name *(COMMA package-name)
Supported = "Supported:" SP supported-alphanum *(COMMA supported-alphanum)
Keep-alive = "Keep-Alive:" SP kalive-seconds

dialog-id-string = alpha-num-token
package-name = alpha-num-token
supported-alphanum = alpha-num-token
kalive-seconds = 1*DIGIT

alpha-num-token = ALPHANUM  3*31alpha-num-tokent-char
alpha-num-tokent-char = ALPHANUM / "." / "-" / "+" / "%" / "="

control-content = *OCTET

Content-Type = "Content-Type:" SP media-type
media-type = type "/" subtype *( ";" gen-param )
type = token
subtype = token

gen-param = pname [ "=" pval ]
pname = token
pval  = token / quoted-string

token = 1*(%x21 / %x23-27 / %x2A-2B / %x2D-2E
           / %x30-39 / %x41-5A / %x5E-7E)
           ; token is compared case-insensitive

quoted-string = DQUOTE *(qdtext / qd-esc) DQUOTE
qdtext = SP / HTAB / %x21 / %x23-5B / %x5D-7E
            / UTF8-NONASCII
qd-esc = (BACKSLASH BACKSLASH) / (BACKSLASH DQUOTE)
BACKSLASH = "\"
UPALPHA  = %x41-5A
ALPHANUM = ALPHA / DIGIT



Boulton, et al.           Expires June 6, 2009                 [Page 29]

Internet-Draft       Media Control Channel Framework       December 2008


ext-header = hname ":" SP hval CRLF

hname = ALPHA *token
hval = utf8text

utf8text = *(HTAB / %x20-7E / UTF8-NONASCII)

UPALPHA  = %x41-5A



UTF8-NONASCII = %xC0-DF UTF8-CONT
              / %xE0-EF 2UTF8-CONT
              / %xF0-F7 3UTF8-CONT
              / %xF8-FB 4UTF8-CONT
              / %xFC-FD 5UTF8-CONT
UTF8-CONT     = %x80-BF


   The following table details a summary of the headers that can be
   contained in Control Framework interactions.  The "where" columns
   details where headers can be used:

       R: header field may only appear in requests;

       r: header field may only appear in responses;

       Blank indicates the header field may appear in either requests or responses.

       2xx, 4xx, etc.: A numerical value or range indicates response
           codes with which the header field can be used;

       An empty entry in the "where" column indicates that the header
           field may be present in all requests and responses.

   The remaining columns list the specified methods and the presence of
   a specific header:


           m: The header field is mandatory.
           o: The header field is optional.
           -: The header field is not applicable (ignored if present).









Boulton, et al.           Expires June 6, 2009                 [Page 30]

Internet-Draft       Media Control Channel Framework       December 2008


         Header field        Where    CONTROL REPORT SYNC  K-ALIVE
         ___________________________________________________________
         Content-Length                  o      o      -      -
         Control-Package       R         m      -      -      -
         Seq                             -      m      -      -
         Status                R         -      m      -      -
         Timeout               R         -      m      -      -
         Timeout              202        -      m      -      -
         Dialog-ID             R         -      -      m      -
         Packages                        -      -      m      -
         Supported             r         -      -      o      -
         Keep-Alive            R         -      -      o      -
         Content-Type                    o      o      -      -


                             Figure 3: Table 1

9.2.  Control Framework Dialog Identifier SDP Attribute

   This specification defines a new media-level value attribute:
   'cfw-id'.  Its formatting in SDP is described by the following
   ABNF[RFC5234].


            cfw-dialog-id = "a=cfw-id:" 1*(SP cfw-id-name) CRLF

              cfw-id-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 [RFC4566] but
   included here to provide support for the implementer of this SDP
   feature.


10.  Examples

   The following examples provide an abstracted flow of Control Channel
   establishment and Control Framework message exchange.  The SIP
   signaling is prefixed with the token 'SIP'.  All other messages are
   Control Framework interactions defined in this document.

   In this example, the Control Client establishes a control channel,
   SYNCs with the Control Server, and issues a CONTROL request that



Boulton, et al.           Expires June 6, 2009                 [Page 31]

Internet-Draft       Media Control Channel Framework       December 2008


   can't be completed within the 'Transaction-Timeout', so the Control
   Server returns a 202 response code to extend the transaction.  The
   Control Server then follows with REPORTs until the requested action
   has been completed.  The SIP dialog is then terminated.


            Control Client                                Control Server
                   |                                             |
                   |       (1) SIP INVITE                        |
                   |  ---------------------------------------->  |
                   |                                             |
                   |       (2) SIP 200                           |
                   |  <---------------------------------------   |
                   |                                             |
                   |       (3) SIP ACK                           |
                   |  ---------------------------------------->  |
                   |                                             |
                   |==>=======================================>==|
                   |         Control Channel Established         |
                   |==>=======================================>==|
                   |                                             |
                   |       (4) SYNC                              |
                   |  ---------------------------------------->  |
                   |                                             |
                   |       (5) 200                               |
                   |  <---------------------------------------   |
                   |                                             |
                   |       (6) CONTROL                           |
                   |  ---------------------------------------->  |
                   |                                             |
                   |       (7) 202                               |
                   |  <---------------------------------------   |
                   |                                             |
                   |       (8) REPORT (update)                   |
                   |  <----------------------------------------  |
                   |                                             |
                   |       (9) 200                               |
                   |  ---------------------------------------->  |
                   |                                             |
                   |       (10) REPORT (update)                  |
                   |  <----------------------------------------  |
                   |                                             |
                   |       (11) 200                              |
                   |  ---------------------------------------->  |
                   |                                             |
                   |       (12) REPORT (terminate)               |
                   |  <----------------------------------------  |
                   |                                             |



Boulton, et al.           Expires June 6, 2009                 [Page 32]

Internet-Draft       Media Control Channel Framework       December 2008


                   |       (13) 200                              |
                   |  ---------------------------------------->  |
                   |                                             |
                   |       (14) SIP BYE                          |
                   |  ---------------------------------------->  |
                   |                                             |
                   |       (15) SIP 200                          |
                   |  <---------------------------------------   |
                   |=============================================|
                   |         Control Channel Terminated          |
                   |=============================================|
                   |                                             |



   1.   Control Client->Control Server (SIP): INVITE
        sip:control-server@example.com

   INVITE sip:control-server@example.com SIP/2.0
   To: <sip:control-server@example.com>
   From: <sip:control-client@example.com>;tag=8937498
   Via: SIP/2.0/UDP control-client.example.com;branch=z9hG412345678
   CSeq: 1 INVITE
   Call-ID: 893jhoeihjr8392@example.com
   Contact: <sip:control-client@pc1.example.com>
   Content-Type: application/sdp
   Cotent-Length: [..]

   v=0
   o=originator 2890844526 2890842808 IN IP4 controller.example,com
   s=-
   c=IN IP4 control-client.example.com
   m=application 7575 TCP/CFW *
   a=setup:active
   a=connection:new
   a=cfw-id:fndskuhHKsd783hjdla

   2.   Control Server->Control Client (SIP): 200 OK













Boulton, et al.           Expires June 6, 2009                 [Page 33]

Internet-Draft       Media Control Channel Framework       December 2008


   SIP/2.0 200 OK
   To: <sip:control-server@example.com>;tag=023983774
   From: <sip:control-client@example.com>;tag=8937498
   Via: SIP/2.0/UDP control-client.example.com;branch=z9hG412345678
   CSeq: 1 INVITE
   Call-ID: 893jhoeihjr8392@example.com
   Contact: <sip:control-client@pc2.example.com>
   Content-Type: application/sdp
   Content-Length: [..]

   v=0
   o=originator 2890844526 2890842808 IN IP4 controller.example,com
   s=-
   c=IN IP4 control-server.example.com
   m=application 7575 TCP/CFW *
   a=setup:passive
   a=connection:new
   a=cfw-id:fndskuhHKsd783hjdla


   3.   Control Client->Control Server (SIP): ACK
   4.   Control Client opens a TCP connection to the Control Server.
        The connection can now be used to exchange control framework
        messages.  Control Client-->Control Server (Control Framework
        Message): SYNC.

   CFW 8djae7khauj SYNC
   Dialog-ID: fndskuhHKsd783hjdla
   K-Alive: 100
   Packages: msc-ivr-basic/1.0

   5.   Control Server-->Control Client (Control Framework Message):
        200.

   CFW 8djae7khauj 200
   Keep-Alive: 100
   Packages: msc-ivr-basic/1.0
   Supported: msc-ivr-vxml/1.0,msc-conf-audio/1.0


   6.   Once the SYNC process has completed, the connection can now be
        used to exchange control framework messages.  Control
        Client-->Control Server (Control Framework Message): CONTROL.








Boulton, et al.           Expires June 6, 2009                 [Page 34]

Internet-Draft       Media Control Channel Framework       December 2008


   CFW i387yeiqyiq CONTROL
   Control-Package: <package-name>
   Content-Type: example_content/example_content
   Content-Length: 11

   <XML BLOB/>

   7.   Control Server-->Control Client (Control Framework Message):
        202.

   CFW i387yeiqyiq 202
   Timeout: 10


   8.   Control Server-->Control Client (Control Framework Message):
        REPORT.

   CFW i387yeiqyiq REPORT
   Seq: 1
   Status: update
   Timeout: 10

   9.   Control Client-->Control Server (Control Framework Message):
        200.

   CFW i387yeiqyiq 200
   Seq: 1

   10.  Control Server-->Control Client (Control Framework Message):
        REPORT.

   CFW i387yeiqyiq REPORT
   Seq: 2
   Status: update
   Timeout: 10
   Content-Type: example_content/example_content
   Content-Length: 11

   <XML BLOB/>

   11.  Control Client-->Control Server (Control Framework Message):
        200.

   CFW i387yeiqyiq 200
   Seq: 2






Boulton, et al.           Expires June 6, 2009                 [Page 35]

Internet-Draft       Media Control Channel Framework       December 2008


   12.  Control Server-->Control Client (Control Framework Message):
        REPORT.

   CFW i387yeiqyiq REPORT
   Seq: 3
   Status: terminate
   Timeout: 10
   Content-Type: example_content/example_content
   Content-Length: 11

   <XML BLOB/>

   13.  Control Client-->Control Server (Control Framework Message):
        200.

   CFW i387yeiqyiq 200
   Seq: 3

   14.  Control Client->Control Server (SIP): BYE

   BYE sip:control-client@pc2.example.com SIP/2.0
   To: <sip:control-server@example.com>
   From: <sip:control-client@example.com>;tag=8937498
   Via: SIP/2.0/UDP control-client.example.com;branch=z9hG423456789
   CSeq: 2 BYE
   Call-ID: 893jhoeihjr8392@example.com

   15.  Control Server->Control Client (SIP): 200 OK

   SIP/2.0 200 OK
   To: <sip:control-server@example.com>;tag=023983774
   From: <sip:control-client@example.com>;tag=8937498
   Via: SIP/2.0/UDP control-client.example.com;branch=z9hG423456789
   CSeq: 2 BYE
   Call-ID: 893jhoeihjr8392@example.com


11.  Security Considerations

   The Channel Framework provides confidentiality and integrity for the
   messages it transfers.  It also provides assurances that the
   connected host is the host that it meant to connect to and that the
   connection has not been hijacked.

   The Channel Framework in design complies with the security-related
   requirements documented in the control protocol requirements
   document[RFC5167], more specifically REQ-MCP-11, REQ-MCP-12
   REQ-MCP-13, and REQ-MCP-14.  Specific security measures employed by



Boulton, et al.           Expires June 6, 2009                 [Page 36]

Internet-Draft       Media Control Channel Framework       December 2008


   the Channel Framework are summarized in the following subsections.

11.1.  Session Establishment

   Channel Framework sessions are established as media sessions
   described by SDP within the context of a SIP dialog.  In order to
   ensure secure rendezvous between Control Framework clients and
   servers, the Media Channel Control Framework should make full use of
   mechanisms provided by the SIP protocol.  The use of the 'cfw-id' SDP
   attribute results in important session information being carried
   across the SIP network.  For this reason SIP clients using this
   specification MUST use appropriate security mechanisms, such as
   TLS[RFC4346] and SMIME[RFC3851], when deployed in open networks.

11.2.  Transport Level Protection

   When using only TCP connections, the Channel Framework security is
   weak.  Although the Channel Framework requires the ability to protect
   this exchange, there is no guarantee that the protection will be used
   all the time.  If such protection is not used, anyone can see data
   exchanges.

   Sensitive data, such as private and financial data, is carried over
   the Control Framework channel.  Clients and servers must be properly
   authenticated/authorized and the control channel must permit the use
   of confidentiality, replay protection and integrity for the data.  To
   ensure control channel protection, Control Framework clients and
   servers MUST support TLS and SHOULD use it by default unless
   alternative control channel protection is used or a protected
   environment is guaranteed by the deployer of the network.
   Alternative control channel protection MAY be used if desired
   (e.g.IPSEC).

   TLS is used to authenticate devices and to provide integrity, replay
   protection and confidentiality for the header fields being
   transported on the control channel.  Channel Framework elements MUST
   implement TLS and MUST also implement the TLS ClientExtendedHello
   extended hello information for server name indication as described in
   [RFC4366].  A TLS cipher-suite of
   TLS_RSA_WITH_AES_128_CBC_SHA[RFC3261] MUST be supported.  Other
   cipher-suites MAY also be supported.

11.3.  Control Channel Policy Management

   This specification permits the establishment of a dedicated control
   channel using SIP.  It is also permitted for entities to create
   multiple channels for the purpose of failover and redundancy.  As a
   general solution, the ability for multiple entities to create



Boulton, et al.           Expires June 6, 2009                 [Page 37]

Internet-Draft       Media Control Channel Framework       December 2008


   connections and have access to resources could be the cause of
   potential conflict in shared environments.  It should be noted that
   this document does not specifically carry any specific mechanism to
   overcome such conflicts but will provide a summary of how it can be
   achieved.

   It can be determined that access to resources and use of control
   channels relates to policy.  It can be considered implementation and
   deployment detail that dictates the level of policy that is adopted.
   The authorization and associated policy of a control channel can be
   linked to the authentication mechanisms described in this section.
   For example, strictly authenticating a control channel either using
   SIP digest or TLS authentication allows entities to protect resources
   and ensure the required level of granularity.  Such policy can be
   applied at the package level or even as low as a structure like a
   conference instance (control channel X is not permitted to issue
   commands for control package y OR control channel A is not permitted
   to issue commands for conference instance B).  Systems should ensure
   that if required, an appropriate policy framework is adopted to
   satisfy the requirements for implemented packages.  The most robust
   form of policy can be achieved using a strong authentication
   mechanism such as mutual TLS authentication on the control channel.
   This specification provide a control channel response code(403) to
   indicate to the issuer of a command that it is not permitted.  It
   should be noted that additional policy requirements to those covered
   in this section might be defined and applied in individual packages
   that specify a finer granularity for access to resources etc.


12.  IANA Considerations

   This specification instructs IANA to create a new registry for SIP
   Control Framework parameters.  The Channel Framework Parameter
   registry is a container for sub-registries.  This section further
   introduces sub-registries for Channel Framework packages, method
   names, status codes, header field names, port and transport protocol.

   Additionally, Section 12.6 registers new parameters in existing IANA
   registries.

12.1.  Control Packages Registration Information

   This specification establishes the Control Packages sub-registry
   under Control Framework Packages.  New parameters in this sub-
   registry must be published in an RFC (either as an IETF submission or
   RFC Editor submission), using the IANA policy [RFC5226] "RFC
   Required".




Boulton, et al.           Expires June 6, 2009                 [Page 38]

Internet-Draft       Media Control Channel Framework       December 2008


   As this document specifies no package or template-package names, the
   initial IANA registration for control packages will be empty.  The
   remainder of the text in this section gives an example of the type of
   information to be maintained by the IANA; it also demonstrates all
   three possible permutations of package type, contact, and reference.

   The table below lists the control packages defined in the "Media
   Control Channel Framework".

    Package Name      Contact      Reference
    ------------      -------      ---------
    example1          [Boulton]
    example2          [Boulton]    [RFCXXX]
    example3                       [RFCXXX]


12.1.1.  Control Package Registration Template

      To: ietf-sip-control@iana.org
      Subject: Registration of new Channel Framework package

      Package Name:

          (Package names must conform to the syntax described in
          section 8.1.)

      Published Specification(s):

          (Control packages require a published RFC.).

      Person & email address to contact for further information:

12.2.  Control Framework Method Names

   This specification establishes the Methods sub-registry under Control
   Framework Parameters and initiates its population as follows.  New
   parameters in this sub-registry must be published in an RFC (either
   as an IETF submission or RFC Editor submission).

    CONTROL - [RFCXXX]
    REPORT  - [RFCXXX]
    SYNC   - [RFCXXX]


   The following information MUST be provided in an RFC publication in






Boulton, et al.           Expires June 6, 2009                 [Page 39]

Internet-Draft       Media Control Channel Framework       December 2008


   o  The method name.
   o  The RFC number in which the method is registered.

12.3.  Control Framework Status Codes

   This specification establishes the Status-Code sub-registry under
   Channel Framework Parameters.  New parameters in this sub-registry
   must be published in an RFC (either as an IETF submission or RFC
   Editor submission).  Its initial population is defined in Section 9.
   It takes the following format:


    Code [RFC Number]

   The following information MUST be provided in an RFC publication in
   order to register a new Control Framework status code:

   o  The status code number.
   o  The RFC number in which the method is registered.

12.4.  Control Framework Header Fields

   This specification establishes the header field-Field sub-registry
   under Channel Framework Parameters.  New parameters in this sub-
   registry must be published in an RFC (either as an IETF submission or
   RFC Editor submission).  Its initial population is defined as
   follows:


      Control-Package - [RFCXXXX]
      Status - [RFCXXXX]
      Seq - [RFCXXXX]
      Timeout - [RFCXXXX]
      Dialog-id - [RFCXXXX]
      Packages - [RFCXXXX]
      Supported - [RFCXXXX]
      Keep-Alive - [RFCXXXX]
      Content-Type - [RFCXXXX]
      Content-Length - [RFCXXXX]


   The following information MUST be provided in an RFC publication in
   order to register a new Channel Framework header field:

   o  The header field name.
   o  The RFC number in which the method is registered.





Boulton, et al.           Expires June 6, 2009                 [Page 40]

Internet-Draft       Media Control Channel Framework       December 2008


12.5.  Control Framework Port

   The Control Framework uses TCP port XXXX, from the "registered" port
   range.  Usage of this value is described in Section 4.1.

12.6.  SDP Transport Protocol

   The Channel Framework defines the new SDP protocol field values 'TCP/
   CFW', 'TCP/TLS/CFW', 'SCTP/CFW' and 'SCTP/TLS/CFW", which should be
   registered in the sdp-parameters registry under "proto".  The values
   have the following meaning:

   o  TCP/CFW: Indicates the SIP Channel Framework when TCP is used as
      an underlying transport for the control channel.
   o  TCP/TLS/CFW: Indicates the Channel Framework when TLS over TCP is
      used as an underlying transport for the control channel.
   o  SCTP/CFW: Indicates the Channel Framework when SCTP is used as an
      underlying transport for the control channel.
   o  SCTP/TLS/CFW: Indicates the Channel Framework when TLS over SCTP
      is used as an underlying transport for the control channel.

   Specifications defining new protocol values must define the rules for
   the associated media format namespace.  The 'TCP/CFW', 'TCP/TLS/CFW',
   'SCTP/CFW' and 'SCTP/TLS/CFW' protocol values allow only one value in
   the format field (fmt), which is a single occurrence of "*".  Actual
   format determination is made using the control package extension
   specific payloads.

12.7.  'cfw-id' SDP Attribute


    Contact name:          Chris Boulton cboulton@avaya.com.

    Attribute name:        "cfw-id".

    Type of attribute      Media level.

    Subject to charset:    Not.

    Purpose of attribute:  The 'cfw-id' attribute indicates
    an identifier that can be used to correlate the control
    channel with the SIP dialog used to negotiate it, when
    the attribute value is used within the control channel.

    Allowed attribute values:  A token.






Boulton, et al.           Expires June 6, 2009                 [Page 41]

Internet-Draft       Media Control Channel Framework       December 2008


12.8.  URN Sub-Namespace for
       urn:ietf:params:xml:ns:control:framework-attributes

   This section registers a new XML namespace,
   "urn:ietf:params:xml:ns:control:framework-attributes", per the
   guidelines in RFC 3688 [RFC3688].

      URI: urn:ietf:params:xml:ns:control:framework-attributes

      Registrant Contact: IETF, MEDIACTRL working group,
      (mediactrl@ietf.org), Chris Boulton (cboulton@avaya.com).
      XML:

         BEGIN
           <?xml version="1.0"?>
           <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
             "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
           <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
             <head>
               <title>Media Control Channel attributes</title>
             </head>
             <body>
               <h1>Namespace for Media Control Channel attributes</h1>
               <h2>urn:ietf:params:xml:ns:control:framework-attributes</h2>
       [NOTE TO IANA/RFC-EDITOR: Please replace XXXX
       with the RFC number for this specification.]
               <p>See RFCXXXX</p>
             </body>
           </html>
         END


12.9.  XML Schema Registration

   This section registers an XML schema as per the guidelines in RFC
   3688 [RFC3688].


   URI:  urn:ietf:params:xml:ns:control:framework-attributes
   Registrant Contact:  IETF, MEDIACTRL working group, (mediactrl@ietf.org),
      Chris Boulton (cboulton@avaya.com).
   Schema:  The XML for this schema can be found as the entirety of
      Section 16 of this document.








Boulton, et al.           Expires June 6, 2009                 [Page 42]

Internet-Draft       Media Control Channel Framework       December 2008


12.10.  MIME Media Type Registration for 'application/
        framework-attributes+xml'

   This section registers the "application/framework-attributes+xml"
   MIME type.


  To:  ietf-types@iana.org
   Subject:  Registration of MIME media type application/framework-attributes+xml
   MIME media type name:  application
   MIME subtype name:  framework-attributes+xml
   Required parameters:  (none)
   Optional parameters:  charset
      Indicates the character encoding of enclosed XML.  Default is
      UTF-8.
   Encoding considerations:  Uses XML, which can employ 8-bit
      characters, depending on the character encoding used.  See RFC
      3023 [RFC3023], section 3.2.
   Security considerations:  No known security considerations outside
      of those provided by core Media Control Channel Framework.
   Interoperability considerations:  This content type provides common
      constructs for related Media Control Channel packages.
   Published specification:  RFC XXXX [NOTE TO IANA/RFC-EDITOR: Please
      replace XXXX with the RFC number for this specification.]
   Applications which use this media type:  Implementations of appropriate
   Media Control Channel packages.
   Additional Information:  Magic Number(s): (none)
      File extension(s): .xml
      Macintosh File Type Code(s): (none)
   Person & email address to contact for further information:  Chris
      Boulton <cboulton@avaya.com>
   Intended usage:  LIMITED USE
   Author/Change controller:  The IETF
   Other information:  None.



13.  Changes

   Note to RFC Editor: Please remove this whole section.

13.1.  Changes from 07 Version

   o  Added '*' to SDP 'm=' line in examples.







Boulton, et al.           Expires June 6, 2009                 [Page 43]

Internet-Draft       Media Control Channel Framework       December 2008


13.2.  Changes from 06 Version

   o  Added 202 Timeout entry to table.
   o  Fixed some general nits and language.
   o  Fixed ABNF to be 'control-content = *OCTET'.
   o  Added general qualifier to sections 6.3.3.1 and 6.3.3.2 so that
      rules for either tearing down or reconnecting are applied.

13.3.  Changes from 05 Version

   o  Reworded 'must' used in Introduction.
   o  Added urn namespace definition in IANA section.
   o  Added XML schema registration in IANA section.
   o  Added MIME registration in IANA section.

13.4.  Changes from 04 Version

   o  Fixed nits as reported by Brian Weis.
   o  Amended Security text as per secdir review.
   o  Removed optional 'label' part of dialog identifier as per interim
      call.
   o  Added clarifying text at the beginning of section 4 to help
      describe what the section is about.
   o  Added text at the beginning of section 8 clarifying that the
      template is not the basis for packages BUT only needs to be
      included as part of a Control Package.

13.5.  Changes from 03 Version

   o  Removed comment from XML schema in appendix.
   o  Changed dialog-id-string in section 9.1 to be dialog-id-string =
      alpha-num-token.
   o  Changed status-code in section 9.1 to status-code = 3*DIGIT
   o  Aligned use of Keep-Alive header terms in document.
   o  Added text to clarify connection and session relationship - as per
      thread with Roni on use of 'new' and 'existing'.
   o  Use of K-Alive control message now aligned.
   o  Clarified that a CONTROL with no payload should be dealt with at
      the package level.
   o  Scrubbed ABNF + XML.

13.6.  Changes from 02 Version

   o  RAI review version.  See comments.
   o  Fixed broken IANA subsections ordering + naming.






Boulton, et al.           Expires June 6, 2009                 [Page 44]

Internet-Draft       Media Control Channel Framework       December 2008


13.7.  Changes from 01 Version

   o  Restructured text for readability.
   o  Changed SYNCH method name to SYNC.
   o  Removed 'pending' state to be replaced by 'update' with no
      payload.
   o  Replaced construction of dialog-id with new SDP parameter and
      revised text.
   o  Removed problem with K-Alive mechanism.  K-Alive timers are now
      separate from any other Control messages as the delay in
      processing allows for un-sync on both sides.
   o  Added transaction timeout of 5 seconds - as per meeting.
   o  Added Upper Limit for transaction timeout on REPORT to 15 seconds.
   o  Added Content-Type to table and missing examples etc.
   o  Simplified Security Section as per meeting feedback.
   o  Added proposed 'holdconn' text.
   o  Added Default port text - as per meeting.
   o  Added Audit text.

13.8.  Changes from 00 Version

   o  Aligned tokens to be 'CFW' (removed ESCS).
   o  Content-Length not mandatory for messages with no payload.
   o  Corrected changes to call flows from legacy versions.
   o  Use of term 'Active UA' in section 7 + others.
   o  Added 'notify' to status header of ABNF.
   o  Changed 481 to be transaction specific.
   o  Added '423' duplicate transaction ID response.
   o  Added '405' method not allowed.
   o  Added IANA section.
   o  Added Security Considerations section (used MSRP and MRCPv2 as a
      template).
   o  Removed noisy initial REPORT message - *Lorenzo please check
      text*.
   o  Fixed ABNF - PLEASE CHECK.
   o  Removed separate event mechanism and now all tied to CONTROL
      transaction (extended).
   o  General scrub of text.
   o  Organised 'Editors Notes' for discussion on the mailing list.
   o  Fixed ABNF in relation to extra CRLF on Content-Type.


14.  Contributors

   Asher Shiratzky from Radvision provided valuable support and
   contributions to the early versions of this document.





Boulton, et al.           Expires June 6, 2009                 [Page 45]

Internet-Draft       Media Control Channel Framework       December 2008


15.  Acknowledgments

   The authors would like to thank Ian Evans and Michael Bardzinski of
   Avaya, Adnan Saleem of Radisys, and Dave Morgan for useful review and
   input to this work.  Eric Burger contributed to the early phases of
   this work.

   Expert review was also provided by Spencer Dawkins, Krishna Prasad
   Kalluri, Lorenzo Miniero, and Roni Even.  Hadriel Kaplan provided
   expert guidance on the dialog association mechanism.  Lorenzo Miniero
   has constantly provided excellent feedback based on his work.

   Ben Campbell carried out the RAI expert review on this draft and
   provided a great deal of invaluable input.  Brian Weis carried out a
   thorough security review.  Text from Eric Burger was used in the
   introduction in the explanation for using SIP.


16.  Appendix A

   During the creation of the Control Framework it has become clear that
   there are number of components that are common across multiple
   packages.  It has become apparent that it would be useful to collect
   such re-usable components in a central location.  In the short term
   this appendix provides the place holder for the utilities and it is
   the intention that this section will eventually form the basis of an
   initial 'Utilities Document' that can be used by Control Packages.

16.1.  Common Dialog/Multiparty Reference Schema

   The following schema provides some common attributes for allowing
   Control Packages to apply specific commands to a particular SIP media
   dialog (also referred to as Connection) or conference.  If used
   within a Control Package the Connection and multiparty attributes
   will be imported and used appropriately to specifically identify
   either a SIP dialog or a conference instance.  If used within a
   package, the value contained in the 'connectionid' attribute MUST be
   constructed by concatenating the 'Local' and 'Remote' SIP dialog
   identifier tags as defined in [RFC3261].  They MUST then be separated
   using the '~' character.  So the format would be:

               'Local Dialog tag' + '~' + 'Remote Dialog tag'

   As an example, for an entity that has a SIP Local dialog identifier
   of '7HDY839' and a Remote dialog identifier of 'HJKSkyHS', the
   'connectionid' attribute for a Control Framework command would be:

                 7HDY839~HJKSkyHS



Boulton, et al.           Expires June 6, 2009                 [Page 46]

Internet-Draft       Media Control Channel Framework       December 2008


   It should be noted that Control Framework requests initiated in
   conjunction with a SIP dialog will produce a different 'connectionid'
   value depending on the directionality of the request, for example
   Local and Remote tags are locally identifiable.

   As with the Connection attribute previously defined, it is also
   useful to have the ability to apply specific control framework
   commands to a number of related dialogs, such as a multiparty call.
   This typically consists of a number of media dialogs that are
   logically bound by a single identifier.  The following schema allows
   for control framework commands to explicitly reference such a
   grouping through a 'conf' XML container.  If used by a Control
   Package, any control XML referenced by the attribute applies to all
   related media dialogs.  Unlike the dialog attribute, the
   'conferenceid' attribute does not need to be constructed based on the
   overlying SIP dialog.  The 'conferenceid' attribute value is system
   specific and should be selected with relevant context and uniqueness.

   The full schema follows:


<?xml version="1.0" encoding="UTF-8"?>

<xsd:schema targetNamespace="urn:ietf:params:xml:ns:control:framework-attributes"
       xmlns:xsd="http://www.w3.org/2001/XMLSchema"
       xmlns="urn:ietf:params:xml:ns::control:framework-attributes"
       elementFormDefault="qualified" attributeFormDefault="unqualified">

       <xsd:attributeGroup name="framework-attributes">
         <xsd:annotation>
           <xsd:documentation>SIP Connection and Conf Identifiers</xsd:documentation>
         </xsd:annotation>

         <xsd:attribute name="connectionid" type="xsd:string"/>

         <xsd:attribute name="conferenceid" type="xsd:string"/>

       </xsd:attributeGroup>
</xsd:schema>




17.  References







Boulton, et al.           Expires June 6, 2009                 [Page 47]

Internet-Draft       Media Control Channel Framework       December 2008


17.1.  Normative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

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

   [RFC2234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3262]  Rosenberg, J. and H. Schulzrinne, "Reliability of
              Provisional Responses in Session Initiation Protocol
              (SIP)", RFC 3262, June 2002.

   [RFC3263]  Rosenberg, J. and H. Schulzrinne, "Session Initiation
              Protocol (SIP): Locating SIP Servers", RFC 3263,
              June 2002.

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

   [RFC3268]  Chown, P., "Advanced Encryption Standard (AES)
              Ciphersuites for Transport Layer Security (TLS)",
              RFC 3268, June 2002.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC3851]  Ramsdell, B., "Secure/Multipurpose Internet Mail
              Extensions (S/MIME) Version 3.1 Message Specification",
              RFC 3851, July 2004.

   [RFC4145]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              September 2005.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security



Boulton, et al.           Expires June 6, 2009                 [Page 48]

Internet-Draft       Media Control Channel Framework       December 2008


              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [RFC4366]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 4366, April 2006.

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474, August 2006.

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

   [RFC4574]  Levin, O. and G. Camarillo, "The Session Description
              Protocol (SDP) Label Attribute", RFC 4574, August 2006.

   [RFC5167]  Dolly, M. and R. Even, "Media Server Control Protocol
              Requirements", RFC 5167, March 2008.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

17.2.  Informative References

   [I-D.burger-mscl-thoughts]
              Burger, E., "Media Server Control Language and Protocol
              Thoughts", draft-burger-mscl-thoughts-01 (work in
              progress), June 2006.

   [I-D.ietf-sip-outbound]
              Jennings, C. and R. Mahy, "Managing Client Initiated
              Connections in the Session Initiation Protocol  (SIP)",
              draft-ietf-sip-outbound-16 (work in progress),
              October 2008.

   [RFC3525]  Groves, C., Pantaleo, M., Anderson, T., and T. Taylor,
              "Gateway Control Protocol Version 1", RFC 3525, June 2003.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3725]  Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
              Camarillo, "Best Current Practices for Third Party Call



Boulton, et al.           Expires June 6, 2009                 [Page 49]

Internet-Draft       Media Control Channel Framework       December 2008


              Control (3pcc) in the Session Initiation Protocol (SIP)",
              BCP 85, RFC 3725, April 2004.

   [RFC3840]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
              "Indicating User Agent Capabilities in the Session
              Initiation Protocol (SIP)", RFC 3840, August 2004.

   [RFC3841]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
              Preferences for the Session Initiation Protocol (SIP)",
              RFC 3841, August 2004.


Authors' Addresses

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

   Email: cboulton@avaya.com


   Tim Melanchuk
   Rain Willow Communications

   Email: tim.melanchuk@gmail.com


   Scott McGlashan
   Hewlett-Packard
   Gustav III:s boulevard 36
   SE-16985 Stockholm, Sweden

   Email: scott.mcglashan@hp.com















Boulton, et al.           Expires June 6, 2009                 [Page 50]

Internet-Draft       Media Control Channel Framework       December 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.











Boulton, et al.           Expires June 6, 2009                 [Page 51]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/