Media Control Channel Framework
RFC 6230
| Document | Type | RFC - Proposed Standard (May 2011; No errata) | |
|---|---|---|---|
| Authors | Chris Boulton , Scott McGlashan , Tim Melanchuk | ||
| Last updated | 2018-12-20 | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | WG Document | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 6230 (Proposed Standard) | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Robert Sparks | ||
| Send notices to | (None) | ||
Internet Engineering Task Force (IETF) C. Boulton
Request for Comments: 6230 NS-Technologies
Category: Standards Track T. Melanchuk
ISSN: 2070-1721 Rainwillow
S. McGlashan
Hewlett-Packard
May 2011
Media Control Channel Framework
Abstract
This document describes a framework and protocol for application
deployment where the application programming logic and media
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.
The motivation for the creation of this framework is to provide an
interface suitable to meet the requirements of a centralized
conference system, where the conference system can be distributed, as
defined by the XCON working group in the IETF. It is not, however,
limited to this scope.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6230.
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RFC 6230 Media Control Channel Framework May 2011
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. 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 Behavior for Constructing Requests . . . . . . . . 17
6.2. General Behavior for Constructing Responses . . . . . . . 17
6.3. Transaction Processing . . . . . . . . . . . . . . . . . . 18
6.3.1. CONTROL Transactions . . . . . . . . . . . . . . . . . 18
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 . . . . . . . . . . . . . . . . . . . . 25
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. 406 Response Code . . . . . . . . . . . . . . . . . . . . 25
7.7. 420 Response Code . . . . . . . . . . . . . . . . . . . . 25
7.8. 421 Response Code . . . . . . . . . . . . . . . . . . . . 25
7.9. 422 Response Code . . . . . . . . . . . . . . . . . . . . 25
7.10. 423 Response Code . . . . . . . . . . . . . . . . . . . . 25
7.11. 481 Response Code . . . . . . . . . . . . . . . . . . . . 26
7.12. 500 Response Code . . . . . . . . . . . . . . . . . . . . 26
8. Control Packages . . . . . . . . . . . . . . . . . . . . . . . 26
8.1. Control Package Name . . . . . . . . . . . . . . . . . . . 26
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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
9.2. Control Framework Dialog Identifier SDP Attribute . . . . 31
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
11. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 35
12. Security Considerations . . . . . . . . . . . . . . . . . . . 36
12.1. Session Establishment . . . . . . . . . . . . . . . . . . 36
12.2. Transport-Level Protection . . . . . . . . . . . . . . . . 36
12.3. Control Channel Policy Management . . . . . . . . . . . . 37
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
13.1. Control Packages Registration Information . . . . . . . . 38
13.1.1. Control Package Registration Template . . . . . . . . 39
13.2. Control Framework Method Names . . . . . . . . . . . . . . 39
13.3. Control Framework Status Codes . . . . . . . . . . . . . . 39
13.4. Control Framework Header Fields . . . . . . . . . . . . . 40
13.5. Control Framework Port . . . . . . . . . . . . . . . . . . 40
13.6. Media Type Registrations . . . . . . . . . . . . . . . . . 40
13.6.1. Registration of MIME Media Type application/cfw . . . 41
13.6.2. Registration of MIME Media Type
application/framework-attributes+xml . . . . . . . . . 42
13.7. 'cfw-id' SDP Attribute . . . . . . . . . . . . . . . . . . 42
13.8. URN Sub-Namespace for
urn:ietf:params:xml:ns:control:framework-attributes . . . 43
13.9. XML Schema Registration . . . . . . . . . . . . . . . . . 43
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 44
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 44
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 44
16.1. Normative References . . . . . . . . . . . . . . . . . . . 44
16.2. Informative References . . . . . . . . . . . . . . . . . . 46
Appendix A. Common Package Components . . . . . . . . . . . . . . 47
A.1. Common Dialog/Multiparty Reference Schema . . . . . . . . 47
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1. Introduction
Real-time media applications are often developed using an
architecture where the application logic and media 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 "Media
Server Control Protocol Requirements" [RFC5167]. While the Framework
is not specific to media server control, it is the primary driver and
use case for this work. It is intended that the framework contained
in this document be able to be used for a variety of device control
scenarios (for example, conference control).
This document does not define a particular SIP extension for the
direct control of external components. Rather, other documents,
known as "Control Packages", extend the Control Framework described
by this document. Section 8 provides a comprehensive set of
guidelines for creating such Control Packages.
Current IETF device control protocols, such as Megaco [RFC5125],
while excellent for controlling media gateways that bridge separate
networks, are troublesome for supporting media-rich applications in
SIP networks. This is because Megaco duplicates many of the
functions inherent in SIP. Rather than using a single protocol for
session establishment and application media processing, application
developers need to translate between two separate mechanisms.
Moreover, the model provided by the framework presented here, using
SIP, better matches the application programming model than does
Megaco.
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
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, [RFC2119], as
scoped to those conformance targets.
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The following additional terms are defined for use in this document:
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 has a direct Real-Time Transport Protocol (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
might 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
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transaction is referenced throughout the document as a
'Transaction-Timeout'.
Transaction-Timeout: The maximum allowed time between a Control
Client or Server issuing a Framework message and it arriving at
the destination. The value for 'Transaction-Timeout' is 10
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
[MSCL-THOUGHTS], established the following. One might ask, "If all
we are doing is establishing a TCP connection to control the media
server, why do we need SIP?" This is a reasonable question. The key
is that we use 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 to negotiate the Control Channel provides many
inherent capabilities, which include:
o Service location - Use SIP Proxies and Back-to-Back User Agents
for locating Control Servers.
o Security mechanisms - Leverage established security mechanisms
such as Transport Layer Security (TLS) and Client Authentication.
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RFC 6230 Media Control Channel Framework May 2011
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 both at 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 the client to request multiple Control Channels using separate
SIP INVITE dialogs 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 orthogonal to any given media session. Specific
media session information is incorporated in control interaction
commands, which themselves are defined in external packages, using
the XML schema defined in Appendix A. 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
logical and can change during a session, if the Control Package
allows.
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The Client constructs and sends a standard SIP INVITE request, as
defined in [RFC3261], to the external Server. The Session
Description Protocol (SDP) payload includes the required information
for Control Channel negotiation and is the primary mechanism for
conveying support for this specification. The application/cfw MIME
type is defined in this document to convey the appropriate SDP format
for compliance to this specification. The Connection-Oriented Media
(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 also includes
the 'cfw-id' SDP attribute, as defined in this specification, which
is a unique identifier 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=z9hG4bK72d
Call-ID: 7823987HJHG6
Max-Forwards: 70
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 49153 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 and
formatted using the application/cfw MIME type specified in this
document. The Server inserts its own unique 'cfw-id' SDP attribute,
which differs from the one received in the INVITE (offer).
External Server Sends to Client:
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=z9hG4bK72d;received=192.0.2.4
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Call-ID: 7823987HJHG6
CSeq: 1 INVITE
Contact: <sip:External-Server@servermachine.example.com>
Content-Type: application/sdp
Content-Length: [..]
v=0
o=responder 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:U8dh7UHDushsdu32uha
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 set up, media sessions
can be established using standard SIP Third Party Call Control (3PCC)
[RFC3725].
Figure 2 provides a simplified example where the framework is used to
control a User Agent's RTP session.
+--------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
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The link (1) represents the SIP INVITE dialog usage and dedicated
Control Channel previously described in this overview section. The
link (2) from Figure 2 represents the User Agent SIP INVITE dialog
usage interactions and associated media flow. A User Agent creates a
SIP INVITE dialog usage with the Control Client entity. The Control
Client entity then creates a SIP INVITE dialog usage to the Control
Server, using 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 3PCC.
[RFC3725].
4. Control Channel Setup
This section describes the setup, using SIP, of the dedicated Control
Channel. 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. The
UAC MUST construct the INVITE request as defined in [RFC3261].
If a reliable response is received (as defined in [RFC3261] and
[RFC3262]), the mechanisms defined in this document are applicable to
the newly created SIP INVITE dialog usage.
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] but MAY choose an offer-
less INVITE as per [RFC3261]. The SDP SHOULD be formatted in
accordance with the steps below and using the MIME type application/
cfw, which is registered in Section 13. The following information
defines the composition of specific elements of the SDP payload the
offerer MUST adhere to when used in a SIP-based offer/answer exchange
using SDP and the application/cfw MIME type. The SDP being
constructed MUST contain only a single occurrence of a Control
Channel definition outlined in this specification but can contain
other media lines if required.
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
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supplies a representation of the SDP originator's address, for
example, DNS/IP representation. The address is the address used for
connections.
Example:
c=IN IP4 controller.example.com
The SDP MUST contain a corresponding Media Description entry:
m=<media> <port> <proto> <fmt>
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 entity constructing the SDP can't receive incoming
connections, it must still enter a valid port entry. The use of the
port value '0' has the same meaning as defined in a SIP offer/answer
exchange [RFC3264]. The Control Framework has a default port defined
in Section 13.5. This value is default, although a client is free to
choose explicit port numbers. However, SDP SHOULD use the default
port number, unless local policy prohibits its use. Using the
default port number allows network administrators to manage firewall
policy for Control Framework interactions. The third sub-field,
<proto>, compliant to this specification, MUST support the values
"TCP" and "TCP/TLS". 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. When an
entity identifies a transport value but is not willing to establish
the session, it MUST respond using the appropriate SIP mechanism.
The <fmt> sub-field MUST contain the value "cfw".
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.
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
COMEDIA attributes is:
a=setup:active
a=connection:new
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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 INVITE dialog usage 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 INVITE dialog usage.
The 'cfw-id' attribute MUST be unique in the context of the
interaction between the UAC and UAS and MUST NOT clash with instances
of the 'cfw-id' used in other SIP offer/answer exchanges. The value
chosen for the 'cfw-id' attribute MUST be used for the entire
duration of the associated SIP INVITE dialog usage and not be changed
during updates to the offer/answer exchange. This applies
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 uses 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 the connection, it uses the value of 'new' in the
'connection' attribute (for example, a=connection:new). Throughout
this, the connection identifier specified in the 'cfw-id' SDP
parameter MUST NOT change. One is 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 INVITE
dialog usage.
A non-2xx-class final SIP response (3xx, 4xx, 5xx, and 6xx) received
for the INVITE request indicates that no SIP INVITE dialog usage has
been created and is treated as specified by SIP [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 such as "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 indicates 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, as defined in [RFC3264]. 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".
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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 session description of the offer message and identifying
support for the application/cfw MIME type in the SDP. 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], [RFC3311], 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 follows:
a=setup:passive
a=connection:new
A client constructing an answer MUST include the 'cfw-id' SDP
attribute as defined in Section 9.2. This attribute MUST be unique
in the context of the interaction between the UAC and UAS and MUST
NOT clash with instances of the 'cfw-id' used in other SIP offer/
answer exchanges. The 'cfw-id' MUST be different from the 'cfw-id'
value received in the offer as it is used to uniquely identify and
distinguish between multiple endpoints that generate SDP answers.
The value chosen for the 'cfw-id' attribute MUST be used for the
entire duration of the associated SIP INVITE dialog usage and not be
changed during updates to the offer/answer exchange.
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 INVITE dialog usage 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
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SIP BYE request or appropriate response in an early SIP INVITE dialog
usage). The Control Channel therefore lives for the duration of the
SIP INVITE dialog usage.
A UAS receiving a SIP OPTIONS request MUST respond appropriately as
defined in [RFC3261]. The UAS MUST include the media types supported
in the SIP 200 OK response in a SIP 'Accept' header to indicate the
valid media types.
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
multiple specific Control Package commands to media sessions
established by SIP INVITE dialogs (media dialogs) with a given remote
server. For example, the Control Server might send a command to
generate audio media (such as an announcement) on an RTP stream
between a User Agent and a media server.
SIP INVITE 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 MUST include a 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=).
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 the repetitive
specifying of dialog reference language. The schema can be found in
Appendix A.1.
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 reused, for example, playing a
prompt to all participants in a Conference. The schema for such
operations can also be found in Appendix A.1.
Support for both the common attributes described here is specified as
part of each Control Package definition, as detailed in Section 8.
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6. Control Framework Interactions
In this document, the use of the COMEDIA specification 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 it with the SIP INVITE dialog
usage implemented 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 INVITE dialog usage
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 (that is, the UA with the active role
in COMEDIA) to identify the associated SIP INVITE dialog usage that
triggered the connection. Unless there is an alternative dialog
association mechanism used, the UAs MUST carry out these steps before
any other signaling on the newly created Control Channel.
o Once the connection has been established, the UA acting in the
active role (active UA) to initiate the connection MUST send a
Control Framework SYNC request. The SYNC request MUST be
constructed as defined in Section 9.1 and MUST contain the
'Dialog-ID' message header.
o The 'Dialog-ID' message header is populated with the value of the
local 'cfw-id' media-level attribute that was inserted by the same
client in the SDP offer/answer exchange to establish the Control
Channel. This allows for a correlation between the Control
Channel and its associated SIP INVITE dialog usage.
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 UA in the active role for the connection creation MUST then
send the SYNC request. If the UA in the active role for the
connection creation is a SIP UAS and has generated its SDP
response in a 2xx-class SIP response, it MUST wait for an incoming
SIP ACK message before issuing the SYNC. If the UA in the active
role for the connection creation is a SIP UAS and has generated
its SDP response in a reliable 1XX class SIP response, it MUST
wait for an incoming SIP PRACK message before issuing the SYNC.
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If the UA in the active role for the connection creation is a SIP
UAC, it MUST send the SYNC message immediately on establishment of
the Control Channel. It MUST then wait for a period of at least
2*'Transaction-Timeout' to receive a response. It MAY choose a
longer time to wait, but it MUST NOT be shorter than 'Transaction-
Timeout'. In general, a Control Framework transaction MUST
complete within 20 (2*'Transaction-Timeout') seconds and is
referenced throughout the document as 'Transaction-Timeout'.
o If no response is received for the SYNC message, a timeout occurs
and the Control Channel is terminated along with the associated
SIP INVITE dialog usage. The active UA MUST issue a BYE request
to terminate the SIP INVITE dialog usage.
o If the active UA receives a 481 response from the passive UA, this
means the SYNC request was received, but the associated SIP INVITE
dialog usage specified in the SYNC message does not exist. The
active client MUST terminate the Control Channel. The active UA
MUST issue a SIP BYE request to terminate the SIP INVITE dialog
usage.
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 INVITE
dialog usage. The active UA MUST issue a BYE request to terminate
the SIP INVITE dialog usage.
o The receipt of a 200 response to a SYNC message implies that the
SIP INVITE dialog usage 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
Sections 4.1 and 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 behavior for constructing Control
Framework requests and responses. Section 6.3 specifies the core
Control Framework methods and their transaction processing.
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6.1. General Behavior 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 that 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 Sections 4.1 and 4.2 of this document. A Control Client MUST
create a unique 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 unique in the context
of the interaction between the Control Client and Control Server.
This unique property helps avoid 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 request 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 message discussed in Section 6.3.4.2.
Any Framework message that contains an associated payload MUST also
include the 'Content-Type' and 'Content-Length' message headers,
which indicate the MIME type of the payload specified by the
individual Control Framework packages and the size of the message
body represented as a whole decimal number of octets, respectively.
If no associated payload is to be added to the message, the 'Content-
Length' header MUST have a value of '0'.
A Server receiving a Framework message request MUST respond with an
appropriate response (as defined in Section 6.2). Control Clients
MUST wait for a minimum of 2*'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 Behavior for Constructing Responses
An entity acting as a Control Server, on receiving a request, MUST
generate a response within the 'Transaction-Timeout', as measured
from the Control Client. The response MUST conform to the ABNF
defined in Section 9. The first line of the response MUST contain
the transaction identifier used in the first line of the request, as
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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 include a status code in the first line of the
response. If there is no error, the Server responds with a 200
Control Framework status code, as defined in Section 7.1. The 200
response MAY include message bodies. If the response contains a
payload, the message MUST include the 'Content-Length' and 'Content-
Type' headers. When the Control Client receives a 2xx-class
response, the Control Command transaction is complete.
If the Control Server receives a request, like CONTROL, that the
Server understands, but the Server knows processing the command will
exceed the 'Transaction-Timeout', then the Server MUST respond with a
202 status code in the first line of the response. Following the
initial response, the server will send one or more REPORT messages as
described in Section 6.3.2. A Control Package MUST explicitly define
the circumstances under which the server sends 200 and 202 messages.
If a Control Server encounters problems with a Control Framework
request (like REPORT or CONTROL), an appropriate error code MUST 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 transaction state and resources MUST 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 these four methods.
The following sub-sections specify each Control Framework method and
its associated transaction processing.
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
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message, as discussed 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. Separate
Control Package specifications MUST conform to the format defined in
Section 8.4. A CONTROL message containing a payload MUST include a
'Content-Type' header. The payload MUST be one of the payload types
defined by the Control Package. Individual packages MAY allow a
CONTROL message that does not contain a payload. This could in fact
be a valid message exchange within a specific package; if it's not,
an appropriate package-level error message MUST be generated.
6.3.2. REPORT Transactions
A 'REPORT' message is used by a Control Server when processing of a
CONTROL command extends beyond the 'Transaction-Timeout', as measured
from the Client. In this case, the Server returns a 202 response.
The Server returns status updates and the final results of the
command 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 correlates extended transactions with the original
CONTROL transaction. A REPORT message containing a payload MUST
include the 'Content-Type' and 'Content-Length' headers indicating
the payload MIME type [RFC2045] defined by the Control Package and
the length of the payload, respectively.
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 processing of the command completes
within that time, a 200 response code MUST be sent. If the command
does not complete within that time, the response code 202 MUST be
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. The Control Server should not wait until the last
possible opportunity to make the decision of issuing a 202 response
code and should ensure that it has plenty of time for the response to
arrive at the Control Client. If it does not have time, transactions
will be terminated (timed out) at the Control Client before
completion.
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A Control Server issuing a 202 response MUST ensure the message
contains a 'Timeout' message header. This header MUST have a value
in seconds that is 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.
The initial REPORT message MUST contain a 'Seq' (Sequence) message
header with a value equal to '1'. Note: 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 is 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 and no intended REPORT messages have been
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, if the timeout period is 10
seconds, the Server would refresh the transaction 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. A REPORT message received
that has not been incremented by 1 MUST be responded to with a 406
response and the extended transaction MUST be considered terminated.
On receiving a 406 response, the extended transaction MUST be
terminated. REPORT messages 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 8.5.
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.
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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
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. It MUST also
contain a 'Timeout' message header with a valid value. The inclusion
of the 'Timeout' header is for consistency, and its value is ignored.
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 includes 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 (NATs) and firewalls. A keep-alive
mechanism enables the Control Channel to be kept active during times
of inactivity. This is because many 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 only to the Control Channel being
created. For details relating to the SIP keep-alive mechanism,
implementers should seek guidance from SIP Outbound [RFC5626].
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 inactivity.
Once the SIP INVITE dialog usage 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.
This is the value from the 'Keep-Alive' header in seconds.
6.3.3.1. Behavior for an Entity in an Active Role
When in an active role, a K-ALIVE message MUST be generated before
the local keep-alive timer fires. An active entity is free to send
the K-ALIVE message whenever it chooses. It is RECOMMENDED for the
entity to issue a K-ALIVE message after 80% of the local keep-alive
timer. On receiving a 200 OK Control Framework message for the
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K-ALIVE request, the active entity MUST reset the local keep-alive
timer. If no 200 OK response is received to the K-ALIVE message, or
a transport-level problem is detected by some other means, before the
local keep-alive timer fires, the active entity MAY use COMEDIA re-
negotiation procedures to recover the connection. Otherwise, the
active entity MUST tear down the SIP INVITE dialog and recover the
associated Control Channel resources.
6.3.3.2. Behavior for an Entity in a Passive Role
When acting as a passive entity, a K-ALIVE 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 MUST tear down the
SIP INVITE dialog and recover the associated Control Channel
resources.
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
MUST 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 to 120
seconds (this is consistent with SIP Outbound [RFC5626]). The
value of the 'Keep-Alive' header MUST NOT exceed 600 seconds. The
client that generated the SDP "Answer" (the 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 to
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120 seconds. The client that generated the SDP offer (the 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 '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 COMEDIA 'setup'
attribute, the original UA making the SDP 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 the
active/passive roles are resolved using COMEDIA.
The previous steps ensure 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 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 contains 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 Channel
Framework package names MUST be tokens 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
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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
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 about 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 a failure. This would lead to termination of the
associated SIP INVITE 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 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.
An entity MAY honor Control Framework commands relating to a Control
Package it no longer supports after package re-negotiation. When the
entity does not wish to honor such commands, it MUST respond to the
request with a 420 response.
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.
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7.1. 200 Response Code
The framework protocol transaction completed successfully.
7.2. 202 Response Code
The framework protocol transaction completed successfully and
additional information will be provided at a later time through the
REPORT mechanism defined in Section 6.3.2.
7.3. 400 Response Code
The request was syntactically incorrect.
7.4. 403 Response Code
The server understood the request, but is refusing to fulfill it.
The client SHOULD NOT repeat the request.
7.5. 405 Response Code
Method not allowed. The primitive is not supported.
7.6. 406 Response Code
Message out of sequence.
7.7. 420 Response Code
Intended target of the request is for a Control Package that is not
valid for the current session.
7.8. 421 Response Code
Recipient does not wish to re-negotiate Control Packages at this
moment in time.
7.9. 422 Response Code
Recipient does not support any Control Packages listed in the SYNC
message.
7.10. 423 Response Code
Recipient has an existing transaction with the same transaction ID.
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7.11. 481 Response Code
The transaction of the request does not exist. In response to a SYNC
request, the 481 response code indicates that the corresponding SIP
INVITE dialog usage does not exist.
7.12. 500 Response Code
The recipient does not understand the request.
8. Control Packages
Control Packages specify behavior that extends the capability defined
in this document. Control Packages MUST NOT weaken statements of
"MUST" and "SHOULD" strength in this document. A Control Package MAY
strengthen "SHOULD", "RECOMMENDED", and "MAY" to "MUST" if justified
by the specific usage of the framework.
In addition to the usual sections expected in Standards-Track RFCs
and SIP extension documents, authors of Control Packages need to
address each of the issues detailed in the following sub-sections.
The following sections MUST be used as a template and included
appropriately in all Control-Package specifications. To reiterate,
the following sections do not solely form the basis of all Control-
Package specifications but are included as a minimum to provide
essential package-level information. A Control-Package specification
can take any valid form it wishes as long as it includes at least the
following information listed in this section.
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 13.
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 MUST
explicitly detail the types of Framework messages (Methods) that can
be used as well as provide an indication of directionality between
entities. This will include which role type is allowed to initiate a
request type.
Boulton, et al. Standards Track [Page 26]
RFC 6230 Media Control Channel Framework May 2011
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 Appendix A.1. The Control Package will make
strong statements (using language from RFC 2119 [RFC2119]) if the XML
schema defined in Appendix A.1 is to be supported. If only part of
the schema is required (for example, just 'connectionid' or
'conferenceid'), the Control Package will make equally strong
statements (using language from RFC 2119 [RFC2119]).
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
MUST 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. For Control Packages that do not have a Control Package
body, making such a statement satisfies the "MUST" strength of this
section in the Control Package document.
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
MUST 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. For Control Packages that do
not have a Control Package body, stating such satisfies the "MUST"
strength of this section in the Control Package document.
8.6. Audit
Auditing of various Control Package properties such as capabilities
and resources (package-level meta-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.
Boulton, et al. Standards Track [Page 27]
RFC 6230 Media Control Channel Framework May 2011
This section SHOULD include the following information:
o If an auditing capability is available in this package.
o How auditing information is triggered (for example, using a
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 [RFC5234] including
types 'DIGIT', 'CRLF', and 'ALPHA'.
Unless otherwise stated in the definition of a particular header
field, field values, parameter names, and parameter values are not
case-sensitive.
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 trans-id SP method CRLF
control-resp-start = pCFW SP trans-id SP status-code CRLF
pCFW = %x43.46.57; CFW in caps
trans-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
Boulton, et al. Standards Track [Page 28]
RFC 6230 Media Control Channel Framework May 2011
headers = header-name CRLF
header-name = (Content-Length
/Content-Type
/Control-Package
/Status
/Seq
/Timeout
/Dialog-ID
/Packages
/Supported
/Keep-alive
/ext-header)
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 supprtd-alphanum *(COMMA supprtd-alphanum)
Keep-alive = "Keep-Alive:" SP kalive-seconds
dialog-id-string = alpha-num-token
package-name = alpha-num-token
supprtd-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 *(SP ";" gen-param )
type = token ; Section 4.2 of RFC 4288
subtype = token ; Section 4.2 of RFC 4288
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)
Boulton, et al. Standards Track [Page 29]
RFC 6230 Media Control Channel Framework May 2011
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
ext-header = hname ":" SP hval CRLF
hname = ALPHA *token
hval = utf8text
utf8text = *(HTAB / %x20-7E / UTF8-NONASCII)
UTF8-NONASCII = UTF8-2 / UTF8-3 / UTF8-4 ; From RFC 3629
The following table details a summary of the headers that can be
contained in Control Framework interactions.
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 - -
Table 1: Summary of Headers in Control Framework Interactions
The notation used in Table 1 is as follows:
R: header field may only appear in requests.
r: header field may only appear in responses.
2xx, 4xx, etc.: response codes with which the header field can be used.
[blank]: header field may appear in either requests or responses.
m: header field is mandatory.
o: header field is optional.
-: header field is not applicable (ignored if present).
Boulton, et al. Standards Track [Page 30]
RFC 6230 Media Control Channel Framework May 2011
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
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 INVITE dialog is then terminated.
Boulton, et al. Standards Track [Page 31]
RFC 6230 Media Control Channel Framework May 2011
Control Client Control Server
| |
| (1) SIP INVITE |
| ----------------------------------------> |
| |
| (2) SIP 200 |
| <--------------------------------------- |
| |
| (3) SIP ACK |
| ----------------------------------------> |
| |
|==>=======================================>==|
| Control Channel Established |
|==>=======================================>==|
| |
| (4) SYNC |
| ----------------------------------------> |
| |
| (5) 200 |
| <--------------------------------------- |
| |
| (6) CONTROL |
| ----------------------------------------> |
| |
(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 client.example.com;branch=z9hG4bK123
CSeq: 1 INVITE
Max-Forwards: 70
Call-ID: 893jhoeihjr8392@example.com
Contact: <sip:control-client@pc1.example.com>
Content-Type: application/sdp
Content-Length: 206
v=0
o=originator 2890844526 2890842808 IN IP4 controller.example.com
s=-
c=IN IP4 control-client.example.com
m=application 49153 TCP cfw
a=setup:active
a=connection:new
a=cfw-id:fndskuhHKsd783hjdla
Boulton, et al. Standards Track [Page 32]
RFC 6230 Media Control Channel Framework May 2011
(2) 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 client.example.com;branch=z9hG4bK123;received=192.0.2.5
CSeq: 1 INVITE
Call-ID: 893jhoeihjr8392@example.com
Contact: <sip:control-server@pc2.example.com>
Content-Type: application/sdp
Content-Length: 203
v=0
o=responder 2890844600 2890842900 IN IP4 controller.example.com
s=-
c=IN IP4 control-server.example.com
m=application 49153 TCP cfw
a=setup:passive
a=connection:new
a=cfw-id:7JeDi23i7eiysi32
(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
Keep-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.
CFW i387yeiqyiq CONTROL
Control-Package: <package-name>
Content-Type: example_content/example_content
Boulton, et al. Standards Track [Page 33]
RFC 6230 Media Control Channel Framework May 2011
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
(12) Control Server-->Control Client (Control Framework message):
REPORT.
CFW i387yeiqyiq REPORT
Seq: 3
Status: terminate
Boulton, et al. Standards Track [Page 34]
RFC 6230 Media Control Channel Framework May 2011
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-server@pc2.example.com SIP/2.0
To: <sip:control-server@example.com>;tag=023983774
From: <sip:client@example.com>;tag=8937498
Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK234
CSeq: 2 BYE
Max-Forwards: 70
Call-ID: 893jhoeihjr8392@example.com
Contact: <sip:control-client@pc1.example.com>
Content-Length: 0
(15) Control Server-->Control Client (SIP): 200 OK
SIP/2.0 200 OK
To: <sip:control-server@example.com>;tag=023983774
From: <sip:client@example.com>;tag=8937498
Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK234;received=192.0.2.5
CSeq: 2 BYE
Call-ID: 893jhoeihjr8392@example.com
Contact: <sip:control-server@pc1.example.com>
Content-Length: 0
11. Extensibility
The Media Control Channel Framework was designed to be only minimally
extensible. New methods, header fields, and status codes can be
defined in Standards-Track RFCs. The Media Control Channel Framework
does not contain a version number or any negotiation mechanism to
require or discover new features. If an extension is specified in
the future that requires negotiation, the specification will need to
describe how the extension is to be negotiated in the encapsulating
signaling protocol. If a non-interoperable update or extension
occurs in the future, it will be treated as a new protocol, and it
MUST describe how its use will be signaled.
Boulton, et al. Standards Track [Page 35]
RFC 6230 Media Control Channel Framework May 2011
In order to allow extension header fields without breaking
interoperability, if a Media Control Channel device receives a
request or response containing a header field that it does not
understand, it MUST ignore the header field and process the request
or response as if the header field was not present. If a Media
Control Channel device receives a request with an unknown method, it
MUST return a 500 response.
12. 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, as discussed in the remainder of
this section.
In design, the Channel Framework complies with the security-related
requirements documented in "Media Server Control Protocol
Requirements" [RFC5167] -- more specifically, REQ-MCP-11, REQ-MCP-12,
REQ-MCP-13, and REQ-MCP-14. Specific security measures employed by
the Channel Framework are summarized in the following sub-sections.
12.1. Session Establishment
Channel Framework sessions are established as media sessions
described by SDP within the context of a SIP INVITE 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 SIP. 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 [RFC5246] and SMIME
[RFC5751], when deployed in open networks.
12.2. 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 protection for
the data. To ensure Control Channel protection, Control Framework
clients and servers MUST support TLS and SHOULD use it by default
Boulton, et al. Standards Track [Page 36]
RFC 6230 Media Control Channel Framework May 2011
unless alternative Control Channel protection is used or a protected
environment is guaranteed by the administrator of the network.
Alternative Control Channel protection MAY be used if desired (e.g.,
IPsec [RFC5246]).
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
[RFC5246]. A TLS cipher-suite of TLS_RSA_WITH_AES_128_CBC_SHA
[RFC3261] MUST be supported. Other cipher-suites MAY also be
supported.
When a TLS client establishes a connection with a server, it is
presented with the server's X.509 certificate. Authentication
proceeds as described in Section 7.3 ("Client Behavior") of RFC 5922
[RFC5922].
A TLS server conformant to this specification MUST ask for a client
certificate; if the client possesses a certificate, it will be
presented to the server for mutual authentication, and authentication
proceeds as described in Section 7.4 ("Server Behavior") of RFC 5922
[RFC5922].
12.3. 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
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 carry any specific mechanism to overcome such
conflicts but will provide a summary of how to do so.
It can be determined that access to resources and use of Control
Channels relate 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 using 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
Boulton, et al. Standards Track [Page 37]
RFC 6230 Media Control Channel Framework May 2011
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 provides a Control Channel response code (403) to
indicate to the issuer of a command that it is not permitted. The
403 response MUST be issued to Control Framework requests that are
not permitted under the implemented policy. If a 403 response is
received, a Control Framework client MAY choose to re-submit the
request with differing requirements or to abandon the request. The
403 response does not provide any additional information on the
policy failure due to the generic nature of this specification.
Individual Control Packages can supply additional information if
required. The mechanism for providing such additional information is
not mandated in this specification. 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.
13. IANA Considerations
IANA has created a new registry for SIP Control Framework parameters.
The "Media Control Channel Framework Parameters" registry is a
container for sub-registries. This section further introduces sub-
registries for control packages, method names, status codes, header
field names, and port and transport protocol.
Additionally, Section 13.6 registers a new MIME type for use with
SDP.
For all registries and sub-registries created by this document, the
policy applied when creating a new registration is also applied when
changing an existing registration.
13.1. Control Packages Registration Information
This specification establishes the Control Packages sub-registry
under Media Control Channel Framework Packages. New parameters in
this sub-registry must be published in an RFC (either in the IETF
stream or Independent Submission stream), using the IANA policy
[RFC5226] "RFC Required".
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.
Boulton, et al. Standards Track [Page 38]
RFC 6230 Media Control Channel Framework May 2011
The table below lists the Control Packages defined in the "Media
Control Channel Framework".
Package Name Reference
------------ ---------
example1 [RFCXXXX]
13.1.1. Control Package Registration Template
Package Name:
(Package names must conform to the syntax described in
Section 8.1.)
Published Specification(s):
(Control Packages require an RFC.)
Person & email address to contact for further information:
13.2. Control Framework Method Names
This specification establishes the Method Names sub-registry under
Media Control Channel Framework Parameters and initiates its
population as follows. New parameters in this sub-registry must be
published in an RFC (either in the IETF stream or Independent
Submission stream).
CONTROL - [RFC6230]
REPORT - [RFC6230]
SYNC - [RFC6230]
K-ALIVE - [RFC6230]
The following information MUST be provided in an RFC in order to
register a new Control Framework method:
o The method name.
o The RFC number in which the method is registered.
13.3. Control Framework Status Codes
This specification establishes the Status Code sub-registry under
Media Control Channel Framework Parameters. New parameters in this
sub-registry must be published in an RFC (either in the IETF stream
or Independent Submission stream). Its initial population is defined
in Section 9. It takes the following format:
Boulton, et al. Standards Track [Page 39]
RFC 6230 Media Control Channel Framework May 2011
Code Description Reference
The following information MUST be provided in an RFC 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.
o A brief description of the status code.
13.4. Control Framework Header Fields
This specification establishes the Header Field sub-registry under
Media Control Channel Framework Parameters. New parameters in this
sub-registry must be published in an RFC (either in the IETF stream
or Independent Submission stream). Its initial population is defined
as follows:
Control-Package - [RFC6230]
Status - [RFC6230]
Seq - [RFC6230]
Timeout - [RFC6230]
Dialog-ID - [RFC6230]
Packages - [RFC6230]
Supported - [RFC6230]
Keep-Alive - [RFC6230]
Content-Type - [RFC6230]
Content-Length - [RFC6230]
The following information MUST be provided in an RFC 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.
13.5. Control Framework Port
The Control Framework uses TCP port 7563, from the "registered" port
range. Usage of this value is described in Section 4.1.
13.6. Media Type Registrations
This section describes the media types and names associated with
payload formats used by the Control Framework. The registration uses
the templates defined in [RFC4288]. It follows [RFC4855].
Boulton, et al. Standards Track [Page 40]
RFC 6230 Media Control Channel Framework May 2011
13.6.1. Registration of MIME Media Type application/cfw
Type name: application
Subtype name: cfw
Required parameters: None
Optional parameters: None
Encoding considerations: Binary and see Section 4 of RFC 6230
Security considerations: See Section 12 of RFC 6230
Interoperability considerations:
Endpoints compliant to this specification must
use this MIME type. Receivers who cannot support
this specification will reject using appropriate
protocol mechanism.
Published specification: RFC 6230
Applications that use this media type:
Applications compliant with Media Control Channels.
Additional Information:
Magic number(s): (none)
File extension(s): (none)
Macintosh file type code(s): (none)
Person & email address to contact for further information:
Chris Boulton <chris@ns-technologies.com>
Intended usage: COMMON
Restrictions on usage:
Should be used only in conjunction with this specification,
RFC 6230.
Author: Chris Boulton
Change controller:
IETF MEDIACTRL working group, delegated from the IESG.
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RFC 6230 Media Control Channel Framework May 2011
13.6.2. Registration of MIME Media Type application/
framework-attributes+xml
Type name: application
Subtype name: framework-attributes+xml
Required parameters: (none)
Optional parameters: Same as charset parameter of application/xml as
specified in RFC 3023 [RFC3023].
Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [RFC3023].
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 6230
Applications that use this media type: Implementations of
appropriate Media Control Channel packages.
Additional information:
Magic number(s): (none)
File extension(s): (none)
Macintosh file type code(s): (none)
Person & email address to contact for further information:
Chris Boulton <chris@ns-technologies.com>
Intended usage: LIMITED USE
Author/Change controller: The IETF
Other information: None.
13.7. 'cfw-id' SDP Attribute
Contact name: Chris Boulton <chris@ns-technologies.com>
Attribute name: "cfw-id".
Type of attribute Media level.
Boulton, et al. Standards Track [Page 42]
RFC 6230 Media Control Channel Framework May 2011
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 INVITE dialog used to negotiate it, when the attribute
value is used within the Control Channel.
Allowed attribute values: A token.
13.8. URN Sub-Namespace for
urn:ietf:params:xml:ns:control:framework-attributes
IANA has registered 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 <chris@ns-technologies.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>
<p>See <a href="http://www.rfc-editor.org/rfc/rfc6230.txt">
RFC 6230</a>.</p>
</body>
</html>
END
13.9. 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
Boulton, et al. Standards Track [Page 43]
RFC 6230 Media Control Channel Framework May 2011
Registrant Contact: IETF MEDIACTRL working group <mediactrl@ietf.org>,
Chris Boulton <chris@ns-technologies.com>.
Schema: The XML for this schema can be found in Appendix A.1 of this
document.
14. Contributors
Asher Shiratzky from Radvision provided valuable support and
contributions to the early versions of this document.
15. Acknowledgments
The authors would like to thank Ian Evans of Avaya, Michael
Bardzinski and John Dally of NS-Technologies, 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 document and
provided a great deal of invaluable input. Brian Weis carried out a
thorough security review. Jonathan Lennox carried out a thorough SDP
review that provided some excellent modifications. Text from Eric
Burger was used in the introduction in the explanation for using SIP.
16. References
16.1. 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.
[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.
Boulton, et al. Standards Track [Page 44]
RFC 6230 Media Control Channel Framework May 2011
[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.
[RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP)
UPDATE Method", RFC 3311, October 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.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
September 2005.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
[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.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, February 2007.
[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.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
Boulton, et al. Standards Track [Page 45]
RFC 6230 Media Control Channel Framework May 2011
[RFC5922] Gurbani, V., Lawrence, S., and A. Jeffrey, "Domain
Certificates in the Session Initiation Protocol (SIP)",
RFC 5922, June 2010.
16.2. Informative References
[MSCL-THOUGHTS]
Burger, E., "Media Server Control Language and Protocol
Thoughts", Work in Progress, June 2006.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[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
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.
[RFC5125] Taylor, T., "Reclassification of RFC 3525 to Historic",
RFC 5125, February 2008.
[RFC5167] Dolly, M. and R. Even, "Media Server Control Protocol
Requirements", RFC 5167, March 2008.
[RFC5626] Jennings, C., Mahy, R., and F. Audet, "Managing Client-
Initiated Connections in the Session Initiation Protocol
(SIP)", RFC 5626, October 2009.
Boulton, et al. Standards Track [Page 46]
RFC 6230 Media Control Channel Framework May 2011
Appendix A. Common Package Components
During the creation of the Control Framework, it has become clear
that there are a number of components that are common across multiple
packages. It has become apparent that it would be useful to collect
such reusable components in a central location. In the short term,
this appendix provides the placeholder 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.
A.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
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 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
'conferenceid' 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.
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RFC 6230 Media Control Channel Framework May 2011
It should be noted that the values contained in both the
'connectionid' and 'conferenceid' identifiers MUST be compared in a
case-sensitive manner.
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>
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Authors' Addresses
Chris Boulton
NS-Technologies
EMail: chris@ns-technologies.com
Tim Melanchuk
Rainwillow
EMail: timm@rainwillow.com
Scott McGlashan
Hewlett-Packard
Gustav III:s boulevard 36
SE-16985 Stockholm, Sweden
EMail: smcg.stds01@mcglashan.org
Boulton, et al. Standards Track [Page 49]