Network Working Group C. Boulton
Internet-Draft Ubiquity Software Corporation
Expires: August 11, 2007 T. Melanchuk
BlankSpace
S. McGlashan
Hewlett-Packard
A. Shiratzky
Radvision
February 7, 2007
A Control Framework for the Session Initiation Protocol (SIP)
draft-boulton-sip-control-framework-05
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Copyright (C) The IETF Trust (2007).
Abstract
This document describes a Framework and protocol for application
deployment where the application logic and processing are
distributed. The framework uses the Session Initiation Protocol
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(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 distributed,
centralized conference system, as defined by the XCON work group of
the IETF. It is not, however, limited to this scope and it is
envisioned that this generic Framework will be used for a wide
variety of de-coupled control architectures between network entities.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Locating External Server Resources . . . . . . . . . . . . . . 10
5. Control Client SIP UAC Behavior - Control Channel Setup . . . 10
5.1. Control Client SIP UAC Behavior - Media Dialogs . . . . . 12
6. Control Server SIP UAS Behavior - Control Channel Setup . . . 12
7. Control Channel Keep-Alive . . . . . . . . . . . . . . . . . . 14
7.1. Timeout Negotiation . . . . . . . . . . . . . . . . . . . 14
7.2. Generating Keep-Alive Messages . . . . . . . . . . . . . . 15
8. Control Framework Interactions . . . . . . . . . . . . . . . . 16
8.1. Constructing Requests . . . . . . . . . . . . . . . . . . 17
8.1.1. Sending CONTROL . . . . . . . . . . . . . . . . . . . 18
8.1.2. Sending REPORT . . . . . . . . . . . . . . . . . . . . 18
8.2. Constructing Responses . . . . . . . . . . . . . . . . . . 20
9. Response Code Descriptions . . . . . . . . . . . . . . . . . . 21
9.1. 200 Response Code . . . . . . . . . . . . . . . . . . . . 21
9.2. 202 Response Code . . . . . . . . . . . . . . . . . . . . 21
9.3. 400 Response Code . . . . . . . . . . . . . . . . . . . . 21
9.4. 403 Response Code . . . . . . . . . . . . . . . . . . . . 21
9.5. 481 Response Code . . . . . . . . . . . . . . . . . . . . 21
9.6. 500 Response Code . . . . . . . . . . . . . . . . . . . . 22
10. Control Packages . . . . . . . . . . . . . . . . . . . . . . . 22
10.1. Control Package Name . . . . . . . . . . . . . . . . . . . 22
10.2. Framework Message Usage . . . . . . . . . . . . . . . . . 22
10.3. Common XML Support . . . . . . . . . . . . . . . . . . . . 23
10.4. CONTROL Message Bodies . . . . . . . . . . . . . . . . . . 23
10.5. REPORT Message Bodies . . . . . . . . . . . . . . . . . . 23
10.5.1. Events . . . . . . . . . . . . . . . . . . . . . . . . 23
10.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 24
11. Network Address Translation (NAT) . . . . . . . . . . . . . . 24
12. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 24
12.1. SIP Formal Syntax . . . . . . . . . . . . . . . . . . . . 24
12.2. Control Framework Formal Syntax . . . . . . . . . . . . . 24
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13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
14. Security Considerations . . . . . . . . . . . . . . . . . . . 32
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
15.1. IANA Registration of the 'escs' Option Tag . . . . . . . . 32
15.2. Control Package Registration Information . . . . . . . . . 32
15.2.1. Control Package Registration Template . . . . . . . . 32
15.3. SDP Transport Protocol . . . . . . . . . . . . . . . . . . 32
15.3.1. TCP/ESCS . . . . . . . . . . . . . . . . . . . . . . . 32
15.3.2. TCP/TLS/ESCS . . . . . . . . . . . . . . . . . . . . . 32
15.4. SDP Attribute Names . . . . . . . . . . . . . . . . . . . 32
15.5. SIP Response Codes . . . . . . . . . . . . . . . . . . . . 32
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32
17. Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . 32
17.1. Common Dialog/Multiparty Reference Schema . . . . . . . . 32
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
18.1. Normative References . . . . . . . . . . . . . . . . . . . 34
18.2. Informative References . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36
Intellectual Property and Copyright Statements . . . . . . . . . . 37
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1. Introduction
Applications are often developed using an architecture where the
application logic and processing activities are distributed.
Commonly, the application logic runs on "application servers" whilst
the processing runs on external servers, such as "media servers".
This document focuses on the framework and protocol between the
application server and external processing server. The motivation
for this framework comes from a set of requirements for Media Server
Control, which can be found in the 'Media Control Protocol Framework'
document[8]. While the Framework is not media server control
specific, it is the primary driver and use case for this work. It is
intended that the framework contained in this document will be used
for a plethora of appropriate device control scenarios.
This document does not define a SIP based extension that can be used
directly for the control of external components. The framework
mechanism must be extended by other documents that are known as
"Control Packages". A comprehensive set of guidelines for creating
"Control Packages" is described in Section 10.
Current IETF transport device control protocols, such as megaco [7],
while excellent for controlling media gateways that bridge separate
networks, are troublesome for supporting media-rich applications in
SIP networks, because they duplicate many of the functions inherent
in SIP. Rather than relying on single protocol session
establishment, application developers need to translate between two
separate mechanisms.
Application servers traditionally use SIP third party call control
RFC 3725 [12] to establish media sessions from SIP user agents to a
media server. SIP, as defined in RFC 3261 [2], also provides the
ideal rendezvous mechanism for establishing and maintaining control
connections to external server components. The control connections
can then be used to exchange explicit command/response interactions
that allow for media control and associated command response results.
2. Conventions and Terminology
In this document, BCP 14/RFC 2119 [1] defines the key words "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL". In
addition, BCP 15 indicates requirement levels for compliant
implementations.
The following additional terms are defined for use in this document:
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B2BUA: A B2BUA is a Back-to-Back SIP User Agent.
Control Server: A Control Server is an entity that performs a
service, such as media processing, on behalf of a Control Client.
For example, a media server offers mixing, announcement, tone
detection and generation, and play and record services. The
Control Server in this case, has a direct RTP [15] relationship
with the source or sink of the media flow. In this document, we
often refer to the Control Server simply as "the Server".
Control Client: A Control Client is an entity that requests
processing from a Control Server. Note that the Control Client
may not have any processing capabilities whatsoever. For example,
the Control Client may be an Application Server (B2BUA) or other
endpoint requesting manipulation of a third-party's media stream,
that terminates on a media server acting in the role of a Control
Server. In this document, we often refer to the Control Client
simply as "the Client".
Control Channel: A Control Channel is a reliable connection between
a Client and Server that is used to exchange Framework messages.
The term "Connection" is used synonymously within this document.
Framework Message: A Framework Message is a message on a Control
Channel that has a type corresponding to one of the Methods
defined in this document. A Framework message is often referred
to by its method, such as a "CONTROL message".
Method: A Method is the type of a framework message. Three Methods
are defined in this document: SYNCH, CONTROL, REPORT, and K-ALIVE.
Control Command: A Control Command is an application level request
from a Client to a Server. Control Commands are carried in the
body of CONTROL messages. Control Commands are defined in
separate specifications known as "Control Packages".
framework transaction: A framework transaction is defined as a
sequence composed of a control framework message originated by
either a Control Client or Control Server and responded to with a
control Framework response code message. Note that the control
framework has no "provisional" responses. A control framework
transaction MUST complete within Transaction-Timeout time.
extended framework transaction: An extended framework transaction is
used to extend the lifetime of a CONTROL method transaction when
the Control Command it carries cannot be completed within Command-
Timeout milliseconds. A Server extends the lifetime of a CONTROL
method transaction by sending a 202 response code followed by one
or more REPORT transactions as specified in Section 8.1.2.
Extended framework transactions allow command failures to be
discovered at the transaction layer.
Transaction-Timeout: the maximum allowed time between a control
Client or Server issuing a framework message and receiving a
corresponding response. The value for the timeout should be based
on a multiple of the network RTT plus Command-Timeout milliseconds
to allow for message parsing and processing.
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3. Overview
This document details mechanisms for establishing, using, and
terminating a reliable channel using SIP for the purpose of
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 voice session.
Figure 1 illustrates a simplified view of the proposed 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.
The use of SIP for the specified mechanism provides many inherent
capabilities which include:-
o Service location - Use SIP Proxies or Back-to-Back User Agents for
discovering Control Servers.
o Security mechanisms - Leverage established security mechanisms
such as Transport Layer Security (TLS) and Client Authentication.
o Connection maintenance - The ability to re-negotiate a connection,
ensure it is active, audit parameters, and so forth.
o Agnostic - Generic protocol allows for easy extension.
As mentioned in the previous list, one of the main benefits of using
SIP as the session control protocol is the "Service Location"
facilities provided. This applies at both a routing level, where RFC
3263 [4] provides the physical location of devices, and at the
Service level, using Caller Preferences[13] and Callee
Capabilities[14]. 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 5 of this
document.
+--------------SIP Traffic--------------+
| |
v v
+-----+ +--+--+
| SIP | | SIP |
|Stack| |Stack|
+---+-----+---+ +---+-----+---+
| Control | | Control |
| Client |<----Control Channel---->| Server |
+-------------+ +-------------+
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Figure 1: Basic Architecture
The example from Figure 1 conveys a 1:1 connection between the
Control Client and the Control Server. It is possible, if required,
for multiple control channels using separate SIP dialogs to be
established between the Control Client and the Control Server
entities. Any of the connections created between the two entities
can then be used for Server control interactions. The control
connections are agnostic to any media sessions. Specific media
session information can be incorporated in control interaction
commands (which themselves are defined in external packages) using
the XML schema defined in Section 17. The ability to have multiple
control channels allows for stronger redundancy and the ability to
manage high volumes of traffic in busy systems.
[Editors Note: Still under discussion. How does an app server know,
when there are multiple external servers, which specific server has
any given media session? Next version of the draft will discuss the
correlation procedures. The App server needs a control channel with
the media server and needs to know which channel to use once the
media session has been established. Sounds like a GRUU usage?]
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.
The Client constructs and sends a SIP INVITE request to the external
Server. The request contains the SIP option tag "escs" in a SIP
"Require" header for the purpose of forcing the use of the mechanism
described in this document. The SDP payload includes the required
information for control channel negotiation. The COMEDIA [6]
specification for setting up and maintaining reliable connections is
used (more detail available in later sections).
The client MUST include details of control packages that are
supported and, more specifically, that will be used within the
control channel created. This is achieved through the inclusion of a
SIP "Control-Packages" header. The "Control-Packages" header is
defined and described later in this document.
Client Sends to External Server:
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INVITE sip:External-Server@example.com SIP/2.0
To: <sip:External-Server@example.com>
From: <sip:Client@example.com>;tag=64823746
Require: escs
Control-Packages: <example-package>
Call-ID: 7823987HJHG6
Content-Type: application/sdp
v=0
o=originator 2890844526 2890842808 IN IP4 controller.example,com
s=-
c=IN IP4 controller.example.com
m=application 7575 TCP/ESCS
a=setup:active
a=connection:new
On receiving the INVITE request, the external Server supporting this
mechanism generates a 200 OK response containing appropriate SDP.
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
Call-ID: 7823987HJHG6
Content-Type: application/sdp
v=0
o=originator 2890844526 2890842808 IN IP4 controller.example,com
s=-
c=IN IP4 mserver.example.com
m=application 7563 TCP/ESCS
a=setup:passive
a=connection:new
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) TCP connection
to the Control Server. The connection address (taken from 'c=') and
port (taken from 'm=')are used to identify the remote part in the new
connection.
Once established, the newly created connection can be used to
exchange control language requests and responses. If required, after
the control channel has been setup, media sessions can be established
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using standard SIP third party call control.
[Editors Note: See previous note:this is where we may need to mention
how an App Server knows which external Server is responsible for any
given media session.]
Figure 4 provides a simplified example where the proposed framework
is used to control a User Agent's RTP session. (1) in brackets
represents the SIP dialog and dedicated control channel previously
described in this overview section.
+--------Control SIP Dialog(1)---------+
| |
v v
+-----+ +--+--+
+------(2)------>| SIP |---------------(2)------------->| SIP |
| |Stack| |Stack|
| +---+-----+---+ +---+-----+---+
| | | | |
| | Control |<--Control Channel(1)-->| |
| | Client | | Control |
| +-------------+ | Server |
+--+--+ | |
|User | | |
|Agent|<=====================RTP(2)===================>| |
+-----+ +-------------+
Figure 4: Participant Architecture
(2) from Figure 4 represents the User Agent SIP dialog interactions
and associated media flow. A User Agent would create a SIP dialog
with the Control Client entity. The Control Client entity will also
create a related dialog to the Control Server (B2BUA type
functionality). Using the interaction illustrated by (2), the User
Agent is able to negotiate media capabilities with the Control Server
using standard SIP mechanisms as defined in RFC 3261 [2] and RFC 3264
[5].
If not present in the SDP received by the Control Client from the
User Agent(2), a media label SDP attribute, which is defined in [10],
should be inserted for every media description (identified as m= line
as defined in [9]). This provides flexibility for the Control
Client, because it can generate control messages that specify a
particular Media stream (between User Agent and Control Server)
within a SIP media dialog. If a Media label is not included in the
control message, it applies to all media associated with the dialog.
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A non 2xx class SIP response received for the INVITE request
indicates that no SIP dialog has been created and is treated as
specified RFC 3261 [2]. One exception to this is the "496" (TODO:
need to pick an appropriate response code) response code whose
operation is defined in Section 6.
4. Locating External Server Resources
Section will describe mechanisms for locating an external Server.
5. Control Client SIP UAC Behavior - Control Channel Setup
On creating a new SIP INVITE request, a UAC can insist on using the
mechanisms defined in this document. This is achieved by inserting a
SIP Require header containing the option tag 'escs'. A SIP Require
header with the value 'escs' MUST NOT be present in any other SIP
request type.
If on creating a new SIP INVITE request, a UAC does not want to
insist on the usage of the mechanisms defined in this document but
merely that it supports them, a SIP Supported header MUST be included
in the request with the option tag 'escs'.
The SIP INVITE MUST include a SIP "Control-Packages" header which
MUST contain at least one valid entry and can contain multiple
control packages if required.
If a reliable response is received (as defined RFC 3261 [2] and RFC
3262 [3]) that contains a SIP Require header containing the option
tag 'escs', the mechanisms defined in this document are applicable to
the newly created dialog.
Before the UAC can send a request, it MUST include a valid session
description using the Session Description Protocol defined in [9].
The following information defines the composition of some specific
elements of the SDP payload that MUST be adhered to for compliancy to
this specification.
The Connection Data line in the SDP payload is constructed as
specified in [9]:
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 originators address, for example
dns/IP representation. The address will be the network address used
for connections in this specification.
Example:
c=IN IP4 controller.example.com
The SDP MUST contain a corresponding Media Description entry for
compliance to this specification:
m=<media> <port> <proto>
The first "sub-field" <media> MUST equal the value "application".
The second sub-field, <port>, MUST represent a port on which the
constructing client can receive an incoming connection if required.
The port is used in combination with the address specified in the
'Connection Data line defined previously to supply connection
details. If the constructing client can't receive incoming
connections it MUST still enter a valid port range entry. The use of
the port value '0' has the same meaning as defined in the SDP
specification[9]. The third sub-field, <proto>, MUST equal the value
"TCP/ESCS" as defined in Section 15.3.2 of this document.
[Editors note: Need to cover other protocols so not TCP specific]
The SDP MUST also contain a number of SDP media attributes(a=) that
are specifically defined in the COMEDIA specification. The
attributes provide connection negotiation and maintenance parameters.
A client conforming to this specification SHOULD support all the
possible values defined for media attributes from the COMEDIA [6]
specification but MAY choose not to support values if it can
definitely determine they will never be used (for example will only
ever initiate outgoing connections). It is RECOMMENDED that a
Controlling UAC initiate a connection to an external Server but that
an external Server MAY negotiate and initiate a connection using
COMEDIA, if network topology prohibits initiating connections in a
certain direction. An example of the attributes is:
a=setup:active
a=connection:new
This example demonstrates a new connection that will be initiated
from the owner of the SDP payload. The connection details are
contained in the SDP answer received from the UAS. A full example of
an SDP payload compliant to this specification can be viewed in
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Section 3. Once the SDP has been constructed along with the
remainder of the SIP INVITE request (as defined in RFC 3261 [2]), it
can be sent to the appropriate location. The SIP dialog and
appropriate control connection is then established.
5.1. Control Client SIP UAC Behavior - Media Dialogs
It is intended that the Control framework will be used within a
variety of architectures for a wide range of functions. One of the
primary functions will be the use of the control channel to apply
specific Control package commands to co-existing SIP dialogs that
have been established with the same remote server, for example the
manipulation of audio dialogs connected to a media server.
Such co-existing dialogs will pass through the Control Client (see
Figure 4) entity and may contain more than one Media Description (as
defined by "m=" in the SDP). The Control Client SHOULD include a
media label attribute (B2BUA functionality), as defined in [10], for
each "m=" definition. A Control Client constructing the SDP MAY
choose not to include the media label SDP attribute if it does not
require direct control on a per media stream basis.
This framework identifies the common re-use of referencing media
dialogs and has specified a connection reference attribute that can
optionally be imported into any Control Package. It is intended that
this will reduce repetitive specifying of dialog reference language.
The schema can be found in Section 17.1 in Appendix A.
Similarly, the ability to identify and apply commands to a group of
media dialogs is also identified as a common structure that could be
defined and re-used (for example playing a prompt to all participants
in a Conference). The schema for such operations can also be found
in Section 17.1 in Appendix A.
Support for both the common attributes described here is specified as
part of each Control Package definition, as detailed in Section 10.
6. Control Server SIP UAS Behavior - Control Channel Setup
On receiving a SIP INVITE request, an external Server(UAS) inspects
the message for indications of support for the mechanisms defined in
this specification. This is achieved through the presence of the SIP
Supported and Require headers containing the option tag 'escs'. If
the external Server wishes to construct a reliable response that
conveys support for the extension, it should follow the mechanisms
defined in RFC 3261 [2] for responding to SIP supported and Require
headers. If support is conveyed in a reliable SIP provisional
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response, the mechanisms in RFC 3262 [3] MUST also be used.
When constructing a SIP success response, the SDP payload MUST be
constructed using the semantics(Connection, Media and attribute)
defined in Section 5 using valid local settings and also with full
compliance to the COMEDIA[6] specification. For example, the SDP
attributes included in the answer constructed for the example offer
provided in Section 5 would look as illustrated below:
a=setup:passive
a=connection:new
Once the SIP success response 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 connection is now available to
exchange commands, as defined in "Control Packages" and described in
Section 10. The state of the SIP Dialog and the associated Control
channel are now explicitly linked. If either party wishes to
terminate a Control channel is simply issues a SIP termination
request (SIP BYE request). The Control Channel therefore lives for
the duration of the SIP dialog.
If the UAS does not support the extension contained in a SIP
Supported or Require header it MUST respond as detailed in RFC 3261
[2]. If the UAS does support the SIP extension contained in a SIP
Require or Supported header but does not support one or more of the
Control packages, as represented in the "Control-Packages" SIP
header, it MUST respond with a SIP "496 Unknown Control Package"
response code. The error response MUST conform to RFC 3261 [2] and
MUST also include a "Control-Packages" SIP header which lists the
control packages from the request that the UAS does not support.
This provides the Controlling UAC with an explicit reason for failure
and allows for re-submission of the request without the un-supported
control package.
A SIP entity receiving a SIP OPTIONS request MUST respond
appropriately as defined in RFC 3261 [2]. This involves providing
information relating to supported SIP extensions in the 'Supported'
message header. For this extension a value of 'escs' MUST be
included. Additionally, a SIP entity MUST include all the additional
control packages that are associated with the Control channel. This
is achieved by including a 'Control-Packages' SIP message header
listing all relevant supported Control package tokens.
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7. Control Channel Keep-Alive
It is reasonable to expect this document to be used in various
network architectures. This will include a wide range of deployments
where the clients could be co-located in a secured, private domain or
spread across disparate domains that require traversal of devices
such as Network Address Translators (NAT) and Firewalls (which is
covered in Section 11). It is important, therefore, that this
document provides a 'keep-alive' mechanism that enables the control
channel being created to firstly be kept active during times of
inactivity (most Firewalls have a timeout period after which
connections are closed) and also provide the ability for application
level failure detection. It should be noted at this point that the
following procedures apply explicitly to the control channel being
created and for details relating to a SIP keep-alive mechanism
implementers should seek guidance from SIP Outbound [11]. The
following 'keep-alive' procedures SHOULD be implemented by all
entities but MAY NOT be implemented if it can be guaranteed that
deployments will only occur with entities in a co-located domain. It
should be noted that choosing to not implement the 'keep-alive'
mechanism in this section, even when in a co-located architecture,
will reduce the ability to detect application level errors -
especially during long periods of in-activity.
7.1. Timeout Negotiation
During the SIP dialog negotiation the clients will also negotiate a
timeout period for the control channel 'keep-alive' mechanism. The
following rules MUST be obeyed in conjunction with COMEDIA[6]:
o If the Client initiating the SIP INVITE request has a COMEDIA
'setup' attribute equal to 'active', the 'k-alive' 'Control-
Packages' SIP header parameter MUST be included. The value of the
'k-alive' header parameter SHOULD be in the range of 95 and 120
seconds (this is consistent with SIP Outbound[11]). The client
generating the subsequent answer ('passive' client) MUST copy the
'k-alive' 'Control-Packages' header parameter into the response
with the same value.
o If the Client initiating the SIP INVITE request has a COMEDIA
'setup' attribute equal to 'passive', the 'k-alive' Control-
Packages SIP header parameter MUST NOT be included. The client
generating the subsequent answer ('active' client) MUST include
the 'k-alive' header parameter. The value of the 'k-alive' header
parameter SHOULD be in the range of 95 and 120 seconds.
o If the Client initiating the SIP INVITE request has a COMEDIA
'setup' attribute equal to 'actpass', the 'k-alive' 'Control-
Packages' header parameter MUST be included. The value of the
'k-alive' header parameter SHOULD be in the range of 95 to 120
seconds. If the client generating the subsequent answer places a
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value of 'active' in the COMEDIA 'setup' attribute, It MUST
include a 'k-alive' header parameter and MAY choose a value that
is different from that received in the request. The value SHOULD
be in the range 95 to 120 seconds. If the client generating the
subsequent answer places a value of 'passive' in the COMDEDIA
'setup' attribute, it MUST copy the 'k-alive' header and value
from the request into the 'k-alive' 'Control-Packages' SIP header
parameter.
o The 'Control-Packages' 'k-alive' header parameter MUST not be
included when the COMEDIA 'setup' attribute is equal to
'holdconn'.
o Following the previous steps ensures that the entity initiating
the control channel connection is always the one specifying the
keep-alive timeout period. It will always be the initiator of the
connection who generates the 'K-ALIVE' Control Framework level
messages. The following section describes in more detail how to
generate the Control Framework 'K-ALIVE' message.
7.2. Generating Keep-Alive Messages
Once the SIP dialog has been established using the offer answer
mechanism and the control channel has been established (including the
initial identity handshake using SYNCH as discussed in section
Section 8), both the 'active' and 'passive' (as defined in
COMEDIA[6]) clients MUST start a keep-alive timer equal to the value
negotiated during the offer/answer exchange (from the 'k-alive'
'Control-Packages' SIP header parameter).
When acting as an 'active' client, a 'K-ALIVE' Control Framework
message MUST be generated before the local 'keep-alive' timer fires.
An active client is free to send the K-ALIVE Control Framework
message when ever it chooses. A guideline of 80% of the local 'keep-
alive' timer is suggested. The 'passive' client MUST generate a 200
OK Control Framework response to the K-ALIVE message and reset the
local 'keep-alive' timer. No other Control Framework response is
valid. On receiving the 200 OK Control Framework message, the
'active' client MUST reset the local 'keep-alive' timer. If no 200
OK response is received to the K-ALIVE Control Framework message,
before the local 'keep-alive' timer fires, the 'active' client SHOULD
tear down the SIP dialog and recover the associated control channel
resources. The 'active' client MAY choose to try and recover the
connection by renegotiation using COMEDIA.
When acting as a 'passive' client, a 'K-ALIVE' Control Framework
message MUST be received before the local 'keep-alive' timer fires.
The 'passive' client MUST generate a 200 OK control framework
response to the K-ALIVE Control Framework message. On sending the
200 OK response, the 'passive' client MUST reset the local 'keep-
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alive' timer. If no K-ALIVE message is received before the local
'keep-alive' timer fires, the 'passive' client SHOULD tear down the
SIP dialog and recover the associated control channel resources. The
'active' client MAY try to and recover the connection by
renegotiating using COMEDIA.
8. Control Framework Interactions
The use of the COMEDIA specification in this document allows for a
Control Channel to be set up in either direction as a result of the
SIP INVITE transaction. While providing a flexible negotiation
mechanism, it does provide certain correlation problems between the
channel and the overlying SIP dialog. Remember that the two are
implicitly linked and so need a robust correlation mechanism. A
Control Client receiving an incoming connection (whether it be acting
in the role of UAC or UAS) has no way of identifying the associated
SIP dialog as it could be simply listening for all incoming
connections on a specific port. As a consequence, some rules are
applied to allow a connecting (defined as 'active' role in COMEDIA)
client to identify the associated SIP dialog that triggered the
connection. The following steps provide an identification mechanism
that MUST be carried out before any other signaling is carried out on
the newly created Control channel.
o Once connected, the client initiating the connection (as
determined by COMEDIA) MUST immediately send a Control Framework
SYNCH request. The SYNCH request will be constructed as defined
in Section 12.2 and MUST only contain one message header,
'dialog-id', which contains the SIP dialog information.
o The 'dialog-id' message header is constructed by concatenating the
Local-tag, Call-ID and Remote-tag (as defined in Section 12.2)
from the SIP dialog and separating with a '~'. See syntax defined
in Section 17.1 in Appendix A and examples in Section 10.6. For
example, if the SIP dialog had values of 'Local-tag=HKJDH',
'Remote-tag=JJSUSHJ' and 'Call-ID=8shKUHSUKHW@example.com' - the
'dialog-id' header would look like this:
'dialog-id=HKJDH~8shKUHSUKHW@example.com~JJSUSHJ'.
o The client who initiated the connection MUST then send the SYNCH
request. It should then wait for a period of 5 seconds to receive
a response. It MAY choose a longer time to wait but it should not
be shorter than 5 seconds.
o If no response is received for the SYNCH control message, a
timeout occurs and the control channel is terminated along with
the associated SIP dialog (issue a BYE request).
o If the client who initiated a connection receives a 481 response,
this implies that the SYNCH request was received but no associated
SIP dialog exists. This also results in the control channel being
terminated along with the associated SIP dialog (issue a BYE
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request).
o All other error responses received for the SYNCH request are
treated as detailed in this specification and also result in the
termination of the control channel and the associated SIP dialog
(issue a BYE request).
o The receipt of a 200 response to a SYNCH message implies that the
SIP dialog and control connection have been successfully
correlated. The control channel can now be used for further
interactions.
Once a successful control channel has been established, as defined in
Section 5 and Section 6 (and the connection has been correlated, as
described in previous paragraph), the two entities are now in a
position to exchange relevant control framework messages. The
remainder of this section provides details of the core set of methods
and responses that MUST be supported for the core control framework.
Future extensions to this document MAY define new methods and
responses.
8.1. Constructing Requests
An entity acting as a Control Client is now able to construct and
send new requests on a control channel and MUST adhere to the syntax
defined in Section 12. Control Commands MUST also adhere to the
syntax defined by the Control Packages negotiated in Section 5 and
Section 6 of this document. A Control Client MUST create a unique
transaction and associated identifier per request transaction. 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 12). The first line starts with the SCFW token
for the purpose of easily extracting the transaction identifier. The
transaction identifier MUST be globally unique over space and time.
All required mandatory and optional control framework headers are
then inserted into the control message with appropriate values (see
relevant individual header information for explicit detail). A
"Control-Package" header MUST also be inserted with the value
indicating the Control Package to which this specific request applies
(Multiple packages can be negotiated per control channel).
Any framework message that contains an associated payload MUST also
include a 'Content-Length' message header which represents the size
of the message body in decimal number of octets. If no associated
payload is to be added to the message, a 'Content-Length' header with
a value of '0' MUST be included.
When all of the headers have been included in the framework message,
it is sent down the control channel established in Section 5.
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It is a requirement that a Server receiving such a request respond
quickkly with an appropriate response (as defined in Section 8.2). A
Control Client entity needs to wait for Transaction-Time time for a
response before considering the transaction a failure.
8.1.1. Sending CONTROL
A 'CONTROL' message is used by Control Client to invoke control
commands on a Control Server. The message is constructed in the same
way as any standard Control Framework message, as discussed
previously in Section 8.1 and defined in Section 12. A CONTROL
message MAY contain a message body. The explicit control command(s)
of the message payload contained in a CONTROL message are specified
in separate Control Package specifications. These specifications
MUST conform to the format defined in Section 10.4.
8.1.2. Sending REPORT
A 'REPORT' message is used by a Control Server in two situations.
The first situation occurs when processing of a Control Command
extends beyond a Command-Timeout. In this case a 202 response is
returned. Status updates and the final results of the command are
then returned in subsequent REPORT messages. The second situation
allows REPORT to be used as an event notification mechanism where
events are correlated with the original CONTROL message. In this
case, REPORT messages may be sent after the original transaction or
extended transaction has completed.
All REPORT messages MUST contain the same transaction ID in the
request start line that was present in the original CONTROL
transaction. This allows both extended transactions and event
notifications to be correlated with the original CONTROL transaction.
8.1.2.1. Reporting the Status of Extended Transactions
On receiving a CONTROL message, a Control Server MUST respond within
Command-Timeout with a status code for the request, as specified in
Section 8.2. If the command completed within that time, a 200
response code would have been sent. If the command did not complete
within that time, the response code 202 would have been sent
indicating that the requested command is still being processed and
the CONTROL transaction is being extended. The REPORT method is used
to update the status of the extended transaction.
A Control Server issuing a 202 response MUST immediately issue a
REPORT message. The initial REPORT message MUST contain a 'Seq'
(Sequence) message header with a value equal to '1' (It should be
noted that the 'Seq' numbers at both Control Client Control Server
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for framework messages are independent). The initial REPORT message
MUST also contain a 'Status' message header with a value of
'pending'. This initial REPORT message MUST NOT contain a message
body and is primarily used to establish a subsequent message
transaction based on the initial CONTROL message.
All REPORT messages for an extended CONTROL transaction MUST contain
a 'Timeout' message header. This header will contain a value in
delta seconds that represents the amount of time the recipient of the
REPORT message must wait before assuming that there has been a
problem and terminating the extended transaction and associated
state. On receiving a REPORT message with a 'Status' header of
'pending' or 'update', the Control Client MUST reset the counter for
the associated extended CONTROL transaction to the indicated timeout
period. If the timeout period approaches with no intended REPORT
messages being generated, the entity acting as a Control Framework
UAS for the interaction MUST generate a REPORT message containing, as
defined in this paragraph, a 'Status' header of 'pending'. 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 of ?? is used
for the value of the 'Timeout' message header. It is also
RECOMMENDED that a Control Server refresh the timeout period of the
CONTROL transaction at an interval that is not too close to the
expiry time. A value of 80% of the timeout period could be used, for
example a timeout period of 10 seconds would be refreshed after 8
seconds.
Subsequent REPORT messages that provide additional information
relating to the extended CONTROL transaction MUST also include and
increment by 1 the 'Seq' header value. They MUST also include a
'Status' header with a value of 'update'. These REPORT messages sent
to update the extended CONTROL transaction status MAY contain a
message body, as defined by individual Control Packages and specified
in Section 9.5. A REPORT message sent updating the extended
transaction also acts as a timeout refresh, as described earlier in
this section. This will result in a transaction timeout period at
the initiator of the request being reset to the interval contained in
the 'Timeout' message header.
When all processing for an extended CONTROL transaction has taken
place, the entity acting as a Control Server MUST send a terminating
REPORT message. The terminating REPORT message MUST increment the
value in the 'Seq' message header by the value of '1' from the
previous REPORT message. It MUST also include a 'Status' header with
a value of 'terminate' and MAY contain a message body. A Control
Framework UAC can then clean up any pending state associated with the
original control transaction.
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8.1.2.2. Reporting Asynchronous Events
Commands that are carried in CONTROL messages can request that the
Server notify the Client about events that occur sometime in the
future. It is not desirable to use extended Control transactions for
these types of commands for two reasons. First, an event never
occurring is often correct behavior. Second, events may occur long
after the original request for their notification.
REPORT messages can be used to notify events. REPORT messages that
notify events MUST contain a 'Status' header of 'Notify'. They MUST
NOT contain either a 'Timeout' or 'Seq' header and any such headers
MUST be ignored when the REPORT message has a 'Status' of 'notify'.
The REPORT message MAY contain a message body.
8.2. Constructing Responses
A Control Client or Server, on receiving a request, MUST generate a
response within Command-Time time. The response MUST conform to the
ABNF defined in Section 12. The first line of the response MUST
contain the transaction identifier used in first line of the request,
as defined in Section 8.1. Responses MUST NOT include the 'Status'
or 'Timeout' message headers - if they are included they have no
meaning or semantics.
A Control Client or Server MUST then include a status code in the
first line of the constructed response. A CONTROL request that has
been understood, and either the relevant actions for the control
command have completed or a control command error is detected, uses
the 200 status code as defined in Section 9.1. A 200 response MAY
include message bodies. If a 200 response does contain a payload it
MUST include a Content-Length header. A 200 is the only response
defined in this specification that allows a message body to be
included. A client receiving a 200 class response then considers the
control command completed. A CONTROL request that is received and
understood but requires processing that extends beyond Command-Time
time will return a 202 status code in the response. This will be
followed immediately by an initial REPORT message as defined in
Section 8.1.2. A Control Package SHOULD explicitly define the
circumstances under which either 200 or 202 with subsequent
processing takes place.
If a Control Client or Server encounters problems with either a
REPORT or CONTROL request, an appropriate error code should be used
in the response, as listed in Section 9. The generation of a non 2xx
class response code to either a CONTROL or REPORT message will result
in failure of the transaction, and all associated state and resources
should be terminated. The response code may provide an explicit
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indication of why the transaction failed, which might result in a re-
submission of the request.
[timm]: how can an error response provide an explicit indication of
the reason for the transaction failure when only a 200 response
allows message bodies?
9. Response Code Descriptions
The following response codes are defined for transaction responses to
methods defined in Section 8.1. 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.
9.1. 200 Response Code
The 200 code indicates the completion of a successful transaction.
9.2. 202 Response Code
The 202 response code indicates the completion of a successful
transaction with additional information to be provided at a later
time through the REPORT mechanism defined in Section 8.1.2.
9.3. 400 Response Code
The 400 response indicates that the request was syntactically
incorrect.
9.4. 403 Response Code
The 400 response indicates that the requested operation is illegal.
9.5. 481 Response Code
The 481 response indicates that the intended target of the request
does not exist.
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9.6. 500 Response Code
The 500 response indicates that the recipient does not understand the
request
10. Control Packages
"Control Packages" are intended to specify behavior that extends the
the capability defined in this document. "Control Packages" are not
allowed to weaken "MUST" and "SHOULD" strength statements that are
detailed in this document. A "Control Package" may strengthen
"SHOULD" to "MUST" if justified by the specific usage of the
framework.
In addition to normal sections expected in a standards-track RFC and
SIP extension documents, authors of "Control Packages" need to
address each of the issues detailed in the following subsections.
The following sections MUST be used as a template and included
appropriately in all Control-Packages.
10.1. 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 event tokens is
contained in Section 15. The package name MUST also register a
version number for the package. This enables updates to the package
to be registered where appropriate. An initial version of a package
MUST start with the value '1.0'. Subsequent versions MUST increment
this number if the same package name is to be used. The exact
increment is left to the discretion of the package author.
10.2. Framework Message Usage
The Control Framework defines a number of message primitives that can
be used to exchange commands and information. There are no
limitations restricting the directionality of messages passed down a
control channel. This section of a Control package document should
explicitly detail the control messages that can be used as well as
provide an indication of directionality between entities. This will
include which role type is allowed to initiate a request type.
[Editors Note: Need to examine text.]
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10.3. Common XML Support
This optional section is only included in a Control Package if the
attributes for media dialog or Conference reference are required.
The Control Package will make strong statements (MUST strength) if
the XML schema defined in Section 17.1 in Appendix A is to be
supported. If only part of the schema is required (for example just
'connection-id' or just conf-id), the Control Package will make
equally strong (MUST strength) statements.
10.4. 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 8 (or that no control package body is required). This
section should indicate the location of detailed syntax definitions
and semantics for the appropriate body types.
10.5. 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 8 (or that no report package body is required). This section
should indicate the location of detailed syntax definitions and
semantics for the appropriate body types. 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.
10.5.1. Events
A Control Package can optionally include one or more subscriptions
that allow a controlling client to receive specific event updates in
REPORT message bodies. The mechanisms that installs/un-installs
subscriptions is not specified in document and is considered out of
scope. Event notifications are always carried in REPORT messages
MUST conform to the rules detailed in Section 8.1.2.2. This section
of a Control Package definition MUST specify details of the payload
expected to be received from subscriptions that have been installed.
[Editors Note: Ongoing discussions relating to a generic
subscription/event mechanism across all packages.]
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10.6. 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.
11. Network Address Translation (NAT)
[Editors Note: This section will look at geographically distributed
systems where NAT traversal might be an issue. It will look at both
the SIP media dialog traversal and the control channel traversal.]
12. Formal Syntax
12.1. SIP Formal Syntax
The ABNF for the "Control-Packages" SIP header is as follows:
Control-Packages = "Control-Packages" HCOLON control-package-value
*(COMMA control-package-value) *( SEMI package-params )
control-package-value = control-package-name "/" control-package-version
control-package-name = token
control-package-version = 1*DIGIT "." 1*DIGIT
package-params = k-alive-param *(SEMI extension-param)
k-alive-param = "keep-alive" EQUAL delta-seconds
delta-seconds = 1*DIGIT
extension-param = generic-param
12.2. Control Framework Formal Syntax
The Control Framework interactions use the UTF-8 transformation
format as defined in RFC3629 [16]. The syntax in this section uses
the Augmented Backus-Naur Form (ABNF) as defined in RFC2234 [17].
control-req-or-resp = control-request / control-response
control-request = control-req-start headers [control-content]
control-response = control-resp-start headers
control-req-start = pSCFW SP transact-id SP method CRLF
control-resp-start = pSCFW SP transact-id SP status-code [SP comment] CRLF
comment = utf8text
pSCFW = %x53.43.46.57; SCFW in caps
transact-id = alpha-num-token
method = mCONTROL / mREPORT / mSYNCH / mK-ALIVE / other-method
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mCONTROL = %x43.4F.4E.54.52.4F.4C; CONTROL in caps
mREPORT = %x52.45.50.4F.52.54; REPORT in caps
mSYNCH = %x53.59.4E.43.48; SYNCH in caps
mK-ALIVE = %x4B.2D.41.4C.49.56.45;K-ALIVE in caps
other-method = 1*UPALPHA
status-code = 3DIGIT ; any code defined in this and other documents
headers = Content-Length
/Control-Package
/Status
/Seq
/Timeout
/Dialog-id
/ext-header
Content-Length = "Content-Length:" SP 1*DIGIT
Control-Package = "Control-Package:" SP 1*alpha-num-token
Status = "Status:" SP ("pending" / "update" / "terminate" )
Timeout = "Timeout:" SP 1*DIGIT
Seq = "Seq:" SP 1*DIGIT
Dialog-id = "Dialog-id:" SP dialog-id-string
dialog-id-string = alpha-num-token "~" alpha-num-token ["~" alpha-num-token]
alpha-num-token = alphanum 3*31alpha-num-tokent-char
alpha-num-tokent-char = alphanum / "." / "-" / "+" / "%" / "="
control-content = Content-Type 2CRLF data CRLF
Content-Type = "Content-Type:" SP media-type
media-type = type "/" subtype *( ";" gen-param )
type = token
subtype = token
gen-param = pname [ "=" pval ]
pname = token
pval = token / quoted-string
token = 1*(%x21 / %x23-27 / %x2A-2B / %x2D-2E
/ %x30-39 / %x41-5A / %x5E-7E)
; token is compared case-insensitive
quoted-string = DQUOTE *(qdtext / qd-esc) DQUOTE
qdtext = SP / HTAB / %x21 / %x23-5B / %x5D-7E
/ UTF8-NONASCII
qd-esc = (BACKSLASH BACKSLASH) / (BACKSLASH DQUOTE)
BACKSLASH = "\"
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UPALPHA = %x41-5A
ALPHANUM = ALPHA / DIGIT
data = *OCTET
ext-header = hname ":" SP hval CRLF
hname = ALPHA *token
hval = utf8text
utf8text = *(HTAB / %x20-7E / UTF8-NONASCII)
UTF8-NONASCII = %xC0-DF 1UTF8-CONT
/ %xE0-EF 2UTF8-CONT
/ %xF0-F7 3UTF8-CONT
/ %xF8-Fb 4UTF8-CONT
/ %xFC-FD 5UTF8-CONT
UTF8-CONT = %x80-BF
The following table details a summary of the headers that can be
contained in Control Framework interactions. The "where" columns
details where headers can be used:
R: header field may only appear in requests;
r: header field may only appear in responses;
2xx, 4xx, etc.: A numerical value or range indicates response
codes with which the header field can be used;
An empty entry in the "where" column indicates that the header
field may be present in all requests and responses.
The remaining columns list the specified methods and the presence of
a specific header:
m: The header field is mandatory.
o: The header field is optional.
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Header field Where CONTROL REPORT SYNCH
___________________________________________________
Content-Length o o -
Control-Package R m - -
Seq - m -
Status R - m -
Timeout R - m -
Dialog-id R - - m
Figure 11: Table 1
13. 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.
Control Client Control Server
| |
| (1) SIP INVITE |
| ----------------------------------------> |
| |
| (2) SIP 200 |
| <--------------------------------------- |
| |
| (3) SIP ACK |
| ----------------------------------------> |
| |
|==>=======================================>==|
| Control Channel Established |
|==>=======================================>==|
| |
| (4) SYNCH |
| ----------------------------------------> |
| |
| (5) 200 |
| <--------------------------------------- |
| |
| (6) CONTROL |
| ----------------------------------------> |
| |
| (7) 202 |
| <--------------------------------------- |
| |
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| (8) REPORT (pending) |
| <---------------------------------------- |
| |
| (9) 200 |
| ----------------------------------------> |
| |
| (10) REPORT (update) |
| <---------------------------------------- |
| |
| (11) 200 |
| ----------------------------------------> |
| |
| (12) REPORT (terminate) |
| <---------------------------------------- |
| |
| (13) 200 |
| ----------------------------------------> |
| |
| (14) SIP BYE |
| ----------------------------------------> |
| |
| (15) SIP 200 |
| <--------------------------------------- |
|=============================================|
| Control Channel Terminated |
|=============================================|
| |
1. Control Client->Control Server (SIP): INVITE
sip:control-server@example.com
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INVITE sip:control-server@example.com SIP/2.0
To: <sip:control-server@example.com>
From: <sip:control-client@example.com>;tag=8937498
Via: SIP/2.0/UDP control-client.example.com;branch=z9hG412345678
CSeq: 1 INVITE
Require: escs
Control-Packages: <example-package>
Call-ID: 893jhoeihjr8392@example.com
Contact: <sip:control-client@pc1.example.com>
Content-Type: application/sdp
v=0
o=originator 2890844526 2890842808 IN IP4 controller.example,com
s=-
c=IN IP4 control-client.example.com
m=application 7575 TCP/ESCS
a=setup:active
a=connection:new
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 control-client.example.com;branch=z9hG412345678
CSeq: 1 INVITE
Require: escs
Control-Packages: <example-package>
Call-ID: 893jhoeihjr8392@example.com
Contact: <sip:control-client@pc2.example.com>
Content-Type: application/sdp
v=0
o=originator 2890844526 2890842808 IN IP4 controller.example,com
s=-
c=IN IP4 control-server.example.com
m=application 7575 TCP/ESCS
a=setup:passive
a=connection:new
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): SYNCH.
SCFW 8djae7khauj SYNCH
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Dialog-id: 8937498~893jhoeihjr8392@example.com~023983774
5. Control Server-->Control Client (Control Framework Message):
200.
SCFW 8djae7khauj 200
6. 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): CONTROL.
SCFW i387yeiqyiq CONTROL
Control-Package: <package-name>
Content-Length: 11
<XML BLOB/>
7. Control Server-->Control Client (Control Framework Message):
202.
SCFW i387yeiqyiq 202
8. Control Server-->Control Client (Control Framework Message):
REPORT.
SCFW i387yeiqyiq REPORT
Seq: 1
Status: pending
Timeout: 10
9. Control Client-->Control Server (Control Framework Message):
200.
SCFW i387yeiqyiq 200
Seq: 1
10. Control Server-->Control Client (Control Framework Message):
REPORT.
SCFW i387yeiqyiq REPORT
Seq: 2
Status: update
Timeout: 10
<XML BLOB/>
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11. Control Client-->Control Server (Control Framework Message):
200.
SCFW i387yeiqyiq 200
Seq: 2
12. Control Server-->Control Client (Control Framework Message):
REPORT.
SCFW i387yeiqyiq REPORT
Seq: 3
Status: terminate
Timeout: 10
<XML BLOB/>
13. Control Client-->Control Server (Control Framework Message):
200.
SCFW i387yeiqyiq 200
Seq: 3
14. Control Client->Control Server (SIP): BYE
BYE sip:control-client@pc2.example.com SIP/2.0
To: <sip:control-server@example.com>
From: <sip:control-client@example.com>;tag=8937498
Via: SIP/2.0/UDP control-client.example.com;branch=z9hG423456789
CSeq: 2 BYE
Require: escs
Control-Packages: <example-package>
Call-ID: 893jhoeihjr8392@example.com
15. Control Server->Control Client (SIP): 200 OK
SIP/2.0 200 OK
To: <sip:control-server@example.com>;tag=023983774
From: <sip:control-client@example.com>;tag=8937498
Via: SIP/2.0/UDP control-client.example.com;branch=z9hG423456789
CSeq: 2 BYE
Require: escs
Control-Packages: <example-package>
Call-ID: 893jhoeihjr8392@example.com
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14. Security Considerations
Security Considerations to be included in later versions of this
document.
15. IANA Considerations
15.1. IANA Registration of the 'escs' Option Tag
15.2. Control Package Registration Information
15.2.1. Control Package Registration Template
15.3. SDP Transport Protocol
15.3.1. TCP/ESCS
15.3.2. TCP/TLS/ESCS
15.4. SDP Attribute Names
15.5. SIP Response Codes
16. Acknowledgments
The authors would like to thank Ian Evans and Michael Bardzinski of
Ubiquity Software, Adnan Saleem of Convedia, and Dave Morgan for
useful review and input to this work. Eric Burger contributed to the
early phases of this work.
17. Appendix A
During the creation of the Control Framework it has become clear that
there are number of components that are common across multiple
packages. It has become apparent that it would be useful to collect
such re-usable components in a central location. In the short term
this appendix provides the place holder for the utilities and it is
the intention that this section will eventually form the basis of an
initial 'Utilities Document' that can be used by Control Packages.
17.1. 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
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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 'connection-id' attribute MUST be
constructed by concatenating the 'Local' and 'Remote' SIP dialog
identifier tags as defined in RFC3261 [2]. 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
'connection-id' attribute for a Control Framework command would be:
7HDY839~HJKSkyHS
If a session description has more than one media description (as
identified by 'm=' in [9]) it is possible to explicitly reference
them individually. When constructing the 'connection-id' attribute
for a command that applies to a specific media ('m=') in an SDP
description, an optional third component can be concatenated to the
Connection reference key. It is again separated using the '~'
character and uses the 'label' attribute as specified in [10]. So
the format would be:
'Local Dialog tag' + '~' + 'Remote Dialog tag' + '~' + 'Label Attribute'
As an example, for an entity that has a SIP Local dialog identifier
of '7HDY839', a Remote dialog identifier of 'HJKSkyHS' and an SDP
label attribute of 'HUwkuh7ns', the 'connection-id' attribute for a
Control Framework command would be:
7HDY839~HJKSkyHS~HUwkuh7ns
It should be noted that Control Framework requests initiated in
conjunction with a SIP dialog will produce a different
'connection-id' value depending on the directionality of the request,
for example Local and Remote tags are locally identifiable.
As with the Connection attribute previously defined, it is also
useful to have the ability to apply specific control framework
commands to a number of related dialogs, such as a multiparty call.
This typically consists of a number of media dialogs that are
logically bound by a single identifier. The following schema allows
for control framework commands to explicitly reference such a
grouping through a 'conf' XML container. If used by a Control
Package, any control XML referenced by the attribute applies to all
related media dialogs. Unlike the dialog attribute, the 'conf-id'
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attribute does not need to be constructed based on the overlying SIP
dialog. The 'conf-id' attribute value is system specific and should
be selected with relevant context and uniqueness.
The full schema follows:
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema targetNamespace="urn:ietf:params:xml:ns:control:framework-attributes"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="urn:ietf:params:xml:ns::control:framework-attributes"
elementFormDefault="qualified" attributeFormDefault="unqualified">
<!-- xs:include schemaLocation="common-schema.xsd"/ -->
<xsd:attributeGroup name="framework-attributes">
<xsd:annotation>
<xsd:documentation>SIP Connection and Conf Identifiers</xsd:documentation>
</xsd:annotation>
<xsd:attribute name="connection-id" type="xsd:string"/>
<xsd:attribute name="conf-id" type="xsd:string"/>
</xsd:attributeGroup>
</xs:schema>
18. References
18.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
18.2. Informative References
[2] 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.
[3] Rosenberg, J. and H. Schulzrinne, "Reliability of Provisional
Responses in Session Initiation Protocol (SIP)", RFC 3262,
June 2002.
[4] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
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[5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[6] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the
Session Description Protocol (SDP)", RFC 4145, September 2005.
[7] Groves, C., Pantaleo, M., Anderson, T., and T. Taylor, "Gateway
Control Protocol Version 1", RFC 3525, June 2003.
[8] Dolly, M., "Media Control Protocol Requirements",
draft-dolly-xcon-mediacntrlframe-02 (work in progress),
September 2006.
[9] Handley, M., "SDP: Session Description Protocol",
draft-ietf-mmusic-sdp-new-26 (work in progress), January 2006.
[10] Levin, O. and G. Camarillo, "The SDP (Session Description
Protocol) Label Attribute",
draft-ietf-mmusic-sdp-media-label-01 (work in progress),
January 2005.
[11] Jennings, C. and R. Mahy, "Managing Client Initiated
Connections in the Session Initiation Protocol (SIP)",
draft-ietf-sip-outbound-07 (work in progress), January 2007.
[12] 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.
[13] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating
User Agent Capabilities in the Session Initiation Protocol
(SIP)", RFC 3840, August 2004.
[14] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.
[15] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", STD 64,
RFC 3550, July 2003.
[16] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
STD 63, RFC 3629, November 2003.
[17] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
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Authors' Addresses
Chris Boulton
Ubiquity Software Corporation
Building 3
Wern Fawr Lane
St Mellons
Cardiff, South Wales CF3 5EA
Email: cboulton@ubiquitysoftware.com
Tim Melanchuk
BlankSpace
Email: tim.melanchuk@gmail.com
Scott McGlashan
Hewlett-Packard
Gustav III:s boulevard 36
SE-16985 Stockholm, Sweden
Email: scott.mcglashan@hp.com
Asher Shiratzky
Radvision
24 Raoul Wallenberg st
Tel-Aviv, Israel
Email: ashers@radvision.com
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