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 126.96.36.199. This provides details of
the negotiation mechanism used to determine the Protocol Data
Units (PDUs) that can be exchanged on the established Control
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.
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
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
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.
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 188.8.131.52.
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
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
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.
184.108.40.206. 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
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
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.
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.
220.127.116.11. 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
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.
18.104.22.168. 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
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.
22.214.171.124. 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
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
126.96.36.199. 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
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
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.
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
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.
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.
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).
It is strongly RECOMMENDED that Control Packages provide a range of
message flows that represent common flows using the package and this
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
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 = %x188.8.131.52F.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
quoted-string = DQUOTE *(qdtext / qd-esc) DQUOTE
qdtext = SP / HTAB / %x21 / %x23-5B / %x5D-7E
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).
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
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
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.
(2) Control Server-->Control Client (SIP): 200 OK
SIP/2.0 200 OK
Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK123;received=192.0.2.5
CSeq: 1 INVITE
o=responder 2890844600 2890842900 IN IP4 controller.example.com
c=IN IP4 control-server.example.com
m=application 49153 TCP cfw
(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
CFW 8djae7khauj SYNC
(5) Control Server-->Control Client (Control Framework message):
CFW 8djae7khauj 200
(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
(13) Control Client-->Control Server (Control Framework message):
CFW i387yeiqyiq 200
(14) Control Client-->Control Server (SIP): BYE
BYE sip:email@example.com SIP/2.0
Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK234
CSeq: 2 BYE
(15) Control Server-->Control Client (SIP): 200 OK
SIP/2.0 200 OK
Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK234;received=192.0.2.5
CSeq: 2 BYE
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.
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.