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RFC 6230

 
 
 

Media Control Channel Framework

Part 2 of 3, p. 15 to 36
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6.  Control Framework Interactions

   In this document, the use of the COMEDIA specification allows for a
   Control Channel to be set up in either direction as a result of a SIP
   INVITE transaction.  SIP provides a flexible negotiation mechanism to
   establish the Control Channel, but there needs to be a mechanism
   within the Control Channel to correlate it with the SIP INVITE dialog
   usage implemented for its establishment.  A Control Client receiving
   an incoming connection (whether it be acting in the role of UAC or
   UAS) has no way of identifying the associated SIP INVITE dialog usage
   as it could be simply listening for all incoming connections on a
   specific port.  The following steps, which implementations MUST
   support, allow a connecting UA (that is, the UA with the active role
   in COMEDIA) to identify the associated SIP INVITE dialog usage that
   triggered the connection.  Unless there is an alternative dialog
   association mechanism used, the UAs MUST carry out these steps before
   any other signaling on the newly created Control Channel.

   o  Once the connection has been established, the UA acting in the
      active role (active UA) to initiate the connection MUST send a
      Control Framework SYNC request.  The SYNC request MUST be
      constructed as defined in Section 9.1 and MUST contain the
      'Dialog-ID' message header.

   o  The 'Dialog-ID' message header is populated with the value of the
      local 'cfw-id' media-level attribute that was inserted by the same
      client in the SDP offer/answer exchange to establish the Control
      Channel.  This allows for a correlation between the Control
      Channel and its associated SIP INVITE dialog usage.

   o  On creating the SYNC request, the active UA MUST follow the
      procedures outlined in Section 6.3.3.  This provides details of
      connection keep-alive messages.

   o  On creating the SYNC request, the active UA MUST also follow the
      procedures outlined in Section 6.3.4.2.  This provides details of
      the negotiation mechanism used to determine the Protocol Data
      Units (PDUs) that can be exchanged on the established Control
      Channel connection.

   o  The UA in the active role for the connection creation MUST then
      send the SYNC request.  If the UA in the active role for the
      connection creation is a SIP UAS and has generated its SDP
      response in a 2xx-class SIP response, it MUST wait for an incoming
      SIP ACK message before issuing the SYNC.  If the UA in the active
      role for the connection creation is a SIP UAS and has generated
      its SDP response in a reliable 1XX class SIP response, it MUST
      wait for an incoming SIP PRACK message before issuing the SYNC.

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      If the UA in the active role for the connection creation is a SIP
      UAC, it MUST send the SYNC message immediately on establishment of
      the Control Channel.  It MUST then wait for a period of at least
      2*'Transaction-Timeout' to receive a response.  It MAY choose a
      longer time to wait, but it MUST NOT be shorter than 'Transaction-
      Timeout'.  In general, a Control Framework transaction MUST
      complete within 20 (2*'Transaction-Timeout') seconds and is
      referenced throughout the document as 'Transaction-Timeout'.

   o  If no response is received for the SYNC message, a timeout occurs
      and the Control Channel is terminated along with the associated
      SIP INVITE dialog usage.  The active UA MUST issue a BYE request
      to terminate the SIP INVITE dialog usage.

   o  If the active UA receives a 481 response from the passive UA, this
      means the SYNC request was received, but the associated SIP INVITE
      dialog usage specified in the SYNC message does not exist.  The
      active client MUST terminate the Control Channel.  The active UA
      MUST issue a SIP BYE request to terminate the SIP INVITE dialog
      usage.

   o  All other error responses received for the SYNC request are
      treated as detailed in this specification and also result in the
      termination of the Control Channel and the associated SIP INVITE
      dialog usage.  The active UA MUST issue a BYE request to terminate
      the SIP INVITE dialog usage.

   o  The receipt of a 200 response to a SYNC message implies that the
      SIP INVITE dialog usage and control connection have been
      successfully correlated.  The Control Channel can now be used for
      further interactions.

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

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

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6.1.  General Behavior for Constructing Requests

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

   Any Framework message that contains an associated payload MUST also
   include the 'Content-Type' and 'Content-Length' message headers,
   which indicate the MIME type of the payload specified by the
   individual Control Framework packages and the size of the message
   body represented as a whole decimal number of octets, respectively.
   If no associated payload is to be added to the message, the 'Content-
   Length' header MUST have a value of '0'.

   A Server receiving a Framework message request MUST respond with an
   appropriate response (as defined in Section 6.2).  Control Clients
   MUST wait for a minimum of 2*'Transaction-Timeout' for a response
   before considering the transaction a failure and tidying state
   appropriately depending on the extension package being used.

6.2.  General Behavior for Constructing Responses

   An entity acting as a Control Server, on receiving a request, MUST
   generate a response within the 'Transaction-Timeout', as measured
   from the Control Client.  The response MUST conform to the ABNF
   defined in Section 9.  The first line of the response MUST contain
   the transaction identifier used in the first line of the request, as

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   defined in Section 6.1.  Responses MUST NOT include the 'Status' or
   'Timeout' message headers, and these MUST be ignored if received by a
   Client in a response.

   A Control Server MUST include a status code in the first line of the
   response.  If there is no error, the Server responds with a 200
   Control Framework status code, as defined in Section 7.1.  The 200
   response MAY include message bodies.  If the response contains a
   payload, the message MUST include the 'Content-Length' and 'Content-
   Type' headers.  When the Control Client receives a 2xx-class
   response, the Control Command transaction is complete.

   If the Control Server receives a request, like CONTROL, that the
   Server understands, but the Server knows processing the command will
   exceed the 'Transaction-Timeout', then the Server MUST respond with a
   202 status code in the first line of the response.  Following the
   initial response, the server will send one or more REPORT messages as
   described in Section 6.3.2.  A Control Package MUST explicitly define
   the circumstances under which the server sends 200 and 202 messages.

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

6.3.  Transaction Processing

   The Control Framework defines four types of requests (methods):
   CONTROL, REPORT, K-ALIVE, and SYNC.  Implementations MUST support
   sending and receiving these four methods.

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

6.3.1.  CONTROL Transactions

   A CONTROL message is used by the Control Client to pass control-
   related information to a Control Server.  It is also used as the
   event-reporting mechanism in the Control Framework.  Reporting events
   is simply another usage of the CONTROL message, which is permitted to
   be sent in either direction between two participants in a session,
   carrying the appropriate payload for an event.  The message is
   constructed in the same way as any standard Control Framework

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   message, as discussed in Section 6.1 and defined in Section 9.  A
   CONTROL message MAY contain a message body.  The explicit Control
   Command(s) of the message payload contained in a CONTROL message are
   specified in separate Control Package specifications.  Separate
   Control Package specifications MUST conform to the format defined in
   Section 8.4.  A CONTROL message containing a payload MUST include a
   'Content-Type' header.  The payload MUST be one of the payload types
   defined by the Control Package.  Individual packages MAY allow a
   CONTROL message that does not contain a payload.  This could in fact
   be a valid message exchange within a specific package; if it's not,
   an appropriate package-level error message MUST be generated.

6.3.2.  REPORT Transactions

   A 'REPORT' message is used by a Control Server when processing of a
   CONTROL command extends beyond the 'Transaction-Timeout', as measured
   from the Client.  In this case, the Server returns a 202 response.
   The Server returns status updates and the final results of the
   command in subsequent REPORT messages.

   All REPORT messages MUST contain the same transaction ID in the
   request start line that was present in the original CONTROL
   transaction.  This correlates extended transactions with the original
   CONTROL transaction.  A REPORT message containing a payload MUST
   include the 'Content-Type' and 'Content-Length' headers indicating
   the payload MIME type [RFC2045] defined by the Control Package and
   the length of the payload, respectively.

6.3.2.1.  Reporting the Status of Extended Transactions

   On receiving a CONTROL message, a Control Server MUST respond within
   'Transaction-Timeout' with a status code for the request, as
   specified in Section 6.2.  If the processing of the command completes
   within that time, a 200 response code MUST be sent.  If the command
   does not complete within that time, the response code 202 MUST be
   sent indicating that the requested command is still being processed
   and the CONTROL transaction is being extended.  The REPORT method is
   then used to update and terminate the status of the extended
   transaction.  The Control Server should not wait until the last
   possible opportunity to make the decision of issuing a 202 response
   code and should ensure that it has plenty of time for the response to
   arrive at the Control Client.  If it does not have time, transactions
   will be terminated (timed out) at the Control Client before
   completion.

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   A Control Server issuing a 202 response MUST ensure the message
   contains a 'Timeout' message header.  This header MUST have a value
   in seconds that is the amount of time the recipient of the 202
   message MUST wait before assuming that there has been a problem and
   terminating the extended transaction and associated state.

   The initial REPORT message MUST contain a 'Seq' (Sequence) message
   header with a value equal to '1'.  Note: the 'Seq' numbers at both
   Control Client and Control Server for Framework messages are
   independent.

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

   Subsequent REPORT messages that provide additional information
   relating to the extended CONTROL transaction MUST also include and
   increment by 1 the 'Seq' header value.  A REPORT message received
   that has not been incremented by 1 MUST be responded to with a 406
   response and the extended transaction MUST be considered terminated.
   On receiving a 406 response, the extended transaction MUST be
   terminated.  REPORT messages MUST also include a 'Status' header with
   a value of 'update'.  These REPORT messages sent to update the
   extended CONTROL transaction status MAY contain a message body, as
   defined by individual Control Packages and specified in Section 8.5.
   A REPORT message sent updating the extended transaction also acts as
   a timeout refresh, as described earlier in this section.  This will
   result in a transaction timeout period at the initiator of the
   original CONTROL request being reset to the interval contained in the
   'Timeout' message header.

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   When all processing for an extended CONTROL transaction has taken
   place, the entity acting as a Control Server MUST send a terminating
   REPORT message.  The terminating REPORT message MUST increment the
   value in the 'Seq' message header by the value of '1' from the
   previous REPORT message.  It MUST also include a 'Status' header with
   a value of 'terminate' and MAY contain a message body.  It MUST also
   contain a 'Timeout' message header with a valid value.  The inclusion
   of the 'Timeout' header is for consistency, and its value is ignored.
   A Control Framework UAC can then clean up any pending state
   associated with the original CONTROL transaction.

6.3.3.  K-ALIVE Transactions

   The protocol defined in this document may be used in various network
   architectures.  This includes a wide range of deployments where the
   clients could be co-located in a secured, private domain, or spread
   across disparate domains that require traversal of devices such as
   Network Address Translators (NATs) and firewalls.  A keep-alive
   mechanism enables the Control Channel to be kept active during times
   of inactivity.  This is because many firewalls have a timeout period
   after which connections are closed.  This mechanism also provides the
   ability for application-level failure detection.  It should be noted
   that the following procedures apply only to the Control Channel being
   created.  For details relating to the SIP keep-alive mechanism,
   implementers should seek guidance from SIP Outbound [RFC5626].

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

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

6.3.3.1.  Behavior for an Entity in an Active Role

   When in an active role, a K-ALIVE message MUST be generated before
   the local keep-alive timer fires.  An active entity is free to send
   the K-ALIVE message whenever it chooses.  It is RECOMMENDED for the
   entity to issue a K-ALIVE message after 80% of the local keep-alive
   timer.  On receiving a 200 OK Control Framework message for the

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   K-ALIVE request, the active entity MUST reset the local keep-alive
   timer.  If no 200 OK response is received to the K-ALIVE message, or
   a transport-level problem is detected by some other means, before the
   local keep-alive timer fires, the active entity MAY use COMEDIA re-
   negotiation procedures to recover the connection.  Otherwise, the
   active entity MUST tear down the SIP INVITE dialog and recover the
   associated Control Channel resources.

6.3.3.2.  Behavior for an Entity in a Passive Role

   When acting as a passive entity, a K-ALIVE message must be received
   before the local keep-alive timer fires.  When a K-ALIVE request is
   received, the passive entity MUST generate a 200 OK Control Framework
   response and reset the local keep-alive timer.  No other Control
   Framework response is valid.  If no K-ALIVE message is received (or a
   transport level problem is detected by some other means) before the
   local keep-alive timer fires, the passive entity MUST tear down the
   SIP INVITE dialog and recover the associated Control Channel
   resources.

6.3.4.  SYNC Transactions

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

6.3.4.1.  Timeout Negotiation for the Initial SYNC Transaction

   The initial SYNC request allows the timeout period for the Control
   Channel keep-alive mechanism to be negotiated.  The following rules
   MUST be followed for the initial SYNC request:

   o  If the Client initiating the SDP offer has a COMEDIA 'setup'
      attribute equal to active, the 'Keep-Alive' header MUST be
      included in the SYNC message generated by the offerer.  The value
      of the 'Keep-Alive' header SHOULD be in the range of 95 to 120
      seconds (this is consistent with SIP Outbound [RFC5626]).  The
      value of the 'Keep-Alive' header MUST NOT exceed 600 seconds.  The
      client that generated the SDP "Answer" (the passive client) MUST
      copy the 'Keep-Alive' header into the 200 response to the SYNC
      message with the same value.

   o  If the Client initiating the SDP offer has a COMEDIA 'setup'
      attribute equal to passive, the 'Keep-Alive' header parameter MUST
      be included in the SYNC message generated by the answerer.  The
      value of the 'Keep-Alive' header SHOULD be in the range of 95 to

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      120 seconds.  The client that generated the SDP offer (the passive
      client) MUST copy the 'Keep-Alive' header into the 200 response to
      the SYNC message with the same value.

   o  If the Client initiating the SDP offer has a COMEDIA 'setup'
      attribute equal to 'actpass', the 'Keep-Alive' header parameter
      MUST be included in the SYNC message of the entity who is the
      active participant in the SDP session.  If the client generating
      the subsequent SDP answer places a value of 'active' in the
      COMEDIA SDP 'setup' attribute, it will generate the SYNC request
      and include the 'Keep-Alive' header.  The value SHOULD be in the
      range 95 to 120 seconds.  If the client generating the subsequent
      SDP answer places a value of 'passive' in the COMEDIA 'setup'
      attribute, the original UA making the SDP will generate the SYNC
      request and include the 'Keep-Alive' header.  The value SHOULD be
      in the range 95 to 120 seconds.

   o  If the initial negotiated offer/answer results in a COMEDIA
      'setup' attribute equal to 'holdconn', the initial SYNC mechanism
      will occur when the offer/answer exchange is updated and the
      active/passive roles are resolved using COMEDIA.

   The previous steps ensure that the entity initiating the Control
   Channel connection is always the one specifying the keep-alive
   timeout period.  It will always be the initiator of the connection
   who generates the K-ALIVE messages.

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

6.3.4.2.  Package Negotiation

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

   A server receiving the initial SYNC request MUST examine the contents
   of the 'Packages' header.  If the server supports at least one of the
   packages listed in the request, it MUST respond with a 200 response

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   code.  The response MUST contain a 'Packages' header that lists the
   supported packages that are in common with those from the 'Packages'
   header of the request (either all or a subset).  This list forms a
   common set of Control Packages that are supported by both parties.
   Any Control Packages supported by the server that are not listed in
   the 'Packages' header of the SYNC request MAY be placed in the
   'Supported' header of the response.  This provides a hint to the
   client that generated the SYNC request about additional packages
   supported by the server.

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

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

   An entity MAY honor Control Framework commands relating to a Control
   Package it no longer supports after package re-negotiation.  When the
   entity does not wish to honor such commands, it MUST respond to the
   request with a 420 response.

7.  Response Code Descriptions

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

   Note that these response codes apply to Framework Transactions only.
   Success or error indications for Control Commands MUST be treated as
   the result of a Control Command and returned in either a 200 response
   or REPORT message.

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7.1.  200 Response Code

   The framework protocol transaction completed successfully.

7.2.  202 Response Code

   The framework protocol transaction completed successfully and
   additional information will be provided at a later time through the
   REPORT mechanism defined in Section 6.3.2.

7.3.  400 Response Code

   The request was syntactically incorrect.

7.4.  403 Response Code

   The server understood the request, but is refusing to fulfill it.
   The client SHOULD NOT repeat the request.

7.5.  405 Response Code

   Method not allowed.  The primitive is not supported.

7.6.  406 Response Code

   Message out of sequence.

7.7.  420 Response Code

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

7.8.  421 Response Code

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

7.9.  422 Response Code

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

7.10.  423 Response Code

   Recipient has an existing transaction with the same transaction ID.

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7.11.  481 Response Code

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

7.12.  500 Response Code

   The recipient does not understand the request.

8.  Control Packages

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

   In addition to the usual sections expected in Standards-Track RFCs
   and SIP extension documents, authors of Control Packages need to
   address each of the issues detailed in the following sub-sections.
   The following sections MUST be used as a template and included
   appropriately in all Control-Package specifications.  To reiterate,
   the following sections do not solely form the basis of all Control-
   Package specifications but are included as a minimum to provide
   essential package-level information.  A Control-Package specification
   can take any valid form it wishes as long as it includes at least the
   following information listed in this section.

8.1.  Control Package Name

   This section MUST be present in all extensions to this document and
   provides a token name for the Control Package.  The section MUST
   include information that appears in the IANA registration of the
   token.  Information on registering Control Package tokens is
   contained in Section 13.

8.2.  Framework Message Usage

   The Control Framework defines a number of message primitives that can
   be used to exchange commands and information.  There are no
   limitations restricting the directionality of messages passed down a
   Control Channel.  This section of a Control Package document MUST
   explicitly detail the types of Framework messages (Methods) that can
   be used as well as provide an indication of directionality between
   entities.  This will include which role type is allowed to initiate a
   request type.

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8.3.  Common XML Support

   This optional section is only included in a Control Package if the
   attributes for media dialog or conference reference are required, as
   defined and discussed in Appendix A.1.  The Control Package will make
   strong statements (using language from RFC 2119 [RFC2119]) if the XML
   schema defined in Appendix A.1 is to be supported.  If only part of
   the schema is required (for example, just 'connectionid' or
   'conferenceid'), the Control Package will make equally strong
   statements (using language from RFC 2119 [RFC2119]).

8.4.  CONTROL Message Bodies

   This mandatory section of a Control Package defines the control body
   that can be contained within a CONTROL command request, as defined in
   Section 6, or that no Control Package body is required.  This section
   MUST indicate the location of detailed syntax definitions and
   semantics for the appropriate MIME [RFC2045] body type that apply to
   a CONTROL command request and, optionally, the associated 200
   response.  For Control Packages that do not have a Control Package
   body, making such a statement satisfies the "MUST" strength of this
   section in the Control Package document.

8.5.  REPORT Message Bodies

   This mandatory section of a Control Package defines the REPORT body
   that can be contained within a REPORT command request, as defined in
   Section 6, or that no report package body is required.  This section
   MUST indicate the location of detailed syntax definitions and
   semantics for the appropriate MIME [RFC2045] body type.  It should be
   noted that the Control Framework specification does allow for
   payloads to exist in 200 responses to CONTROL messages (as defined in
   this document).  An entity that is prepared to receive a payload type
   in a REPORT message MUST also be prepared to receive the same payload
   in a 200 response to a CONTROL message.  For Control Packages that do
   not have a Control Package body, stating such satisfies the "MUST"
   strength of this section in the Control Package document.

8.6.  Audit

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

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   This section SHOULD include the following information:

   o  If an auditing capability is available in this package.

   o  How auditing information is triggered (for example, using a
      Control Framework CONTROL message) and delivered (for example, in
      a Control Framework 200 response).

   o  The location of the audit query and response format for the
      payload (for example, it could be a separate XML schema OR part of
      a larger XML schema).

8.7.  Examples

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

9.  Formal Syntax

9.1.  Control Framework Formal Syntax

   The Control Framework interactions use the UTF-8 transformation
   format as defined in [RFC3629].  The syntax in this section uses the
   Augmented Backus-Naur Form (ABNF) as defined in [RFC5234] including
   types 'DIGIT', 'CRLF', and 'ALPHA'.

   Unless otherwise stated in the definition of a particular header
   field, field values, parameter names, and parameter values are not
   case-sensitive.

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

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

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

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  headers = header-name CRLF

  header-name = (Content-Length
   /Content-Type
   /Control-Package
   /Status
   /Seq
   /Timeout
   /Dialog-ID
   /Packages
   /Supported
   /Keep-alive
   /ext-header)

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

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

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

  control-content = *OCTET

  Content-Type = "Content-Type:" SP media-type
  media-type = type "/" subtype *(SP ";" gen-param )
  type = token    ; Section 4.2 of RFC 4288
  subtype = token ; Section 4.2 of RFC 4288

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

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

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

  ext-header = hname ":" SP hval CRLF

  hname = ALPHA *token
  hval = utf8text

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

  UTF8-NONASCII = UTF8-2 / UTF8-3 / UTF8-4 ; From RFC 3629

   The following table details a summary of the headers that can be
   contained in Control Framework interactions.

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

       Table 1: Summary of Headers in Control Framework Interactions

   The notation used in Table 1 is as follows:

 R: header field may only appear in requests.
 r: header field may only appear in responses.
 2xx, 4xx, etc.: response codes with which the header field can be used.
 [blank]: header field may appear in either requests or responses.
 m: header field is mandatory.
 o: header field is optional.
 -: header field is not applicable (ignored if present).

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9.2.  Control Framework Dialog Identifier SDP Attribute

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

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

            cfw-id-name   = token

            token         = 1*(token-char)

            token-char    = %x21 / %x23-27 / %x2A-2B / %x2D-2E / %x30-39
                            / %x41-5A / %x5E-7E

   The token-char and token elements are defined in [RFC4566] but
   included here to provide support for the implementer of this SDP
   feature.

10.  Examples

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

   In this example, the Control Client establishes a Control Channel,
   SYNCs with the Control Server, and issues a CONTROL request that
   can't be completed within the 'Transaction-Timeout', so the Control
   Server returns a 202 response code to extend the transaction.  The
   Control Server then follows with REPORTs until the requested action
   has been completed.  The SIP INVITE dialog is then terminated.

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            Control Client                                Control Server
                   |                                             |
                   |       (1) SIP INVITE                        |
                   |  ---------------------------------------->  |
                   |                                             |
                   |       (2) SIP 200                           |
                   |  <---------------------------------------   |
                   |                                             |
                   |       (3) SIP ACK                           |
                   |  ---------------------------------------->  |
                   |                                             |
                   |==>=======================================>==|
                   |         Control Channel Established         |
                   |==>=======================================>==|
                   |                                             |
                   |       (4) SYNC                              |
                   |  ---------------------------------------->  |
                   |                                             |
                   |       (5) 200                               |
                   |  <---------------------------------------   |
                   |                                             |
                   |       (6) CONTROL                           |
                   |  ---------------------------------------->  |
                   |                                             |

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

   INVITE sip:control-server@example.com SIP/2.0
   To: <sip:control-server@example.com>
   From: <sip:control-client@example.com>;tag=8937498
   Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK123
   CSeq: 1 INVITE
   Max-Forwards: 70
   Call-ID: 893jhoeihjr8392@example.com
   Contact: <sip:control-client@pc1.example.com>
   Content-Type: application/sdp
   Content-Length: 206

   v=0
   o=originator 2890844526 2890842808 IN IP4 controller.example.com
   s=-
   c=IN IP4 control-client.example.com
   m=application 49153 TCP cfw
   a=setup:active
   a=connection:new
   a=cfw-id:fndskuhHKsd783hjdla

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

SIP/2.0 200 OK
To: <sip:control-server@example.com>;tag=023983774
From: <sip:control-client@example.com>;tag=8937498
Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK123;received=192.0.2.5
CSeq: 1 INVITE
Call-ID: 893jhoeihjr8392@example.com
Contact: <sip:control-server@pc2.example.com>
Content-Type: application/sdp
Content-Length: 203

v=0
o=responder 2890844600 2890842900 IN IP4 controller.example.com
s=-
c=IN IP4 control-server.example.com
m=application 49153 TCP cfw
a=setup:passive
a=connection:new
a=cfw-id:7JeDi23i7eiysi32

   (3)   Control Client-->Control Server (SIP): ACK

   (4)   Control Client opens a TCP connection to the Control Server.
         The connection can now be used to exchange Control Framework
         messages.  Control Client-->Control Server (Control Framework
         message): SYNC.

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

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

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

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

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

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   Content-Length: 11

   <XML BLOB/>

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

   CFW i387yeiqyiq 202
   Timeout: 10

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

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

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

   CFW i387yeiqyiq 200
   Seq: 1

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

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

   <XML BLOB/>

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

   CFW i387yeiqyiq 200
   Seq: 2

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

   CFW i387yeiqyiq REPORT
   Seq: 3
   Status: terminate

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   Timeout: 10
   Content-Type: example_content/example_content
   Content-Length: 11

   <XML BLOB/>

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

   CFW i387yeiqyiq 200
   Seq: 3

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

   BYE sip:control-server@pc2.example.com SIP/2.0
   To: <sip:control-server@example.com>;tag=023983774
   From: <sip:client@example.com>;tag=8937498
   Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK234
   CSeq: 2 BYE
   Max-Forwards: 70
   Call-ID: 893jhoeihjr8392@example.com
   Contact: <sip:control-client@pc1.example.com>
   Content-Length: 0

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

SIP/2.0 200 OK
To: <sip:control-server@example.com>;tag=023983774
From: <sip:client@example.com>;tag=8937498
Via: SIP/2.0/UDP client.example.com;branch=z9hG4bK234;received=192.0.2.5
CSeq: 2 BYE
Call-ID: 893jhoeihjr8392@example.com
Contact: <sip:control-server@pc1.example.com>
Content-Length: 0

11.  Extensibility

   The Media Control Channel Framework was designed to be only minimally
   extensible.  New methods, header fields, and status codes can be
   defined in Standards-Track RFCs.  The Media Control Channel Framework
   does not contain a version number or any negotiation mechanism to
   require or discover new features.  If an extension is specified in
   the future that requires negotiation, the specification will need to
   describe how the extension is to be negotiated in the encapsulating
   signaling protocol.  If a non-interoperable update or extension
   occurs in the future, it will be treated as a new protocol, and it
   MUST describe how its use will be signaled.

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   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.



(page 36 continued on part 3)

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