MGCP - Media Gateway Control Protocol - I

The Media Gateway Control Protocol (MGCP) implements the media gateway control
interface as a set of transactions. The transactions are composed of a command
and a mandatory response. There are nine commands:

* EndpointConfiguration

* CreateConnection

* ModifyConnection

* DeleteConnection

* NotificationRequest

* Notify

* AuditEndpoint

* AuditConnection
* RestartInProgress

The first five commands are sent by the Call Agent to a gateway. The
Notify command is sent by the gateway to the Call Agent.
The Call Agent may send either of the Audit commands to the gateway, and
the gateway may send a RestartInProgress command to the Call Agent.

General Description

All commands are composed of a Command header, optionally followed by
a session description.

All responses are composed of a Response header, optionally followed
by session description information.

Headers and session descriptions are encoded as a set of text lines,
separated by a carriage return and line feed character (or,
optionally, a single line-feed character). The session descriptions
are preceded by an empty line.

MGCP uses a transaction identifier to correlate commands and
responses. The transaction identifier is encoded as a component of
the command header and repeated as a component of the response header
Commands and responses SHALL be encoded in accordance with the
grammar, which, per RFC 2234, is case-insensitive except for the SDP
part. Similarly, implementations SHALL be capable of decoding
commands and responses that follow the grammar. Additionally, it is
RECOMMENDED that implementations tolerate additional linear white
space.

Some productions allow for use of quoted strings, which can be
necessary to avoid syntax problems. Where the quoted string form is
used, the contents will be UTF-8 encoded [20], and the actual value
provided is the unquoted string (UTF-8 encoded). Where both a quoted
and unquoted string form is allowed, either form can be used provided
it does not otherwise violate the grammar.

In the following, we provide additional detail on the format of MGCP
commands and responses.



Command Header

The command header is composed of:

* A command line, identifying the requested action or verb, the
transaction identifier, the endpoint towards which the action is
requested, and the MGCP protocol version,

* A set of zero or more parameter lines, composed of a parameter
name followed by a parameter value.

Unless otherwise noted or dictated by other referenced standards
(e.g., SDP), each component in the command header is case
insensitive. This goes for verbs as well as parameters and values,
and hence all comparisons MUST treat upper and lower case as well as
combinations of these as being equal.

Command Line

The command line is composed of:

* The name of the requested verb,

* The identification of the transaction,

* The name of the endpoint(s) that are to execute the command (in
notifications or restarts, the name of the endpoint(s) that is
issuing the command),

* The protocol version.

These four items are encoded as strings of printable ASCII
characters, separated by white spaces, i.e., the ASCII space (0x20)
or tabulation (0x09) characters. It is RECOMMENDED to use exactly
one ASCII space separator. However, MGCP entities MUST be able to
parse messages with additional white space characters.