MEGACO Commands

MEGACO defines the following eight
commands. Most of the commands are sent from an MGC to an MG. The
exceptions are the Notify command, which is always sent from an MG to
an MGC, and the ServiceChange command, which can be sent from either
an MG or an MGC.
Add The Add command adds a termination to a context. If the command
does not specify a particular context to add the termination to, then a new
context is created. If the command does not indicate a specific TerminationID,
but instead uses the choose ($) wildcard, the MG will create a new
ephemeral termination and add it to the context.

Modify The Modify command is used to change the property values of a
termination, to instruct the termination to issue one or more signals, or to
instruct the termination to detect and report specific events.
Subtract The Subtract command is used to remove a termination from a
context. The response to the command is used to provide statistics related
to the termination’s participation in the context. These statistics depend
upon the type of termination in question. For an RTP termination, the statistics
may include items such as packets sent, packets received, and jitter.
If the result of a Subtract command is the removal of the last termination
from a context, then the context itself is deleted.
Move The Move command is used to move a termination from one context
to another. It should not be used to move a termination from or to the
null context, as these operations must be performed with the Add and Subtract
commands respectively. The capability to move a termination from
one context to another provides a useful tool for accomplishing the callwaiting
service.
Audit Value The Audit Value command is used by the MGC to retrieve current
values for properties, events, and signals associated with one or more
terminations.
Audit Capabilities The Audit Capabilities command is used by an MGC to
retrieve the possible values of properties, signals, and events associated
with one or more terminations. At first glance, this command may appear
very similar to the Audit Value command. The difference between them is
that the Audit Value command is used to determine the current status of
a termination, whereas the Audit Capabilities command is used to determine
the possible statuses that a termination might assume. For example,
Audit Value would indicate any signals that are currently being applied by
a termination, while Audit Capabilities would indicate all of the possible
signals that the termination could apply if required.
Notify The Notify command is issued by an MG to inform the MGC of
events that have occurred within the MG. The events to be reported will
have previously been requested as part of a command from the MGC to the
MG, such as a Modify command. The events reported will be accompanied
by a RequestID parameter to enable the MGC to correlate reported events
with previous requests.

Service Change The Service Change command is used by an MG to inform
an MGC that a group of terminations is about to be taken out of service
or is being returned to service. The command is also used in a situation
where an MGC is handing over control of an MG to another MGC. In that
case, the command is first issued from the controlling MGC to the MG to
instigate the transfer of control. Subsequently, the MG issues the Service
Change command to the new MGC as a means of establishing the new
relationship.