The IMS: IP Multimedia Concepts And Services, Second Edition

20.3. Protocol operation

The protocol contains a set of commands that are used to manipulate the logical entities described in the connection model (namely, terminations and contexts). Specifically, the set of commands offered by MEGACO are:

• Add – adds a termination to a context. It is also used to implicitly create a context (a context is created as soon as the first termination is added to it).

• Modify – modifies the state properties of a termination and properties specific to media streams.

• Subtract – removes a termination from a context. It is also used to implicitly delete a context. Similar to creating one, subtracting the last termination of a context deletes the context.

• Move – moves a specific termination from one context to another.

• AuditValue – returns the current termination properties as well as the events,^[] signals^[] and statistics of a termination.

  ^[] "Events" describe situations in a stream which the media gateway can detect and report (e.g., on-hook, off-hook).

  ^[] "Signals" are media generated by the media gateway (e.g., announcements and tones).

• AuditCapabilities – returns all possible values for the termination properties as well as the signals and events allowed by a particular media gateway.

• Notify – used by the media gateway to report to the media gateway controller when certain events occur.

• ServiceChange – used by the media gateway to inform the media gateway controller of specific changes in service (e.g., when a particular termination has been taken out of service ...