Abstract: In a telecommunications network, a method of controlling a media gateway to handle a multiplex session, using a media gateway controller, the media gateway and the media gateway controller communicating using a standardised interface protocol, e.g. H.248, providing for a set of command messages each of which contains: a context field for identifying a context of the media gateway; a termination field for identifying one or more terminations of the media gateway; at least one descriptor for defining properties of the context; and optionally a package identity and at least one associated property.