Media Gateway Control Protocol (MGCP) RFC 2705 – breaks up the role of traditional voice switches into the components of media gateway, media gateway controller and signaling gateway functional units. This facilitates the independent managing of each VoIP gateway as a separate entity.
MGCP is a master-slave control protocol that coordinates the actions of media gateways. The media gateway controller in MGCP nomenclature is sometimes referred to as a call agent. The call agent manages the call-related signaling control intelligence, while the media gateway informs the call agent of service events. The call agent instructs the media gateway to create and tear down connections when the calls are generated. In most cases, the call agent informs the media gateways to start an RTP session between two endpoints.