MGCP separates the functions of call control and media translation into two separate devices: The voice gateway handles media translation, and a call agent handles call control. The role of an MGCP gateway is media translation between the PSTN and the IP network. MGCP gateways are divided into Residential gateways and Trunking gateways.
The methodology of MGCP reflects the structure of the PSTN with the power of the network residing in a call control center softswitch much the same as the central office in the telephone network. MGCP is a text-based protocol consisting of commands and responses. It uses the Session Description Protocol (SDP) for specifying and negotiating the media streams to be transmitted in a call session and the Real-time Transport Protocol (RTP) for framing the media streams.
The media gateway control protocol architecture, methodologies and programming interfaces are described in RFC 2805 Media Gateway Control Protocol Architecture and Requirements (April 2000.)