Media Gateway Control Protocol

Media Gateway Control Protocol also known as MGCP is one of the implementation of the Media Gateway Control Protocol Architecture for controlling media gateways on Internet Protocol (IP) networks and the public switched telephone network (PSTN). The general base architecture and programming interface is described in RFC 2805 and the current specific MGCP definition is RFC 3435. It is a successor to the Simple Gateway Control Protocol (SGCP).

MGCP is a signaling and call control protocol used within Voice over IP (VoIP) systems that typically inter-operate with the public switched telephone network (PSTN). As such it implements a PSTN-over-IP model with the power of the network residing in a call control center (softswitch, similar to the central office of the PSTN) and the endpoints being "low-intelligence" devices, mostly simply executing control commands. The protocol represents a decomposition of other VoIP models, such as H.323, in which the media gateways (e.g., H.323's gatekeeper) have higher levels of signaling intelligence.

MGCP 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 of the media streams.

Another implementation of the Media Gateway Control Protocol Architecture which exists is the H.248/Megaco protocol.

MGCP is a master/slave protocol that allows a call control device such as Call Agent to take control of a specific port on a Media Gateway. In MGCP context Media Gateway Controller is referred to as Call Agent. This has the advantage of centralized gateway administration and provides for largely scalable IP Telephony solutions. The distributed system is composed of a Call Agent, at least one Media Gateway (MG) that performs the conversion of media signals between circuits and packets switched networks, and at least one Signaling gateway (SG) when connected to the PSTN (conversion from TDM voice to Voice over IP).

MGCP assumes a call control architecture where there is limited intelligence at the edge (endpoints, Media Gateways) and intelligence at the core Call Agent. The MGCP assumes that Call Agents will synchronize with each other to send coherent commands and responses to the gateways under their control.