Gateway protocols are used to connect networks with different structures or switching technology, for example, to connect classic, circuit-switched telephone networks with packet-oriented IP networks. The gateway protocols control the edge gateways in master- slave operation from the softswitch. The softswitch forms the master and the gateways located at the edge of the network are the slaves.
Media Control Protocol activities began in 1998 with the development of the Simple Gateway Control Protocol( SGCP), which replicated the functions of a Class 5 switch. As an extension to the SGCP protocol, Level 3 developed the Internet Gateway Control Protocol (IGCP). The Internet Engineering Task Force( IETF) adopted key features from both protocols and used them to develop the MGCP protocol, Media Gateway Control Protocol (MGCP), which supported both video and telephony and used the ASCII character set for control functions. The MGCP protocol is suitable for non-intelligent terminals and gateways. Later, Lucent got on board with the Media Device Control Protocol( MDCP), and the International Telecommunication Union ( ITU) adopted the best features from MDCP and MGCP, which it combined into H. GCP (H. Gateway Control Protocol).
To address some of the problems with MGCP, the IETF developed the Megaco protocol. Megaco assumes that terminal devices are non-intelligent devices. It replaces the gatekeeper function ofH.323, supports time division multiplexing(TDM), ATM, and the IP protocol.
In 1999, the IETF and ITU agreed to continue working on only one protocol, resulting in Megaco/H.248.