Megaco

A joint standardization effort of the ITU-T (H.248) and the IETF (RFC 3525) that defines the call control protocols employed in a physically decomposed gateway with subcomponents distributed across multiple devices that may be in multiple physically distinct locations. Those subcomponents take the form of a Media Gateway (MG) and a Media Gateway Controller (MGC), also known as a softswitch or a call agent. A single MGC can control a large number of MGs, each of which is optimized for a particular gateway application function to convert the media format between a packet network and another form of network, such as a public switched telephone network (PSTN) or an asynchronous transfer mode (ATM) network. The call control and signaling logic are centralized in the MGC and can include features such as dial tone, collect dialed digits, call hold, call transfer, call forward, and call conference. The MGC signals the MGs, which then execute the feature commands and process the call, performing gateway functions as required to interface the incompatible networks or network elements (NEs). There is a master/slave relationship between the centralized MGC and decentralized MGs, much like that of a traditional PSTN, except that the MGs that execute the features and perform the switching are distributed across the network. See also ATM, call transfer, conference call, dial tone, gateway, H.248, hold, IETF, ITU-T, master/slave, protocol, PSTN, and softswitch.