MGCP/MEGACO

(Media Gateway Control Protocol/MEdia GAteway COntroller) An IP telephony signaling protocol from the IETF. MGCP was the original protocol, which evolved into MEGACO. Both protocols are designed for implementation in IP phones that are lower cost than SIP or H.323 phones. MGCP/MEGACO requires the use of softswitches for call control and more resembles the telephony model of the circuit-switched PSTN than do SIP and H.323. The softswitch is aware of the entire call throughout its duration (it manages state) and enables operator intervention like the PSTN. MCGP/MEGACO is a combination of the SGCP and IPCD protocols, and many devices that implement MGCP/MEGACO also support SIP and/or H.323.

At the IETF, MGCP evolved into MEGACO, while work on MGCP continued at the International Packet Communications Consortium (www.packetcomm.org). Network Call Signaling (NCS) is CableLab's version of MGCP, and H.248 is the ITU's version.

MGCP/MEGACO uses "terminations" and "contexts." Terminations are points of connection that are assigned an ID by the media gateway and can be permanent or ephemeral (temporary). Contexts are the sessions between these terminations and are managed by the media gateway controller. Like SIP, MEGACO is a text-based protocol, unlike H.248, which is binary based. See H.323 and SIP.