Switching to VoIP

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Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

MGCP

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MEGACO/H.248

MEGACO is a protocol that describes a standard set of signaling functions for

groups of media gateway devices that are physically decomposed—that’s distributed

for all us mere mortals—on a packet voice network. MEGACO was jointly devel-

oped with the IETF, which published RFC 3015, and the ITU-T, which published

recommendation H.248: the documents are identical.

MEGACO provides a next-generation framework for building gateway devices,

MCUs, and other types of telephony servers, but doesn’t make specific provisions for

any of them as H.323 does. In this regard, MEGACO is more extensible than H.323,

but less so than SIP.

Depending on how they’re implemented, MEGACO gateways can offer support for

standard PSTN signaling technologies like DTMF, SS7, and ISDN. They can also

provide modular or monolithic support of several packet-based network protocols,

including TCP/IP, ATM, and frame-relay.

MEGACO fills in some of the telephony blanks in SIP. Since SIP doesn’t make a spe-

cific recommendation for media conversion applications, MEGACO complements it

nicely in this role. Likewise, an H.323 gateway may use MEGACO/H.248 for com-

munication with the PSTN. Because of that, MEGACO and its predecessor MGCP

aren’t as commonly used for endpoint signaling as H.323 and SIP. In fact, ...