Switching to VoIP

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Chapter 7: Replacing Call Signaling with VoIP

It isn’t likely, however, that MEGACO interfacing will be installed in each home and

office served by the telco. Rather, SIP, and to a lesser degree SCCP or MGCP, which

can be provisioned as trunk media types on a MEGACO gateway, will eventually

dominate last-mile signaling. Since SIP phones are already exploding in popularity, it

will be far cheaper for the telephone carriers to bring SIP signaling, rather than

MEGACO, to your doorstep, because SIP phones are already in great abundance and

are cheap.

ICG, Qwest, AT&T, and many other large phone companies have started to offer

VoIP dial-tone services in this very fashion—SIP or SCCP for the last mile and

MEGACO connecting the CO switches.

Cisco SCCP

SCCP is a signaling protocol developed by Cisco. Though proprietary, open imple-

mentations of Cisco SCCP do exist. There is an SCCP module for Asterisk that is free

and open source. The Skinny Client Control Protocol is so named because it is a far

less ambitious suite than H.323. In this regard, SCCP is more akin to IAX.

Like IAX, SCCP is a leg-only signaling solution; it doesn’t dictate how multiple legs of

a single call path should be conducted as H.323 and SIP do. It doesn’t mention any-

thing about proxies either. In fact, SCCP is used ...