Switching to VoIP

This is the Title of the Book, eMatter Edition

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

SIP

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SIP

The Session Initiation Protocol (SIP) was developed by the Internet Engineering Task

Force as a way of signaling multiuser distributed telephony and messaging applica-

tions on an IP network. SIP has garnered much praise from IT professionals, while

suffering some criticism from traditional telecommunications people. The main rea-

son for its less-than-perfect repute with telecom pros is its origin outside the telecom

world. But many telecom guys have had to forgive this, because they’re learning that

SIP has almost no shortcomings when compared to its ITU-inspired cousin.

The essential duties and formulaic pieces of SIP are the same as H.323. That is, there

are VoIP endpoints of varying capabilities, and there are servers that participate in

the signaling process and establish policy for the voice network. Unlike H.323, how-

ever, SIP is far more extensible. It is more than just a set of voice and video tele-

phony protocols. Rather, it’s a packaging framework for all types of message-based

applications, from intercom calling to instant messaging and AV services.

Companies like Broadvox, Voicepulse, Broadvoice, Packet8, and others have

emerged as frontier providers for dial-tone–style services delivered over the Internet,

using SIP as the signaling system. Under these service ...