tures. It is the feature set that gives voice its range of capability; a typical local switch-such as Lucent Technologies' 5ESS-offers more than 3,000 features, and more will certainly follow. Of course, these features and services are possible because of the protocols that have been developed to provide them across an IP infrastructure. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Telephony Telephony Media Gateway Control Protocol (MGCP)-and Friends Many of the protocols that are guiding the successful development of VoIP efforts today stem from work performed early on by Level 3 and Tel- cordia, which together founded an organization called the International SoftSwitch Consortium. In 1998, Level 3 brought together a collection of vendors that collaboratively developed and released the Internet Proto- col Device Control (IPDC). At the same time, Telcordia created and released the Simple Gateway Control Protocol (SGCP). The two were later merged to form the Media Gateway Control Protocol (MGCP), dis- cussed in detail in RFC 2705. MGCP allows a network device responsible for establishing calls to control the devices that actually perform IP voice streaming. It permits software call agents and media gateway controllers to control streaming media gateways at the edge of the network. These gateways can be cable modems, set top boxes, PBXs, VTOA gateways, and VoIP gateways. Under this design, the gateways manage the circuit-switch-to-IP voice conversion, while the agents manage signaling and call processing. MGCP makes the assumption that call control in the network is soft- ware based, resident in external, intelligent devices that perform all call- control functions. It also makes the assumption that these devices will communicate with one another in a primary-secondary arrangement, under which the call agents send instructions to the gatewa