deliver advanced ca- pabilities to their customers. Some communications servers send the voice over the same pair of wires as the data communications and may use IP or some other communications protocol to accomplish this. Softswitch Networks According to the International Softswitch Consortium a softswitch is a software-based entity that provides telephone call control functionality. The Telecom Handbook $ 145 CONVERGENCE OF VOICE & DATA Softswitches support different protocols (sets of rules for communicating) including MGCP, H.248, SIP, H.323 along with CAS; SS7 ISUP, TCAP and INAP; ISDN; and TCP/IP. (For more detail on these go to www.softswitch.org or check Newton's Telecom Dictionary). Elements Of A Softswitch Network The functional elements of a softswitch network may include the following: MEDIA GATEWAY CONTROLLER (ALSO KNOWN AS CALL AGENT OR CALL CONTROLLER) The media gateway controller maintains the "call state" for the endpoints of every call on a media gateway. Its primary role is to provide the call logic and call control signaling for one or more media gateways. It may also: Manage network resources such as ports or bandwidth. Interact with the application server to provide a service or feature to a user. Interface with call routing and accounting functions Participate in management tasks in a mobile communi- cations environment. The media gateway controller interfaces with the applications server or media server using SIP (session initiation protocol). The softswitch or the application server uses what is known as third party call control to control the media server. MEDIA GATEWAY (A SUB-COMPONENT OF A MEDIA GATEWAY CONTROLLER) As viewed by an IP network, a media gateway is an endpoint or a collection of endpoints. Its primary role is to transform me- dia from one transmission format to another, most often from 146 2 The Telecom Handbook CHAPTER 7 SIP - Session Initiation Protocol A protocol is a set of rules governing the format of messages that are exchanged between computers and people. Session 