Chapter 19 - Media Servers and Conferencing

Abstract

This chapter describes various types of media services used in the context of Internet communications and defines the architectures required to support these media services. Basic media services refer to three different types of functions, which include playing announcements or video messages, prompting and collecting information (user interaction), and mixing media (basic conferencing), and these can be combined to provide interesting applications. Multiparty communication (i.e., conferencing) in session initiation protocol (SIP) can be classified into three main groups, which include loosely coupled conferences, fully distributed multiparty conferences, and tightly coupled conferences. Many SIP applications also require media handling, and from the functional perspective, these applications are made up of two entities, the service logic and the media-handling functions. [RFC 4245] gives a high-level view of more advanced requirements for tightly coupled conferences such as conference creation, conference termination, dial-in, where participants dial in to the conference, and dial-out, in which the conference calls the participants. Some enhanced media applications also require functions such as text-to-speech or automatic speech recognition (ASR) and a possible protocol for allowing a client to control the ASR functions, called MRCP (media resource control protocol).