Overview

The idea of multimedia communications is very appealing text, graphics, sound, and video all combined to enrich the ways in which we communicate and to transform communications from a one-dimensional to a multidimensional experience. Many believe that multimedia content will drive the continued growth of the Internet.

Traditionally, voice has been carried on circuit-switched lines. During the past decade, work on VoIP has grown, for a variety of reasons that will be discussed in Section 4.1. More recently, interest in multimedia over IP is rapidly rising. With increasing availability of high-bandwidth links and advances in QoS technologies, a future is often envisaged in which multimedia telecommunications carried over IP networks becomes an ordinary way of communicating.

Our concept of multimedia over IP includes the more familiar concept of VoIP as a special case. Multimedia over IP, as compared to a single media over IP, adds one other complication the various media streams need to be synchronized. However, whether the subject is a single medium like voice or multimedia, we are dealing with real-time traffic. ^[1] Real-time traffic has stringent requirements on the playback of the voice and video at the receiving side. Even if a stream is broken into segments (a requirement for transmission in packet form, as is the case for multimedia over IP), the playing of the voice or video needs to be "smooth." In other words, the time relationships between when the segments are played needs to match the time relationships between when the segments were recorded...