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A demonstration of multimedia application sharing between California and Copenhagen seen recently [EIUF94] took several days to set up and cost about 100,000 dollars in time, equipment, and communication costs.

When was this? Not in 1984, but late in 1994. We are told that the Information Super Highway is driving towards us in the fast lane, but no one can quite say from which direction. Trials of video on demand are continuing but roll out of services have been delayed. We are told that home services on the highway will have to be kept simple for us to take in, and will be affordable. In education multimedia learning packages have been mounted on file-servers, use of the World Wide Web is widespread, and some video conferencing is being used.

So networking of computer based multimedia is possible. However network delivery of multimedia is not new, the broadcast television system has been available since the 1950's. The difference now is that the information which has previously been presented on radio, TV, or in books, is now being presented or can be accessed by computer networks. Or looking at this development in another way computer technology has almost caught up with the broadcasters. The drive to deliver multimedia information over a computer network is fuelled by protagonists of the Information Superhighway who need multimedia to justify the requirement for the highway. Multimedia producers are also looking for a wider market and lecturers are excited both by the new learning environments offered and possible efficiency gains.

1.1. Networked Multimedia Applications

Multimedia can roughly be defined as a technology that enables humans to use computers capable of processing textual data, audio and video, still pictures, and animation. Applications range over entertainment, education, information provision, design e.g. CAD/CAM, co-operative working such as video conferencing, application sharing, remote working and virtual reality experiences.

Multimedia applications for computers have been developed for single computing platforms such as the PC, Apple Mac and games machines. The importance of communications or networking for multimedia lies in the new applications that will be generated by adding networking capabilities to multimedia computers, and hopefully gains in efficiency and cost of ownership and use when multimedia resources are part of distributed computing systems.Widening of access to multimedia sources and potential markets in multimedia, video and information are commercial driving force for networking multimedia.

The reality of networking multimedia is that :-
The characteristics of multimedia make heavy demands on storage and transmission systems.

Data compression can be used to reduce the demands of multimedia, particularly of video and audio on these systems, but usually at the expense of some loss in the detail compared with the source and at extra cost.

The ways in which users or participants in multimedia sessions access multimedia or connect with others have important consequences for the storage and transmission systems. For instance multimedia learning material can be accessed directly from a server during a class or downloaded to student machines prior to a session. The demands on a connecting network are very different in each access mode.

The cost of transmitting multimedia information will determine the pace of development of networked multimedia applications.

The availability of standards for multimedia networking, particularly for inter-working between applications, the development of networked applications, and interworking between networks are essential to reduce the complexity and level of skill required in using multimedia.

1.2. An Example

Using your desktop conferencing from Fujitsu which works on ISDN at 64 Kbps, and the Olivetti PCC video conferencing, you want to do some work with a colleague at Imperial College in London who fortuitously has a Super JANET Asynchronous Transfer Mode (ATM) connection at 34 Mbps, and has a workstation with UNIX based desktop conferencing and a codec for H.320 compatible video conferencing. Hard luck, you can't. While the video conference systems are compatible, both use H.320, the ISDN network cannot connect right through the ATM network. Also the desktop conferencing systems use different standards for sharing applications, whiteboards etc. and would not inter-work even if directly connected.

1.3. Report Structure

The rest of this report is divided into twelve sections where the different subsystems that impact on multimedia networking are reviewed. Section 2 reviews the requirements of multimedia before introducing some of the issues to be considered by users in section 3. Section 4 reviews the development in compression standards before leading to a an investigation of networking - from hardware to software technology (section 5 to 10). In section 11 we review some of the networked multimedia systems. Finally section 12 points to the leading edge research and developments efforts and issues in networking.
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