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Introduction

Multimedia Conferencing, in the context of the activities to be discussed in this paper, implies that voice, video and computer data are to be shared amongst geographically distributed groups. A great deal of research has been done in the individual areas, to the extent that communication Service Providers (PTOs) now offer video/voice facilities as commercial services, whilst communication equipment providers are offering video-conferencing studios complete with workstations.

In practice, most of the facilities which are currently available fall into one of the following categories:

1. High quality studios, often used by large commercial organisations, and connected by high quality codecs at fairly high data rates (1.5Mbps (T1) or 2Mbps (E1)), or by analogue TV channels. The communication channels are circuit-switched, and usually only two site point-point, though sometimes multi-point is possible.

2. Simpler, lower quality studios connected over lower rate circuit-switched channels. These usually operate at 384 - 1024 Kbps, though more recently some use has been made of Basic Rate ISDN (64 or 128 Kbps) to connect such studios.

3. Lower-end workstations which operate using one or two Basic Rate ISDN channels (64 or 128 Kbps); if one channel only is used for the A/V, it is often possible to put data on the second channel of a Basic Rate ISDN termination. Such workstations usually require a codec board to perform video compression.

4. Multimedia conferencing facilities have been set up on higher-end workstations. Software compression of video in such workstations is possible, typically at speeds of around 64 - 512 Kbps. Usually the frame rate or picture quality is lower than video from hardware codecs at comparable data rates, due to limitations on available processing power. Such systems [1], [2], have been deployed to a limited extent in the research communities on wide area networks This systems are particularly interesting as the operate over packet switched networks rather than circuits.

In conference room systems, the traffic is usually carried over circuit-switched channels. This requires a constant bit rate service for video, and that any voice or data facilities have a negligible impact on the additional communication requirements. Clark [3] has shown that this is an erroneous assumption, and that there can be considerable advantages in packet-switched operation.

Under DARPA auspices, there are several facilities for providing multimedia services over the US Internet; DARTNET [3] and the SIMNET (Defense Simulation Internet, [4]) are two examples. Both facilities use codecs, and different mechanisms for conference control and multiplexing have been incorporated. Typically, they operate at 128 - 384 Kbps speeds, with bandwidth allocations in the routers to ensure that adequate performance is achieved, so that the codecs do not lose synchronisation. Since the European research networks have much the same technological characteristics as the US Internet, it would be desirable to provide multimedia facilities for European researchers over the same communication infrastructure, and link them to the US. This is what the MICE project aims to provide on a small scale.

In the European context, there are some significant differences to the earlier US activities. Firstly, there is a recent international standard for codecs (H.261 for video coding, H.221 for multimedia streams over serial lines, and various other standards for audio coding). In accordance with European policies, MICE will use these standards [5] wherever possible. Secondly, ISDN has become widely available: 2-4 channels at a speed of 128 - 256 Kbps are compatible with the bandwidth that should be available over the research packet networks. MICE therefore aims to provide access and coordination for conference rooms or workstations using H.261/H.221 codecs operating both over research packet-switched networks and over ISDN.

Over the last few years, workstations have become increasingly powerful. Manufacturers have been determined to develop new applications, and multimedia has tremendous sales potential. Since codecs have been prohibitively expensive, most manufacturers' activities have concentrated on the Local Area Network (LAN), but they have recognised also the need for interoperation and standardisation. Two standards have emerged: the Joint Photographic Experts Group (JPEG, [6]) for still pictures, and the Motion Picture Experts Group (MPEG, [7]) for moving pictures. Both standards provide very good results at speeds above about 512 Kbps, and again specialised chip sets are becoming available for them.

Even without these special chipsets, current workstations are capable of providing codec functionality in software, albeit with reduced performance. Such software is often aimed purely at packet network users. There are users who want multimedia facilities with more modest video which can be provided software codecs.

In summary, the current situation requires facilities for users of both conference rooms and workstations, plus connectivity between the two approaches.

• The MICE Aims and Participants