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Introduction to Video Conferencing

This briefing paper has been written to provide an introduction to video conferencing, the technologies behind it, current hardware and software and the likely impact video conferencing will have on the higher education community in the near future. It draws heavily on a number of reports on video conferencing written as part of the Support Initiative for Multimedia Applications project.

Video conferencing has been around for sometime, and is now gaining in popularity. It cannot replace person to person completely, but in many situations being able to see and hear remote co-workers, does improve communication and cut down on travel time and costs.


Video conferencing actually encompasses a range of technologies used in a wide range of situations, often it is not just video and audio that is transmitted, but also data, allowing collaborative working though shared applications. Video conferencing may be:-
  • One-to-one meetings, also known as point to point communications, usually involving full two-way audio and video.
  • One-to-many involving full audio and video broadcast from the main site, where other sites may be able to send audio. For example in a lecture situation, students could ask questions.
  • Many-to-many, known as multi-point communication, provides audio and video between more than two sites. With most multi-point systems only one site in a conference can be seen at time, with switching between sites either controlled manually or voice activated (i.e., the loudest site is on screen).
Physically, the most common scenarios of video conferencing are:
  • desktop video conferencing - usually a small camera is located on top of the PC or workstation monitor. The actual video is usually displayed in a small window, and shared applications, such as a shared whiteboard are often used.
  • studio-based systems - a studio is specially equipped for video conferencing. This will normally include one or more cameras, microphones, one or more large monitors, and possibly other equipment such as an overhead camera for document viewing. Usually used for more formal meetings
    In practice a 'studio' may not be a dedicated room, but a standard seminar room with portable equipment that can be set up when required.

Bandwidth and Compression

The bandwidth, or baud rate, is the amount of information which can be transmitted every second. The higher the bandwidth, the better quality the signal that can be transmitted. For a video conference audio and video signals must be transmitted in real time, i.e., a lot of information has to be sent every second, requiring a very high bandwidth. For example a 'true colour' image will need 24 bits (3 bytes) per pixel. A full screen image might be 640x480 pixels, over 7 million bits. For full motion video, the image is refreshed 25 times per second. This adds to over 184 million bits per second. It is not realistically possible to transmit this amount of information, and your PC certainly could not receive it at this rate. Therefore for digital video some form of compression is required. The type and degree of compression used varies from system to system. It is interesting to note that for most uses, we are more tolerant of poor video than poor audio, and so some systems concentrate on providing consistently good audio.


Most major vendors now support the H.320 suite of ITU recommendations that define videoconferencing mechanisms over switched digital services such as ISDN. Similar recommendations have also been defined for high-speed wide area networks (H.321), isochronous networks (H.322), packet-switched local area networks (H.323) and POTS phone lines (H.324).



Integrated Services Digital Network (ISDN) is offered by many telephone companies that provides fast, high-capacity digital transmission of voice, data, still images and full-motion video over the worldwide telephone network.

In the UK service providers such as British Telecom and Cable and Wireless offer basic and primary rate ISDN services.

Basic rate services provide 2 65kbit/s data channels or B channels, and one control or D channel. This can provide reasonable quality video conferencing, delivering about 10 frames per second (fps) for a small window (160x120).

Primary rate access can carry 30 B channels, and one or D channel. This level of access will give very good quality video and audio. B.T.'s primary rate service is now ISDN 30 I.421, bringing it into line with the rest of Europe. Support is still provided for ISDN 30 DASS, B.T.'s own British Standard, and switching between the two is available. It should be noted that primary rate services in non-European countries such as the USA and Japan usually use 23 data channels and one D channel, giving them a lower bandwidth.

ISDN is rapidly growing in popularity and is widely accepted in industry as the way to access multimedia over a network. Although it is still expensive when compared to a standard line, particularly for primary rate access, it may be suitable for inter-site conferencing.


Video conferencing systems based on IP rather than ISDN offer several advantages, the main one being that many people already have a connection to an existing IP infrastructure. Codecs supporting the H.323 standard are widely available, some of which are free, making an IP based system the cheapest solution in many cases. The main disadvantage is bandwidth.

Though often not a problem on an internal Local Area Network (LAN), IP videoconferencing across the Internet can be subject to many delays, producing a poor frame rate (1 or 2 fps) and often unacceptable quality audio.

Satellite broadcast

Satellite transmission is usually used for one-to-many conferences, as described for cable. Although it is expensive, cost is not affected by distance, and therefore it may be of use where very large distances or many sites are involved.

Using Video Conferencing

Desk Top Video Conferencing

The basic hardware components are:
  • camera, usually attached to the top of the monitor
  • microphone
  • speakers - even where speakers are built in to a workstation, external ones will provide better quality audio. Alternatively headphones may be useful, particularly in a shared office.
  • video board - to capture the signal from the camera and convert it to digital form
  • network card - usually an Ethernet card for connection to the LAN, or an ISDN card

There is a very wide range of software available, some of which is described in the SIMA reports 'A Study into Video Conferencing Using the Apple Macintosh Platform' and 'The Dos and Don'ts of Video conferencing in Higher Education' . The usefulness of any particular system will depend on the kind of tasks it is expected to perform, e.g., are shared applications are required, very good video, very good audio?

When using LANs, full screen full motion video (25fps) will not normally be possible. The software will incorporate some kind of codec to compress the video. The level of compression can be up to 100:1, though the higher the level of compression, the lower the quality, and the quality will be much lower if there is a lot of movement. Even at high levels of compression, full screen video may not be possible. LANs were not designed to handle the constant bandwidth necessary for good video conferencing, but more 'bursty' data, which does not require real time transmission or synchronisation, and as the traffic on the LAN increases video conferencing may become unusable.

Multicast is one solution allowing many to many conferences over bursty networks. Multicast means that data is only sent once, but can be received by every participant, so only one channel is required regardless of the number of participants. The Multicast Backbone (MBONE) allows video conferencing to take place over the Internet. MBONE is known as a virtual network because physically it shares the same media as the Internet, using routers that can support multicast. Audio and video are compressed and they must still compete with other traffic on parts of the network, so the quality of MBONE video conferencing is limited.


Support is provided for the use of video conferencing over JANET and SuperJANET through the JANET Videoconferencing Advisory Service (VCAS). VCAS provides support and advise on videoconferencing systems, equipment and environments and will run consultancy and training services. A switching service is provided which allows multipoint videoconferences through Janet to conferences on the public ISDN network (ISDN 2 or 6) or other networks such as Scottish MANs (Meteropolitan Area Networks).

Studio-based systems used for more formal meetings in higher education will usually use SuperJANET, . The codec, which converts the analogue signal to digital for transmission, used in the SuperJANET system provides a data rate of 2Mbps, which gives a very good quality, full screen video and audio signal. Multiple sites can be linked into a conference, with voice switching being used to switch between sites. SuperJANET is now entering Phase III, in which the backbone (155 Mbits/s) will be provide by Cable and Wireless Communications, with 13 'Backbone Edge Nodes' linked to it at 155 or 34 Mbits/s. These will then be connected to MANs, providing wide access to the service.

Uses of Video Conferencing

Video conferencing is used for a variety of purposes, including:
  • Personal communication. Informal communication would normally use desk top systems. More formal meetings with several participants at each site would probably use dedicated studio settings.
  • Collaborative work between researchers using shared applications
  • Presentations
  • Education. Teaching usually involves one to many connections. The student sites may receive audio and video but only send audio.
Video Conferencing is very useful whenever there is a clear communication need, and the benefits described by those using video conferencing systems include:
  • reduced travel costs
  • face to face rather than telephone meetings
  • better quality teaching
  • easier collaborative working


Desktop video conferencing using Apple Macintosh computers and the CUSeeMe program is being used at the University of Derby. The computers are mainly connected over a LAN with a 64K Internet connection. The system is used to link students with tutors, small group meetings between different sites, and informal contact between dispersed colleagues. Livenet at the University of London provides videoconferencing to several of its colleges over three ISDN 2 lines. A range of equipment allows the system to be used for one to one meetings through to lectures.

Staff at the Council for the Central Laboratory of the Research Councils hold regular meetings between two remote sites at Daresbury Laboratory in Cheshire and Rutherford Appleton Laboratory in Oxfordshire, using SuperJANET. Since staff from the two sites need to meet regularly this arrangement saves a great deal in travel time and costs.

A directory of UK education users of desktop videoconferencing is maintained at:


It is likely that the use of video conferencing will continue to increase over the next few years. PCs and workstations often have many of the components of a video conferencing system built in, and networks, particularly internal ones, will be better able to cope with the increased traffic. These factors, and others such as increased travel problems and financial restraints will encourage the uptake of video conferencing to provide remote lecturers, remote seminars and courses, distance learning and telecommuting.

Apart from technological aspects, there are a number of other factors that affect the success of a video conference. It is necessary to be aware of the conventions used in a conference, how to ask questions or interrupt, how to switch site and so on. Although many of the conventions may be those used in traditional face to face meetings, the environment is slightly different, and some training will be required. In particular teaching staff will need to learn an additional set of skills to use video conferencing facilities. Different strategies for presenting material and encouraging student interaction will be required.

Without training the video conferencing systems will be under used. Therefore there will be an increasing need for courses on using the basic video conferencing hardware and software, and on presentation skills.


JTAP Focus Club

A focus club for video conferencing and collaborative working has been funded under the JISC Technology Applications Porgramme (JTAP). The club offers support and advice to the HE community and runs workshops on related topics.

All the SIMA reports can be found online at


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