Video Conferencing Systems > Standard & Bandwidth

Standards

Video conferencing systems rely on standards to enable them to link to each other, particularly if the systems or software are from different manufacturers. A range of standards exists and advice should be sought when purchasing a system to ensure compatibility.

It may be useful to be able to recognise the main standards such as H.320 - ISDN based
conferencing and H.323 - IP based conferencing. T.120 is the standard that enables
application and data sharing. Others may be included such as H.281 - far-end camera control or H.243 - multipoint conferencing. Most systems will also adhere to a wide range of audio and video standards.



Bandwidth


Video and audio streams are very demanding of the capacity of the communications link. To overcome the potential constraints imposed by the link, methods of compression have been developed and refined. Video conferencing systems are built around CODECs (COmpressor - DECompressor) that handle the compression. To enable different makes of video conferencing system to communicate with each other, standards have been developed, including the compression standards.

Some manufacturers include features which will only work if communicating with systems of the same make, often resulting in better quality sound and vision.
The capacity of a link is referred to as the bandwidth. This is generally measured in kilobits per second (kbs) or megabits per second (Mbs). This is a measure of the theoretical maximum throughput.

A single ISDN 2e installation supplies 2 x 64kbs channels, enabling a video conference to utilise 128kbs of bandwidth. This is the minimum required for acceptable video conferencing.

Even at 128kbs the pictures will take time to stabilise and fast movements will blur.
Some group systems have the capacity for more than a single ISDN 2e line, giving better quality audio and video. If two, three or four ISDN 2e lines are available the system can run at 256, 384 or 512kbs respectively. To use this feature the system at the far-end also needs to have the same number of lines. This can be expensive as each line will incur a rental cost and a single conference may cost the equivalent of up to eight calls.

IP based video conferencing potentially increases the bandwidth available but this may be constrained by other users sending data across the network at the same time. A user may have to select a lower bandwidth setting so as not conflict with other users. All video conferencing units will have a maximum data rate at which they can operate over IP. Protocols are being implemented to alleviate the problem of congestion on a network.