Delivery

ISDN - Phone

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.

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 supported by Sheffield University however call charges and restricted bandwidth make it inferior to our IP service.

IP - Internet

Video conferencing systems based on IP (Internet Protocol) 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, which makes an IP based system the cheapest solution in many cases. The main disadvantage is the fact that it is based on a protocol that uses best effort delivery. This means that connection quality can be quite variable. Though not a common problem, IP videoconferencing across the Internet can be subject to firewall and access problems. This can be resolved by using a switching service or bridge (JANET) in some cases.

However costs are much less for IP and there are no call charges so long term it is far most cost effective. With network speeds increasing all the time and IP videoconferencing improving this technology can keep improving.