ISDN is a dial-up service. Once the link is established it is dedicated to that call and is
unaffected by other users. This means that the quality of a video conference over ISDN is generally predictable. Currently, the majority of users of video conferencing in education use ISDN.
There are two main options for the supply of ISDN in the UK: BRI - Basic Rate Interface or PRI - Primary Rate Interface.
BRI is supplied as ISDN 2e, which is 2 x 64kbs channels with an additional signal or control channel. Many schools have or have had BRI ISDN for Internet access prior to the installation of broadband. Most video conferencing units expect BRI ISDN.
PRI is supplied with up to 30 x 64kbs channels in options starting with six channels.
A number of schools and colleges use PRI ISDN for their phone system. Some of these phone installations can be configured to offer BRI ISDN by the addition of internal interface cards. This can be very expensive equipment and it is usually cheaper to get a PRI based video conferencing system and a PRI line with only six channels activated. Contact your phone system installer for details.
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