What is ISDN
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What is ISDN?

ISDN (Integrated Services Digital Network) is the digital version the Plain Old Telephone System (POTS). ISDN offers many services in addition to those provide by the POTS, such as private virtual networks, high-speed facsimile (fax), video-conferencing, and most importantly high-speed data communcations.

Basic rate access is comprised of two 64Kbps B channels and one 16Kbps D channel. The B channels carry traffic, and the D channels is used for circuit setup, and can also be effectively for telemetry such as house alarm monitoring. Primary rate access is comprised of twenty-three B channels and one 16Kbps D channel in the North American System or thirty B channels and one 16Kbps D channel in the European System. Primary rate access is popular with large companies, routing telephone traffic for management by their own ISDN-compatible telephone switching system.

One of ISDNs main advantages is circuit setup speed. Connecting to the Internet is made in a few seconds, compared to almost a minute using an ordinary line. Also, ISDN provides guaranteed bandwidth - where an ordinary line that is within internationally agreed specifications is expected to carry data at a rate of at least 4800bps, a basic rate ISDN line is guaranteed to be capable of carrying 128Kbps.

Of course, for Internet users, ISDN is equally affected by Internet congestion - connecting using an ISP providing poor bandwidth to their Point-Of-Presence will not be significantly better than using an ordinary line.

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