What is Broadband ISDN?

Broadband Integrated Service Digital Network (B-ISDN) is a standard for transmitting voice data and video at the same time over fiber optic telephone lines. Boadband ISDN can support data rates up to 2 Mbps which is an improvement on the original ISDN bandwidth rate of 64Kbps or 128Kbps when using both connections. The B-ISDN was envisaged to run over ATM carrying both the synchronous voice and the asynchronous data on the same transport bearer.

One of the underlying motives to develop ISDN was to provide subscribers with a wide variety of services direct to their home. These included video telephony, video surveillance, high speed Internet, High Definition TV, and these services would require delivery at different bit rates and with different time constraints. For example video and TV have greater time constraints’ than data. B-ISDN over ATM was considered a good fit as ATM could handle various contracts based on the service required. The only problem was that ATM had a small payload size of only 48KB and an overhead of 5 Bytes making it an extensive transport protocol. I.E. 5/53 x 100/1 = 9.9% overhead.

There were plans to use B-ISDN over fiber optic cables in a Fiber in the loop scenario whereby the fiber replaced the aging copper loop. This would have mitigated the high overhead due to the vast increases in speeds that could be leveraged from a fiber implementation.

However the time it took to become an agreed standard meant that other telecommunication protocols such as xDSL overtook B-ISDN and it never managed to build a sufficient market. ATM survived due to the hefty investment in its infrastructure and it became the low leve

Alasdair Gilchrist

Alasdair is a technical writer with interest in business practice, operational strategy, start up philosophy and affordable technology. He lives in Nonthaburi, Thailand with his wife and daughter, and writes terrible novels as a hobby.