led the broadband ISDN (B-ISDN) and forced the previous service of ISDN to be named the narrowband ISDN (N-ISDN). With greater rates than the N-ISDN, B-ISDN has become more popular among residential and business customers. The primary triggers for moving towards the B-ISDN concept includes an increasing demand for high bit rate services, especially image and video services, and most important of all, the evolution of Digital Hierarchies - PDH and SDH new technology, which has stood up perfectly to support these high bandwidth services with minimal transmission errors. These important developments are: 1. The fibre optic transmission system offers transmissions at high data rates with a very low probability of transmission error for subscriber lines and the network trunks. With widespread use the cost has also gone down, making it the perfect wired medium to transmit high capacity data. 2. The VLSI and ULSI developments in the integrated circuit technology has also made it possible for switching and transmitting circuits to do their respective jobs at a faster rate comparable to the fibre optic speeds. 3. Apart from the voice and data services on the same channel, B-ISDN has brought with it the much- awaited video service. Thus video conferencing and online video services have been deployed. This has been possible due to high quality video devices with good refreshing rates. As part of its I series of recommendations on ISDN, ITU-T (formerly CCITT) in 1988 issued the first two recommendations relating to B-ISDN: (i) I.113: Vocabulary of Terms for Broadband Aspects of ISDN (ii) I.121: Broadband Aspects of ISDN These recommendations provided a preliminary description of the future standardisation of B-ISDN and formed the basis of the development work, but this proved to be time consuming. The delays were due to standards being made which would help in B-ISDN transmission and would play a very significant role in this area. This new technology was the asynchronous transfer mode (ATM). Due to the importance of this ne