• ISDN is the Integrated Services Digital Network and the ultimate goal this network intends is to provide world wide public telecommunications, replacing the existing networks, and to deliver a wider variety of services than is in existence today. The second generation of ISDN is called Broadband - ISDN and this supports very high data rates, and the major technical contribution of B-ISDN has been ATM, which is a major new transmission technology.
• A major Broadband - ISDN concept is to support a wide range of traffic types - audio, video, and data services - within the same network, as opposed to more conventional old-fashioned networks, it is designed to carry more than just voice and data.. ATM is essentially a packet-switched mode of transfer across the B-ISDN which can be used to provide this functionality.
• Services provided by B-ISDN can be categorised into interactive and distributive. The interactive services include video and multimedia conferencing and image transmission. The distribution services involve centralised service providers distributing to network users - this includes stored video clips, movies, images and other types of retrievable material.
• ATM is, in a sense, the culmination of all the developments in switching networks over the past 20 years. It is a technique that has the ability to solve multiple network requirements in a single protocol. ATM has been chosen for B-ISDN because it is the only protocol capable of integrating the many different services with any degree of surety, while maintaining the levels of quality required for each. It is effectively a scalable transfer mode that copes with multiple data rates (speeds of transfer) and with the different types of traffic in the system (ranging from bursts of data to more continuous streams of transmission).
• Currently, the development of services on B-ISDN is proceeding at a fast pace with emphasis on data and multimedia networking via the ATM technology. ATM is also the formal standard supporting cell (packet) based voice, data, video and multimedia communication in a public network (Figure 0-9).

Figure 0-9 ATM

• Advantages of ATM
• ATM considerations