ISDN: Broadband-ISDN, ATM

Two standards exist for ISDN: Narrowband-ISDN (N-ISDN) which is already in operation and Broadband-ISDN (B-ISDN). This B-ISDN is planned to support multimedia applications (video, audio, etc.) because of its high performance. Thus, a B-ISDN is able to connect the following devices for example even if they are very distant:

The challenge in developing B-ISDN is to combine network services that vary not only in performance requirements but also in delay sensitivity (e. g. even short breaks in videos will be realized immediately). To reach this goal Asynchronous Transfer Mode (ATM) is the technology that will be used. ATM takes advantage of the very low rates of error and the reliability of modern networks. So, ATM reduces the error control overhead as much as possible. Short packets of data with a fixed length (53 Byte) are used, called cells (this technique in general is referred to as Cell Relay).

The reachable performance is higher than of high-speed LANs (up to a data rate of 2 Billion bits per second) and ATM networks are full scaleable, i. e. if more capacity is needed it can be added without problems. Thus, even if you take into consideration the developments in compression technology, which increase the usability of narrowband networks, in future ATM will be interesting for smaller networks too. And therefore ATM could provide a single connectivity solution for networks of all sizes (LANs to WANs). The transition from current networks to B-ISDN represents a major technological discontinuity, because it affects services, protocols, signalling and equipment.

There is more information about ATM and the connection to B-ISDN available.