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B-ISDN (Broadband Integrated Digital Network) - an explanation

Digital network with ATM switching operating at data rates in excess of 1.5 Mbps. ATM enables transport and switching of voice, data, image, and video over same infrastructure.ISDN stands for Integrated Service Digital Network, and as the name suggests it allows digital communication. This is favourable as digital technology is a lot faster, and more accurate than the old analogue lines as they no longer require the process of modulation and demodulation. ISDN relies on already existing copper cable systems, causing itís integration into our existing communications system to be smoother and less disruptive.

According to ITU-T(formerly CCITT) "an ISDN is a network, in general evolving from a telephony IDN, that provides end-to-end digital connectivity to support a wide range of services, including voice and non-voice services, to which users have addressed by a limited set of standard multi-purpose user-network interfaces." The key point of this definition is the ability to support voice services adequately, this has not been achieved using any other concept.

ISDN has four major aspects; telephone network; integrated services; digital; network. These will be explored in a little more detail later.

Narrowband ISDN has been designed to operate over the current communications infrastructure, which is heavily dependent on the copper cable. B-ISDN however, relies mainly on the evolution of fibre optics. According to CCITT B-ISDN is best described as Ďa service requiring transmission channels capable of supporting rates greater than the primary rate.í Behind this statement lies the plan for a network and services that will have far more impact on the world we know today, than ISDN ever would.

When ISDN is referred to as a network it is to be considered a telephone network, not a computer network. Broadband ISDN allows its users to communicate over high speed, high quality digital channels. The media is supports include Telex, fax, voice telephone, video telephone, audio, high definition TV and computer networking.

In the past video, audio, voice and data services needed different types of communication channels. One of the main advantages of ISDN is the ability to integrate these features over the same network and cable plant. Not only is this possible using ISDN technology but the quality of the transmission is better also. In the past four networks were needed and video was distributed on coaxial lines, audio over balanced lines, voice used copper cable pairs and data services required coaxial or twisted pair cables. Using one network allows reductions in installation costs, as well as easier installation. Other features available include demand networking, automatic bandwidth and on the fly connectivity. Advances in the services available are due to ISDN being digital.

Data applications, in particular, seemed to have problems with the old analogue services. This is due to the fact that computers are digital devices and the transmission of data needs to be modified form binary to analogy tones, then changed back to binary when it is received. This process requires a modem, which handles the MODulation and DEModulation of the data. Whilst the data is in transit it is susceptible to outside influences like noise, line spikes and echoes. Bandwidth is also limited, with the speed of modems being close to the maximum possible.

Networks require high speed connectivity if they are going to be useful. ISDN is an excellent vehicle for connecting LANs, because it scales in increments of 64 kilobits per second (kbps). Computers are digital devices, as is ISDN, meaning that no translation of information is required, improving quality and speed. Due to the characteristics of ISDN it can be used, with the same level of performance, across a room or halfway across the continent. This has unlimited benefits.

The suggested architecture for the B-ISDN protocol is depicted in figure 1 below. As can be seen the B-ISDN protocol uses a three plane approach. These three separate planes are referenced as:
  • User Plane
  • Control Plane
  • Management Plane
The user plane is responsible for user information transfer including flow control and error control. The control plane manages the call-control and connection-control functions. While the management plane includes plane management, and layer management.