Integrated Service Digital Network (ISDN): The ISDN is an integrated digital network in which the same digital switches and digital paths are used to establish different services. Eg. Telephony, data, etc. It already upgrades today’s telephone network to a digital system.
a) Definition: ISDN “is a network, in general evolving from telephony IDN (Integrated Digital Network) that provides end to end digital connectivity to support a wide range of services, including voice and non-voice services to which users have access by a limited set of standard multipurpose user-network interfaces. The key points of this definition are:
a) It is an infrastructure to support a wide variety of services and is not a network designed for any specific services.
b) It provides end to end digital connectivity to support a wide range of services and the digitization process begins right at the user premises.
c) It should be possible to support every conceivable service on ISDN for any such service is either a voice or non voice service.
d) A small set of carefully chosen interfaces should enable the support of all possible services.
The use of ISDN should not be burden with too many specialized interfaces but at the same time an expensive universal interface.
b) Factors for Development of ISDN: ISDN truly represents the next generation of the worlds telephone service for all forms of telecommunication, including voice.
i) Sociological or Societal Need: The society is looking for a telecommunication infrastructure that can carry voice, data, image, graphic, videos, etc. supported by sophisticated signaling system.
ii) Economic Necessities: Network providers have to put up separate and independent network to support different services, which demand separate maintenance staff, building for housing switching system, etc. All these leads to higher capital cost. The introduction of ISDN is the only solution to this.
iii) Technological Development: Technology is developed up to the level that now a days a single network can support integrated digital services.
c) Services of ISDN: ISDN can operate at speed up to 128 kbps which is five or more times faster than that of todays analog modem. Basic rate ISDN divides the telephone line into 3 digital channels, 2 “B” channel (Bearer) and one “D” channel (Delta). Each of which can be used simultaneously. The B channels are used to transmit data at the rate of 64k or 56k. The D channel does the administrative work such as setting up and tearing down the call and communication with the telephone network. ISDN will support the following list of services:
ii) Database Access
iii) Image and graphic exchange.
iv) Document storage and transfer;
v) Electronic fund transfer;
vi) Audio and video conferencing.
ix) Digital facsimile
x) Automatic alarm service (Smoke fire, etc).