Chapter 27: Integrated Services Digital Network | Principles Digital Communication System & Computer Networks (Charles River Media Computer Engineering)

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When you buy a house, the house has standard electric power sockets into which you can plug any electric device and start using it. How about a similar setup for telecommunication as well? Imagine a standard communication socket into which we can plug a device for sending data, voice, fax, or video? Technology fiction? No. Integrated Services Digital Network (ISDN) is aimed at achieving precisely this objective—to develop standard interfaces and standard terminals to integrate data, voice, and video services, all in digital format. The standardization work on ISDN was initiated in the 1970s. Today, ISDN has a good installation base in the developed world, and the developing world is catching up fast. This chapter covers the principles and standards of ISDN.

27.1 OBJECTIVES OF ISDN

The main objective of ISDN is to replace the Public Switched Telephone Network (PSTN), which is based on analog technology. As the name implies, ISDN is a fully digital network to provide integrated services—voice, data, and video—through standard interfaces. To provide services to meet the requirements of different users, narrowband ISDN and broadband ISDN standards have been developed. Narrowband ISDN supports services up to 2.048Mbps, and broadband ISDN supports services up to 622.08Mbps. International Telecommunications Union Telecommunications Sector (ITU-T) I-series recommendations specify the ISDN standards. The objectives of ISDN are:

To support voice and nonvoice applications using a set of standard interfaces.
To support switched and nonswitched applications.
To have a layered architecture so that the advantages of layered architecture can be exploited.
To support a variety of configurations to meet varying user requirements.
To provide intelligence in the network.
To provide integration with the existing networks such as Public Switched Telephone Network (PSTN) and Public Data Network (PDN) and to rely on 64kbps connections.
To standardize all the interfaces for access equipment so that there will be competition among the equipment suppliers, which will benefit the subscribers.
To support transparency so that the services and applications are independent of the underlying network.
To develop a tariff strategy that is based on the volume of the traffic and not the type of data. Whether the user is transmitting voice or video should not matter; the tariff should be based only on the amount of data sent.

The objective of Integrated Services Digital Network (ISDN) is to provide data, voice, and video services with standard interfaces using completely digital technology.

Note

ISDN can cater to different user requirements. Users at homes or small offices can subscribe to low-speed ISDN services, and large organizations can subscribe to high-speed services.

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