Integrated Services Digital Network (ISDN)


The data and telephone communications business is continuously evolving to suit the demands of telephone, video, and computer communications systems. More individuals are communicating with one another than ever before. To satisfy this need, previous standards are updated daily, while new standards are established and deployed regularly.  A hypothetical network developed by major telephone companies to offer worldwide telecommunications support for voice, data, video, and fax information inside the same network is known as an Integrated Services Digital Network (ISDN). ISDN is the combination of several services into a single multipurpose network. ISDN is a network that allows an unlimited number of independent users to be connected over the same communication network.

Principles of ISDN

The capacity to handle various voice (telephone) and non-speech (digital data) applications in the same network utilizing a variety of standard facilities is an essential aspect of the ISDN concept. ISDN is compatible with a wide range of applications, including switched and unmodified (dedicated) connections. ISDN's fundamental concept is a digital connection at 64 kbps. Customers connect to the ISDN system via a local interface that is linked to a digital transmission medium known as a digital pipeline. Depending on the customer's needs, several tube diameters are available with varying capacity (i.e. bit rates). A home client, for example, may just want a minimal capacity to contain a phone and a personal computer. Office complexes, on the other hand, may necessitate conduits with adequate capacity to handle a big number of interconnected digital telephones via private branch exchanges (PBXs) or a high number of computers on a local area network (LAN).

ISDN Architecture

The figure shows the block diagram of the ISDN function architecture. The ISDN network is intended to accommodate the customer's completely new physical connection. There are several protocols available that allow control information to be sent between the customer's device and the ISDN network. ISDN channels may be divided into three kinds. They are namely:

1) B channel: 64 Kbps

2) D channel: 16 Kbps or 64 Kbps

3) H channel: 384 Kbps

1536 Kbps

1920 Kbps

Figure: ISDN Architecture

According to ISDN standards, home network customers are given three full-duplex, time-division multiplexed digital channels, two running at 64 Kbps (called B channels, forbearer) and one at 16 Kbps (designated as D channel, for data). The D channel is used for signaling and sharing network control information. One B channel is utilized for digitally encoded audio and the other for data transfer.

The 2B+D service is known as the basic rate interface (BRI). BRI systems require bandwidth that can support two 64 Kbps B channels, one 16 Kbps D channel, and additional special bits. As a result, the overall bit rate of BRI is 192 Kbps.

Features of ISDN

The features of ISDN are given below

1) ISDN can handle a large range of voice (telephone) and non-voice (digital data) applications on the same network by utilizing a small number of defined facilities.

2) ISDN connections can be switched or non-switched (dedicated).

3) An ISDN will have intelligence for delivering service features, maintenance, and network management tasks.

4) The 64-Kbps digital link is the foundation of ISDN. New ISDN services should be compatible with 64 Kbps switched digital connections.

5) OSI (open system interconnection) standards can be utilized for ISDN.

6) Depending on national regulations, ISDN can be deployed in a variety of ways.

Sreejith Hrishikesan

Sreejith Hrishikesan is a ME post graduate and has been worked as an Assistant Professor in Electronics Department in KMP College of Engineering, Ernakulam. For Assignments and Projects, Whatsapp on 8289838099.

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