ISDN is a relatively new form of telephone service. The basic design concept of; ISDN is simple - A digital telephone line to handle digital data as opposed to the; traditional, analogue line which requires that digital data be converted to analogue format before being transmitted.

In fact, the ISDN network resembles a modern computer network more than a traditional telephone line. The lines themselves can be supplied on the same, copper-wire pair infrastructure of the Plain Old Telephone Service (POTS) the modern ISDN system employed by Etisalat, is highly effective over long distances between the user and local telephone exchange.

ISDN traffic is limited by bandwidth (measured in bits per second, bps) and is supplied in two variants. The first variant - the Basic Rate, ISDN line has a bandwidth capability of 128Kbps. This 128 K is divided into two 'bearer' channels of 64K each. One of the reasons for dividing ISDN into 64K bearer (also known as 'B' channels) is that 64 K is the bandwidth required to handle high quality voice. A BRI can therefore handle two simultaneous voice calls, one voice call and one 64K data call or one 128K data call. A third channel, the 'D' channel is used by the ISDN network to control the line and the traffic traveling along it. It uses 16Kbps for these purposes.

The second variant is the Primary Rate ISDN line (also known as PRI or EI). The PRI is a 2Mb line. It contains 30 'B'; channels (and one 64K "D" channel) which can be combined in many different ways depending on bandwidth requirements.

 I The ISDN T/A (Terminal Adapter) provides the necessary interface between the ISDN network and the devices it is connecting to.

Standard telephone equipment will not work on an ISDN line without an appropriate terminal adapter and ISDN equipment will never work on a standard telephone line.

Like most countries, Etisalat have implemented a modern, ETSI standards based ISDN network. , the standard offers many configuration options so ISDN equipment may not operate correctly on every network. This potential hazard is once again avoided by purchasing Etisalat type- approved, ISDN equipment.

Given the superior data capabilities of ISDN it is not surprising to find that ISDN equipment is focused, to a large extent on data applications. Devices such as BRI modems (particularly useful for personal and small LAN, Internet access), PRI modems (useful for sharing Internet access among a large Local Area Network or for connecting remote locations (and routers) for connecting one location/network/device to many others across the ISDN network are most common but other ISDN; devices include video conferencing equipment, telephone and fax equipment as well as large, enterprise and corporate telecom solutions.

At Emirates Telecom Lab we ensure that ISDN equipment meet international standards and are compatible with the Etisalat networks