Integrated services digital network (ISDN) is a telecommunications system that allows data to be transmitted clearly, easily and quickly, along with voice communications. At the moment many organisations have their own dedicated lines for their internal computer networks, or else use the ordinary telephone network, with its inefficiencies, but ISDN is a common service specially designed for easy computer communications. It offers one all-embracing, multimedia network for carrying voice, data, text and graphics.
ISDN is designed to cope with the limitations imposed on millions of homes and businesses linked to telephone exchanges by standard copper wire. It is a clever way of extending the capabilities of the existing technology. Ideally, all homes and businesses would be plumbed into fibre optic cable capable of carrying information at vast speed - but the cost of this would be enormous, so copper cable will remain with us for a long time to come.
BT has been working with ISDN since 1985. It has developed a number of in-house standards for its own network. These are 'standards' in name only, however, as each of the 17 countries with ISDN networks are implementing the system in their own way, so straightforward compatibility is some way off.
At present BT has not undertaken to provide national coverage, but it does plan to have a complete service in place by the end of 1994.
BT has two services: ISDN 2 and ISDN 30. The ISDN 2 service provides two lines capable of transmitting data at a rate of 64 kilobits per second. This looks as if it will become an industry standard for small business and home use. Its big brother, ISDN 30, offers up to 30 64k lines and is aimed at large companies. This article, as an 80k file, would take about a second to send to the Independent through ISDN.
The European Commission, acting as honest broker, has worked with BT and its French and German counterparts to formulate a EuroFile protocol governing the use of ISDN. BT says it will conform to this standard. With Norway and Portugal likely to join this group, Europe is suddenly at the centre of compatible ISDN developments. Japan, Australia, a number of Pacific rim countries and the United States make up the rest of the global ISDN community, each with their own particular standard, and each slowly migrating towards a common format that would enable the same equipment to be used on a completely common network.
One result of widespread ISDN will be vastly to increase the speed and clarity of fax transmission. At the Integrated Communications Exhibition and Conference at Wembley earlier this month, the Japanese manufacturer Ricoh launched the first reasonably cheap high-speed fax. Costing about pounds 5,100, it uses ISDN lines to provide double the resolution and 10 times the speed of ordinary faxes. As I watched, the average time to send or receive each page of a fax was 1.5 seconds, faster than most photocopiers.
Computers are connected to ordinary telephone networks through modems, boxes that convert digital information into a series of audible bleeps which are sent down the line. Working from home, or teleworking, will become a more realistic proposition as a result of the tenfold increase in the speed of communication that ISDN offers over traditional transmission. As the computer and ISDN speak the same digital language, there is no need for signals to be converted.
At present, computers need to be fitted with networking cards - additional circuitry that manages the sending and receiving of information - to allow them to communicate via ISDN. These cost about pounds 1,000. Sun Microsystems has launched a machine that comes with an ISDN port, however, and other manufacturers are likely to do likewise.
ISDN also provides an alternative to expensive leased lines for linking an organisation's networks across large distances. Transfer rates for data are about a megabyte a minute, which means the complete works of Shakespeare could be sent in seven minutes.
ISDN could also be useful for collaborative work spanning long distances. For instance, a designer could sit in his London studio with the book cover he has created on the screen of his Apple Macintosh computer. The person who commissioned the work could be as far away as Newcastle and still see the same image. The two could discuss the artwork over the phone and make changes. With everyone satisfied, the designer could instruct his machine in London to print out the image in the Newcastle office. ISDN 2 is useful for such work, as one of the twin lines carries the data while the other handles the conversation.
Faster access to central stores of information may finally make it sensible to create and interrogate large multimedia databases. One example from the Netherlands on show at the exhibition offered 'hairstyling by ISDN'. Participants chose four styles from a book and a main computer in Utrecht was then called via an ISDN link. Within a minute graphics files of four elaborate hairstyles had arrived and wrapped themselves around a digitised image of the subject's face.
The main drawback is that to gain access to ISDN each user has to install a dedicated phone line, and in the UK they must pay a pounds 400 connection charge for ISDN 2. In France, the connection cost is pounds 70 and in Germany pounds 50. BT's explanation is that regulations prevent it subsidising the embryonic service by using money generated through its other activities. As line sales increase, connection charges should fall. With 122,000 ISDN channels installed in the UK (counting 30 for an ISDN 30 connection, 2 for an ISDN 2), we should not have long to wait.Reuse content