ISDN is clearer, more stable, and can carry far more information than conventional, analogue networks. For computer users, data sent on ISDN can take a fifth of the time of modem connections.
ISDN does not need coaxial cable or optical fibre, though sometimes you will be offered it: it works on clever electronics, which in effect increases the bandwidth of an ordinary copper line.
In much of Europe, ISDN is seen as a viable alternative to traditional phone lines. In the UK, unfortunately, it is still marketed as a premium service, targeted at very high-volume data users. In Germany and France, many more users install it for voice as well as data.
France Telecom charges around £80 to install an entry-level ISDN 2 line; in Germany, a connection is £50. In the UK, BT charges £400 plus VAT for ISDN 2. Quarterly rental is £84, compared with £34.17 for an ordinary business line, although ISDN 2 - also known as basic rate - does have two channels, effectively giving two lines.
It is not possible to connect standard telephone equipment to ISDN, and you will have to spend a fair amount on hardware to get the best out of the system. High-speed data cards costing up to £1,000 are available for PCs and Macintoshes, though slower external adaptors sell for not much more than a fast modem. Conventional faxes, phones and answering machines need to be connected via a converter, or terminal adaptor.
You can buy ISDN digital phones with a port for ordinary analogue devices such as a fax from around £500. But if you want a fax machine that will take advantage of ISDN speeds, you will have to pay £6,000 for a Group Four fax machine.
British businesses that have switched to ISDN have done so mainly to cut the costs of transferring data between sites. In the publishing industry, ISDN is a popular alternative to couriers for moving photographs or documents. But ISDN is more than a fast replacement for bikes or modems. The network opens a range of features to businesses, and even home users, including video phone calls, and access to data-rich Internet services such as the World Wide Web.
ISDN can also set up a call far more quickly than an ordinary phone line. For computer users who need to access a remote network, perhaps at head office, it is possible to fool the computer into thinking that it is physically attached to that network. The ISDN card dials out when the remote computer needs to read or save a file, without any intervention from the user.
ISDN has several extra features, such as caller identification and multiple subscriber numbering (MSN). With MSN, up to eight devices can be connected to a single ISDN 2 line, each with its own telephone number. Faxes, computers, and direct lines to key members of staff can be set up this way, avoiding the need for separate lines or an office switchboard.
People who are not installing the line on their own behalf, for example teleworkers, should note that on a per line basis, it is cheaper to install "primary rate" ISDN, which is normally targeted at larger businesses. Be warned, though, that primary and ISDN 2 equipment is not always compatible.
Installing ISDN makes sense now for heavy data users, but transferring all calls to it remains a relatively expensive option. Manufacturers say that hardware prices will fall as the ISDN market grows, but that will only happen if the cost of a line falls first. BT says it will reduce connection charges as new technology makes it cheaper to supply ISDN at the exchange, but it is unable to give a time-scale for this. Until it does, ISDN will remain a niche service in the UK.
BT ISDN Helpdesk is on 0800 181514; Mercury business customers call 0500 700 101.Reuse content