Direct Inward Dialing

communications (DID) A service offered by telephone

companies which allows the last 3 or 4 digits of a phone

number to be transmitted to the destination exchange.

For example, a company could have 10 incoming lines, all with

the number 234 000. If a caller dials 234 697, the call is

sent to 234 000 (the company's exchange), and the digits 697

are transmitted. The company's exchange then routes the call

to extension 697. This gives the impression of 1000 direct

dial lines, whereas in fact there are only 10. Obviously,

only 10 at a time can be used.

This system is also used by fax servers. Instead of an

exchange at the end of the 234 000 line, a computer running

fax server software and fax modem cards uses the last three

digits to identify the recipient of the fax. This allows 1000

people to have their own individual fax numbers, even though

there is only one 'fax machine'.

Dictionary of PC Hardware and Data Communications Terms.

(1997-06-29)