direct inward dialing

Direct Inward Dialing
DID

   <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
   
(http://ora.com/reference/dictionary/terms/D/Direct_Inward_Dialing.htm).

   (1997-06-29)