Integrated Services Digital Network
in the days of 28, 33 and 56k modem an ISDN was the gadget to have, people
were in awe of the incredible speed of the 64Kbps ISDN. Available in
various flavours giving the option of multiple 64Kbps channels to up the
bandwidth available, common installations where 2 channels and a control
Pretty much obsolete now other than in places where
is not available.