The device that terminates a 2 wire ISDN line and changes the U (2 wire) interface to the S/T (four wire) interface. In Some countries the telephone company supplies this and the customer plugs his equipment into the S/T interface. In the US the customer must supply the NT-1 and plug into the U interface. Many ISDN devices for use in the US include this circuit internally.
Network Termination 1. Located at the end-user side of an ISDN connection. This device represents the termination of the ISDN system at the end-user’s location.
Device that is required to connect ISDN terminal equipment to an ISDN line. The NT-1 connects to the two-wire line (twisted pair copper wiring) that your telephone company has assigned for your ISDN service. Your ISDN service will not work if the NT-1's plug is not connected to a working electrical outlet.