Network termination 1

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NT1 stands for Network Termination 1. It is the equipment at the customer’s location that ends the ISDN network and handles basic signal conversion and timing (layer 1 of the OSI model). In a Basic Rate Interface (BRI) setup, the NT1 connects to the provider’s line termination (LT) in the telephone exchange over a two-wire U interface, and it connects to your devices over a four-wire S or T interface. The S and T interfaces are electrically the same, and the customer port is usually labeled S/T.

There are many types of NT1 devices. In the United States, NT1 is treated as customer premises equipment (CPE) and is typically provided by the customer or integrated into the customer’s equipment. In this case, the ISDN network terminates at the U interface. In Europe, NT1 is usually provided by the network provider, and the S/T interface is the termination point of the ISDN network.