[1][2] The NT1 network termination provides signal conversion and timing functions which correspond to layer 1 of the OSI model.
[2] In a Basic Rate Interface, the NT1 connects to line termination (LT) equipment in the provider's telephone exchange via the local loop two wire U interface and to customer equipment via the four wire S interface or T interface.
In the United States, the NT1 is considered customer-premises equipment (CPE) and is as such generally provided by the customer or integrated into the customer's equipment.
In this case, the U interface is the termination point of the ISDN network.
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