An interface to an intelligent ISDN-compatible device (e.g., PBX or router) responsible for the user side of the connection to the network, performing such functions as multiplexing and switching. Such functions correspond to Layer 2 (Data Link Layer) of the OSI Reference Model. An NT2 commonly is actually an NT1/2 device, performing the combined functions, and operating at Layers 1, 2, and 3 of the OSI Reference Model. See also ISDN, NT, NT1, and OSI Reference Model.