A T-interface is used for basic rate access in an Integrated Services Digital Network (ISDN) environment. It is a User-Network Interface reference point that is characterized by a four-wire, 144 kbit/s (2B+D) user rate.

Other characteristics of a T-interface are:

• it accommodates the link access and transport layer function in the ISDN architecture
• it is located at the user premises
• it is distance sensitive to the servicing Network termination 1
• it functions in a manner similar to that of the Channel service units (CSUs) and the Data service units (DSUs).

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