Gives minimum requirements to provide satisfactory transmission between the network and NT, while complying with the I-Series of International Telegraph and Telephone Consultative Committee Recommendations. Presents the electrical characteristics of the integrated services digital network (ISDN) basic access signals appearing at the network side of the NT. It also describes the physical interface between the network and the NT. The transport medium of the signal is a single twisted-wire pair that supports full-duplex (i.e., simultaneous two-way) service.