Outlines user-network interface layer-1 characteristics to be applied at the S or T reference points for the basic interface structure as per CCITT Recommendation 1.412. Presents the electrical characteristics of the Integrated Services Digital Network (ISDN) Basic Access signals appearing at the S and T reference points. It also describes the physical interface between a TE and an NT. This interface standard was written to provide the minimal set of requirements to provide for satisfactory transmission between a TE and an NT.