Report: Basic access network termination chip for ISDN 4-wire loops

In-this article, we describe an AT&T CMOS chip, the T7252, which simplifies the line interface design on the network side of a fourwire ISDN basic access subscriber loop. (CMOS stands for complementary metal oxide semiconductor; ISDN is the Integrated Services Digital Network.) Called UNITS (user to network interface terminationfor switches), the T7252 implements the CCITT (International Telegraph and Telephone Consultative Committee) 1.430 Layer 1 physical link “2B + D” standard. 1 This customer premises subscriber loop provides integrated voice and data transmission at 192 kilobits per second (kb/s) on separate transmit and receive twisted pairs. The basic transmission interface supports two 64-kb/s B channels and one 16-kb/s D channel, with 48 kbls used for framing, control, link maintenance, and synchronization. (B stands for bearer channel; D stands for demand channel.)