ABSTRACT: Digital Data System (DDS) provides full-duplex, synchronous, end-to-end digital transmission at the primary channel speeds of 2, 4, 4.8, 9.6 and 56 kb/s on dedicated private line 2-point and multipoint access and intra-LATA (Local Access and Transport Area) circuits. The secondary channel capability offers a companion digital transmission channel independent of the primary channel at a lower bit rate.

This Technical Reference (TR) describes the view of Telcordia on the functional requirements, design criteria, and network compatibility specifications for a secondary channel capability in the DDS. The document provides all necessary information to enable implementation of the DDS secondary channel service capability with the Network Interface (NI) as defined by the Federal Communications Commission (FCC) 81-216 ruling. The NI is the point of demarcation between the network communication channel and the customer-provided equipment; the signal at this point is not in the format of a standard digital signal.