A multiplexed transmission system in which the rates of the carrier and its tributaries are not traceable to the same master clocking source. Note: In this type of system, extra signal elements are usually appended to the individual tributary signals for the purpose of interleaving them at a rate consistent with the carrier rate. [T1.X1]

A transmission system in which (a) all circuits carry digital signals and (b) the signals are combined into one or more serial bit streams that include all framing and supervisory signals. Note: A-D/D-A conversion, if required, is accomplished external to the system.

Synonym neutral direct-current telegraph system.