Digital signal transmission system with switchable substitute path - performs multistep switching to this path from manually switched channel or one having excessive error rate

摘要

Signals are transmitted normally over parallel paths (B1-Bn) between channel units (K) linked to input and output multiplex arrangements (MI1,MII1 etc.). Each path (e.g. B1) includes two line termination units (L) and one or more repeaters (R). The substitute channel (E) may be used for low-priority messages (LP) while the other channels operate normally. When the bit error rate of any signal (e.g. D1) exceeds a predetermined threshold, that signal is switched to the substitute channel between the low-priority transmission multiplexes (MIe,MIIe). ADVANTAGE - A smaller rise in bit error rate occurs when transmission is switched from the normal to the substitute path.