Abstract: In a switching location for TDM multiplexing of a combination of a plurality of channels for digital signals to form a common channel in one transmission direction and for demultiplexing a common transmission channel into a plurality of channels in the opposite transmission direction, the signals of the individual communications channels are combined to form pulse messages each of which is preceeded by a frame identifier word monitored by a monitoring memory with respect to its bit sequence and with respect to its periodicity. Double monitoring devices and one's density monitoring devices are provided for the input signals arriving via the individual communications channels. Potentially, code converter monitoring devices for the input and output signals are provided. A stepping bit monitoring device is provided for the input signals arriving via the individual communications channels. A level monitoring device is provided for the input signals arriving via the common communications channel.