Abstract: Interchange of data between two way loops and a data trunk is provided by way of channel units, submultiplexer/demultiplexers and a common multiplexer/demultiplexer. Submultiplexers have five, 10 or 20 ports, creating time frames with corresponding numbers of time slots, all of equal duration. The channel units, which terminate 9.6, 4.8 or 2.4 Kbs data subscribers, assemble the incoming data into bytes, repeat each byte five, 10 or 20 times, respectively, and align each successive one of the repeated bytes with successive time slots. Any port of a five port submultiplexer can be connected to any 9.6, 4.8 or 2.4 channel unit. Similarly, any port of a ten port submultiplexer can be connected to any 4.8 or 2.4 channel unit and any port of a twenty port submultiplexer can be connected to any 2.4 channel unit. The outputs of all submultiplexers are interleaved by the common multiplexer and applied to the trunk.