A plurality of digital signals of one or more digital transmission bit rates are combined into a single transmission signal by employing a unique common channel frame format and one step multiplexing process. The channel frame format includes a plurality of data bit positions and a plurality of overhead bit positions. The number of data bit positions used is dependent on the particular incoming signal. Similarly, the number of frames generated during a specific common framing interval is dependent on the digital transmission bit rate of the particular signal. Specifically, the number of channel frames generated during the common channel frame interval is dependent on a number of equivalent so-called lowest transmission bit rate signals included in the particular signal being formatted. The overhead bits are distributed in the channel frame format. Digital words from the channel frames are inserted into predetermined groups of data word positions in a repetitive frame of a single transmission signal. The number of data words in a group is also dependent on the number of equivalent lowest transmission bit rate signals in the particular signal being combined.