A multiplexer/demultiplexer (MUX/DEMUX) system for multiplexing and demultiplexing information from a plurality of traffic channels is configured according to a Plesiochronous Digital Hierarchy (PDH) standard into a composite signal transferred to and from a telecommunciations interface. A PDH traffic interface receives PDH channel signals from a plurality of PDH channels and a bit-pipe interface receives bit-pipe traffic transported as a packet data stream. A composite signal generation module and interface then creates, outputs and receives a single composite serial data stream including, in a single composite format, information from the received PDH channel signals as well as the packet data stream. The rate of the bit-pipe traffic may be adaptively modulated as a function of the composite rate.