A time division switching matrix capable of effecting rate conversion comprises a plurality of serial inputs for connection to respective serial input links, each capable of carrying time division multiplexed PCM channels, a plurality of serial outputs for connection to respective serial output links, each capable of carrying time division multiplexed PCM channels, and a serial-to-parallel converter associated with each input for converting a serial input stream to parallel format, each said serial-to-parallel converter being independently configurable to produce the same net parallel throughput regardless of the bit rate of the associated input link. The output side of the switching matrix can be similarly configured.