An inverse multiplexer or demultiplexer (often abbreviated to "inverse mux", "imux" or "demux") allows a data stream to be broken into multiple lower data rate communications links. Note that this is the reverse of a multiplexor.

example:

                                    |---low rate communications link #1
DTE ---high rate data---inverse mux |---low rate communications link #2
                                    |---low rate communications link #3

DTE = Data terminal equipment
This provides an end to end connection of 3 x the data rate available on each of the low rate data links. (Strictly, slightly less than 3 x, because the inverse mux will use some of the available bandwidth to communicate with the inverse mux at the far end of the link, i.e. checksum or other error checking codes)

Inverse muxes are used, for example, to combine a number of ISDN channels together into one high rate circuit, where the DTE needs a higher rate connection than is available from a single ISDN connection.

A real world example is the reception of telemetry from the computer/instrumentation system of a satellite, space craft or other remote vehicle.

See also MDM