One cost-saving use for multiplexers is connecting a multiplexer and a demultiplexer ( or demux ) together ( called mul-dex ) over a single communication channel ( by connecting the multiplexer 's single output to the demultiplexer 's single input ) . One use for multiplexers is cost savings by connecting a multiplexer and a demultiplexer ( or demux ) together over a single channel ( by connecting the multiplexer 's single output to the demultiplexer 's single input ) .