Multiplexer :

This device enables several devices to share one communication line. The multiplexer scans each device to collect and transmit data on a single line to the CPU. It also communicates transmission from the CPU to the appropriate terminal linked to the Multiplexer. The devices are polled and periodically asked whether there is any data to transmit. This function may be very complex and on some systems, there is a separate computer processor devoted to this activity and this is called a "front-end-processor".