Time Division Multiplex (TDM) is a technique of transmitting multiple digitized data, voice, and video signals simultaneously over one communication media by interleaving pulses representing bits from different channels or time slots. The basic channel bandwidth in the telecommunication is DS0, which channel width of 64kbps.

The Public-Switched Telephony Network (PSTN) is based on the TDM technologies and often called a TDM access network. Telephony switches support TDM in a few formats: DS0, T1/E1 TDM and BRI TDM. E1 TDM provides a 2.048Mbps communications link divided into 32 time slots of 64kbps each. T1 TDM provides a 1.544Mbps communication link divided into 24 time slots of 64kbps each and an 8kbps channel for synchronisation and maintenance. E1 and T1 TDM were first used by telephone companies for the transport of digitised voice, but since there is no difference between digitized voice and other kinds of data E1 and T1 TDM are now also used for wide area network links. BRI TDM support is provided by a switch Basic Rate Interface which can be used for Basic Rate ISDN and as a data channel for one or more static PPP links. The Basic Rate Interface has 2 time slots of 64kbps. TDMA is also used in the cellular network for mobile wireless communications.

Time Division Multiplexer is a device using the TDM techniques to combine several slower speed data streams into a single high speed data stream. Data from multiple sources is broken into portions (bits or bit groups) and these portions are transmitted in a defined sequence. Each of the input data streams then becomes a time slice in the output stream. The transmission order must be maintained so that the input streams can be reassembled at the destination. Typically, the same device can also perform the reverse process with the same TDM techniques: de-compose the high speed data streams into multiple low speed data stream, a process call de-multiplexing. Therefore, it is very often a Time Division Multiplexer and Demultiplexer are in the same box.

TDM: Time Division Multiplex and Multiplexer

Related Terms: TDMA, PSTN, Class 5 Switch, Multiplexing, Multiplexer, T1, E1, BRI, DS0

Reference Links: http://www.alliedtelesyn.co.nz/documentation/rapier/261/pdf/tdm.pdf: Time Division Multiplex