Time-division multiplexing (TDM) is a type of digital multiplexing in which two or more apparently simultaneous channels are derived from a given frequency spectrum, i.e., bit stream, by interleaving pulses representing bits from different channels.

In some TDM systems, successive pulses represent bits from successive channels, e.g., voice channels in a T1 system. In other systems different channels take turns using the channels for a group of successive pulse-times (a so-called "time slot").

What distinguishes coarse time-division multiplexing from packet switching is that the time-slots are pre-allocated to the channels, rather than arbitrated on a per-time slot basis.

Uses of time-division multiplexing:

• The PDH and SDH network transmission standards
• The GSM telephone system
• Fitted to locomotives to allow push-pull operation, and/or multiple working with another locomotive

This article was originally based on a Federal Standard 1037C entry is support of MIL-STD-188.

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