Apps Communications,Inc.- Time-Division Multiplexing (TDM)

Time-division multiplexing (TDM) is the 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 Plesiochronous Digital Hierarchy (PDH) and Synchronous Digital Hierarchy (SDH) network transmission standards

The Global System for Mobile Communications (GSM) telephone system.

Time Division Multiplexing (TDM) is the means by which multiple digital signals (or analogue signals carrying digital data) can be carried on a single transmission path by interleaving portions of each signal in time [1]. Interleaving can be done at bits or blocks of bytes [1]. This enables digitally encoded speech signals to be transmitted and switched optimally within a circuit-switched network [2]. This article consists of two sections, namely, Transmission using TDM and Synchronous Digital Hierarchy (SDH). The first section examines the basic principles underlying TDM, while the second section discusses how SDH is used to switch TDM frames.

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