TDMA multiplexing systems divide a radio frequency into time slots which are allocated for multiple data streams, for example cellular phone calls. This means that a short piece of data from each stream is inserted after each other, this way a single frequency can support multiple simultaneous channels. In GSM networks one time slot burst is usually 156.25 bits long. 8 separate time slots are used, they form a TDMA frame which is transmitted every 4.615 ms.

Here is a diagram which shows the use of a frequency and the way it is split into 8 individual time slots:

--->
time

_________________________________________
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 1 | 2 | ...
|___|___|___|___|___|___|___|___|___|___|

|---|
 slot

|-------------------------------|
 frame

Sources of information:
A Brief Overview of GSM by John Scourias
Radio Transmission in GSM, http://www.handytel.com/

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