# Difference between Synchronous TDM and Asynchronous TDM

Prerequisite – Time division multiplexing (TDM) 1. Synchronous TDM : In synchronous TDM, every device which is present in this has given the same time slot to transmit data. It does not consider whether the device contains data or not. The devices place their data on the link when their time slots arrive, if somehow any device does not contain data its time-slot remains empty. There are various kinds of time slots that are organized into frames and each frame consist of one or more time slots dedicated to each sending device. 2. Asynchronous TDM : Other name of asynchronous TDM is statistical division multiplexing. It is called so because time-slots are not fixed i.e. slots are flexible. As slots are not fixed, a device which wants to send data allotted time-slot.
Difference between Synchronous TDM and Asynchronous TDM :
S. No. Synchronous TDM Asynchronous TDM
1. In this, multiplexer allocates same time slots to each device without considering fact that device contains data or not. In this, multiplexer does not allocates same time slots to each device without considering fact that device contains data or not.
2. Number of slots per frame are equal to number of input lines i.e., If it contains n input lines, then it must have n slots in one frame. Number of slots per frame are less than number of input lines i.e., If there are n input lines, then there are m slots in one frame (m<n).
3. There is no guarantee that full capacity link is used. There is guarantee that full capacity link is used.
4. Total speed of input lines cannot be greater than capacity of path. Total speed of input lines can be greater than capacity of path.
5. Usage of devices is less. Usage of devices is more.
6. Number of time slots in a frame as always based on number of input lines. Number of time slots in a frame as always based on statistical analysis of number of input lines that are likely to be transmitting at any given time.
7. Time slots are fixed and pre-defined. Time-slots are not pre-defined.

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