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Thursday, February 6, 2014

Difference Between Synchronous TDM and Statistical TDM

Parameter
Synchronous TDM
Statistical TDM
Working
In Synchronous TDM data flow of each input connection is divided into units and each input occupies one output time slot.
In Statistical TDM slots are allotted dynamically. i.e. input line is given slots in output frame if and only if it has data to send.
No. of Slots
In Synchronous TDM no. of slots in each frame are equal to no. of input lines.
In Statistical TDM, No. of slots in each frame are less than the no. of input lines.
Buffers
Buffering is not done, frame is sent after a particular interval of time whether someone has data to send or not.
Buffering is done and only those inputs are given slots in output frame whose buffer contains data to send.
Addressing
Slots in Synchronous TDM carry data only and there is no need of addressing. Synchronization and pre assigned relationships between input and outputs that serve as an address.
Slots in Statistical TDM contain both data and address of the destination.
Synchronization
Synchronization bits are used at the beginning of each frame.
No synchronization bits are used
Capacity
Max. Bandwidth utilization if all inputs have data to send.
The capacity of link is normally is less than the sum of the capacity of each channel.
Data Separation
In Synchronous TDM de-multiplexer at receiving end decomposes each frame, discards framing bits and extracts data unit in turn. This extracted data unit from frame is then passed to destination device.
In Statistical TDM de-multiplexer at receiving end decomposes each frame by checking local address of each data unit. This extracted data unit from frame is then passed to destination device.

Figure Given below illustrates both concepts: