1. Synchronous TDM :
Synchronous time division multiplexing (STDM), every device which is present in this has given the same time slot to transmit data. This does not consider whether the device contains data or not. The devices place their data on the link when their time slots arrive, when 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. Statistical TDM :
Statistical time division multiplexing (STDM) is technique for transmitting several types of data at the same time across a single transmission cable or line. It is often used for managing data being transmitted via a local area network (LAN) or a wide area network (WAN). In this situations, the data is often transmitted at the same time from any number of input devices attached to the network, including computers, printers, or fax machines. It can also be used in telephone switchboard settings to manage the simultaneous calls going to or coming from multiple, internal telephone lines.
Difference between Synchronous TDM and Statistical TDM :
|S.No.||Synchronous TDM||Statistical TDM|
|1.||The data flow of each input connection is divided into units and each input control one output time slot.||The slots are allotted dynamically. Input line is given slots in output frame only if it has data to send.|
|2.||In this, number of slots in each frame are equal to number of input lines.||In this, number of slots in each frame are less than the number of input lines.|
|3.||The maximum bandwidth utilization is done when all inputs have data to send.||The volume of link is normally is less than the sum of the volume of each channel.|
|4.||In this de-multiplexer at receiving end decomposes each frame, discards framing bits and draw out data unit in turn. This draw out data unit from frame is then passed to destination device.||In this de-multiplexer at receiving end decomposes each frame, by checking local address of each data unit. This draw out data unit from frame is then passed to destination device.|
|5.||It uses synchronization bits at the beginning of each frame.||It does not used synchronization bits.|
|6.||Slots in this carry data only and there is no need of addressing.||Slots in this contain both data and address of the destination.|
|7.||In this, buffering is not done, frame is sent after a specific interval of time whether it has data to send or not.||In this, buffering is done and only those inputs are given slots in output frame whose buffer contains data to send.|
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