What is the difference between Synchronous TDM and Statistical TDM?

Let us understand what synchronous TDM is.

Synchronous TDM

Synchronous TDM is known as synchronous. It is essential because each time slot is pre-assigned to a constant source. The time slots are sent regardless of whether the sources have some data to send or not. TDM devices can handle the source of several data cost. This is completed by authorizing fewer slots per cycle to the passive input devices than the rapid device.

In STDM, the multiplexer authorizes a similar time slot to every device at sometimes, whether or not a device has something to send. Time slot A, for instance, is authorized to device A alone and cannot be used by any other device. Each time an assigned time slot shows up, and a device has the time to transmit a portion of its data.

The time slots are centralized into frames, and each frame contains one or more time slots committed to each sending device. If there are n sending devices, the frame consists of n slots where each slot will be allocated to each of the sending devices if all the sending devices transmit at the same rate.

The disadvantage of synchronous TDM is the capacity of the channel is not fully used as the null slots are also transmitted which is having no records. The first frame is completely filled, but in the previous two frames, some slots are null. Thus, it can say that the capacity of the channel is not used effectively.

Statistical TDM

A statistical TDM is also known as Asynchronous TDM. ATDM has been created to solve the issue of wastage of the multiplexed channels in synchronous TDM. In ATDM, the multiplexer scans all the input lines and gets the portions of information till the frame is full. When the frame is full, it is transmitted across the link.

The limitation of the TDM approach is that multiple time slots in the frame are wasted. A particular terminal has no data to share to a particular instant of time and will share an unfilled time slot. It is also referred to as TDM or intelligent TDM.

The variation between Asynchronous TDM and Synchronous TDM is that few slots in Synchronous TDM are unused, but in Asynchronous TDM, slots are entirely used. This leads to the smaller transmission time and efficient uses of the volume of the channel.

It firmly assigns the time slots on demand to free input channels, hence storing the channel size. Similarly, as with synchronous TDM, statistical multiplexers can have several I/O lines with a buffer related to each of them. During the input, the multiplexer filters the input buffers, accumulating records until the frame is filled and transmitting the frame.

In Asynchronous TDM, each slot’s information should have an address element, which recognizes the origin of information. Therefore, data appears from and is broadcasted to I/O lines unpredictably, and address information is needed to ensure suitable delivery. This generates more overhead per slot.

Updated on: 22-Nov-2021


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