Difference between Synchronous TDM and Asynchronous TDM

Last Updated : 17 Sep, 2024

Time Division Multiplexing is a technique in digital communication that deals with the transmission of several streams of data over a single communication channel. Mainly, there are two categories of TDM: Synchronous TDM and Asynchronous TDM, often referred to as Statistical TDM. Understanding these two concepts is important for optimization in the efficiency of data transmission in various applications, including telecommunications and networking.

What is 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.

Advantages of Synchronous TDM

Benefits of Synchronous TDM are that a bandwidth is guaranteed because each data stream has a statically assigned time slot, which makes the data transmission steady and continuous.
Predictable latency: Fixed time slots ensure lower delays and, therefore, predictable data delivery times.
Simpler synchronization: Time slots are pre-allotted; therefore, synchronization between multiple streams of data is easier to manage.
Efficient for continuous data: These are perfect for those applications that require a steady stream of data for smooth and continuous transmission.

Disadvantages of Synchronous TDM

Inefficient use of bandwidth: Time slots are fixed in number, and if any data stream has nothing to send, its slot remains unused. Hence, bandwidth is wasted.
Rigid Allocation: Time slots are pre-deﬁned and can be difﬁcult to adjust for data streams that either require more or less bandwidth.
Unsuitable for bursty data: Synchronous TDM works poorly when there is irregular transmission, or in bursts, because of no scope for dynamic allocation of slots due to demand.
Higher cost even in unutilized slots: Even when no data is being transmitted, it considers the channel as busy, which may further raise the operational cost.

What is Asynchronous TDM ?

The asynchronous time division multiplexing, which is also called statistical TDM, allocates the time slots dynamically to the data streams based on requirements. In such types of multiplexing, the time slot is assigned only when the data stream has some information to be sent, making it more flexible.

Advantages of Asynchronous TDM

Efficient usage of bandwidth: Time slots are utilized only in case data needs to be sent, thus avoiding bandwidth wastage.
Dynamic allocation: this would allow for more flexible usage of the available bandwidth, in assigning more slots to those data streams that have higher demand.
Better for bursty data: Suitable for applications where the data to be transferred is irregular.

Disadvantages of Asynchronous TDM

Increased complexity: In reality, there is a need for more sophisticated mechanisms for controlling the dynamic allocation of time slots.
Delays: The streams may then experience delays, particularly during peak times, due to the absence of fixed time slots.
Synchronization problems: Because time slots are allocated dynamically, it is more difficult to keep the streams of data synchronized.