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ATM vs TDM | Difference between ATM and TDM

This page compares ATM and TDM and mentions difference between ATM and TDM. As we know ATM stands for Asychronous Transfer Mode and TDM stands for Time Division Multiplexing.

Refer Following links to subtopics on this ATM tutorial:
ATM Network Architecture & Interfaces   ATM Protocol Stack  ATM services  ATM Switch  ATM Call Flow  ATM vs STM  ATM vs TDM  ATM versus Frame Relay  ATM AAL Layer Types 

ATM-Asynchronous Transfer Mode

ATM operation
Fig-1: ATM-Asynchronous Transfer Mode

• ATM operates on cells.

• It multiplexes or combines cells similar to TDM operation. But is has fixed size of cells of size equal to 53 bytes. This 53 bytes is divided into 5 bytes of header and 48 bytes of payload containing information. It has basic transmission rate equal to 149.76 Mbps which is equal to STM-1 rate of SDH hierarchy of transmission.

• It incorporates minimal amount of error detection and flow control are incorporated. Error control is provided for header part using HEC (Header Error Control) field. It is not provided for payload or information part, the same should be taken care by end terminal equipments.

• As the information field is fixed and has lesser size, this results into minimum packet delay.

• It has policing function. Hence digit transmission rate is restricted below the requirement rate limit.

TDM-Time Division Multiplexing

TDD vs TDMA using TDM concept
Fig-2: TDM-Time Division Multiplexing

The figure-2 depicts TDD and TDMA utilizing frequency resource sharing in LTE and GSM system consecutively using TDM concept. As shown, LTE uses frequency-f1 between UE and eNodeB at different time slots 0 to 10. This type of LTE frame is referred as LTE-TDD frame. As shown, GSM uses same frequency channel 124 at different time slots TS0 to TS7 for communication between GSM base station and subscriber stations.

• TDM operates on packets. The frame transmission and reception follows TDM concept where in various fields are arranged in TDM fashion one after the other consecutively. The packet length in TDM is variable and depends on the configuration.

• It multiplexes or combines packets irrespective of technology. Hence it is used in different technologies in order to utilize frequency resources efficiently. For example, same frequency is assigned to multiple users on time shared basics.

• It does not incorporate error detection and flow control, it is the duty of parent technologies utilizing TDM service to take of the same.

•  The rate limit depends on number of packet transmitted over some time duration and it depends on clock.

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