Difference between ATM and TDM

Key Difference: ATM and TDM are two types of data transfer technologies. TDM stands for Time-division multiplexing, which is a method of combining multiple data streams into one and sending it together over one signal. ATM stands for Asynchronous Transfer Mode. It is a type of TDM, in which the timeslots are not fixed.

TDM ATM and TDM are two types of data transfer technologies. TDM stands for Time-division multiplexing, which is a method of combining multiple data streams into one signal via the use of a multiplexer. The multiplexer accepts the input from each individual end user and combines it together. The advantage of it is that it allows the combination of media, such as data, text, graphics, voice and video, to be transferred together.

This signal is then separated into many segments, each having a very short duration. These separate segments can then be transmitted almost simultaneously using the same link. The received segments can then be put together via the help of a demultiplexer. The demultiplexer the separates the data and routes it to the proper end users.

ATM

The technology of TDM was developed in the 1800s for use in telegraphy systems. In the digital age, it was utilized in the second half of the 20th century. It is primarily used for digital signals. TDM might also me used for analog multiplexing. In analog multiplexing, two or or more signals or bit streams are transferred appearing simultaneously as sub-channels in one communication channel. However, they are physically taking turns on the channel.

ATM, on the other hand, stands for Asynchronous Transfer Mode. It is a type of TDM, in which the timeslots are not fixed. They are assigned dynamically as needed; hence the name asynchronous, not synced. The advantage of ATM is that it uses a constant data stream to allow the transference of data.

Comparison between ATM and TDM:

Details for the table taken from Cisco Factsheet.

	ATM	TDM
Stands for	Asynchronous Transfer Mode	Time-division multiplexing
Description	A dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology.	A method of putting multiple data streams in a single signal by separating the signal into many segments, each having a very short duration.
Cost of ownership	ATM lowers recurring bandwidth and operation costs	TDM increases recurring bandwidth and operation costs
Bandwidth efficiency	ATM enables different applications to share bandwidth while preserving QoS	TDM does not allow different applications to share bandwidth while preserving QoS
Multi-service capability	ATM delivers multi-service capability without affecting bandwidth efficiency;	TDM provides multi-service capability at the expense of bandwidth efficiency
Quality of service (QoS)	ATM enables QoS without affecting bandwidth efficiency	TDM enables QoS at the expense of bandwidth efficiency
Features	Bandwidth is dynamically shared among all applications Multiservice integration saves bandwidth Silence suppression for voice and repetitive pattern suppression for circuit data save bandwidth Use of public ATM services for trunking provides a cost-effective alternative to leased lines Efficient traffic management optimizes application throughput ABR with VS/VD enables monitoring and adjusting of the cell rate of connections, avoiding congestion Large dynamically assigned buffers User applications firewalled and fair allocation of excess bandwidth provided QoS is guaranteed with Per-virtual circuit queuing, Per-virtual circuit rate scheduling, and Multiple classes of services (CoSs), including CBR, RT-VBR, NRT-VBR, UBR, ABR Traffic growth is accommodated by offering a migration path to broadband networking Architected specifically for multiservice networks—enabling New World application Seamless integration into existing environments	High recurring bandwidth cost Bandwidth inefficiency Bandwidth is wasted with statically mapped CBR-like connections (MCR=SCR=PCR) During periods of no traffic, bandwidth is not reassigned to other applications Inability to efficiently accommodate bursty data applications When all available bandwidth is allocated, additional bandwidth must be procured Limited application performance QoS is delivered at the expense of bandwidth Limited bursting capability Cannot support bursty data, even during periods of voice silence, because bandwidth is statically allocated Limited scalability to support traffic growth and new applications Bandwidth generally limited to T3/E3 No trunking over public ATM services Cannot support bursty data, even during periods of voice silence, because bandwidth is statically allocated Increasing traffic and new applications require a migration path to broadband connectivity Architecture is not optimal for broadband services, especially for New World IP-based applications Public ATM services cannot be used for trunking