What Is Asynchronous Transfer Mode (ATM)?

Ken Black

Asynchronous transfer mode (ATM) is a switching technology that facilitates the movement of data from one point to another. The technology emerged in the 1990s and seemed very promising as it could potentially integrate local area networks (LAN) and wide area networks (WAN). However critics soon felt that it did not turn out to be the single integration solution everyone had hoped for. It was eventually replaced by transmission control protocol / internet protocol (TCP/IP).

Once the preferred transport protocol, asynchronous transfer mode (ATP) was later replaced by TCP/IP network protocol.
Once the preferred transport protocol, asynchronous transfer mode (ATP) was later replaced by TCP/IP network protocol.

At the time of its release, the main advantage of ATM technology was the ability to transfer many different types of data at the same time. This is because all bandwidth is utilized, as long as it is available. Other types of technologies did not allow all the bandwidth to be used once a particular function was started. Therefore, ATM was a more efficient way to transfer video files, pictures, e-mail and even live streaming audio and video.

Encoding data in asynchronous transfer mode is remarkably consistent, with each cell being 53 bytes in length. This helps during the processing of the data because there is no need to worry about where each cell starts and ends, unlike what is required with other technologies. Therefore, dealing with more known factors means there is a greater ability to contribute resources to to encoding and decoding, thus speeding up the data transmission.

The cells of ATM are broken down into two main parts. There is a five bit header, which helps identify the routing the cell will take to reach its destination. The other part is known as the payload. This is the practical information that is supposed to be conveyed. There is no information marking the end of the cell because, as stated previously, the hardware is set up to automatically "know" when the cell ends.

The speed of asynchronous transfer mode can reach up to 10 billion bytes per second, also written as 10 Gbps. This makes it one of the fastest network protocols in existence. Thus, in addition to general Internet use, it can also be used to transfer very large amounts of data over wide area networks and local area networks. Asynchronous transfer mode can also be used between the two types of networks as well.

There are two major divisions of asynchronous mode. Which one is used is determined by the type of data. For example, constant bit rate is used to stream live video and audio over the Internet. Unspecified bit rate can be used when there is no critical time element involved. This, however, does not necessarily mean the transfer of unspecified bit rate will seem slower than constant bit rate to the end user.

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