What is ATM?

Asynchronous Transfer Mode

ATM is the emerging standard for communications. It is based on the ITU-T Broadband Integrated Services Digital Network (BISDN) standard.

Today, in most instances, separate networks are used to carry voice, data and video. The different networks are used because these traffic types have very different characteristics. ATM is the only standards based technology which has been designed from the beginning to accommodate the simultaneous transmission of these different types of information: data, voice and video.

Basically ATM is a switched technology, instead using a shared bus. The switched data transfer has several benefits: dedicated access speeds, dedicated bandwith per connection and well defined connection procedures.
The goal of ATM is one international standard for transmitting data. ATM can be used as the basis for both LAN and WAN technologies. ATM coexists with current LAN/WAN Technology. ATM has a layered architecture.

How it works:
In the network the sender needs to negotiate a so-called 'requested path' for a connection to the chosen destination. The sender specifies the type, speed and all necessary attributes of the connection, which determine the end-to-end quality of the service.

The sent information is segmented into cells with a fixed length of 53 bytes. This packet switching technology breaks down messages into fixed-length pieces called cells and sent through a network individually. After sending the cells to the destination, the data is re-assembled. The cell consists of the header (5 bytes) and the payload (48 bytes), which carries the actual information (voice, data or video).

ATM lines are available in various multi-megabit speeds. An ATM network is made up of ATM switches and ATM endpoints. The switch accepts the incoming cell from an ATM endpoint or another ATM switch, it then reads and updates the header of the cell and switches the cell to another switch or an output interface toward its destination.