Asynchronous Transfer Mode, or ATM, is a computer network technology that transfers data in cells or packets of a fixed size of 53 bytes. Cells with the same source, destination and class of service follow the identical path. If a given path does not meet performance criteria, the packets are rerouted to a pre-determined secondary route.
ATM equipment takes advantage of its standardized cell size to transmit video, audio and computer data over the same network. ATM is connection-oriented, meaning a sender and receiver set up a fixed path on a network before transmitting data, and data is received in the order it is sent. Other transfer protocols, such as TCP/IP, do not have fixed connections or routes, so data packets may go to different destinations, be delayed or arrive out of order.
The orderly transfer of data gives Asynchronous Transfer Mode an advantage over other transfer protocols for real-time communication, such as audio and video. On an ATM network, real-time data takes precedence over other data. If a sender transmits voice and e-mail traffic simultaneously, for example, the voice traffic packets are relayed before those of the e-mail. If the path is optimized, voice transmission will equal telephone quality, and video transmission will be indistinguishable from cable television.