2.3.6 ATM

2.3.6 ATM
ATM, Asynchronous Transfer Mode, is a high-bandwidth switching technology developed by the ITU Telecommunications Standards Sector (ITU-TSS). ATM uses 53-byte cells for all transmissions. Because ATM cells are uniform in length, switching mechanisms can operate with a high level of efficiency. This high efficiency results in high data-transfer rates. Some ATM systems can operate at 622Mbps; a typical working speed for an ATM, however, is around 155Mbps.
The unit of transmission for ATM is called a cell. All cells are 53 bytes long and consist of a 5-byte header and 48 bytes of data. The "Asynchronous" aspect refers to the fact that transmission time slots don't occur periodically but are granted at irregular intervals. Traffic that is time-critical, such as voice or video, can be given priority over data traffic that can be delayed slightly with no ill effect. Devices communicate on ATM networks by establishing a virtual path, within which virtual circuits can be established.