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Asynchronous Transfer Mode is a telecommunications standard defined by ANSI and ITU-T for digital transmission of multiple types of traffic. ATM was developed to meet the needs of the Broadband Integrated Services Digital Network as defined in the late 1980s, and designed to integrate telecommunication networks. It can handle both traditional high-throughput data traffic and real-time, low-latency content such as telephony and video. ATM provides functionality that uses features of circuit switching and packet switching networks by using asynchronous time-division multiplexing.
In the OSI reference model data link layer , the basic transfer units are called frames. In ATM these frames are of a fixed length called cells. This differs from approaches such as IP or Ethernet that use variable-sized packets or frames. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the data exchange begins. These virtual circuits may be either permanent , or switched.