Asynchronous Transfer Mode

Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by the American National Standards Institute and ITU-T (formerly CCITT) 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,[1] and designed to integrate telecommunication networks. It can handle both traditional high-throughput data traffic and real-time, low-latency content such as telephony (voice) and video.[2][3] ATM provides functionality that uses features of circuit switching and packet switching networks by using asynchronous time-division multiplexing.[4][5]

In the OSI reference model data link layer (layer 2), the basic transfer units are called frames. In ATM these frames are of a fixed length (53 octets) called cells. This differs from approaches such as Internet Protocol (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.[5] These virtual circuits may be either permanent (dedicated connections that are usually preconfigured by the service provider), or switched (set up on a per-call basis using signaling and disconnected when the call is terminated).

The ATM network reference model approximately maps to the three lowest layers of the OSI model: physical layer, data link layer, and network layer.[6] ATM is a core protocol used in the synchronous optical networking and synchronous digital hierarchy (SONET/SDH) backbone of the public switched telephone network and in the Integrated Services Digital Network (ISDN) but has largely been superseded in favor of next-generation networks based on IP technology. Wireless and mobile ATM never established a significant foothold.