ATM is a high-speed networking standard designed to support both voice and data communications. ATM can support speeds ATM operates at the data link layer over either fiber or twisted-pair cable.
ATM differs from more common data link technologies like Ethernet in several ways. ATM does not involve routing for example. Hardware devices known as ATM switches establish point-to-point connections between endpoints and data flows directly from source to destination. Instead of using variable-length packets, ATM utilizes fixed-sized cells. ATM cells are 53 bytes in length, that includes 48 bytes of data and 5 bytes of header information.

The performance of ATM is often expressed in the form of OC (Optical Carrier) levels, written as "OC-xxx." Performance levels as high as 10 Gbps (OC-192) are technically feasible with ATM. More common performance levels for ATM are 155 Mbps (OC-3) and 622 Mbps (OC-12).
ATM is designed to support easier bandwidth management. Without routing and with fixed-size cells, one can much more easily monitor and control bandwidth under ATM than under Ethernet, for example. The high cost of ATM relative to Ethernet is one factor that has limited its adoption to "backbone" and other high-performance applications.

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