ATM (Asynchronous Transfer Mode)

ATM (Asynchronous Transfer Mode): a high-speed switching service capable of carrying voice, data, video, and multimedia images. ATM is used primarily in frame relay networks, carrier networks and enterprises for private lines. The key advantage of ATM is that it enables providers and end users to carry multiple types of traffic at assigned quality-of-service levels. ATM carries parallel streams of traffic at different levels of service quality over the same circuit. In frame relay networks, carriers deploy multiplatform switches with both frame relay and ATM ports. The switch converts the frames from enterprise sites to ATM cells and transports them through the network. It converts them back to the frame relay format before sending data to the enterprise site to which the frames were addressed.

Because of improvements in IP protocols - in particular, MPLS's (Multi-Protocol Label Switching) capability to "tag" traffic so that voice and video can be prioritized - and the lower cost and easier programming of IP, ATM is becoming displaced by IP equipment. In addition, in carrier networks, IP services achieve higher speeds. On the enterprise side, Gigabit Ethernet and individual wavelengths offer lower-cost options than ATM for end users who need to send large files between sites. However, GigE and individual wavelength services are still not universally available, and wavelength service has distance limitations. (We'll elaborate on these technologies/services in the future.)

ATM is expensive and complex for carriers to install and program. As older equipment is depreciated, carriers will transition to IP with MPLS for voice, data and video traffic.

Source: The Essential Guide to Telecommunications, 4th Edition by Annabel Z. Dodd