ATM - A high-speed cell switching network technology for LANs and WANs that handles data and real-time voice and video. It combines the high efficiency of packet switching used in data networks, with the guaranteed bandwidth of circuit switching used in voice networks. It is currently used mostly by large WANS such as telephone companies or as backbones in large LAN installations. It was once thought that ATM would become popular to the desktop but its expense, coupled with tremendous improvements in Ethernet technology took ATM out of the running. ATM is widely implemented by telephone companies in their fiber loops, such as Synchronous Optical Network, ATM provides "bandwidth on demand" so customers can be charged for the amount of data they send rather than fixed-cost digital lines that often go underutilized.