ATM
ATM is considered both a WAN and LAN protocol. It is based on frame relay and beginning to replace it because it is faster.
ATM stands for Asynchronous Transfer Mode. ATM supports voice, data, video, audio, and imaging.
It is very fast, currently operating at speeds up to 622 mbps.
ATM is very expensive because it requires special ATM-compatible hardware. It works over T1, fractional T1, T3, and other fiber systems. It can be wired directly to end systems via ATM adapters and hubs.
ATM packets are called cells and have a fixed length (53 bytes) instead of a variable length like frame relay and X.25.