ATM
acronymISP & telecomnetworking
Stands for: Asynchronous Transfer Mode
Asynchronous Transfer Mode - the 1990s bet that all traffic, voice to data, should ride fixed 53-byte cells with hard QoS. Ethernet and IP won instead.
ATM cut everything into 48-byte payloads behind 5-byte headers, switched by VPI/VCI circuit labels, with service classes (CBR, VBR, ABR, UBR) giving telcos the guarantees they trusted. It ran the B-ISDN vision over SONET/SDH at OC-3 and OC-12, carried DSL's back end for years, and dominated carrier cores around the turn of the century. What killed it: the ~10% cell-tax overhead, the complexity of adaptation layers like AAL5 and of pretending to be a LAN, and Ethernet ports that got fast and cheap faster than ATM could. MPLS took the traffic-engineering ideas and left the cells behind.
ATM carried everything in fixed 53-byte cells, a size chosen by committee compromise between voice and data requirements, and it promised deterministic quality of service that IP could not offer. For a period in the 1990s it was widely expected to become the universal network layer.
It lost, and the reasons are instructive. The cell tax, five bytes of header per forty-eight of payload, wasted around ten percent of capacity, the equipment was expensive, and running IP over it required an adaptation layer that added complexity to the thing everyone actually wanted to use. Ethernet got faster and cheaper on a curve ATM could not match, which is the same story as DECnet and Token Ring: good enough and open beat better and closed.
Also known as: atm, asynchronous transfer mode, cell relay, aal5, vpi/vci