ATM

ISP & 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.

Also known as: atm, asynchronous transfer mode, cell relay, aal5, vpi/vci

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