In telecommunications, cell relay refers to a method of statistically multiplexing fixed-length packets, i.e. cells, to transport data between computers or kinds of network equipment. It is an unreliable, connection-oriented packet switched data communications protocol. Cell relay transmission rates usually are between 56 kbit/s and several gigabits per second. ATM, a particularly popular form of cell relay, is most commonly used for home DSL connections, which often runs between 128 kbit/s and 1.544 Mbit/s (DS1), and for high-speed backbone connections (OC-3 and faster). Cell relay protocols have neither flow control nor error correction capability, are information-content independent, and correspond only to layers one and two of the OSI Reference Model. Cell relay systems enclose variable-length user packets in fixed-length packets, i.e. cells, that add addressing and verification information. Frame length is fixed in hardware, based on time delay and user packet-length considerations. One user data message may be segmented over many cells. Cell relay is an implementation of fast packet-switching technology that is used in connection-oriented broadband integrated services digital networks (B-ISDN, and its better-known supporting technology ATM) and connectionless IEEE 802.6 switched multi-megabit data service (SMDS). Cell relay is used for time-sensitive traffic such as voice and video.
