X.25

X.25 is an ITU-T standard protocol suite for connection to packet switched wide area networks using  leased lines, the phone or ISDN system as the networking hardware. It was developed before the OSI Reference Model or the equivalent Network Access Layer of the DoD protocol model, and its functionality does not map precisely to either model. Packet switched network was the common name given to the international collection of X.25 providers, typically the various national telephone companies. Their combined network had large global coverage during the 1980s and into the '90s. X.25 remains in use for certain applications and for some marginal transmission media performance conditions. Its major application is in transaction processing for credit card authorization and for automatic teller machines.
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X-25 may refer to Bensen X-25 experimental aircraftX.25, a protocol suite for wide area networks
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<protocol, standard> An ITU-T standard protocol suite for the DTE-DCE interface in a packet-switched network, approved by ISO. X.25 defines standard physical layer, data link layer and network layers (layers 1 through 3). It was developed to describe how data passes into and out of public data communications networks. X.25 networks are in use throughout the world.
Document: ISO 8208.
Several other ITU-T recommendations are relevant to packet switching: X.3, X.28, X.29, X.75.
(1996-08-10)

X.25