X.25

x.25 is an ITU-T standard protocol suite for the DTE-DCE interface in a packet switched network, approved by ISO. It defines standard physical layer, data link layer and network layers (layers 1 through 3) of the OSI model. It was developed to describe how data passes into and out of public data communications networks. It is connection oriented[?] and has rigorous error correction.

X.25 networks are still in use throughout the world although in decline, being largely supplanted by newer layer 2 technologies such as Frame relay, ISDN and ATM and the ubiquitous layer 3 Internet Protocol.

Document: ISO 8208.

based on FOLDOC