< 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)