A popular standard for packet-switching networks. The X.25 standard was approved by the CCITT (now the ITU) in 1976. It defines layers 1, 2, and 3 in the OSI Reference Model.
X.25
Meaning of X.25 in English
DAX English glossary of key connectivity terms. Английский глоссарий основных терминов по коммуникациям DAX. 2012