Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links. X.25 is a family of protocols that was used especially during the 1980s by telecommunications companies and in financial transaction systems such as automated teller machines.