X.25 Protocol - Definition from the Hotspot Shield Glossary

This protocol is one of the oldest protocols in existence and was primarily used for communication over a Wide Area Network. Back in the 1970’s, X.25 was used to carry voice transmissions over old analogue telephone landlines.

Whilst extremely popular and highly used in the 1970’s and 1980’s, other technologies have now replaced this suite of protocols such as the OSI model (Open System Interconnection).

The X.25 protocol works on several different network layers with each packet of data containing just 128 bytes of information, the protocol also deals with all levels of the transmission from packet assembly, error-checking and disassembly. In modern technology, X.25 has mainly been limited to use in ATM machines and Credit card systems.