X.25
More info
- Creator
- CCITT (now ITU-T)
- Released
- 1976
- Type
- Packet-switched network standard
The telcos' packet network before the internet — slow, expensive, and so meticulous about error correction that it worked over terrible lines.
The standard was adopted by CCITT in 1976 and built on virtual circuits: two parties set up a logical channel through the network and packets followed that path. Every hop acknowledged and corrected errors, which cost latency but made the network usable over noisy analogue lines. Public X.25 networks existed in most countries — France's Transpac, Sweden's Datapak, America's Tymnet and Telenet.
In practice it carried all the corporate traffic that must not go wrong: cash machines, card terminals, airline reservation systems and government registers. The internet's model of correcting errors at the endpoints rather than in the network proved cheaper and faster, and X.25 was replaced during the 1990s by Frame Relay and then IP. Isolated installations survived well into the 2000s.