X.25¶

X.25 is a packet switched technology that falls within the domain of PSPSDN (Packet Switched Public Data Network). Contrary to the circuit-switched telephony network, it is based on packet switching technology. It was the first major vendor-independent / interoperable standard for such networks.

Interestingly, despite X.25 being packet switched, it has the notion of establishing "calls" over it, and packets are exchanged between the two ends after a conenction setup. Think in terms of of TCP having a connection abstraction over the packet switched IP network.

The advantages of X.25 compared to using modems in the PSTN / telephony network were mainly:

• the modems were used only on the last mile to the next digital switch / central office, and not end-to-end, rendering higher line quality and hence higher data rates than possible over long/bad analog lines
• billing was usually done based on traffic, not on duration of a call/session

FIXME: more background information. Diagrams.

Community X.25 networks¶

Telebahn / x25.org¶

• https://x25.org/
• https://groups.io/g/x25

BAN AI Systems¶

• https://ban.ai/x25/
• https://github.com/orgs/BAN-AI-X25/repositories