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laforge, 02/02/2022 09:10 PM


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 /

BAN AI Systems

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Updated by laforge about 2 years ago · 1 revisions

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