X.25 packet networks
Compatible with the ITU-T X.25 recommendation
A packet switched international network service
Facilitates closed user groups (Virtual Private Network, VPN)
In Finland DataPak (Sonera) and DigiPak (Finnet)
Protocol layers:
- X.25 packet layer protocol
- LAPB (HDLC)
- X.21 (physical layer)
A heavy protocol that does not adapt well to high transmission speeds
Expensive and complex technology
Not well suited for LAN interconnection
Still widely used, especially in Central Europe and military organizations