X.25
Oldest packet switched service
A standard developed by ITU-T
Offers SVC and PVC services
Uses LAPB and PLP protocols at the data link and network layers, respectively
- Requires protocol translations at PADs (for those users who use different protocols at their LANs)
A reliable protocol (it performs error control and retransmits bad packets)
Not in widespread use in North America
- Low data rates (64 Kbps) (available now at 2.048 Mbps)