Railway Telecommunications and Supervisory Systems
Telecommunications and supervisory systems cover how the railway talks and observes: train radio, transmission, and SCADA. The exam tests coverage, redundancy, protocols, and the boundary between operational and safety systems.
Core rules
- GSM-R provides narrowband voice and data, group calls, and emergency calls; FRMCS is its successor. Train radio coverage must be engineered for tunnels, cuttings, and handover.
- Transmission uses SDH, MPLS-TP, or carrier Ethernet with protected rings. Control centres depend on redundant paths and time synchronization.
- SCADA uses RTUs and master stations; IEC 60870-5-104 and DNP3 are common. SCADA monitors and controls traction power, but it is not the signaling interlocking.
- Cybersecurity uses zones and conduits; remote access must be authenticated and logged.
Worked example
A SCADA master polls 150 RTUs every 2 s, with 80 bytes per poll and 8 bits per byte. Traffic = 150 × 80 × 8 / 2 = 48,000 bit/s = 48 kbit/s before protocol overhead. A 64 kbit/s link leaves little margin after overhead, so a 128 kbit/s or larger protected path is prudent. The calculation ignores retries, which raise the requirement.
Traps
- Treating GSM-R as broadband or as a replacement for signaling.
- Sizing SCADA links on payload only and ignoring overhead.
- Assuming one fiber path is redundant.
- Confusing SCADA control with fail-safe interlocking.