Wayside Status Message (WSM)
In Positive Train Control, a Wayside Status Message (WSM) is a message broadcast by a wayside interface unit reporting the state of signals and switches to approaching trains. Gaps in WSM reception indicate lost radio coverage or equipment faults and can force trains to slow or stop.
How it works
Each wayside interface unit (WIU) monitors the signals, switches and other devices at its location and periodically broadcasts their status over the PTC radio network. A train approaching the location must receive a current WSM to know whether the route ahead is safe; the onboard system validates the message's freshness and integrity before using it.
If a valid WSM is not received in time, PTC treats the wayside device as being in its most restrictive state and enforces a stop or speed restriction.
Why it matters for security
WSM gaps directly translate into operational restrictions and delays, and they may stem from radio interference, equipment failure or deliberate disruption. Tracking WSM reception across a network highlights where the PTC system is fragile and provides an operational signal that can be correlated with security events.
Related solution
PTC system protection for freight rail
Tracking wayside status coverage and anomalies across the PTC network.
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