B) Operator assisted railroad safety (second level of safety)
This level has to provide reduced functionality to the operator.
Similar to SCADA systems, the operator can monitor the status
of the trains and gets only proposals from the computer. But it
is up to the operator to take action when the computer detects
and signals a breach of safety.
All programs at this level have to be written in a different
programming language and be designed and implemented by different
programmers as compared to the programs of the first level. The
process data required to support this second safety level has
also to be acquired differently.
The second security level software is a kind of shadow application.
It is always up and running, collects data in its own way, is
processing this data completely independent from the other software
components and is just waiting to be activated. Activation of
the applications of the second level is done automatically in
case BOTH servers fail to support the first level of safety.
C) Manual operation of railroad (third level of safety)
Two plotters and printers are constantly busy plotting all the
moves of the trains and printing train status, railroad and system
information on paper. In case that all computer systems fail this
is crucial information for the railroad operators. They need those
real-time protocols in order to determine all train locations.
This third level of safety is the last resort and hopefully is
never required, but if it ever is, its present.
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