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A Look at Solid State Interlocking
The
question is however how much we need to tell to the operating system from the
application software. It is like a difference between a
computer programmed to generate a single print statement
and one which can print a page as chosen from among a set of pages or a
case where one prints anything what is typed by the user of the computer. A
computer required to print a single print statement need not have any control
from the application program and everything can be in the operating system.
While flexibility requires that a part resides in the application program.
It is
this business of identifying how much we leave to operating system and how much
to application in the case of signaling that is yet to be rationalized. At one
end we have like the logic input equipments which makes the operating system
concept irrelevant on the other end of the spectrum we have systems which puts
in so much of rules inbuilt in the operating system that even a layout of the
yard is sufficient to make the system work. In the latter system if the rules of
operating the trains are different the interlocking system will not be
operationally applicable for the case.
The
problem therefore boils down to identifying how much is fundamental and how much
can be left free. No track shall be occupied by two trains is a fundamental requirement
but how do we bring a train for
shunting purposes? Hence some rules which is very fundamental has some
conditions under which it has to be changed. Similarly is how much overlap is
sufficient. This varies from system to system and on occasions where the train
is operated.
