
The hardware algorithm behind the security in Stockholm's subway - stkhlm
http://www.google.com/translate?hl=en&ie=UTF8&sl=auto&tl=en&u=http%3A%2F%2Ftechworld.idg.se%2F2.2524%2F1.253031%2Fsa-fungerar-tunnelbanans-sakerhetssystem
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parley
I will confess to not reading the entire article (neither in Swedish nor
"Engswish" ) so I might be mistaken, but if anyone is wondering why the word
"security" is used when "safety" probably would be better suited, it is
probably because they are commonly described using the same word in Swedish
("säkerhet").

It often gets as Lost in Translation as Bill Murray in a big, strange city.
Also, it complicates many discussions between Swedes too because of the
ambiguity and the fact that people seldom add qualifications to indicate which
is intented.

Edit: Grammar.

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stkhlm
Actually I'm danish, but the exact same problem applies. My bad :)

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parley
No worries, I was actually referring to the automagically translated article.
:)

Google can't really know which is which, so the article seems to use a mix of
both english words in different places, which ends up being a little
confusing/inconsistent.

Security is one of my interests and I work with people who have been in the
safety industry, so sometimes we have our little linguistic bouts. :)

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phreeza
The google translation of that is in some kind of uncanny valley.

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tcas
If you're curious how subways signaling/safety mechanisms operate, the
nycsubway site[1] has a pretty good rundown on NYC's procedures, and its
original language is English as well. It basically is a large ad-hoc system (+
some remote control) with lots failsafes.

[1]
[http://www.nycsubway.org/wiki/Subway_Signals:_A_Complete_Gui...](http://www.nycsubway.org/wiki/Subway_Signals:_A_Complete_Guide)

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gvr
My understanding is that one of the reasons that relays are still used for
many these systems is that the latency for going into a safe state is very
low, and that they are easier to verify than so called solid-state
interlocking systems.

A relay-based system like this might look simplistic and archaic to a casual
observer but it's quite complex and there's no room for error. Formal proof
(static analysis) is often used to verify both the formal specification that
dictates what constitutes a safe system state, and the actual system's
compliance with this specification.

There's a Swedish company called Prover specialized in this. I used to work
there and moved to SF when we set up our US subsidiary.

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leoedin
The ingenuity of early computers is fascinating! The progress we've made since
then is quite amazing - a system that fills a room and would have taken some
very complicated design work could be replaced today by a microcontroller. I'd
imagine the reliability of that many relays is a bit limited.

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myself248
If you replaced the logic with a microcontroller, you'd still need a room full
of input and output modules to send those signals hither and yon. You don't
just toss a floppy-drive cable down a 14-mile tunnel, not if you expect it to
work after lightning strikes somewhere in the city.

The whole telephone network used to work this way, and actually many of those
relays (and even the mounting frames) look identical to their telephone
counterparts. And of course those were derived from the telegraph network,
which is where all this stuff was invented. Send simple signals very long
distances, very reliably.

As telephones got into automated switching with relay-based logic, complexity
dictated that the systems be able to diagnose themselves to some degree. It's
cost-effective for fully half the machine to simply monitor and isolate
trouble in the other half, as that increases reliability and serviceability to
the point where a large system can still work.

Even today with solid-state everything, the individual parts are more reliable
than relays or vacuum tubes, but there are more of them, and there's always
pressure to cut down on the manpower required to maintain the whole thing, so
self-monitoring and fault tolerance is as important as ever.

Reliable system design is almost never synonymous with newest-and-fastest-and-
smallest. It means well-understood technology with well-understood failure
modes, airtight logic to control fail-over and fault isolation, and the
hardiest components you can find for the given environment. In tunnels with
cables running along electrified track, spanning city-scale distances with a
whole power grid and weather and stuff happening in parallel, relays are still
a sane choice.

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raphman
Interesting 28C3 talk about German railway safety mechanisms (for people
understanding German): "Can trains be hacked? Die Technik der
Eisenbahnsicherungsanlagen" [1]

[1]
[http://www.youtube.com/watch?v=xwaKYZfgY8k](http://www.youtube.com/watch?v=xwaKYZfgY8k)

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adamgray
Older elevators operate in a similar way - all logic handled by racks of
relays. It's really interesting stuff.

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cfontes
Well, I work with train scheduling and planning software.

If they call me, I promise they will get a new room for a pool table.

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Create
works within specs unless clean?

[http://www.bbc.co.uk/news/world-
europe-21030211](http://www.bbc.co.uk/news/world-europe-21030211)

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tallanvor
I'm pretty sure the commuter trains are a completely separate system from the
subway and have quite different control systems since they operate over longer
distances.

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lessnonymous
Sounds interesting, but .. anyone got a real translation?

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bjrnjs
Unfortunately his swedish isn't as good as it should be, so I wouldn't only
blame Google Translation in this case... Some weird sentencing (in swedish)
that probably makes Google scratch its tin head.

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hedwall
Oldie but goldie, Städje really interesting pieces.

