[LEAPSECS] Schedule for success

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Dec 21 17:30:30 EST 2008

In message <407EB3F6-55BB-4E60-8D20-C909EA92E6B9 at noao.edu>, Rob Seaman writes:

>Consider the iconic issue of timekeeping for trains, one of the

>primary drivers for our current standard time zone system. Trains

>clearly need to be synchronized with external clocks. Trains clearly

>have some mechanism or set of procedures (imperfect or not) for doing

>so. So they don't match the question asked.

Modern trains run at speeds of roughly 100 m/s. They care very much
about seconds and fractions thereof.

In fact, they run so fast that a special version of the GSM mobile
standard called "GSM-R", has been created for train-control

The main difference between plain GSM and GSM-R is that the latter
allows for dopplershift up to 140 m/s, but now railway people have
started bitching about that not being enough margin.

If you want to know what non-antique rail-road control looks like,
search for and study "ERTMS".


Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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