SPUG: On clocks, synchronous packets, and trains

Michael R. Wolf MichaelRWolf at att.net
Thu Jun 21 19:23:45 PDT 2007

> I would think that they would have figured out how to meet a schedule 
> after a hundred years or so.

Trains were, in fact, the driver of coordinated time, and chronographs
(expensive watches) were the cutting edge in the high tech of the era.  

Without any other means of communication (i.e. before radios), reliance on
schedules was critical to prevent half-duplex resource contention (i.e. two
trains on the same track in opposite directions).  

The schedules worked only worked if everyone in the system agreed on what
time it was, something that hadn't previously been important.  A conductor's
watch provided the synchronization, and was therefore the high tech gadget
that, along with other SOP's (i.e. error detection and correction
algorithms) prevented collisions.  Up until this time, folks in New York
didn't usually care if their clock towers were in synch with the ones in
Philadelphia or Baltimore.  Once the railroad corridor opened, it was a
matter of life and death.

Another big push toward creating a universal time was the digital telephone
networks.  Timing bits in asynchronous communications represented lost
bandwidth since they were transmitted in-band.  Creating an out-of-band time
reference allowed synchronous communications across long distances (i.e. New
York to Washington) to prevent packet collision.  Not nearly as spectacular
as locomotive collisions, but important, nevertheless!!!

Michael R. Wolf
    All mammals learn by playing!
        MichaelRWolf at att.net

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