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Re: [gpsd-dev] Clarifications needed for the time-service HOWTO

From: Eric S. Raymond
Subject: Re: [gpsd-dev] Clarifications needed for the time-service HOWTO
Date: Thu, 24 Oct 2013 08:14:10 -0400
User-agent: Mutt/1.5.21 (2010-09-15)

Gary E. Miller <address@hidden>:
> > > > What sorts of jitter are produced by different parts of the
> > > > delivery chain?  What do typical magnitudes look like?
> > > 
> > > The jitter from NMEA on a local GPS can be a few hundred mSec.  Run
> > > a traceroute to a server and you see how bad you network can be.
> > > Cable modems could be up to 500 mSec (and they are wildly
> > > asymetric).  The jitter from a local GPS s defined by the USB
> > > transfer, around 1 mSec for USB 1.1 The jitter from interrupt
> > > processing can be 100uSec and sometimes much worse on a loaded
> > > system.
> > 
> > I'm not sure how to use those figure for the HOWTO.  Can you
> > recommend a specific way to merge them?
> Maybe we just need a table of typical error sources and magnitudes?  No
> need to get into the specifics.

That sounds like an excellent idea. Please make one.
                <a href="";>Eric S. Raymond</a>

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