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

From: Beat Bolli
Subject: Re: [gpsd-dev] Clarifications needed for the time-service HOWTO
Date: Wed, 23 Oct 2013 20:48:02 +0200
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On 22.10.13 04:10, Gary E. Miller wrote:
> 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 just wanted to note that I took the ntpq -p output that got merged
into the tuning HOWTO right at the moment when I wrote the patch and was
not edited in any way. I have a consumer cable setup with 30Mbps upload
and 3 Mbps download, so quite asymmetric.

The servers with the worst jitter are: - my ISP's. Strange because it's just three hops away.
Maybe hosts other services and is under a lot of load. - in a different country and 15 hops away, so
probably network related. - the NTP server of ETH Zurich, one of the two federal
research institutes in Switzerland. Probably half of Switzerland is
synchronizing with this server :-)

mail: echo '<address@hidden>' | tr -d '[A-S]'
pgp: 0x506A903A; 49D5 794A EA77 F907 764F  D89E 304B 93CF 506A 903A
icbm: 47.0452 N, 7.2715 E

"It takes love over gold, and mind over matter" -- Dire Straits

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