CenturyLink

Mon Dec 31 09:52:47 UTC 2018

There isn't a specific regulation on free-running GPS, just "due diligence". I work at a algorithmic program trading company (and have been for 20 years). We have a high ROI, the cost differential for the rubidium OC versus having to drop everything to conform to regulatory requirements due to a short GPS outage, makes this a no-brainer.

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Matthew Huff             | 1 Manhattanville Rd 
Director of Operations   | Purchase, NY 10577
OTA Management LLC       | Phone: 914-460-4039

-----Original Message-----
From: NANOG [mailto:nanog-bounces at nanog.org] On Behalf Of Saku Ytti
Sent: Monday, December 31, 2018 3:28 AM
To: Gary E. Miller <gem at rellim.com>
Cc: nanog at nanog.org
Subject: Re: CenturyLink

Hey Gary,

On Mon, 31 Dec 2018 at 05:02, Gary E. Miller <gem at rellim.com> wrote:

> The Rb frequency reference will be two or three orders of magnitude 
> more stable than an expensive ovenized crystal.

Perhaps, but not supported by this:
https://www.meinbergglobal.com/english/specs/gpsopt.htm

For the tl;dr folk, crystal drifts +-4.5us per day, Rb +-1.1us (both seem like unsatisfactorily high numbers to me, i.e. you don't want to be free-running 24h with Rb). Luckily today we have GPS, Glonass, BeiDou, Galileo and couple smaller ones, so there should be somewhat reasonable amount of redundancy. Unsure which commercially available NTP or PPP master clocks support all four.

But I of course readily accept Rb is objectively more accurate than crystal, I'm just curious where it matters and I'm curious which regulation applies, who fall under the regulation and what specifically does the regulation require about free-running accuracy.

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  ++ytti