[Thumbgps-devel] Project clarification

[Dave Taht]

On Tue, Mar 13, 2012 at 6:28 PM, Ron Frazier (NTP)
<timekeepingntplist at c3energy.com> wrote:
> On 3/13/2012 9:10 PM, Dave Taht wrote:
>>
>> On Tue, Mar 13, 2012 at 4:06 PM, Eric S. Raymond<esr at thyrsus.com>  wrote:
>>
>>>
>>> Mike Hord<mike.hord at sparkfun.com>:

> I'd like to get a further minor clarification on the project goal.  Do you
> want your time reading to be within plus or minus 1 ms of UTC, for a total
> range of 2 ms?  Or do you want it to be within plus or minus 500 us of UTC,
> for a total range of 1 ms?

Heh. Good question.

As good as it is possible to get without having to have rubidium
clocks embedded in the stick?

Better than 10ms is desirable, and the 1ms is something of an
arbitrary goal. Nyquist theorem applies, and then there's slop/noise
elsewhere in the system that will start cropping up (interrupt
latency, etc)

Trying to clearly identify problem hops from multiple sides is
dependent on the 'distance' inherent in the underlying technology. If
we wanted to identify problems on a single 10GigE ethernet segment,
that's measured in *ns*. We don't, thankfully.

First hop out of a router is generally 1ms, same for wireless. Cable
is in the 2ms-8ms range. DSL, up to 60ms, same for wimax...

So < 5ms would be the outside goal, and anything less than that - so
long as it can be thoroughly catagorized - is a bonus.

Continental US distances are 60-100ms...




>
> Sincerely,
>
> Ron
>
>
> --
>
> (PS - If you email me and don't get a quick response, don't be concerned.
> I get about 300 emails per day from alternate energy mailing lists and
> such.  I don't always see new messages very quickly.  If you need a
> reply and have not heard from me in 1 - 2 weeks, send your message again.)
>
> Ron Frazier
> timekeepingdude AT c3energy.com
>
>
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Dave Täht
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