Re: [time-nuts] new year crashes
tractorb@ihug.co.nz said:
The 'landline' networks also have significant (and variable) latency. ISTR
measuring a maximum of around 400/500 mSec some years ago on a WN-CH digital
link. Minimum over the test period of a week was nearer 250 mSec a few days
later.
How can they get a delay that long? Satellite link?
Fiber is 5 microseconds per km. So 1000 km is 5 ms.
--
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You mean the Dominion observatory surely not Carter. It was close by and also had a Danjon Astrolabe.
Bruce
On Tuesday, 3 January 2017 12:10 AM, Hal Murray <hmurray@megapathdsl.net> wrote:
tractorb@ihug.co.nz said:
The 'landline' networks also have significant (and variable) latency. ISTR
measuring a maximum of around 400/500 mSec some years ago on a WN-CH digital
link. Minimum over the test period of a week was nearer 250 mSec a few days
later.
How can they get a delay that long? Satellite link?
Fiber is 5 microseconds per km. So 1000 km is 5 ms.
--
These are my opinions. I hate spam.
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In my prior experience (from approx 5 to 20 years ago) actual wide area net work links delivered over fiber from commercial providers could have latencies of at least several times those figures. I seem to recall efforts were made to lower latencies for applications such as stock trading but I never had any exposure to those connections.
Best regards
Mark Spencer
How can they get a delay that long? Satellite link?
Fiber is 5 microseconds per km. So 1000 km is 5 ms.
--
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It's not the fibre-it's the equipment on the end of it-specifically the multiplex equipment. And with path switching where differing eqpt was used on different links..... you can guess the result!
Different technologies these days but the terminal eqpts, (where your packets are injected/extracted to/from all the rest) collectively are the major contributors to end-to-end latency and its 'variablilty'.
DaveB, NZ
-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of Hal Murray
Sent: Monday, 2 January 2017 11:48 p.m.
To: Discussion of precise time and frequency measurement
Cc: hmurray@megapathdsl.net
Subject: Re: [time-nuts] new year crashes
tractorb@ihug.co.nz said:
The 'landline' networks also have significant (and variable) latency.
ISTR measuring a maximum of around 400/500 mSec some years ago on a
WN-CH digital link. Minimum over the test period of a week was nearer 250 mSec a few days
later.
How can they get a delay that long? Satellite link?
Fiber is 5 microseconds per km. So 1000 km is 5 ms.
--
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Apologies Bruce,
It is a good many years since I was there last.
Cheers,
Will
On 01/03/2017 12:40 AM, Bruce Griffiths wrote:
You mean the Dominion observatory surely not Carter. It was close by and also had a Danjon Astrolabe.
Bruce
Carter did have a couple of small historic brass transit instruments which were never used by them.They also used to have a spectroheliograph which was used. Its long since been dismantled.Ther was also a lunar camera complete with alodined aluminium plate.
Bruce
On Tuesday, 3 January 2017 10:35 AM, Will Kimber <zl1tao@gmx.com> wrote:
Apologies Bruce,
It is a good many years since I was there last.
Cheers,
Will
On 01/03/2017 12:40 AM, Bruce Griffiths wrote:
You mean the Dominion observatory surely not Carter. It was close by and also had a Danjon Astrolabe.
Bruce
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Make that a dual rate moon camera.These were used to measure variations in Earth's rotation period.
Bruce
On Tuesday, 3 January 2017 11:10 AM, Bruce Griffiths <bruce.griffiths@xtra.co.nz> wrote:
Carter did have a couple of small historic brass transit instruments which were never used by them.They also used to have a spectroheliograph which was used. Its long since been dismantled.Ther was also a lunar camera complete with alodined aluminium plate.
Bruce
On Tuesday, 3 January 2017 10:35 AM, Will Kimber zl1tao@gmx.com wrote:
Apologies Bruce,
It is a good many years since I was there last.
Cheers,
Will
On 01/03/2017 12:40 AM, Bruce Griffiths wrote:
You mean the Dominion observatory surely not Carter. It was close by and also had a Danjon Astrolabe.
Bruce
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The number for the fiber is accurate.
However, fiber isn't laid straight path. I add at least 40% as a
precaution, as if laid on the sides of a square, where the original path
is the diagonal. This is however a very conservative measure to real world.
However, equipment delays can be much larger, and if you now have
buffers they can cause much much higher delays. How well the network is
managed controls the additional delay and it's variations.
You milage may vary, indeed.
These are among the things I need to know after half a bottle of wine.
Cheers,
Magnus
On 01/02/2017 05:58 PM, Mark Spencer wrote:
In my prior experience (from approx 5 to 20 years ago) actual wide area net work links delivered over fiber from commercial providers could have latencies of at least several times those figures. I seem to recall efforts were made to lower latencies for applications such as stock trading but I never had any exposure to those connections.
Best regards
Mark Spencer
How can they get a delay that long? Satellite link?
Fiber is 5 microseconds per km. So 1000 km is 5 ms.
--
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