albertson.ch...@gmail.com said:
Even with a very minimal local Ethernet where the path is the same for every
packet you still have variable timing. There are queues and buffers. Also
it is not so easy to measure the time a network packet arrives at a
computer.
The serial port is the best
Le 20/02/2012 07:18, Bill Woodcock a écrit :
Murphy says we won't. Bell curve, again. A very few will have good symmetric
paths to Stratum-1 servers, most will have mediocre asymmetric paths, and some
will have nothing usable at all.
Are you targeting homes, offices, or machine rooms?
The
Hi Bill,
what about White Rabbit?
http://www.ohwr.org/projects/white-rabbit/wiki/Description
Successor of NTP.. PTP: precision time protocol.
It delivers Gigabit Ethernet and precise (1nsec) timing over singlemode
fiber. You would have to connect all devices into a fiber network
instead of a
On 2/20/12 8:34 AM, Achim Vollhardt wrote:
Hi Bill,
what about White Rabbit?
http://www.ohwr.org/projects/white-rabbit/wiki/Description
Successor of NTP.. PTP: precision time protocol.
It delivers Gigabit Ethernet and precise (1nsec) timing over singlemode
fiber. You would have to connect all
Hi
Simple answer:
A rack mount cesium standard is as good as you can get. Figure on 15 ns per day
of drift. That gets you to 15 us in 1000 days. You may or may not get one that
drifts that little, a lot depends on little details. For 3 years, consider
an ensemble of cesiums. At $50K each
On 2/20/12 10:31 AM, Bob Camp wrote:
Hi
Simple answer:
A rack mount cesium standard is as good as you can get. Figure on 15 ns per day of
drift. That gets you to 15 us in 1000 days. You may or may not get one that drifts
that little, a lot depends on little details. For 3 years, consider
@febo.com
Subject: Re: [time-nuts] Low-long-term-drift clock for board level
integration?
On 2/20/12 10:31 AM, Bob Camp wrote:
Hi
Simple answer:
A rack mount cesium standard is as good as you can get. Figure on 15 ns
per day of drift. That gets you to 15 us in 1000 days. You may or may not
get
On Mon, Feb 20, 2012 at 12:15 AM, mike cook michael.c...@sfr.fr wrote:
Le 20/02/2012 07:18, Bill Woodcock a écrit :
Murphy says we won't. Bell curve, again. A very few will have good
symmetric paths to Stratum-1 servers, most will have mediocre asymmetric
paths, and some will have nothing
Hi Bill:
When the TRANSIT navigation satellites were put in orbit the receivers required Cesium clocks. The system worked but
was very expensive.
The GPS system was designed so that cheap clocks could be used in the receiver. This requires getting a lock on 4
satellites instead of the 3 that
You may be able to do a similar thing in your receivers. For example if the
master node were to send a timing message at known times (say once at the
top of every hour) the receivers could use that to determine their local
clock offset and rate for those cases where the path was the same
Think trying to measure the distance between two distant moving spacecraft
with no idea what the gravitational gradient is between them or the ability
to measure the doppler.
Unless, of course, Bill is doing much different things than he was when I
last ran into him. :)
On Mon, Feb 20, 2012 at
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On Feb 20, 2012, at 8:34 AM, Achim Vollhardt wrote:
what about White Rabbit?
It delivers Gigabit Ethernet and precise (1nsec) timing over singlemode
fiber.
Ahah, but if I had singlemode fiber between locations all over the world, I
wouldn't
Hi
Since the network is being measured, I suspect that using it as the time
reference would present a basic problem.
Bob
On Feb 20, 2012, at 2:07 PM, Jim Lux jim...@earthlink.net wrote:
On 2/20/12 10:31 AM, Bob Camp wrote:
Hi
Simple answer:
A rack mount cesium standard is as good as
Hi Bob:
It was my understanding that the receiving station knows the path taken, is that the case? Or are you saying even when
it's the same path the time delay has large variations?
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html
Bob
The path is variable. Internet routing is constantly in flux as routes are
injected and retracted.
On Feb 20, 2012, at 19:56, Brooke Clarke bro...@pacific.net wrote:
Hi Bob:
It was my understanding that the receiving station knows the path taken, is
that the case? Or are you saying
bro...@pacific.net said:
It was my understanding that the receiving station knows the path taken, is
that the case? Or are you saying even when it's the same path the time
delay has large variations?
Even if the path is stable, the delays vary due to queuing delays in routers.
The simple
On Mon, Feb 20, 2012 at 12:13 PM, Brooke Clarke bro...@pacific.net wrote:
You may be able to do a similar thing in your receivers. For example if the
master node were to send a timing message at known times (say once at the
top of every hour) the receivers could use that to determine their
Even if the path is mapped the ques in the switches can change. Say your
packet is first and the next trip its the 50th. Just depends on the overall
network loading.
This has been tried many times and there is the ability to get a feel on
the timing. But not like GPS.
Regards
Paul.
WB8TSL
On Mon,
Hi
My understanding is that the path delay is what is being monitored.
Bob
On Feb 20, 2012, at 7:56 PM, Brooke Clarke bro...@pacific.net wrote:
Hi Bob:
It was my understanding that the receiving station knows the path taken, is
that the case? Or are you saying even when it's the same
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On Feb 20, 2012, at 11:07 AM, Jim Lux wrote:
One question about the 100 microsecond spec.. is that a worst case at any
instant, or is it an average spec over a day (so a consistent diurnal
variation would cancel out)
Well, it's not a hard
Even with a very minimal local Ethernet where the path is the same for
every packet you still have variable timing. There are queues and
buffers. Also it is not so easy to measure the time a network packet
arrives at a computer.
The serial port is the best hardware for timing. The DCD pin is
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Hi. This is my first posting to this list, and I'm not a timekeeping engineer,
so my apologies in advance for my ignorance in this area.
I'm building a small device to do one-way delay measurements through network.
Once I'm done with
What you are looking for is the Caesium standard on a chip that
is presently only available for mostly military projects. This
will become available as war surplus after WW III.
But if you are going to correct it with NTP, a simple crystal
oscillator will do. If you're using NTP, why do you need
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On Feb 19, 2012, at 5:07 PM, Bill Hawkins wrote:
If you are going to correct it with NTP, a simple crystal
oscillator will do.
Yeah, my assumption was that something like a DOCXO or a VCTCXO would be about
the best I'd get within budget. But
On 19 Feb, 2012, at 15:56 , Bill Woodcock wrote:
Hi. This is my first posting to this list, and I'm not a timekeeping
engineer, so my apologies in advance for my ignorance in this area.
I'm building a small device to do one-way delay measurements through network.
Once I'm done with
On Sun, Feb 19, 2012 at 3:56 PM, Bill Woodcock wo...@pch.net wrote:
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Hi. This is my first posting to this list, and I'm not a timekeeping
engineer, so my apologies in advance for my ignorance in this area.
I'm building a small device to do
Hello Bill,
this is potentially possible with the small M9108 or the Jackson Labs
Technologies GPSTCXO.
Some caveats:
1) The Trimble Resolution-T May work, but the above stated units have a 50
channel WAAS/EGNOS/MSAS GPS receiver and are also GPS Disciplined
Oscillators not just timing
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On Feb 19, 2012, at 7:28 PM, Dennis Ferguson wrote:
10, or even 100, microseconds is tough with NTP. I don't think it is
impossible, but it
requires a good, reliable network connection…
We will have a very large mesh of devices, but the
On Sun, Feb 19, 2012 at 5:48 PM, Bill Woodcock wo...@pch.net wrote:
..
So that's something I've been having a hard time understanding… If that's
the amount of inaccuracy _per oscillation_, then at the time-scales I'm
dealing with, it would quickly accumulate and become unuseful…
I think you
... but then they get taken indoors and plugged into the network, and
probably never get a clear view of a GPS or GLONASS satellite again.
A high-sensitivity GPS receiver might still give useful results here,
especially if it has a high-quality reference oscillator like an OCXO.
Even 20 or 30
From that point forward (and we hope the devices will have an operational
life of at least ten years) they'll be dependent on their internal clock and
NTP, but we really need them to stay synchronized to within 100
microseconds. 10 microseconds would be ideal, but 100 would be acceptable.
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On Feb 19, 2012, at 9:02 PM, saidj...@aol.com wrote:
this is potentially possible with the small M9108
or the Jackson Labs Technologies GPSTCXO.
Thanks for the pointer to both of them… It looks like Jackson Labs have
several interesting
On 19 Feb, 2012, at 21:08 , Bill Woodcock wrote:
It's my assumption that some of them will be able to get enough GPS signal
(or GPS via a GSM BTS, as we also have a Sierra Wireless GSM chipset onboard)
and would thus be able to act as Stratum 1 servers for the others.
In the US I suspect
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On Feb 19, 2012, at 10:20 PM, Dennis Ferguson wrote:
I think you may find that in many (most?) other
countries the GSM BTS gear has no idea what time it is.
Pretty wide range there… I've certainly seen some pretty crazy time-and-dates
show up
Here is a typical high end OCXO. (It may blow your budget, but we can use it
as an example.)
http://www.mti-milliren.com/ocxo_270_ocxo.html
The typical 5 MHz aging performance is 5E-10
per day and 5E-08 per year.
That's not in the right ballpark.
Here's another way to look at it.
A
Hi Bill,
should have added a disclaimer, I am involved with Jackson Labs Tech..
The Trimble part with oscillator looks interesting, probably an NCO not a
GPSDO I would think. They are as usually not putting any real data in their
specsheets.. The TCXO they are using will determine
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