RedGrittyBrick wrote:
> Unruh wrote:
>
>> "David J Taylor"
>> writes:
>>
>>
>>> At source, it's recently been within about 10 microseconds:
>>>
>> Sorry, at 10usec, the distance away of the transmitter must be less than 3
>> km.
>>
>
> At *source*, the distance to the transmi
David J Taylor wrote:
> "David J Taylor"
> wrote in
> message news:%xqgm.126$ym4...@text.news.virginmedia.com...
>
>> "Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps82...
>> []
>>
>>> Note that chrony will give you a factor of 2 or three improvement over
>>> ntp in the err
John Hasler wrote:
> Bill Unruh writes:
>> The bandwidth of whatever marks it has to be pretty narrow, or the
>> transmitter would interfer with everything around it. Ie, that means a
>> large time uncertainty.
>
> The 60KHz WWVB signal is synchronously amplitude-modulated at a 1Hz
> rate. The ex
David Woolley writes:
>David Malone wrote:
>> The Rugby unit was built by Ian Dowse, and is described here:
>>
>> http://www.maths.tcd.ie/~dwmalone/time/rugby.html
>>
>This is a simple AM detector for the slow code (I don't know if the fast
>code is still transmitted). It doesn't phase
"Unruh" wrote in message
news:fgmhm.50325$db2.6...@edtnps83...
[]
> This is of course all made totally redundant by the GPS time delivery--
> even makes up for the transmission delay. It begins to look like like
> Morse code in the days of cell phones. Quaint, but not really useful.
"Not really
Unruh wrote:
> John Hasler writes:
>
>
>> The 60KHz WWVB signal is synchronously amplitude-modulated at a 1Hz
>> rate. The exact cycle on which the amplitude changes can be locked in
>> by a digital phase-locked loop. A VCXO can be phase-locked to the
>> carrier to within a small fracti
Bill Unruh writes:
> This is of course all made totally redundant by the GPS time
> delivery-- even makes up for the transmission delay. It begins to look
> like like Morse code in the days of cell phones. Quaint, but not
> really useful.
One could say the same about NTP.
--
John Hasler
jhas...@
John Hasler writes:
>Bill Unruh writes:
>> The bandwidth of whatever marks it has to be pretty narrow, or the
>> transmitter would interfer with everything around it. Ie, that means a
>> large time uncertainty.
>The 60KHz WWVB signal is synchronously amplitude-modulated at a 1Hz
>rate. The exac
Bill Unruh writes:
> The bandwidth of whatever marks it has to be pretty narrow, or the
> transmitter would interfer with everything around it. Ie, that means a
> large time uncertainty.
The 60KHz WWVB signal is synchronously amplitude-modulated at a 1Hz
rate. The exact cycle on which the amplitu
"David Woolley" <> wrote in message
news:hcnjt3$bq...@news.eternal-september.org...
[]
> This is a simple AM detector for the slow code (I don't know if the fast
> code is still transmitted). It doesn't phase lock onto the carrier.
The fast code stopped many years ago. October 1998 according t
David Woolley wrote:
> David Malone wrote:
>
>> The Rugby unit was built by Ian Dowse, and is described here:
>>
>> http://www.maths.tcd.ie/~dwmalone/time/rugby.html
>>
>
> This is a simple AM detector for the slow code (I don't know if the fast
> code is still transmitted). It doesn't phas
David Malone wrote:
> The Rugby unit was built by Ian Dowse, and is described here:
>
> http://www.maths.tcd.ie/~dwmalone/time/rugby.html
>
This is a simple AM detector for the slow code (I don't know if the fast
code is still transmitted). It doesn't phase lock onto the carrier.
_
Unruh wrote:
> John Hasler writes:
>
>> Bill Unruh writes:
>>> Sorry, at 10usec, the distance away of the transmitter must be less than 3
>>> km.
>
>> 10usec at the transmitter.
>
>>> Also your system needs to see the start of the tone to 10usec which
>>> means that the tone would have to be
"David J Taylor"
writes:
>Thanks, David, David and Jan. A few milliseconds is what I had expected,
>so if you are on a consumer line, what implications does that have for
>unruh's comment?
I've been plotting the offset reported by "ntpq -p" for my Rugby
receiver and a GPS-based server over D
Unruh wrote:
> "David J Taylor"
> writes:
>
>> At source, it's recently been within about 10 microseconds:
>
> Sorry, at 10usec, the distance away of the transmitter must be less than 3 km.
At *source*, the distance to the transmitter must surely be a lot less
than 3 km :-)
According to the
Maarten Wiltink wrote:
> "Unruh" wrote in message
> news:iebhm.50125$db2.41...@edtnps83...
> [...]
>> The problem is that I have no idea what the accuracy of any of those
>> items is. YOur ISP's timesever may be a stratum 7 getting time from
>> a bunch of bozos. Or itmay be stratum 1 getting its t
Unruh wrote:
> "David J Taylor"
> writes:
>
>> "Unruh" <> wrote in message news:iebhm.50125$db2.41...@edtnps83...
>> []
>>> MSF?
>
>> See:
>>
>> http://www.npl.co.uk/science-technology/time-frequency/time/products-and-services/msf-radio-time-signal
>
>> UK 60KHz radio time signal.
>
> Ah, O
Unruh wrote:
> John Hasler writes:
>> There isn't any tone. It's the UK equivalent of WWVB.
>
> How is the beginning of the second ( an hour) marked?
> The bandwidth of whatever marks it has to be pretty narrow, or the transmitter
> would interfer with everything around it. Ie, that means a large
John Hasler writes:
>Bill Unruh writes:
>> Sorry, at 10usec, the distance away of the transmitter must be less than 3
>> km.
>10usec at the transmitter.
>> Also your system needs to see the start of the tone to 10usec which
>> means that the tone would have to be about 1MHz which is a bit beyo
Bill Unruh writes:
> Sorry, at 10usec, the distance away of the transmitter must be less than 3 km.
10usec at the transmitter.
> Also your system needs to see the start of the tone to 10usec which
> means that the tone would have to be about 1MHz which is a bit beyond
> audio.
There isn't any to
"David J Taylor"
writes:
>"Unruh" <> wrote in message news:vcjhm.50153$db2.9...@edtnps83...
>[]
>>>UK 60KHz radio time signal.
>>
>> Ah, OK. Its accuracy is probably not much better than a few msec I
>> assume.
>> GPS is a few usec. Since the network gives accuracies of better than a
>> few ms
I wrote:
> Should be as good as WWVB, which is good to within 100usec. The
David Woolley writes:
> Most receivers only use the slow code (including the simple hardware
> solutions for ntpd).
I'm assuming a real receiver. With the single-chip designs intended for
"atomic watches" you'll be lucky
John Hasler wrote:
> Should be as good as WWVB, which is good to within 100usec. The
Most receivers only use the slow code (including the simple hardware
solutions for ntpd). For high accuracy you would have to sync to the
carrier, and possibly use the fast time codes.
> propagation delay is
I wrote:
> Should be as good as WWVB, which is good to within 100usec.
But evidently many commercial receivers are only good to a ms or two.
--
John Hasler
jhas...@newsguy.com
Dancing Horse Hill
Elmwood, WI USA
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David J Taylor writes:
> UK 60KHz radio time signal.
Bill Unruh writes:
> Ah, OK. Its accuracy is probably not much better than a few msec I
> assume.
Should be as good as WWVB, which is good to within 100usec. The
propagation delay is highly predictable at 60KHz. These stations can
also can pr
"Unruh" <> wrote in message news:vcjhm.50153$db2.9...@edtnps83...
[]
>>UK 60KHz radio time signal.
>
> Ah, OK. Its accuracy is probably not much better than a few msec I
> assume.
> GPS is a few usec. Since the network gives accuracies of better than a
> few ms, MSF
> is not a good way of testing
"David J Taylor"
writes:
>"Unruh" <> wrote in message news:iebhm.50125$db2.41...@edtnps83...
>[]
>> MSF?
>See:
>
> http://www.npl.co.uk/science-technology/time-frequency/time/products-and-services/msf-radio-time-signal
>UK 60KHz radio time signal.
Ah, OK. Its accuracy is probably not much b
"Unruh" wrote in message
news:iebhm.50125$db2.41...@edtnps83...
[...]
> The problem is that I have no idea what the accuracy of any of those
> items is. YOur ISP's timesever may be a stratum 7 getting time from
> a bunch of bozos. Or itmay be stratum 1 getting its time from a well
> implimented GP
David Lord writes:
>Unruh wrote:
>> David Lord writes:
>>
>>> David J Taylor wrote:
"Unruh" wrote in message
news:qg_gm.50009$db2.46...@edtnps83...
> "David J Taylor"
> writes:
>
>
>> "David J Taylor"
>> wrote in
>> message news:%xqgm.126$ym4...@text.n
David Lord wrote:
> How do you get the time difference between your GPS and system
> time?
Include the GPS in your ntp.conf, but mark it with "noselect" on the server
line.
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"Unruh" <> wrote in message news:iebhm.50125$db2.41...@edtnps83...
[]
> MSF?
See:
http://www.npl.co.uk/science-technology/time-frequency/time/products-and-services/msf-radio-time-signal
UK 60KHz radio time signal.
David
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"Unruh" <> wrote in message news:rl5hm.50089$db2.40...@edtnps83...
[]
> As I tried to emphasise, if the round trip is not symmetric, then
> neither ntp not
> chrony can compensate for that lack of symmetry, and the absolute time
> will be
> out. If occasionally it has an assymetric round trip, t
Unruh wrote:
> David Lord writes:
>
>> David J Taylor wrote:
>>> "Unruh" wrote in message
>>> news:qg_gm.50009$db2.46...@edtnps83...
"David J Taylor"
writes:
> "David J Taylor"
> wrote in
> message news:%xqgm.126$ym4...@text.news.virginmedia.com...
>> "Unr
"David J Taylor"
writes:
>"Unruh" <> wrote in message news:kx%gm.50022$db2.12...@edtnps83...
>[]
>> As I said, chrony does a linear regression on the last n offsets.
>[]
>Bill,
>I think we have seen these remarks about chrony before.
Some have, some have not. I was just putting out there wha
David Lord writes:
>David J Taylor wrote:
>>
>> "Unruh" wrote in message
>> news:qg_gm.50009$db2.46...@edtnps83...
>>> "David J Taylor"
>>> writes:
>>>
>>>
"David J Taylor"
wrote in
message news:%xqgm.126$ym4...@text.news.virginmedia.com...
> "Unruh" <> wrote in message n
David J Taylor wrote:
>
> "Unruh" wrote in message
> news:qg_gm.50009$db2.46...@edtnps83...
>> "David J Taylor"
>> writes:
>>
>>
>>> "David J Taylor"
>>> wrote in
>>> message news:%xqgm.126$ym4...@text.news.virginmedia.com...
"Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps8
David J Taylor writes:
> It's just an impression I had - that consumers get the worst latency
> and most overloaded network equipment...
Perhaps, but it doesn't follow that they suffer a great deal of
asymmetry.
> ...and no direct connection to an ultra-high-speed academic network.
Of course not
"Unruh" <> wrote in message news:kx%gm.50022$db2.12...@edtnps83...
[]
> As I said, chrony does a linear regression on the last n offsets.
[]
Bill,
I think we have seen these remarks about chrony before.
What I was wanting was a yes/no answer (although numbers would be nice) to
the question:
-
> David J Taylor writes:
>> On consumer-grade circuits the assumption about equal round trip is
>> unlikely to be valid.
>
> Why would you expect the asymmetry to be worse there than elsewhere?
> --
> John Hasler
It's just an impression I had - that consumers get the worst latency and
most overl
"David J Taylor"
writes:
>"Unruh" wrote in message
>news:qg_gm.50009$db2.46...@edtnps83...
>> "David J Taylor"
>> writes:
>>
>>
>>>"David J Taylor"
>>> wrote in
>>>message news:%xqgm.126$ym4...@text.news.virginmedia.com...
"Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps82
"Unruh" wrote in message
news:qg_gm.50009$db2.46...@edtnps83...
> "David J Taylor"
> writes:
>
>
>>"David J Taylor"
>> wrote in
>>message news:%xqgm.126$ym4...@text.news.virginmedia.com...
>>> "Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps82...
>>> []
Note that chrony will
David J Taylor writes:
> On consumer-grade circuits the assumption about equal round trip is
> unlikely to be valid.
Why would you expect the asymmetry to be worse there than elsewhere?
--
John Hasler
jhas...@newsguy.com
Dancing Horse Hill
Elmwood, WI USA
___
"David J Taylor"
writes:
>"David J Taylor"
> wrote in
>message news:%xqgm.126$ym4...@text.news.virginmedia.com...
>> "Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps82...
>> []
>>> Note that chrony will give you a factor of 2 or three improvement over
>>> ntp in the errors, assu
David Woolley wrote:
> I suspect most severe asymmetry cases actually happen because the
> downlink is saturated. That's is exacerbated by the fact that it is
> more difficult to get the ISP to prioritise, than to do it yourself.
There is no point to large amounts of buffering in the ISP's edge r
Jan Ceuleers wrote:
> This is however only the best case, because it assumes that the
> uplink is not saturated. If it is, and if you are able to prioritise your
I suspect most severe asymmetry cases actually happen because the
downlink is saturated. That's is exacerbated by the fact that it is
David J Taylor wrote:
>
> "David J Taylor"
> wrote in
> message news:%xqgm.126$ym4...@text.news.virginmedia.com...
>> "Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps82...
>> []
>>> Note that chrony will give you a factor of 2 or three improvement over
>>> ntp in the errors, assum
"David J Taylor"
wrote in
message news:%xqgm.126$ym4...@text.news.virginmedia.com...
> "Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps82...
> []
>> Note that chrony will give you a factor of 2 or three improvement over
>> ntp in the errors, assuming that the roundtrip is equally
David J Taylor wrote:
> For those without wide-bandwidth academic connections - those folks on
> cable or ADSL - how good is an "equal split round trip" assumption?
I calculated this for my case once (3840 kbit/s down and 512 kbit/s up). The
difference in transmission time due only to the differe
David J Taylor wrote:
> "Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps82...
> []
>> Note that chrony will give you a factor of 2 or three improvement over
>> ntp in the errors, assuming that the roundtrip is equally split on
>> Linux or BSD.
>
> For those without wide-bandwidth aca
"David J Taylor"
writes:
>"Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps82...
>[]
>> Note that chrony will give you a factor of 2 or three improvement over
>> ntp in the errors, assuming that the roundtrip is equally split on
>> Linux or BSD.
>For those without wide-bandwidth ac
"Unruh" <> wrote in message news:34jgm.50898$ph1.36...@edtnps82...
[]
> Note that chrony will give you a factor of 2 or three improvement over
> ntp in the errors, assuming that the roundtrip is equally split on
> Linux or BSD.
For those without wide-bandwidth academic connections - those folks o
"Richard B. Gilbert" writes:
>Juyong Do wrote:
>> Hi,
>>
>> Does anyone know any survey or paper measuring absolute time accuracy over
>> NTP? I saw statistics about offsets, RTT, and dispersion but am not sure how
>> well those parameters reflect or are correlated with absolute accuracy of
>
Juyong Do wrote:
> Hi,
>
> Does anyone know any survey or paper measuring absolute time accuracy over
> NTP? I saw statistics about offsets, RTT, and dispersion but am not sure how
> well those parameters reflect or are correlated with absolute accuracy of
> each NTP servers and clients.
>
> T
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