Re: [ntp:questions] ntp-dev conflicts with ntp
William Unruh writes: > This is not a problem with ntpd but with Debian There is no ntp-dev package in Debian. The "Conflicts" was put in the ntp-dev package by whoever built it. You can take it out or to use --force-conflicts but you'd better know what you are doing. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Thoughts on KOD
Jason Rabel writes: > I do not know if this is the case with NTP, but quite often it takes > considerable hacking of sources to get code to compile on non-x86 > embedded hardware (i.e. ARM & MIPS)... It would probably help boost > usage if someone was assuring NTP sources compile on those platforms > without the need for modification. Debian already builds ntpd on most hardware including ARM and MIPS. Their patches are available, but I should think that they are already sending them upstream. Contact pkg-ntp-maintain...@lists.alioth.debian.org . -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Thoughts on KOD
I wrote: > Would it be useful to offer an "official" minimal implementation > intended for embedded systems so that these people won't feel the need > to code their own? Maybe add minimal NTP support to Busybox? Brian Inglis writes: > AIUI an updated v4 sntp client will be released to replace ntpdate. > How about specifying the sntp core as an RFC for an embedded NTP > client? That would be even better. Designers could then claim they "have to" use it to be standards compliant. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Thoughts on KOD
Jason writes: > The realization is that many clients don't run the standard NTP > distribution, but rather some old hacked down / self-coded minimal NTP > / SNTP version to run on embedded hardware. Likewise many of the > routers don't even use NTPD code with a constantly running daemon, but > rather more along the lines of ntpdate code that cron triggers at > regular intervals. Would it be useful to offer an "official" minimal implementation intended for embedded systems so that these people won't feel the need to code their own? Maybe add minimal NTP support to Busybox? -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Thoughts on KOD
Danny writes: > You haven't read the code. Any client that ignores the KOD flag will > find (if they ever looked) that their clock will be drifting away > further and further from the proper time. When KOD is set the value of > the received and sent timestamps are the same as the initial client > sent timestamp. It doesn't use the system time for the returned > packet. Calculate what this does to the resulting clock. Yes but the consumer running the router of microwave oven or whatever won't notice so you still won't get rid of them. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP Pool Server Costs me $40/mo in Bandwidth--is
Jochen Bern writes: > Having computer clocks run on UTC(frozen) instead of TAI makes the > adaptation easier today, more difficult tomorrow How? You just start distributing the leap second corrections in the zone files. Much simpler and no more need for flag days. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP Pool Server Costs me $40/mo in Bandwidth--is
Jochen Bern writes: > I don't know of any telecopes, satellite dishes, ... with an aperture > / beam so narrow as to being forced to have the tracking mechanism > based on UT1 instead of UTC, but that doesn't mean that there *are no* > cases where you need a better realtime approximation of UT1 > (preferably *without* setting up your own transit observation gear), > and possibly *still* having UTC as well (say, for logging). Astronomers use TT for logging. I believe that they see such things as variations in the Earth's rotation as systematic errors to be corrected and have a system for distributing the relevant data. They certainly need detailed knowledge of the motion of the Earth but I don't think that they consider it the definition of correct time. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP Pool Server Costs me $40/mo in Bandwidth--is
Miroslav writes: > Do these people work just with UTC? I'd think it's not accurate enough > for their purposes and they need to include the current UTC-UT1 offset > anyway. I believe that astronomers use Terrestrial Time, which is defined in terms of TAI. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP Pool Server Costs me $40/mo in Bandwidth--is
Jochen Bern writes: > If those two restrictions were to be removed (assume a giant tooth > fairy if you must ;-), I don't see a reason why the current UT1-UTC > delta could not be communicated through an "NTP-ng" in the same way > today's NTP shoves server-client deltas around and corrects for them - > piecemeal with every poll. And have UTC jump around as erratically as does the Earth's rotation? Why? Might as well set up a tranit and set your clock by the sun. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Attn Linux distributors - pse include PPS
Paul writes: > I seemed to recall a distro that shipped an ntpd with (effectively) > disable-all-clocks and an ntpd with enable-all-clocks. Debian once offered an ntp-simple package which did not include any refclocks as well as an ntp package which did. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Handle ntp conf modification when ntp is already running
David Woolley writes: > A daemon is generally a session leader. The first TTY it opens will > become its controlling terminal. Not if the terminal is opened with O_NOCTTY. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Reasons of NTP not to use GPS source
David Woolley writes: > How do they meet the requirement for unpowered control lines to appear > to be off? If they are unpowered they will never exceed the positive threshold and therefor will never appear to be on. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Time of by 4 min
greg.wayne.smith writes: > If you look at the website for time.gov it does display the time being > off by 4 min. The time that time.gov shows here matches what I am getting from tock2.usshc.com, ntp1.linuxhosted.ca, ns20.alltraders.com, and ns1.your-site.com. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Help with cross-compiling NTP for the Raspberry Pi requested
I believe you want this: libcap-dev - development libraries and header files for libcap2 -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
I wrote: > In any case designers of things like cell towers should no more assume > that GPS is always "just there" than they should assume that electric > power is always "just there". Uwe writes: > This is a _basic_ shortcoming in CDMA as designed and in use. > ( think of it as the NTSC of mobile phone systems ;-) But Terje points out above that they use Rb oscillators so short (or medium) term loss of GPS by cell towers is not actually a problem. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
unruh writes: > The article talks about a truck driving by the airport (ie a few km) > jamming the airport. And that was a trucker probably unwilling to > spend more than a 100 dollars on his jamming gear. And the jammed receivers probably weren't worth much more than that (though the airport undoubtedly paid a lot more for them). -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
I wrote: > 1) Better front-end selectivity > 2) Better front-end dynamic range David Woolley writes: > I don't really see how these help against all but the crudest jammers, > which transmit pure CW carriers or are off frequency. Better dynamic range means that the jammer must be closer or more powerful. Both it and better selectivity help against out-out-band interference, which is one of the concerns (probably a more serious one than jamming) (and most jammers *are* going to be of the crudest sort). I wrote: > 3) Directional antennas for fixed sites such as cell towers David Woolley writes: > That might help a bit, if you rejected signals near the horizon (which are > good for navigation, but may be bad for time). Signals near the horizon are weak and have gone through a lot of atmosphere. You don't really want them for any purpose if you can find better (and you can unless you are in the [ant]arctic). > However, to get full benefit from directionality, you'd need to run > large phased arrays and steer their beams to track the individual > satellites. As most military users want the navigation data, they > would be better off with steerable beams. 99.9% of jammers and 99.99% of interference sources are going to be on the ground. A well-designed "fence" (shielding, really) with a cutoff at, say, 30 degrees above the horizon can easily knock them down 100db or more. Due to the use of spread-spectrum jamming GPS has no effect as long as it stays within the dynamic range of the receiver (spoofing is a different issue entirely, and *much* more difficult to achieve). My point is that this "weakness" is more of a design weakness in commercial receivers than a fundamental weakness in GPS. In any case designers of things like cell towers should no more assume that GPS is always "just there" than they should assume that electric power is always "just there". -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
There are many things that could be done to mitigate the GPS jamming and interference problem. Unfortunately, few if any are being done by anyone outside the military. These include: 1) Better front-end selectivity 2) Better front-end dynamic range 3) Directional antennas for fixed sites such as cell towers -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Is there something with greater detail on "interface" besides the manpage?
mike cook writes: > As a comment to lead OL. We are now in a situation where we can only > trust our enemies. CAcert.org is an Australian based org IIRC. They > are in the same "Trust" league as the US, UK, CAN, all of whom have > proved to be woefully lacking in probity. Are you afraid that the NSA is going to find out how you are setting your clock? -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Is there something with greater detail on "interface" besides the manpage?
David Woolley writes: > Actually I would expect the name on their root certificates, the > generic "Root CA" to send warning bells to anyone who was security > conscious, but not already familiar with them. Anyone who is really serious about security will accept certificates only in person, by hand directly from site operators whom they have thoroughly investigated. But of no one is. The present Web certificate system is badly broken. It's about as secure as a locked convertible with the top down. It should never be relied upon for anything nontrivial. For that purpose CAcert is as good as anything else and better than most. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Is there something with greater detail on "interface" besides the manpage?
The CAcert certificate is included by Debian, most other Linux distributions, and by OpenBSD. It is at least as trustworthy as most commercial certificates. <http://wiki.cacert.org/InclusionStatus> -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Strange refid
Brian Utterback writes: > However, it begs the question of why somebody thought that printing > "M-" before characters with the high order bit turned on would be a > good idea. ASCII characters with the high bit turned on are control characters. "M-" is a common notation for control as in "M-J" for "control-J". -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP not syncing
David Lord writes: > My guess is you're not meant to do it that way but then I'm no expert > at configuring debian. That's something the appliance manufacturer invented. The "Debian way" would be to just edit the configuration file. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Trying to use Dimension 4 time keeper
unruh writes: > Except a power supply, which can be a pain. 5V and 3.3V are available on the Pi board. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Trying to use Dimension 4 time keeper
Dennis Ferguson writes: > If you are doing it with an IC a 3.3V buffer with overvoltage tolerant > inputs would be better. A 74HC4050 run at 3.3V would probably do it, > if you don't need input protection (against >15V or <0V inputs) it > needs no additional external components. There are lots of choices. The point is that the job can be done by a single part. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Trying to use Dimension 4 time keeper
I wrote: > I'm suggesting adding an open-collector driver rather than adding a > network of resistors and diodes. Fewer parts and better results. unruh writes: > Probably. I'm a bit worried if the base voltage is higher than the > collector. A single transistor with a base current limiting resistor would work fine but I had in mind an IC such as the 7407. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Trying to use Dimension 4 time keeper
I wrote: > The Pi GPIO pins have pullups. Just use an open-collector driver. unruh writes: > That of course assumes that you, not the designer of the gps card say, > have designed the output. I'm suggesting adding an open-collector driver rather than adding a network of resistors and diodes. Fewer parts and better results. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Trying to use Dimension 4 time keeper
unruh writes: > The Raspberry Pi specifically states that it is NOT 5V tolerant. The Pi GPIO pins have pullups. Just use an open-collector driver. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Sine wave offset patterns
E-Mail writes: > The only time I've seen anything like that (twice, in 2 different > states), was on a overloaded (grossly over sold bandwidth) cable TV > ISP network, you could watch the latencies (and packet loss) climb, as > kids got out of school, then later as others got home from work; I > would have thought ISPs would have improved their infrastructure > beyond that by now. They may very well have improved their infrastructure and their performance in the ways that matter to most of their customers: fast loading of Web pages and fast downloading of movies. Most of their customers couldn't care less about single-packet latency or asymmetrical delays, though. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Start of new GPS 1024 week epoch
David Taylor writes: > Ah, OK, but I think gpsd for Windows would get a much better reception > were it not to require Cygwin to run i.e, just like ntp, use only the > standard Windows calls. From <http://www.catb.org/gpsd/> : "No, we don't support Windows — get a better operating system." esr is not a big Microsoft fan. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Start of new GPS 1024 week epoch
David Taylor writes: > A pity that they haven't been able to find two or three spare bits to > reduce the 1024 week ambiguity to nearer a half-century or even 100 > years. >From the Wikipedia article: To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal. To address this concern the modernized GPS navigation message uses a 13-bit field that only repeats every 8,192 weeks (157 years), thus lasting until the year 2137 (157 years after GPS week zero). -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Failure modes on Windows Server 2008 R2 64-bit
David Taylor writes: > why are the SSL > sources not in the distributed NTP source files? Harlan Stenn writes: > Originally, ITAR concerns. That stopped being a problem in the USA a long time ago. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Wrong Paris time
David Taylor writes: > Windows also works internally in UTC. It defaults to expecting the BIOS clock to be on local time. There is a registry hack to get it to work with the BIOS clock on UTC but according to all reports it is buggy and not supported by Microsoft. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Accuracy of audio tones via VOIP
Harlan writes: > I have heard (and I haven't checked in to this) that a good number of > local calls are converted to digital pretty quickly, too. By "local" I mean on the same central office. If the call goes over a trunk it probably is digital even if you didn't have to dial one. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Accuracy of audio tones via VOIP
Robert Scott wrote: > That does not sound too encouraging for the pitch accuracy of tones > transmitted over Skype. Of course you would never notice it in normal > speech, which is, I guess, all that Skype is targetting. But for > calibrating to the standard frequency tones from NIST (500 Hz and 600 > Hz), it probably is not trustworthy, right? The waveform at your end of a Skype connection is not the one that started from the other end. It is something that the hardware at your end generated based on instructions from the other end. It is intended to be close enough for you to not hear much difference. Landline long-distance usually goes over packet-switched networks as well these days. Unless your call to NIST is local you probably aren't hearing the tones they sent. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP makes a time jump
unruh writes: > Do you mean none of the slaves ever have to jump to track it? Since > all ntpd does ever is either jump or slew. I mean so that none ever have to slew at the 500PPM max rate. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP makes a time jump
unruh writes: > lets say one computer has a natural offset of 200PPM and another is > -100PPM. When both are slewing at 500PPM, one is effectively slewing > at 300 PPM and the other at 600, which goes out by 50ms in about an > hour. Therefor you should tinker with the slew rate of the master, limiting it so that none of the slaves ever have to slew to track it. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Tighter regulation?
David Woolley writes: > Offset is not offset from true time. And that, I think, is the major point of confusion here. If offset was the offset from true time ntpd would just subtract it out, set the clock to true time, and we'd all be happy. It isn't. It's one of the pieces of information ntpd uses to solve the rather subtle problem of estimating the true time in the presence of noise and variable delays. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] ntp & system without a rtc
E-Mail writes: > The uC likely has a RTC, its just not battery backed up? The Raspberry Pi has no rtc. There is no point in having one without a battery. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Syncing and peering for a multi-continent deployment
unruh writes: > But perhaps if the whole gps goes down, or goes bad, we as a society > will have bigger problems than our computer clocks. Well, it's run out of a single center by a single agency so things other than a loss of satellites could compromise it. Fortunately there's GLONASS and will soon be Galileo. Does anyone sell a timing receiver with GLONASS capability? -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Syncing and peering for a multi-continent deployment
David Wooley writes: > Unless he is doing common view observations on something > extra-terrestrial, I'm not sure how the software would not tolerate > than sort of offset. He might be using something like a distributed database that has an arbitrary definition of simultaneity hard coded. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Syncing and peering for a multi-continent deployment
David Woolley writes: > Intercontinentally he can probably tolerate several milliseconds or > even low tens of milliseconds without any risk that there is any doubt > that two events are not causally related. He might be using software that won't tolerate such offsets, though. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Syncing and peering for a multi-continent deployment
Blair Zajac writes: > 1) Each ntp server should have 4 to 7 upstream clocks [1], [2], [3]. Each NTP server should have a GPS receiver. Fall back to the Internet if GPS goes down. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Extracting ntpq like information programmatically
I wrote: > BTW what kind of accuracy do you need and how quickly must your machines > converge to it? Ntpd may not be your best choice. It's designed to > synchronize always-on machines with relatively low drift rates over the > Internet. Claudio writes: > That depends entirely on the performance of the communication > framework we are using. Which is what I'm trying to measure. Then you will need accuracy at least an order of magnitude better than your most optimistic estimate of the performance of what you are trying to measure. How often do you shut down these machines and how soon after startup do you need to have them synchronized? Depending on your accuracy requirements Ntpd can take many hours to converge. Chrony is faster but still may not be fast enough for you. Also, the NTP protocol is said to perform poorly over WiFi. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Extracting ntpq like information programmatically
Claudio writes: > Then why does NTP give a number to the offset and delay? Because the information is often useful. You can use it to evaluate performance. The name may be a bit misleading. It isn't the actual instantaneous offset: you can never know that. > If the algorithm knows that it's lagging by X s, why doesn't it > correct for that lag? A few measurements don't suffice to be sure that what appears to be offset isn't just noise. The noise in this system has large components at very, very low frequencies. The simple, fast PID controller that I think you are visualizing would just hunt like crazy. You may want to take a look at Dr. Mills' book. BTW what kind of accuracy do you need and how quickly must your machines converge to it? Ntpd may not be your best choice. It's designed to synchronize always-on machines with relatively low drift rates over the Internet. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Extracting ntpq like information programmatically
Claudio Carbone wrote: > I mean that, when I have certain timings from different machines, if I > correct them by their average offset from a common source, doesn't this > augment the precision of the measure? NTP has already used the offset to correct the system clock. You don't need or want to do anything. When NTP says that the clocks are synchronized they are as close as it is possible to get them over the network. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] outlyer / falseticker
unruh writes: > I am positive that no matter where you live, the television show > "Survivor" has made its appearance. I have never seen it: I do not watch television. I have only a vague idea what it is about (and no interest in learning more). > If you do not like humour ( which I agree can in some cases not > translate well, but you are reading it in English) then reading David > Mills' code is probably not for you. I appreciate Dr. Mills' humor. However, I do not think that it is desireable to make detailed familiarity with USA popular culture essential for the comprehension of documentation. It's quite possible to have an adequate grasp of written English without knowing what "Survivor" is (or knowing the rules of baseball: this applies to the ever-popular sports analogies as well as to TV references). -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Confused about pool rotation
Robert Scott writes: > So I am trying to achieve 12 ppm frequency calibration by developing a > temporary local time stamp that is disciplined by SNTP. I figure two > SNTP samples about 2 to 4 hours apart will give the required frequency > accuracy, assuming typical SNTP jitter. I don't see why this should be better than (or even as good as) using the system clock as disciplined by NTP. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] PPS only configuration
unruh writes: > It is entirely possible to put in line breaks manually... Yes. It is also possible to do proper quoting manually. Thus while it is reasonable to ask for suggestions for a newsreader that will automate these tasks it is not reasonable to claim that your newsreader prevents you from posting properly just because it doesn't do it for you. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Loopstats jitter field mostly zero?
David Taylor writes: > I recall seeing /something/ about hardware and software floating point > support in the Raspberry Pi, that some hardware/firmware/software had > it and some not. The cpu in the Pi has hardware floating point but it does not support all the instructions supported by the hardware floating point in newer ARM cpu designs. Consequently software must be compiled specifically for the Pi cpu or else use software floating point. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Do I have a lock to my NMEA GPS?
Ralph Aichinger wrote: > I really hope that in the next version they test and fuse it for > higher current (e.g. 2.1A, that is what iPad chargers supply). >From <http://www.raspberrypi.org/archives/1929>: USB Output Power The resetable fuses protecting the USB outputs have been removed. This feature was implemented on some later revision 1.0 PCBs by replacing the fuses with links; revision 2.0 permanently implements this modification. It is now possible to reliably power the RPI from a USB hub that back feeds power, but it is important that the chosen hub cannot supply more than 2.5A under fault conditions. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] What is the NTP recovery time from 16s step in GPS server?
Rob wrote: > I don't know much about the raspberry. > I think it is sort of standard Linux, Raspbian is just Debian, recompiled for the particular ARM cpu the Raspberry uses and with drivers for the Broadcom video added. The recompilation permits the use of hardware floating point, which is different in the Raspberry and the ARM cpus that Debian supports. Debian also supports ARM cpus with no hardware floating point and that version of Debian runs on the Raspberry but is slower. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using Trimble TSIP under Linux
David Taylor writes: > if I try and compile with the flags for automatic start-up the make > fails due a missing file: sys/capability.h. Happens with both 4.2.6p5 > and 4.2.7p314. Install the linux-headers package appropriate to your kernel. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using Trimble TSIP under Linux
pk writes: > ntpd will be in /usr/bin or /usr/sbin. On my pi the /usr/sbin is the > one in use. Just copy across your newly built binary and restart with > a "sudo /etc/init.d/ntp restart" No, don't do that. /usr/local/, which is intended for locally-compiled software, is at the front of your PATH and so your local ntpd will be found before the one the package-management system installed in /usr/sbin/. You'll want to edit or replace the initscript in /etc/init.d/ntp. Just fix the DAEMON line at the top of the script. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP tunning for OWD measurements
I wrote: > Then you surely have read Dr. Mills' book. Pedro writes: > Unfortunately, I have not, I've only wandered through his website. Can > you give me a pointer to it? Mills, David L. Computer Network Time Synchronization: The Network Time Protocol Taylor & Francis / CRC Press ISBN 0-8493-5805-1 -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP tunning for OWD measurements
pret3nder writes: > I won't have time to investigate the deeps of NTP, but I do want to > know the basics, as that's one of the objectives of my thesis. Then you surely have read Dr. Mills' book. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP tunning for OWD measurements
Terje Mathisen writes: > The crux is this: You _MUST_ have a path to an absolute time > reference, at both ends, which is totally independent of the path you > are trying to measure! And a tunnel is _not_ an independent path. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP tunning for OWD measurements
David Woolley writes: > You can't stop it measuring the delay asymmetry! The trouble is you > will not have any way to obtain that value, which will tend to cancel > out the asymmetry measured by your primary tool, assuming it depends > on accurate time stamps! Read this: <http://www.internet2.edu/performance/owamp/> . I think he wants help configuring the four clocks mentioned in the "requirements" optimally for OWAMP. I don't see why OWAMP is special, though. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Motorola Oncore GPS as Stratum 1 source
Richard B. Gilbert writes: >...not all of us can afford Microsoft to read mail... And some us wouldn't use it if paid to do so. However, some MUAs such as Gnus have "format message" commands that can render such a mess readable. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] NTP.POOL.ORG Server is a shadowserver
sh3120 writes: > Have sites complaining that 72.8.140.222 is showing up on command and > control server. After research determined that IP is listed in the > NTP.POOL.ORG listing of time servers. Unsure who to report this too > to get it off the list. It's not clear what your problem is. > it can b confirmed by going to http://www.threatstop.com/checkip and > checking the ip address. What can be confirmed? -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] System time changes only on restarting ntpd service and query about iterating through the sources
Richard B. Gilbert writes: > On some, or many machines, the hardware clock (time of day) is > sustained by a "coin cell" battery when power is off! On others, such as the Raspberry Pi and many embedded systems, there is no RTC. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Have Pi, have GPS = low powered NTP server?
DaveB writes: > I also found that the Pi would lock up and need a power cycle, if left > running the default NTPD service for anything more than two or three > days. When you get time please file a bug report. I've had one running Chrony for about a month. It's using Raspbian. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Have Pi, have GPS = low powered NTP server?
pktrigg writes: > i opened port 123 for udp so it should work for you. It is showing up as stratum 0 so of course Chrony won't sync to it. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Have Pi, have GPS = low powered NTP server?
pktrigg writes: > I have my pi running on the web right now at http://121.221.94.250/ Now make it available as a public server so that I can point my pi (which is running Chrony) at it :) -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] fr.pool.ntp.org not serving NTP anymore
Jean-Christophe writes: > I have a bunch of communicating objects spread around the country that > are using fr.pool.ntp.org hardcoded to get their date / time. It > worked perfectly until May the 8th, but now, this domain name won't > exchange NTP anymore. Works fine from here (Wisconsin USA). It's currently pointing at sd-28922.dedibox.fr. Perhaps someone noticed what you were doing and blacklisted you. How are these "objects" configured? > I know using a single hardcoded address is not really clever, but is > there a chance "fr.pool.ntp.org" get back serving NTP again? Why don't you contact them and see how much they want for providing you with NTP service? I hope you don't mean that you hardcoded the IP number. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] ntpq -crv gives results in local time, not UTC
Steve Kostecke writes: > Some people are more concerned about having a usable desktop clock > which displays the time in their local time zone than they are about > timestamps. That's what TZ, tzdata, et al. are for. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] ARRGH!!! I woke up to a 50 SECOND clock error.
David J Taylor writes: > But in the UK from Virgin Media I have 30 Mb/s down, 1 Mb/s up. I > have been promised an upload speed increase about 18 months ago to 2 > Mb/s up, which is more sensible... Such a very high cable download speed is a peak burst speeds on a shared medium. Your sustained performance is not likely to be more than a fraction of it. > Not ideal, but I prefer cable to ADSL. You'd get less jitter with DSL. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] ESR looking for good GPS clocks
Ron writes: > ...the NMEA output has to be referenced to something! No it doesn't. They can put it out whenever they find time after they've done all the important stuff, as long as they get it out "within the second". The important stuff can easily take a variable length of time. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Purpose of a leap second file?
nemo_outis writes: > It was specifically chosen, not because of its deep significance as a > 'universal physical constant', but specifically to make the 'new' > second very close to the old 'earth-rotation' second. But not exact. Can't be: the rotation is not stable. I'm not advocating the elimination of leapseconds: just a cessation of the practice of treating them as if they were corrections of errors in the atomic clocks. Let the clocks run on TAI (and so record time stamps) and then look up and insert leapseconds as needed for display. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Purpose of a leap second file?
I wrote: > [UTC] localizes TAI to this particular planet. unruh writes: > That makes it sound as if TAI is some God given time. There being no god, nothing is god-given. > It is not. It was developed and defined in the context of precisely > this planet. It is based on universal physical constants rather then on the motion of a particular object. > If there is a timekeeping species somewhere else in the universe, I > promise you they will NOT use TAI. They probably will use something similarly derived from physical constants. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Purpose of a leap second file?
I wrote: > Thus UTC is just a kind of timezone-like localization and leap-seconds > belong in tzdata. David E. Ross writes: > No, it is not a localization. It localizes TAI to this particular planet. > A leap-second file allows conversions between UTC and TAI. Just as tzdata allows conversions between UTC and your local zone. Thus UTC is the Earth planetary zone as CST is my local zone within that planetary zone. While it is convenient to have solar noon occur at the same time every day the planet is not a clock. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Purpose of a leap second file?
David E. Ross writes: > Why require a UTC adjustment from TAI? If the data represent a > satellite orbiting the earth and the sub-satellite point on the > earth's surface is needed, the TAI is converted to UTC, which is then > converted through UT2 to UT1 and possibly to UT0 before obtaining the > sidereal time. Sidereal time then gives the current angle of the > earth's rotation for computing longitude. Thus UTC is just a kind of timezone-like localization and leap-seconds belong in tzdata. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] how do you like the Trimble Resolution T
Richard B. Gilbert writes: > ISTR that only three satellites are required to determine the location > of your antenna. Only if you already know either one of your three space cooordinates or the time. Four equations, four unknowns. > Once this position is accurately known, you can live with a single > satellite. As long as you stay still. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Sure gps looses all sattelite fixes
I wrote: > It doesn't get location data from the satellite. It uses the > ephemeris[1] to plot satellites that should be above the horizon. > > > > [1]Updated periodically, of course. unruh writes: > Updated how? The only thing it could update them from is the sattelites > themselves. So the sattelites DO give their location to the system. Every satellite preiodically transmits the full ephemeris for all the satellites, not just its own, and the receiver retains it until it gets a new one or it expires. Thus it can have been quite a while since your receiver has gotten data from any satellite but it will still know where they all are. > And why does the Sure plot 12-14 sattelites at all times while the > Gamin only does 9-11? both have the same sattelites above the horizon > at any one time. And the sure plots them right down to the horizon ( > and gets signals from them) while the Garmin only reports them down to > about10 degrees above the horizon. Most likely because Sure decided to show you all above-horizon satellites while Garmin decided to show you only ones they think are high enough to be useful. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Sure gps looses all sattelite fixes
unruh writes: > Surely it does not report based on predicted orbits. Predicted orbits from the ephemeris is all it has. It has no way to actually track anything: it just has a single omnidirectional antenna. > I could imagine that the signal is too weak for timing but strong > enough to get location info from the sattelite. It doesn't get location data from the satellite. It uses the ephemeris[1] to plot satellites that should be above the horizon. [1]Updated periodically, of course. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Sure gps looses all sattelite fixes
unruh writes: > ...there is a sattelite receiver on the roof, but it is blocked by a > row of offices on the roof between the puck and the sattelite > receiver. It could be broadcasting to the sattelite and increasing the > noise at the receiver.(That receiver communicates with the MOST > microsattelite-- a tiny 6" telescope to look at fluctuations in light > from stars to measure the internal structure of the stars). But I do > not believe that they would be broadcasting for 15 hours steadily. I'd suggest investigating it. Even if the transmitter is not on all the time (and I wouldn't be certain it isn't) the receiver may be on and it's local oscillator may be leaking enough to jam you. Those cheap GPS receivers have poor front-end selectivity and are easily overloaded. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Jammers in Use by Criminals - Warping Time for Fraud Suggested
Dave Hart writes: > Given the dwinding number of such clocks and relatively arcane grid > operational reasons, there's been some movement to abandon the > corrections, which seems to be stalled at the moment. I thought that they had already decided to go ahead with it. > <http://www.treehugger.com/corporate-responsibility/clocks-may-drift-while-us-power-grid-adapts-to-increased-use-of-renewable-energy.html> Thus we see that a political blogger can turn even the most arcane techical matter into an attack on the opposition. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Jammers in Use by Criminals - Warping Time for Fraud Suggested
David Woolley writes: > I believe that, in the UK, only the long term timing has ever been > guaranteed. The frequency goes down at peak load and is increased at > other times, to compensate. That was true in the USA as well, but with grids getting larger and the number and types of sources increasing the compensation was getting harder and harder to do while maintaining stbility. Since the grid is no longer an important source of time they relaxed the limit on accummulated phase error. Slashdot was full of cries of doom. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Jammers in Use by Criminals - Warping Time for Fraud Suggested
Chris writes: > A sophisticated jammer would know exactly when to transmit over one > bit or two bits, and in a narrow band just enough to corrupt the GPS > data and would have a very lower average power output. That would be a very sophisticated jammer indeed. GPS is not narrow band. It's spread-spectrum. Spoofing it is much, much harder than jamming it (though not impossible for simple consumer-grade receivers). BTW jamming won't do a bit of good for the "time warping" fraud suggested. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Was this a time sync issue?
rick writes: > http://www.theregister.co.uk/2012/02/22/cable_fault_caused_opera_result/ > http://news.sciencemag.org/scienceinsider/2012/02/breaking-news-error-undoes-faster.html Too bad: I was hoping for new physics (not FTL, but at least something subtle and interesting). -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] how do I lock in average frequency correction
David Woolley writes: > Did the XT have an RTC? No. It had only the 14.31818MHz crystal I mentioned. It differed from the PC in having a hard disk. The RTC came in with the AT. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] how do I lock in average frequency correction
Dave Hart writes: > I believe it had more to do with the Color Graphics Adapter circuitry > needing to operate at NTSC-compatible frequency. According to my Technical Reference manual the XT and the Portable PC used a 14.31818MHz crystal. This was the only crystal on the motherboard. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Very large jitter and offsets on GPS ref clock after upgrade to "p5"
unruh writes: > He said he was using 80 ft of cat 5 cable. That is 100 ohm cable. To > get rid of reflections he needs a 100 ohm termination. This has > nothing to do with 232. RS232 is not intended to be used with speeds and cable lengths such that transmission line effects are significant. When properly implemented (it usually isn't) risetime is limited with rc networks to prevent ringing and the output impedance of the drivers is such that they can withstand a short circuit without damage. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Very large jitter and offsets on GPS ref clock after upgrade to "p5"
David Woolley writes: > If you want fast edges to be reproduced accurately, you must do, as > Unruh says, and terminate the line with its characteristic impedance. But RS232 drivers won't reliably drive 100 ohm loads. Another possible problem with RS232 on long runs is 60Hz interference due to ground loops. As you suggest, it's best to use 422 for long runs. If you must use RS232 drive the cable with +-15 from a 100 ohm source. It is not necessary to terminate the cable with its characteristic impedance at both ends. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Accuracy of NTP - Advice Needed
Danny writes: > GPS is not used for this kind of thing, they are too inaccurate, so it > doesn't matter. They use atomic clocks. The requirement is for synchronization. They use common view GPS. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Accuracy of NTP - Advice Needed
> The open sky nearest the OPERA detector is straight up through 1400m of > rock. Jim Pennino writes: > And the easiest open sky to get to is horizontally down the tunnel to > the entrance which is next to a freeway. Yes, the entrance is next to a freeway. The entrance to the LNGS facility where the OPERA detector is located is near the middle of the 10 km long Gran Sasso highway tunnel. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Accuracy of NTP - Advice Needed
Jim Pennino writes: > The issue is that most people don't seem to be able to understand how > to get an accurate position of a location that is vertically under a > km or so of dirt, yet horizontally feet from wide open sky and GPS > signals. The open sky nearest the OPERA detector is straight up through 1400m of rock. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Accuracy of NTP - Advice Needed
unruh writes: > Surveying is done by GPS, as is timing so mountain ranges do not > really matter. The OPERA team had to survey a traverse through the Gran Sasso highway tunnel to get to suitable benchmarks. You're right though: they did not survey the entire distance. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Accuracy of NTP - Advice Needed
unruh writes: > They require ns accuracy in the timing and m accuracy in the > distance. And the timing is not simply gps ( although they could have > gotten that wrong) but then that timing has to be brought down into > the mine a km or so below ground and horizontally and that also has to > be surveyed for the distance. The NOvA detector is not in a mine so it should be possible to site the GPS receiver directly above it and drop a cable straight down. The same should be possible at the Fermi end. You could set up both timing chains at Fermilab (using indentical components including cable lengths if you want to be fanatical), calibrate them against each other for delay from antenna to output, and then pack one up and ship it up north (of course there may be good reasons not to do it this way). The surveying should be easier than in Europe: there's no mountain range in the way. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Accuracy of NTP - Advice Needed
I wrote: > An upcoming experiment at Fermilab will observe neutrinos at both ends > (the far end will be in Minnesota). unruh writes: > Well, no. At best the electrons or muons at one end. At best the electrical pulse produced by a photomultiplier when struck by a photon generated when a muon or electron emitted as a result of a neutrino collision interacts with the detector medium (there are a variety of detector designs but photomultipliers are almost always involved). However, the use of similar or identical neutrino detectors at both ends means that systemic errors in delay estimation will tend to cancel. I assume that they will try to match up the timing equipment at both ends as well. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Accuracy of NTP - Advice Needed
Richard B. Gilbert wrote: > How do you "tag" a neutrino so that you can say with assurance that the > the neutrino that left Cern is the same neutrino that arrives at Sasso? Jim Pennino writes: > By sending them in a "pulse" of a known width. It should be noted, however, that you cannot observe the same neutrino twice. In fact, no neutrinos at all are observed at the Cern end: just the protons that produce the pions that produce the neutrinos. An upcoming experiment at Fermilab will observe neutrinos at both ends (the far end will be in Minnesota). -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Ntpd in uninterruptible sleep?
unruh writes: > So why are you using X at all? He isn't running X at all (or at least he doesn't need to be). He's just running a couple of X clients that are talking to the X server on his workstation. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] OT: UK - NOTIFICATION OF GPS JAMMING EXERCISES
> I presume, to ensure that the military can continue to function (at > some level) in the absence of usable GPS. They coud do that by turning off their receivers. More likely they are testing anti-jamming techniques (and jamming techniques as well). -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Google and leap seconds
Richard B. Gilbert writes: > I'm not going to do ANYTHING on Mars! We could, in principle, land a > man on Mars. The cost would be enormous. The probable return on the > investment does not appear sufficient to tempt anyone. Well, we have machines on and around Mars that need to keep time and that we need to synchronize with. In any case, the point is that planetary days and years are intervals to be measured, not clocks. I understand and share the desire to localize the representation of time, but that should be done explicitly. It made sense to synchronize our clocks with the Earth when we knew that it was a more stable oscillator than any we could build, but that is no longer true. Leap seconds don't correct an error: they jigger stable clocks so that they track a known drifty one. They should be treated as localization, not as error correction. Put them in tzdata. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Google and leap seconds
Harlan Stenn writes: > Being able to rely on a common timescale is a great way to save huge > amounts of time and money. Such as, for example, a stream of sequentially-numbered TAI seconds. > Put another way, going to a situation where there are multiple > timescales will cause areas of great friction and expense. We're already there. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Google and leap seconds
Richard B. Gilbert writes: > Too bad that the movements of of the planets, moons, etc. are not > better behaved. Lacking the powers of the divine we must work around > the fact that the earth does not rotate exactly once in each > twenty-four hours, and the fact that its revolution around the Sun is > similarly messy, taking 365 days, six hours, and a few odd minutes and > seconds which we account for (mostly) by declaring a "leap year" every > four years. A purely local problem which should be handled by localization tables, not by jiggering the timestream. Are you going to insert leap hours on Mars?. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Google and leap seconds
Richard B. Gilbert writes: > It's unfortunate that the earth DOES NOT rotate exactly 360 degrees in > exactly 24. hours. This bit of poor design causes all > sorts of problems. Leap seconds are just one of the symptoms! Leapseconds are localization, like time zones, daylight saving, and leapyears. It's unfortunate that they are considered part of the timestream. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Adjusting PPS offset
Chris Albertson writes: > If multiple servers all agree on an offset from your GPS you have to > make a decision: Is your GPS correct and all the other servers are > wrong by the same amount or is your system the one that is offset from > true UTC time. Or do your connections to all the servers share a path segment with an asymmetry. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Questions about joining pool.ntp.org
NPG writes: > A Meinberg with GPS & WVV would be cool. WWVB would give you substantially better accuracy than WWV (though not nearly as good as GPS). -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Questions about joining pool.ntp.org
I wrote: > Shipping products lacking adequate filtering for adjacent band > interference just because those bands are not presently in use is just > plain bad engineering. David writes: > The new adjacent channel signal could be arbitrarily strong. You have > to make some assumptions, The consumer products manufacturers seem to have assumed that there would be no adjacent channel signal at all. I see no sign of complaints from the USA military. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
