Re: [ntp:questions] ntp-dev: PPS is a falseticker?
A C agcarver+...@acarver.net wrote: On 2014-06-14 12:57, Rob wrote: A C agcarver+...@acarver.net wrote: I actually disliked having to use a prefer peer for PPS as well. So I modified the source code to remove that requirement. As long as there's a source that is acceptable to the selection algorithm (and marked with the *) then PPS turns on. No perfer peer necessary. I had lots of trouble with preferred peers disappearing and the ATOM driver would never come back even after the preferred peer came back. That is great! Do you have a patch file for that? ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions No, I don't have it in patch form. I'll need to get the machine back up and running (just moved to a new place) but I can send along the modifications I made (just a few lines) directly to you. It's an older version of 4.2.7 (somewhere around p270) but it probably applies to the later versions, too. Ok, don't hesitate to post it here when you have found the time to locate it. Others reading here may be interested as well! ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] ntp-dev: PPS is a falseticker?
Brian Inglis brian.ing...@shaw.ca wrote: On 2014-06-14 12:03, Rob wrote: Brian Inglis brian.ing...@systematicsw.ab.ca wrote: I see no problem, really no problem, in this configuration and I wonder why the software makers do see a problem in it and want me to make a configuration decision that introduces yet more problems. There may be no problem with time only messages: the NMEA driver page, http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html shows support of GLL and GGA which provide only time. Other drivers may allow similarly limited information. There is NO NMEA in or near my system! Everyone seems to think that GPS equates NMEA. Wrong. Could you not put a Y or T from your DO GPS message output to your system serial port, with the PPS on the DCD pin, providing a standard PPS+GPS serial interface? The serial output of the device does not provide the date. Only the time. It is not NMEA. That was just an example that I was aware of. It demonstrates that ntpd doesn't need the date. Check the driver page (and code) for your device. There is no driver for this device in ntpd. I have considered writing something that puts the time in SHM, but it will be a kludge as it will have to use the system date. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
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Re: [ntp:questions] ntp-dev: PPS is a falseticker?
Paul tik-...@bodosom.net wrote: On Sat, Jun 14, 2014 at 2:03 PM, Rob nom...@example.com wrote: Everyone seems to think that GPS equates NMEA. Wrong. ... It apparently assumes anyone who has a PPS signal also has a device that provides date and time information, which is wrong. ... But of course the assumptions of the main author have been wrong nom...@example.com thinks you can run NTP as you imagine it should work rather than reading the documentation ... wrong. You have to be able to number the seconds. If you have any source of date/time you can number the seconds. These include: The network. A supported clock type that provides date+time. Your TOD clock. A clock on the wall. Since you're connected to the network your problem is solved. You will need to make some effort to understand how NTP works though. Maybe you can help me? The following is in the documentation: As the select algorithm scans the associations for selectable candidates, the modem driver and local driver are segregated for later, but only if not designated a prefer peer. If so designated, the driver is included among the candidate population. In addition, if orphan parents are found, the parent with the lowest metric is segregated for later; the others are discarded. For this purpose the metric is defined as the four-octet IPv4 address or the first four octets of the hashed IPv6 address. The resulting candidates, including any prefer peers found, are processed by the select algorithm to produce a possibly empty set of truechimers. As previously noted, the cluster algorithm casts out outliers, leaving the survivor list for later processing. The survivor list is then sorted by increasing root distance and the first entry temporarily designated the system peer. At this point the following contributors to the system clock discipline may be available: (potential) system peer, if there are survivors; orphan parent, if present; local driver, if present; modem driver, if present; prefer peer, if present; PPS driver, if present. The mitigation algorithm proceeds in three steps in turn. 1. If there are no survivors, the modem driver becomes the only survivor if there is one. If not, the local driver becomes the only survivor if there is one. If not, the orphan parent becomes the only survivor if there is one. If the number of survivors at this point is less than the minsane option of the tos command, the algorithm is terminated and the system variables remain unchanged. Note that minsane is by default 1, but can be set at any value including 0. 2. If the prefer peer is among the survivors, it becomes the system peer and its offset and jitter are inherited by the corresponding system variables. Otherwise, the combine algorithm computes these variables from the survivor population. 3. If there is a PPS driver and the system clock offset at this point is less than 0.4 s, and if there is a prefer peer among the survivors or if the PPS peer is designated as a prefer peer, the PPS driver becomes the system peer and its offset and jitter are inherited by the system variables, thus overriding any variables already computed. Note that a PPS driver is present only if PPS signals are actually being received and enabled by the associated driver. If none of the above is the case, the data are disregarded and the system variables remain as they are. After reading this, especially the sentence after 3., 3rd line, I believed I could mark the PPS as the prefer peer and not the other sources, and it would work. But it doesn't. I need to make ALL SIX time sources prefer to make it work. (or at least the five NTP sources) Can you please explain? I don't mind if the situation is complex but that does not mean the documentation has to be written like this. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] ntp-dev: PPS is a falseticker?
Paul tik-...@bodosom.net wrote: On Sat, Jun 14, 2014 at 12:42 PM, Brian Inglis brian.ing...@systematicsw.ab.ca wrote: There may be no problem with time only messages: the NMEA driver page, shows support of GLL and GGA which provide only time. Other drivers may allow similarly limited information. The date has to be provided at some point in some fashion. Yes, I think the only thing I can do is get the time from the device and the existing system date, combine the two and feed it back into ntpd as a valid time. But that will fail when the system date somehow gets reset e.g. because of a failing battery. I thought I could make the system able to independently recover from this situation by only using external NTP sources and let ntpd do its usual thing of determining valid time from about 5 external sources, and once it has done that to within a few hundred milliseconds lock on the PPS signal. But apparently there has been someone who decided that this is a bad idea and I need to prefer some external source. Which I rather not do, because the whole setup will dramatically fail when that source is not available, even for a while. A workaround is to prefer ALL the sources, but that is just a workaround. ___ 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 there a suggested way to rate-limit?
brian.cun...@gmail.com brian.cun...@gmail.com wrote: Hi All, Is there a suggested way to rate-limit queries by broken clients? There isn't any. In fact, many methods to do that are likely to make the problem worse. For example, people suggest to limit the number of queries answered or even to send KOD packets. However, broken clients don't implement KOD and think they just got a damaged answer that they can fix by asking again. And when they don't get an answer on their query they often re-try. The re-try interval may be even shorter than the usual interval between polls. There is really nothing you can do from the serverside to affect the upstream bandwidth usage by clients. When you have to pay for traffic and you cannot afford it, the best solution is to go out of the pool. (and even that will not help immediately, as client software often does a DNS lookup at startup and then keeps using the same IP address until restarted. you will see gradually decreasing traffic, but there may be clients that are still there after a year or more) ___ 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
On 15/06/14 15:16, Jason Rabel wrote: On a related note, is there any way to determine if the requests are made by ntpdate vs ntpd? I realize ntpdate is depreciated but ntpdate cannot send a valid stratum or reference time. Strictly speaking it should obey the SNTP rules and send most of the fields as 0. I don't know if it actually conforms with the SNTP request requirements, but repeated requests with a reference timestamp of zero would indicate ntpdate or SNTP. (Broken thread) ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] ntp-dev: PPS is a falseticker?
On Sun, Jun 15, 2014 at 12:11 PM, Rob nom...@example.com wrote: Did you put prefer on the PPS and not on another source? That was the complete output of ntpq. The local clock is marked prefer; it can reliably number the seconds. This is just a demonstration and I think it unwise to run this way in production. So you suggest that instead of fixing the bug in NTP we should buy new GPSDOs? It's your opinion it's a bug. It doesn't seem like one to me. I think you want a feature enhancement not a bug fix. It could be argued that If you had a correct installation you wouldn't have this problem. ___ 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
Jason Rabel writes: On a related note, is there any way to determine if the requests are made by ntpdate vs ntpd? I realize ntpdate is depreciated but it is still used (or a hacked down version) by a lot of routers, and many distros still include it too. Not that I'm aware of - each sends a normal NTP query request. Ditto for the sntp code. H ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
[ntp:questions] About use of PPS in NTP sync
Hello, I'm looking for a way to speed up the ntp convergence of a system which would be restarted after several days being off. Does the use of PPS improve this convergence time ? This is local configuration, with one LAN and one NTP server, with about 30 NTP clients. Thank you. JT ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] About use of PPS in NTP sync
jthul...@gmail.com writes: Hello, I'm looking for a way to speed up the ntp convergence of a system which would be restarted after several days being off. Does the use of PPS improve this convergence time ? This is local configuration, with one LAN and one NTP server, with about 30 NTP clients. That should help. Where is the PPS signal come from? Can you keep a small GPS/NTP appliance up and running all the time? How well do your 30 client machines need to track the server? Have you measured the cold-start drift? How consistent is that across reboots? How much does the drift change when it goes from cold start to normal running conditions? -- Harlan Stenn st...@ntp.org http://networktimefoundation.org - be a member! ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] About use of PPS in NTP sync
On 16/06/2014 04:29, jthul...@gmail.com wrote: Hello, I'm looking for a way to speed up the ntp convergence of a system which would be restarted after several days being off. Does the use of PPS improve this convergence time ? This is local configuration, with one LAN and one NTP server, with about 30 NTP clients. Thank you. JT How accurate are you wanting the system to appear? Fractions of a second? Milliseconds? Microseconds? I run with maxpoll 32 seconds on my clients connected to a local server, and they converge very rapidly (it takes a short time to get within a few milliseconds, which is their ultimate offset range). The GPS/PPS servers are quickly within a millisecond (say the few minutes it might take GPS to sync if it's been off for a long time and has to download full ephemeris data), but might take an hour or three for them to reach their ultimate microsecond-level offset. -- Cheers, David Web: http://www.satsignal.eu ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
