Has anyone here ever needed microsecond precision? Would love to hear about it.
You probably want to ask about accuracy. Any random microcontroller from the 90s needs microsecond precision.
NIST was 5 μs off UTC after last week's power cut
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Re: NIST was 5 μs off UTC after last week's power cut
#12Has anyone here ever needed microsecond precision? Would love to hear about it.
The high frequency trading guys
edit: also the linked slides in TFA
Re: NIST was 5 μs off UTC after last week's power cut
#13I'm missing the nuance or perhaps the difference between the first scenario where sending inaccurate time was worse than sending no time, versus the present where they are sending inaccurate time. Sorry if it's obvious.
It's a good question, and I wondered the same. I don't know, but I'd postulate:
As it stands at the minute, the clocks are a mere 5 microseconds out and will slowly get better over time. This isn't even in the error measurement range and so they know it's not going to have a major effect on anything.
When the event started and they lost power and access to the site, they also lost their management access to the clocks as well. At this point they don't know how wrong the clocks are, or how more wrong they're going to get.
If someone restores power to the campus, the clocks are going to be online (all the switches and routers connecting them to the internet suddenly boot up), before they've had a chance to get admin control back. If something happened when they were offline and the clocks drifted significantly, then when they came online half the world might decide to believe them and suddenly step change to follow them. This could cause absolute havoc.
Potentially safer to scram something than have it come back online in an unknown state, especially if (lots of) other things are are going to react to it.
In the last NIST post, someone linked to The Time Rift of 2100: How We lost the Future --- and Gained the Past. It's a short story that highlights some of the dangers of fractured time in a world that uses high precision timing to let things talk to each other: https://tech.slashdot.org/comments.pl?sid=7132077&cid=493082...
Re: NIST was 5 μs off UTC after last week's power cut
#14Has anyone here ever needed microsecond precision? Would love to hear about it.
We use nanosecond precision driven by GPS clocks. That timestamp in conjunction with star tracker systems gives us reliable positioning information for orbital entities.
Re: NIST was 5 μs off UTC after last week's power cut
#15I'm missing the nuance or perhaps the difference between the first scenario where sending inaccurate time was worse than sending no time, versus the present where they are sending inaccurate time. Sorry if it's obvious.
The 5us inaccuracy is basically irrelevant to NTP users, from the second update to the Internet Time Service mailing list[1]:
To put a deviation of a few microseconds in context, the NIST time scale usually performs about five thousand times better than this at the nanosecond scale by composing a special statistical average of many clocks. Such precision is important for scientific applications, telecommunications, critical infrastructure, and integrity monitoring of positioning systems. But this precision is not achievable with time transfer over the public Internet; uncertainties on the order of 1 millisecond (one thousandth of one second) are more typical due to asymmetry and fluctuations in packet delay.
[1] https://groups.google.com/a/list.nist.gov/g/internet-time-se...
Re: NIST was 5 μs off UTC after last week's power cut
#16Has anyone here ever needed microsecond precision? Would love to hear about it.
I mean, we routinely benchmark things that take microseconds or less. I've seen a 300 picosecond microbenchmark (single cycle at 3GHz). No requirement that absolute time is correct, though.
Re: NIST was 5 μs off UTC after last week's power cut
#17Has anyone here ever needed microsecond precision? Would love to hear about it.
We need nanosecond precision for trading - basically timestamping exchange/own/other events and to measure latency.
Re: NIST was 5 μs off UTC after last week's power cut
#18Has anyone here ever needed microsecond precision? Would love to hear about it.
Telecom.
Precision Time Protocol gets you sub-microsecond.
Re: NIST was 5 μs off UTC after last week's power cut
#19Gah, just when you think you can trust time.nist.gov Suggestions from the community for more reliable alternatives?
> Gah, just when you think you can trust time.nist.gov You still can... If you're that considered about 5 microseconds: Build your own Stratum 1 time server https://github.com/geerlingguy/time-pi or just use ntppool https://www.ntppool.org/en/
Be aware that there are members of the NTP pool with less-than-honorable intentions and you don't get to pick-and-choose. Yes, they all should provide the time, but they also get your IP address.
For example: unlike the IPv4 space, the IPv6 space is too big too scan, so a number of "researchers" (if you want to call them that) put v6-capable NTP servers in the NTP pool to gather information about active v6 blocks to scan/target.
Re: NIST was 5 μs off UTC after last week's power cut
#20Has anyone here ever needed microsecond precision? Would love to hear about it.
We don't use NTP, but for robotics, stereo camera synchronization we often want the two frames to be within ~10us of eachother. For sensor fusion we then also need a lidar on PTP time to be translated to the same clock domain as cameras, for which we also need We actually disable NTP entirely (run it once per day or at boot) to avoid clocks jumping while recording data.