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Free Clock Democratizes Atomic Accuracy
schliz writes "A new, trial network of software-based clocks could give data centers and networks the accuracy of an atomic clock for free. The so-called RADclock analyses information from multiple computers across the internet by collecting the time from each machine's internal quartz clock, the time it takes for this information to be transmitted across the network, and comparing all the information collected to determine a time that is most likely to be accurate, so machines are calibrated across the network with up to microsecond accuracy — as good as that provided by a $50,000 atomic clock, researchers say."
NTP solved this ages ago by distributing atomic clock accuracy through the network.
The only problem this will solve is where it is a private network not connected to public NTP servers (or organizations that do not trust public NTP). In that case, they would most likely be able to afford a atomic clock.
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I can imagine the speaking clock:
"At the third stroke, it will be, most likely, sixish"
They have atomic clocks on board and GPS receivers therefore give highly accurate time.
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...but in what situation would the time of day on a server or cluster need to be accurate down to a microsecond? Military, I would presume...but what else?
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I'm also pretty sure there are desktop clocks based on microcontrollers that implement ntp, so they display an accurate time without a computer.
Most data centers that really care about time nowadays install a commonly available GPS unit on site, which syncs clock time with all the atomic clocks in the flying GPS constellation.
Seriously, could the editor that greenlighted this have done a google search or something? It's getting embarrassing to read slashdot these days.
The Financial Sector.
Also, synchronized robotics, precisely coordinated CNC, and a host of other applications. Primarily, it's where absolute time isn't the concern, but rather where arbitrary time must be consistent between multiple devices (accounting for propagation delays, failures, etc...). Of course, protocols like PTP solve this fairly neatly: this particular product solves a different problem, and probably isn't actually useful.
There are two time issues to consider. One is how close your environment is to true time. The other is how close your individual devices are to one another. Messaging time-critical information between devices is severely complicated when the two devices are not on the same plane time-wise. Atomic clocks and the like solve the first problem. PTP solves the second problem. NTP almost (95%) solves both, but falls short in certain extremely time-critical situations.
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One of my favorite quotes relates to this;
Credit goes to Mark Twain (IIRC).
"When you have a watch/clock you always know what time it is. When you have 2 you are never quite sure."
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You know what they say. When life gives you unclaimed nuclear material, you get busy creating superheroes.
This reminds me of an old joke about a retired Admiral who is responsible for sounding the morning cannon at the naval base, walking past a watchmaker's shop every morning and setting his pocketwatch to the correct time from a reliable old grandfather clock in the store window.
One day, on the walk in, he happens to see the watchmaker cleaning the store windows and mentions how he finds it amazing that the old grandfather clock keeps such flawless time.
"Oh, that old thing?" says the watchmaker. "It drifts horribly, and I have to reset it almost daily."
The Admiral then asks, "Since I've always noticed that it's reliable, from where do you get the time to set it?"
The watchmaker replied, "I use the report from the morning cannon at the naval base. It's always right on time."
That reminds me, just where exactly did you get that sarcasm detector?
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
NTP has been around for decades. Even Windows phones home for the time every so often.
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It's called NTP. You just have to be careful who you choose as your peers.
That's right. Also, PC clocks tend to be not that great, in terms of reliability of the frequency, and error such as clock drift.
Hence the general recommendation to use NTP to keep your clock in synch with a good time source; a good time source, being something such as an atomic clock, or a radio-based receiver that provides time from a good source.
A PC clock can easily have errors of 100 PPM or higher. Or ~10 seconds of drift per day
Factors that seem small such as temperature can effect the frequency of the clock crystal also
if a computer's clock only has microsecond resolution, then it stands to reason that you can only synch the computer to within 1 microsecond of accuracy, no?
No. You can sync up to fractions of a clock cycle fairly easily. On average you can only report the time at any instant with around 0.5 uS accuracy, but you can set the edge where it cuts over from one uS to the next as accurately as you want, given enough time to sync...
Slashdot car analogy is I change my oil 4 times a year, so you're saying I can't tell you when I change my oil with any accuracy higher than a whopping 3 months. Yet I assure you, if sufficiently motivated, I can "sync up" such that I change the oil precisely at midnight on the 1st of every third month, with a reportable accuracy of like an hour or so.
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NTP is unreliable even on good networks and hopeless on even mildly bad networks. NTP's time synchronization can't be relied on to be better than 1ms, nowhere near the precision of an actual atomic clock.
RADclock can do much better.
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These guys aren't using the PC clock crystal, and they're improving on NTP by a large margin.
Plus they split interval and wall-clock timers for people who really care that their interval measurements don't get screwed with by leap second (or DST) resets and such, and the accuracy of those measurements is down in the ns range.
As always, all IMO. Insert "I think" everywhere grammatically possible.
Admiral walks past clock shop, sets watch to grandfather clock, goes to naval base and fires cannon.
After the Admiral walks past the clock shop, the clockmaker shows up for work. He waits until the cannon is fired and then corrects the grandfather clock.
The admiral is setting his watch to the "corrected" time from yesterday.
The only thing that's off is that the correction that the grandfather clock gets would be fairly minor, as the assumption is the cannon is fired soon after he sets his watch.
But it could be that his pocket watch is REALLY inaccurate and the grandfather clock less so.
If your computer runs Windows it is probably using SNTP to simply set the clock. PCs are notoriously bad timekeepers and so the skew that you're describing is quite commonplace. The beauty of a full NTP implementation like ntpd is that, while it can be made to sync your clock, it's mostly about calculating your clock's drift so that tick intervals can be adjusted in order to obviate "hard" time synchronization. This eliminates those very wrong time readings in the hours/days before SNTP re-syncs.
Let's just not pay attention to things like the difference between precision and accuracy anymore, it's too much work.
I mean, there's no way that the same physical limitations would apply to all quartz clocks, right?