[time-nuts] Trimble Thunderbolt no longer determines the correct date
magnus at rubidium.dyndns.org
Thu Aug 17 03:40:26 EDT 2017
On 08/11/2017 06:26 PM, Tom Van Baak wrote:
>> The E911 installation, in the news, is just one of several. Others are hospitals,
>> fire stations, etc. using different dispatch systems.
> Hey, at least important things like mobile phones, ISP's, Google, Amazon, FedEx and Starbucks aren't affected ;-)
>> In a wide-area simulcast-overlap paging system, the transmitters in the same
>> coverage area are carefully set to all transmit at exactly the same time.
> That's fine. And very clever. But why is this "life safety" system tied to GPS, to a particular vendor, to a particular model of receiver (that clearly states in the documentation that it has a 1024 week / 19.6 year window of valid UTC times)?
Due to ignorance. This is why I have been working for over a decade to
spread the knowledge. What is "generally known" at time-nuts and PTTI
does not reach these folks. There is no common knowledge here.
>> So to me "synchronizing transmitters” means the control system sends the
>> traffic out to all the transmitters (over satellite) and tells them all to hold the
>> messages in a buffer until “the big hand points straight up” or whatever data
>> command the system uses. (excuse the vernacular)
> Exactly. In most of the precise timing world the "big hand" is the "top of the second", or the so-called 1 PPS pulse. The idea is that all 1PPS agree with each other, whether from a cesium clock, or WWVB receiver, or NTP, or GPS (or any other GNSS system).
> Since the paging system failed it sounds like it was synchronized to some "hand" other than 1PPS. The rare GPS rollover events tend not to disrupt the 1PPS output -- it is still perfectly aligned with UTC -- which is why almost no one else worries about the recent TBolt episode, or any other GPS receiver for that matter.
If they also extract the time, and several systems do that, then you are
out of luck thought.
There is great benefits in synchrocasting, something I have worked with
for over a decade too, but then delivering alternative to GPS dependence
on each station.
>> The problems being experienced right now appear to be the interface of the ThunderBolt
>> with the Zetron Model 620 simulcast controller over TSIP. The Zetron box is also called
>> a “wireless data encoder.”
> Ah, ok. So do you or anyone have contact within Zetron? The easy fix would be for them to upgrade their firmware and send out a patch. Probably cheaper than supplying new receivers from Trimble. I don't know; for us, a s/w fix is easy compared to a h/w fix or a h/w swap-out. But in the real world, once technicians have driven to a remote installation, maybe there's no real difference between a s/w fix and a h/w swap.
Might work out, but to be honest, don't hold your breath. Transmitter
vendors have not the best record of understanding the system aspects and
how they can contribute. Worth a try thought. Any user of GPS should
have a workaround for the 1024 weeks wrap-around if they use the time.
Oh, there is a lack of common specification of GPS user equipment
covering stuff like this, every little market have their "unique"
requirements. It ends up that they are not comparing notes, learning
from each other and find common strategies for common problems. Most of
the uniqueness is in interfacing to their environment.
>> It is not our goal to blame a particular piece of equipment for this problem.
> Right, no need to blame. I think many of us would just want to pinpoint the root cause of the problem, out of engineering curiosity. By root cause I mean actual schematics or lines of source code. It's always been my hope, after every one of these widespread infrastructure events, that the actual source code or design decisions be published eventually so that we can all learn from it.
No, it is treated as company secrets. We are far from the point where it
is open source and can be inspected by many eyes. You are expected to
buy a "black box" and trust the vendor to do the right thing. When the
vendor do not do the right thing, throw the box and buy a new one. Some
vendors have been black-listed in the process.
I just wished the vendors was acting better.
I had to go to Washington for this mess.
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