[time-nuts] Lost GPS lock or 1PPS recently?
scmcgrath at gmail.com
Sat Sep 8 13:53:34 EDT 2018
This is precisely the scenario even a short GPS blackout of 1-2 weeks would cause. Its not that GPS is not the finest time transfer system ever devised. Its that with the loss of legacy systems we’ve lost the ability to degrade gracefully.
With a eLORAN system cell networks during a prolonged outage would probably degrade to 3G, but they would still be up. No you cant stream HD video or play GTA Online X, but talk,text email and Facebook would still work Time transfer for most applications would still work. The HFT boyos on Wall St would be SOL. Not sure how to evaluate that eventuality.
People like US need to educate political and business leadership on the need for BACKUPS to GPS mainly because things like the Carrington Event have happened before and WILL happen again.
And having terrestrial systems mean that you can get techs onsite to repair by horse if necessary unlike a space based system where some idiot retired the fleet of repair trucks. So the only remaining option is to launch new ones.
On Sep 8, 2018, at 10:25 AM, jimlux <jimlux at earthlink.net> wrote:
> On 9/7/18 10:05 PM, John Reid wrote:
> Hi all,
> discussion of how to keep accurate time without access to GPS seems very
> on topic to me.
> These people involved in major catastrophe ('end of the world' as you
> put it) scenarios have a wealth of experience in other ways of keeping
> accurate time.
Actually, they don't necessarily have a wealth of experience, because they may have marched themselves down a path where they have a *requirement* for much better timing than they realize, because it is so easy and cheap to get good time today.
Imagine this scenario - you're a bank, and you batch process checks and deposits in one physical location, so you don't much care about when the check was written or the deposit made. Then you move to a distributed system across the US, where the reconciliation is done on the basis of the date of the transaction - still probably ok, because there are no transactions during non-business hours, so as long as you reconcile at 1AM, if transaction time stamps are off by 5 minutes, it doesn't matter.
Now say "we're going to charge you, the customer a fee, if your balance goes negative" and go to 24/7 operations, where transactions are journaled immediately, rather than batch processed at night If a deposit that was made at 12:00 (but timestamped 12:05) is followed by a withdrawal made at 12:03 (but timestamped 12:00), you get unfairly charged the overdraft fee.
For small problems, banks have ways to "unwind" errors. But if it becomes a systemic thing that's a problem.
So the bank sets up GPSDOs at each transaction point - problem solved.
Until GPS fails.
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