[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: time resolution (was Re: six-page binary format draft)
At 01:23 PM 11/24/97 -0800, you wrote:
>From: Carl Ellison <email@example.com>
>To: Paul Leyland <firstname.lastname@example.org>
>Cc: email@example.com <firstname.lastname@example.org>; email@example.com <firstname.lastname@example.org>
>Date: Monday, November 24, 1997 11:28 AM
>Subject: time resolution (was Re: six-page binary format draft)
>>There is no global spacetime. It is not possible to synchronize clocks.
>>The closest we can come to that is with error limits, given our knowledge
>>the minimum and maximum delay in getting a time report. If there were the
>>master atomic clock on the net that still doesn't give us sub-second
>>resolution of time setting.
>>On the other hand, we can be reasonably sure of getting clocks to agree +/-
>>30 seconds, so maybe 1 minute resolution of times would be appropriate.
>> - Carl
>Huh? You are joking right?
>My experience is that NTP stratum 2 and 3 clocks tend to be no more than 30
>ms off from the naval observatory masters. If you are using certs for
>people centric stuff then your 30 seconds is probably good enough. If you
>start doing oltp stuff then clock sync becomes much more of an issue.
>I agree the there is a danger in having more precision represented in the
>data than exists in the source, but to arbitrarily cut the allowable
>precision because today we can't sync clocks is crazy. Didn't this whole
>thing start around the fact that the binary format would break in 2106? 110
>years from now we will probably be able to sync clocks!
Fortunately, individuals in australia, america and austria are all in about
the same inertial frame. So in a decade or two, synchronization to a few
millisecs may be routine. But in 100 years, we may be attempting to conduct
oltp between earth, the moon, and a transport travelling at least a little
bit relativistically. For the relying parties here, agreement on clock sync
cannot exist beyond certain precision. A transaction that might take just
a few seconds may be forced to proceed in pieces separated by minutes or more
just so there can be no disagreement among parties as to the order in which
critical events took place. (Ok, like i'm worried.)
Tony Bartoletti LL
SPI Project Leader LL LL
Computer Security Technology Center LL LL LL
Lawrence Livermore National Lab LL LL LL
PO Box 808, L - 303 LL LL LLLLLLLL
Livermore, CA 94551-9900 LL LLLLLLLL
email: email@example.com phone: 510-422-3881 LLLLLLLL