tick tock

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Julien Goodwin spoke about a brief history of time sync. He started off by mentioning some mechanical clocks, and moved onto quartz crystal oscillator chippy things. Apparently a server keeps pretty good time because they are in a temperature controlled environment, and those chips are fairly temperature sensitive.

Apparently you can buy quartz crystal clocks that are packaged in little ovens. Then he mentioned iridium clocks, and they aren't very big. Then he mentioned a clock built by HP (and now agilent), a cesium based clock. Then he showed a lab hdyrogen maesar clock which is more accurate over the short term, but less accurate over the long term.

Last week a 'quantum' chip scale atomoic clock came out. It's $1500 US each, but is very small. It's not a caesum standard, but it does use caesum, so it's pretty accurate.

He then moved on to talk about syncronziation. Apparently there used to be a clock in each city that was used to sync from. I didn't really understand the syncro stuff he was talking about, it seemed the application for some of this were particular applications. He got onto NTP, the Network Time Protocol.

In NTP parlance a stratum 0 clock is the master clock, and stratum 1 clock is the computer connected to that clock, stratum 2 is a computer connected to the stratum 1 computer. PTP was dveloped to 'replace' ntp. v1 in 2002 was LAN only. v2 can be routed, but isn't much better than NTP.

There are several time standards. GMT, UTC, UT0, UT1, T1R, UT2, UT2R, TAI. There are several time zone databases. DST changes several times a year. He pointed out some silly timezones (Liberia used to be 43 minutes and 08 seconds off an hour shift).

To get accurate time, he says don't use virtual machines as master servers, and he had a few other recommendations (using a GPS clock, using 3 to 5 NTP servers, etc).

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This page contains a single entry by Geoff Crompton published on January 25, 2011 11:45 AM.

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