I noticed that my old Nokia phones kept time better than computers, then I learned that the oscillator in the phone is adjusted to match the BTS carrier [1]. To verify this I ran ntpd in an Android phone synced to a stratum 1 server via USB tethering. (USB has a lower latency and jitter than WLAN.) The frequency offset was between 25 ppb and 50 ppb (loopstats graph attached). When the phone is put in airplane mode, the frequency offset jumped to 11 ppm. Unfortunately Android's timekeeping gets messed up when the phone suspends since the time is restored from a possibly low resolution RTC when waking up [2, sec. 3]. The phone is prevented from suspending when connected to a USB port, another reason for using USB tethering during the test. [1] http://gnuradio.org/redmine/projects/gnuradio/wiki/OpenBTSClocks [2] https://lwn.net/images/pdf/suspend_blockers.pdf On Wed, Sep 4, 2013 at 7:58 AM, Bill Hawkins <bill@iaxs.net> wrote: > Who among you has volunteered to do the research for this? > > I don't have a camera in my cell phone, and I avoid market research > masquerading as insecure social networks. > > Bill Hawkins > > > -----Original Message----- > Tom Van Baak said, > > "For extra credit, further photos can be sent each hour for hours or > days to determine the cell phone frequency drift and stability > parameters." > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

On 09/04/2013 01:59 AM, Jim Lux wrote: > On 9/3/13 11:21 AM, Poul-Henning Kamp wrote: >> In message <5225F8AF.60807@earthlink.net>, Jim Lux writes: >> >>> In this case, all the messages were presumably handled by the same >>> carrier, so the issue of skew in timestamps is negligible; >> >> Anything but. >> >> The text-messages are likely stamped by the SS7-message-gateway >> and the 911 call by the countys 911 equipment. >> > > I was assuming (with no real basis, I realize) that the 911 call time > came from the cell equipment, rather than the Public Safety Answering > Point log. The PSAP log would have no particular reason to be synced > to the carrier equipment. It could well be "what time was on the watch > of the guy starting the equipment", although these days, one would > *think* that they use something like NTP to set the system time. > > However, given my frustrated experience trying to get folks doing > testbeds and ground support equipment here at JPL to *please* > synchronize your computers meaningfully so we can merge logs, I > wouldn't count on it. Or maybe they sync once every 24 hours. That would be luxury! There are so many systems out there ticking away at their free-running clocks, and that does not even have the capability of an external time source. Cheers, Magnus