On 9/3/13 7:07 AM, Poul-Henning Kamp wrote:

Interesting (and of course, this case has been in the news recently)..

In this case, all the messages were presumably handled by the same
carrier, so the issue of skew in timestamps is negligible; they're all
presumably running off the same clock.  I wonder, though, whether this
is always the case. Yes, the cell companies have accurate timing at the
cell site level to do a variety of things, but I could see that getting
lost along the way to the "meta data logging" process.  The time stamp
might be "when the message arrived at the logging process".

And, different companies might have different standards for how those
timestamps get applied and their accuracy requirements.  I can see how a
company might have a legacy billing system that, say, works in 0.1
minute chunks, so a 6 second random scatter is inherent in the system.

Given that cell companies know the location of the radio with at least a
few tens of meters, it would be interesting to see statistics of text
messages sent/received while on freeways.  Indeed, one does not know
that the person with the phone in question is a driver or passenger, but
simple observation (at least in Los Angeles) shows that the vast
majority of cars are "single passenger"  (alas, even in carpool lanes,
there's a significant number of them).

I do know they calculate this sort of thing, because they use it to
determine where to put new cell sites or change capacity.  The question
is whether the information is available in any sort of useful form.  It
could be some horribly ad hoc process where an engineer gets a bunch of
text files, and they load it into Excel spreadsheets to process it.
It's not like they necessarily do site planning on a minute by minute
basis, so a manual process that takes a few days is plausible.

Based on the behavior my cell phone (sending texts in signal denied
areas), I assume the time stamp is actually the "time when message
processed by cell site", which could be many seconds (minutes, hours)
after pushing the "send" button.  I've had text messages queued in my
phone that get sent when I land and turn my phone back on.  More than
once my wife has gotten the "they're closing the door" text from me when
I landed.

Well, Best did take 35 seconds to respond to the text from Colonna.  I
think we can assume that the "incident" occurred slightly after x:58
(although I suppose the sequence could have been

keypress
keypress
keypress
<sound of impact>
keypress
<send message>

Zipping along at 30 mi/hr (14 m/s), 10 seconds is quite a distance.

This was about a half an hour before sunset on that date.
There was a turn in the road involved, etc.

What didn't show up  in the record is the lat/lon estimate for Best's
cell phone.  I would assume that in 2009 they were logging this as well,
but maybe the data was not in evidence (the lawyers may not have wanted
it.. that's the frustrating thing about reading appellate cases: you
have to work with the data as presented at the original trial)

I think it's more the back and forth of messages just before the
incident that are at issue: they imply that there was a "conversation"
of sorts going on, and that the young lady may have had knowledge that
he was driving at the time (which ultimately is what this case is all
about).

I'll bet the marketeers at the cell company have all sorts of models of
texting behavior among people, just waiting for the ability to insert
ads of the appropriate type.  I can see an analysis of "should we go out
to dinner", "Sure, where", and the ad pops up, "why not eat at Dave's
Bar and Grill, would you like me to make a reservation?"

On 9/3/2013 10:56 AM, Jim Lux wrote:

But not necessarily the same time. For instance, some cell systems run
on GPS time, but the carrier may keep records in UTC, since it's the
legal time in most jurisdictions. A phone might time stamp using either
(Google has a years-old bug in Android which lets it use GPS time and
not UTC). So, different devices on the same network may not be in sync.

I remember a lecture by an officer of the (London) Met Police about how
tracable time was essential to demolishing the defence of "wrong clock"  in
accidents involving the illegal use of mobile phones when moving and even
parking meter tickets. They had to argue why the cell time was "more right"
than the defendants watch!! This was part of a meeting of the Time and
Frequency Club at the NPL at Teddington about 6 years ago.

Alan
G3NYK

..
----- Original Message -----
From: "Mike S" mikes@flatsurface.com
To: time-nuts@febo.com
Sent: Tuesday, September 03, 2013 5:19 PM
Subject: Re: [time-nuts] sub-minute time-precision in court-case

In message 5225F8AF.60807@earthlink.net, Jim Lux writes:

Anything but.

The text-messages are likely stamped by the SS7-message-gateway
and the 911 call by the countys 911 equipment.

And yes, there can be quite a delay from you press "send" until
the SS7-message-gateway sees the text-message.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

You can find (for better or worse) NTSB analysis of various recorder
timestamps relative to "cell phone timestamp".

http://www.ntsb.gov/investigations/summary/RAR1001.html

6
In this report, all times associated with the sending or receiving of
calls and text messages are from Verizon
records. In these records, the “sent” and “received” times are based on a
GPS time reference and reflect the time the
Verizon Wireless network equipment either receives or delivers a message.
Thus, the reported “sent” time of a
message does not necessarily correlate to the time the sender pressed the
“send” button on the wireless device.
Because the network must query the receiving device to make sure it is
available before transmitting a message, the
“received” time is more likely to reflect the actual time the message
arrives on the recipient’s device.
7
In this report, all times associated with signal, switch, and locomotive
events are based on signal log and
locomotive event recorder data synchronized to a GPS reference time. This
synchronization correlates train position,
data recorder, signal, and cell phone send/receive times to a common
“master clock” that reflects actual GPS time.

On Tue, Sep 3, 2013 at 1:48 PM, Alan Melia alan.melia@btinternet.comwrote:

PHK,

Correct. This is an age-old problem, whether its minutes or nanoseconds. Time-stamps are inherently relative to a local oscillator's time and rate offset, and affected by frequency drift and stability levels.

A solution to this problem is for the "first responder" to take the cell phone(s) and simultaneously send a text message to himself from each phone. That could help establish a legal time difference (unless, there are variable reception or carrier-specific delays).

They could also simultaneously send cell phone photos of a handheld GPS receiver's time display. That could help establish a legal time accuracy question (unless, the cell phone or GPS receiver were in some sort of hold-over mode).

For extra credit, further photos can be sent each hour for hours or days to determine the cell phone frequency drift and stability parameters.

Then again, realize that a jury of your fellow citizens, not a jury of your "peers", will decide the question of timing. Thus to raise technical issues like syntonization vs. synchronization, or standard vs. Allan deviation, or GPS vs. UTC clocks will probably not help your case.

/tvb

On 09/03/2013 11:47 PM, Tom Van Baak wrote:

"Who is this Allan whos deviation is this or that value?"

Yeah, the question is even if you have a legal support for what correct
time or even traceable time actually is or means. I know countries that
does not even legally accept UTC.

It could be better, way better.

Cheers,
Magnus

Still, imagine Magnus collides with Tom. What time did it really happen?
Does it help if we both have GPS? Both have cesium(s) in the back seat?
At some point the notion of uncertainty and error bars needs to be allowed.

/tvb

On 09/04/2013 12:19 AM, Tom Van Baak wrote:

We both agree, but now it is about convincing a jury... or lawyers.

Cheers,
Magnus