[time-nuts] Time in Phone System

David Malone dwmalone at maths.tcd.ie
Tue Jul 22 04:25:32 EDT 2014

On Mon, Jul 21, 2014 at 11:01:19PM -0700, Hal Murray wrote:
> > I expect that there's date and time information being sent in the header of
> > every phone call, maybe even before the  first ring along with the Caller ID
> > info. 

> Wiki says CallerID is sent between the first and second ring, and includes 
> the date and time.
>   http://en.wikipedia.org/wiki/Caller_ID#Operation

Some old modems will happily decode it for you. I compared it to
NTP at some point last year. The time stamp was only given to the
nearest minute, and for my exchange it was pretty terrible - it was
slow by about 90s for a few months. I was considering adding it to
my leap second measurements, but there didn't seem to be much point.


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