[time-nuts] Time syncing question

Bill Hawkins bill at iaxs.net
Wed Aug 30 12:02:24 EDT 2006


Ah, the hazards of e-mail.

Glenn says, "As for the blind leading the blind, AFAIK many
people on this list make their living designing/building/
selling precise timing products." 

I never meant to say that the blind led the blind. Nor did
I comment on anyone's ability to use precision timing
instruments.

What I did say was that I was blind to the requirements for
the unknown telco device logging project. From the way other
replies were going, it looked like others were having similar
problems.

Maybe what got to me was that others were cheerfully offering
complex solutions to cover all the bases, when the description
of the problem was incomplete. In my 45 years of engineering
experience, that always means that the project will cost more
than it needs to, and that there is a hazard that it will not
work. 

Five years ago, I worked on time synchronization for an industrial
Ethernet project. NTP appeared to be the best choice, so I studied
it and corresponded with David Mills. But the devices on the network
had limited processing power and memory - limited by available
technology and the target cost of the devices. We were able to fall
back to SNTP to meet the project requirements.

I apologize for trying to apply rigorous methods to this incompletely
specified project. As Brooke says, we're here to have fun.

Regards,
Bill Hawkins


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Glenn
Sent: Wednesday, August 30, 2006 8:15 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Time syncing question


Telco's know exactly what time it is. Although, frequency is much more
important than time.  Central Offices use either Rb or Cs for a Time &
Freq. standard. They need to keep all the trunk signals in perfect sync
to keep from loosing bits.

Cell sites generally use GPSDO's. Either OXCO or Rb. Most of the Rb
sources on ebay are from cell site upgrades. Ditto for the Motorola
Oncores.

_Most_ cell phones set their time to "network time." Usually within one
second. Although I have seen cell phones set themselves and be off by
nearly a minute.

If leap seconds are a problem, use TAI, not UTC.

As for who pays, I've found that (in general), if something isn't going
to increase profit, or decrease expenses, it's probably not going to get
funded by a business. Hence, many of us just do this for the fun of it.

As for the blind leading the blind, AFAIK many people on this list make
their living designing/building/selling precise timing products.  
Others have experience using precise timing equipment.

cheers,
glenn


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