[ntp:questions] How to keep Linux server in Chicago and Mumbai in sync to within 5 microseconds

unruh unruh at wormhole.physics.ubc.ca
Wed Jan 12 01:08:34 UTC 2011


On 2011-01-11, Chris Albertson <albertson.chris at gmail.com> wrote:
> On Tue, Jan 11, 2011 at 1:15 PM, Vikas <kedia.vikas at gmail.com> wrote:
>> The vendors are trying to sell me CDMA time clocks
>> http://www.endruntechnologies.com/time-frequency-reference-cdma.htm
>> $1375 each.
>>
>> Also I would need 2 time clocks one in Chicago and other in Mumbai.
>>
>> Is there is a easier/cost effective way ?
>
> That is basically what you need.  Rather then sync to each other they
> both sync to a "standard".  If you need to buy an off the self system
> those prices are reasonable for a turn-key box. Nothing could be
> easieer than a plugin and go box.  Morecost effective?  Maybe yes.
>
> If you  can assemble parts and buy stuff from eBay you can get the
> price down to about $100 on each end.
>
> There is a large middle ground.  All you need is a GPS receiver with a
> one pulse per second output connected to a serial port on each
> computer.   There are retail sources for such GPS receivers.  But then
> you need the serial port too and you need an antenna for the GPS and
> likely a pole to mount the antenna on and some cables.  $100 is a
> realistic price for all those parts if you are willing to work at it
> but if your time is worth $50 and hour, just buy the two $1K boxes.
> As I said the middle ground is to buy a pair of GPSes and wires them
> to a serial port

If he is that bad that it takes him 20 hours to solder on two rs232
connectors and two usb connectors (for power) , I am sure he can find someone to do it for him for less. 

The Garmin comes with an antenna. It comes with 5m of cable (connect the
cable to a twisted pair ethernet cable if you need more than 5m.)

>
> GPS does requires a clear view of the sky nearly to the horizon.  If
> you are in the large building that could be expensive if you have to
> run 200 feet of cable up to a roof mounted mast.   CDMA does not
> require a veiw of the sky, that signal is from a cell tower and can go
> through walls just like cell phones.  The CDMA cell towers use GPS for
> time, so your CDMA signal is in the end GPS based.    But as I said
> GPS receivers are dirt cheap, like $15 on eBay.
>
>
>
> I'm curious why you need micro second level time?  What is the application?
>
>




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