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Re: Interesting stratum 1 NTP clock

  • From: Shawn David Solomon
  • Date: Tue Jul 07 10:25:12 1998

  
 I'm glad we've wandered upon the topic of stratum 1 clocks.  I've been
looking for a clock that has the capability to provide clocking to Cisco
ATM switches (BPX's) and also provide a clock source for our unix hosts.
Do they make such a beast?  is it a good idea to use the clock for both
purposes?

 Any help/comments welcomed..

 shawn




On Thu, 25 Jun 1998, Robert E. Seastrom wrote:

> 
>    From: Tim Pozar <pozar@lns.com>
> 
>    > Would a GPS hooked to the serial port of a Linux box do the same?
> 
>    No.  You need to dectect the event of the second. Some OEM GPS boxes will
>    have another pin that will go low/high when this event occurs.
> 
> In places where I've seen this done, that pin usually ended up tied to
> DCD.  The Cisco appears to permit this to be on { RI, DSR, DTR, CTS,
> RTS, DCD } and also support an "inverted" signal, which I take to mean
> high->low transition is PPS, not low->high.  It is noteworthy that
> certain manufacturers (Rockwell and possibly Trimble come immediately
> to mind) do not synchronize the PPS pulse to the top of the second as
> standardized by USNO (and indirectly BIH) but rather just give you one
> pulse per second starting at an arbitrary (but accurately expressed in
> the NMEA sentence!) point in the second.
> 
>    Also, beware that currently GPS time is 12 seconds fast from UTC.
> 
> Not if you have a "good" GPS that picks up that data in the ephemeris
> and corrects automatically.  Almost all of them will do this now.
> Your average end-user has no interest in the fact that GPS has no
> concept of "leap seconds" to bring itself into compliance with
> international standard time, and thus should not have to compensate
> for it.
> 
>                                         ---Rob
> 
> 





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