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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Interesting stratum 1 NTP clock
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 <[email protected]> > > > 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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