nanog mailing list archives
Re: Interesting stratum 1 NTP clock
From: "Robert E. Seastrom" <rs () bifrost seastrom com>
Date: Thu, 25 Jun 1998 16:21:11 -0400 (EDT)
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
Current thread:
- Interesting stratum 1 NTP clock Tony Li (Jun 23)
- Re: Interesting stratum 1 NTP clock Jerry Scharf (Jun 23)
- Re: Interesting stratum 1 NTP clock dirk (Jun 24)
- Re: Interesting stratum 1 NTP clock Jay R. Ashworth (Jun 24)
- Re: Interesting stratum 1 NTP clock Jerry Scharf (Jun 24)
- Re: Interesting stratum 1 NTP clock Tim Pozar (Jun 25)
- Humour Re: Interesting stratum 1 NTP clock Paul Mansfield (Jun 25)
- Re: Interesting stratum 1 NTP clock Robert E. Seastrom (Jun 25)
- Re: Interesting stratum 1 NTP clock Jerry Scharf (Jun 25)
- Message not available
- Re: Interesting stratum 1 NTP clock Tony Li (Jun 25)
- Re: Interesting stratum 1 NTP clock Stan Hanks (Jun 25)
- <Possible follow-ups>
- RE: Interesting stratum 1 NTP clock S.J.Brannon (Jun 24)
- RE: Interesting stratum 1 NTP clock David Newman (Jun 25)