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Re: NTP, possible solutions, and best implementation

  • From: Robert E. Seastrom
  • Date: Fri Oct 03 15:20:26 2003


"Nathan J. Mehl" <memory-nanog@blank.org> writes:

> >     This is a Stratum 0 source so once placed behind a Unix/Cisco/Juniper
> >     box you have a stratum 1 source.   This will cost you 30,000 -> 
> >     100,000 US per unit.   The beam tube will require replacement
> >     approx every 5 years for about 20,000 US.
> 
> They only cost that much new-in-box. :)
> 
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2560947055&category=25399

The device Nathan references above is a bunch of isolation amplifiers
in a box, used to distribute a standard timing signal to a number of
users without mutual interference to the pulse shape from the end-user
equipment.  It does not contain a primary frequency standard, but has
connections for up to three external references (which are hopefully
running in lockstep :).

While it's true that HP 5061B and 5071 Cs beam frequency standards are
available for far less than the list prices quoted above, they're not
available in working condition on eBay for $350.  :) I think last time
I checked refurbished tubes for the 5061B were a $5-7k proposition.

As others have noted, CDMA-disciplined NTP clocks such as those from
EndRun are indirectly disciplined by GPS in the vast majority of
cases.  It would probably be more honest to configure them to claim to
be stratum 2 NTP servers, but don't tell the marketing folks that;
they'll pitch a fit.

With GPS based NTP appliances, one must pay attention not only to the
manufacturer of the box, but to the actual manufacturer of the GPS
module inside the box.  In years past the Motorola VX and UT OEM
modules have been included by more than one player as the "guts" of
the machine.

Other likely sources are WWV/WWVH (2.5, 5, 10, 15, 20 mhz; medium term
jitter can be problematic due to propagation changes), WWVB (60 khz,
less jitter than WWV, but can be hard to receive ih a high-rfi
commercial environment), CHU (3330, 7335, 14670 khz if you prefer a
Canadian shortwave time/frequency service), DCF77 (for Europe, not too
useful in North America),

Loran-C is of limited life expectancy, and NIST is planning to cease
involvement with time code signals on the GOES satellites after 1
January 2005 (although the birds will continue to provide the
timecode, NIST will no longer be controlling and checking the signal).
Therefore, it's probably not a good idea to make future plans based on
either of these services (although equipment to implement them
short-term may be available at bargain prices!)

The following links may be of interest:

http://tycho.usno.navy.mil/
http://www.boulder.nist.gov/timefreq/
http://www.ntp.org/

                                        ---rob