Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!decwrl!ucbvax!udel.edu!Mills
From: Mills@udel.edu
Newsgroups: comp.protocols.time.ntp
Subject: Re:  DTS vs. NTP
Message-ID: <9102261936.aa23057@huey.udel.edu>
Date: 27 Feb 91 00:36:56 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: inet
Organization: The Internet
Lines: 30

Mark,

Weenie quibble: the NTP stratum number (really, hop count to the root
(primary server) is variable, depending on the subnet configuration
and the whisps and clanks of the Bellman-Ford minimum spanning tree
algorithm. In my discussions with the DECfolk I came to appreciate
the usefulness of the correctness interval so laboriously calculated
in DTS and in fact stole the idea and incorporated it in NTP. It
was my intent that the NTP correctness interval, actually called the
synchronization distance in NTP version 3, provably contain the DEC
correctness interval. I say contain, rather than coincide, because
the vanilla DEC selection algorithm (based on Marzullo's dissertation)
usually results in rather poor accuracy compared with the older
(prior NTP algorithms), so I modified the algorithm slightly to
retain the previous accuracy, while retaining the correctness arguments.

All this to say that (a) an NTP version 3 implementation can (and should)
provide the correctness interval to a client, which could of course
be a DTS time provider interface, and (b) an NTP daemon could in principle
interwork with a DTS daemon, as long as the DEC correctness interval were
mapped to the NTP synchronization distance. I expressed some concern to
the DECfolk on this last issue, since a DTS/NTP interworking subnet
of any real size, like what we now see in the Internet, might become unstable
under the right circumstances. You will note that the current maze is getting
really large and, for all those rambunctions oscillators out there, has
not displayed any instabilities I have seen. You guys may beat me up about
my beloved phase-lock loops and bickering about their parameters, but the
darn things realy do work as designed.

Dave


Brought to you by Super Global Mega Corp .com