David,
The basic definition of SNTP has not changed over the yeas, although
rfc5905 does clarify the intended scope and role of primary servers,
secondary servers and clients. It was the expected, but not required,
model that the Unix adjtime() system call be used if the offset was less
than an unspecified value and the settimeofday() if greater. There was
no intent, either in the earlier SNTP specifications or rfc5905 to
specify the SNTP clock discipline algorithm itself.
Dave
David Woolley wrote:
Danny Mayer wrote:
On 6/16/2010 5:22 PM, Maarten Wiltink wrote:
"Marcelo Pimenta" <[email protected]> wrote in message
news:[email protected]...
[...]
The NTP algorithm is much more complicated than the SNTP algorithm.
The short, short version: there is no SNTP algorithm. SNTP is NTP
_without_ the algorithms. Using NTP means continuously adjusting the
speed of your clock so it tracks real time as best you can make it,
while SNTP is simply asking what time [they think] it is.
This is a totally inaccurate statement. See RFC 5905 Section 14. SNTP is
That RFC was published after this thread was started! You can't go
changing the definitions just for you convenience. Even if it had
been published, say six months earlier, the reality is that de facto
and historic definitions would still dominate the market.
merely a subset of the full NTP protocol. An SNTP server is one with
it's own refclock and not dependent on any other upstream servers while
and SNTP client is one with a single upstream server and no dependent
clients. An SNTP client or an SNTP server should be disciplining the
clock in the same way as an NTP server. An SNTP server should
continuously adjust the speed of your clock otherwise it's not SNTP
compliant.
In reality, most SNTP clients step the clock. A few may use a simple
frequency control scheme. Once you go much beyond that, it becomes
simpler to use a full NTP client, but maybe configure only one server.
In fact, RFC 1305 doesn't require any specific clock discipline for
NTPv3 clients; that is in an appendix, rather than in the main
specification.
The important clarification about SNTP, ignoring any recent attempt to
redefine it, is that it doesn't specify an algorithm, rather than that
it requires the use of only a trivial algorithm.
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