[ntp:questions] Re: Embedded targets

Don Becker debecker3 at verizon.net
Sat Jun 3 18:25:54 UTC 2006


Danny,

Thank you for the reply.

Your description of the polling and broadcast mechanisms do not match what
is described in David Mills book "Computer Network Time Synchronization",
2006. Section 2.4 of the book, in describing the broadcast process,
indicates that the client will use the burst feature to set the system
clock, authenticate the server, and compute the offset between the broadcast
time and the client time.   It goes on to say that once the offset is
computed the client sends no further messages.

You indicate that the delay information from the polls should not be used
with the broadcast messages.
(1) How is the delay for the broadcast messages computed then?  can you
reconcile your statement with the David Mills description in the literature?
(2) You mention that NTP broadcast messages can come in from servers that
have not been polled.   The NTP daemon should not use messages from unknown
servers becasue (a) the server has not been authenticated and (b) there is
no knowledge of the network delay from the server.

The description from the book is close to what I need, my only problem is
that the client NEVER polls again.  I think that never is too long a time on
a standalone, autonomous network.

I have no NTP experience and am relying on documents and feedback from
veterans such as yourself.

Don


"Danny Mayer" <mayer at ntp.isc.org> wrote in message 
news:448076D9.3010508 at ntp.isc.org...
> Don Becker wrote:
>> (1) Can someone direct me to ports of ntp to a micro-kernel os (uCos,
>> ThreadX, RTXC, etc)?
>>
>
> It has been ported to VXWorks, but I couldn't tell you whether it still
> builds on that platform.
>
>> (2) Has anyone implemented kernel clock discipline for a micro-kernel os
>> (uCos, ThreadX, RTXC, etc)?
>>
>> (3) Any thoughts of having the client consume broadcast ntp messages in
>> additoon to the periodic polls?  This would allow the client to benefit 
>> from
>> frequent low bandwidth broadcast messages but still be able to 
>> periodically
>> characterize the round trip delays to the server.  Frequent broadcasts (~ 
>> 1
>> minute) with infrequent polls (1-2 hours) would work well in my stable,
>> standalone network application.
>>
>
> It works quite well. We have that kind of thing running on the various
> nodes at UDel, but you should not assume that it will be able to use the
> delay information provided by the queries for broadcast since those are
> different sockets and interfaces and shouldn't be used since that would
> be an unwarrented assumption especially as you could be receiving
> packets from nodes that you are not querying.
>
> Danny
>
>> Thanks for you help & thoughts.
>> Don
>>
>>
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>
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