[ntp:questions] Very rapid polling

Uwe Klein uwe_klein_habertwedt at t-online.de
Sun Feb 15 10:45:58 UTC 2009


gary.limanapier at elisys.co.uk wrote:
> On Feb 15, 9:15 am, Uwe Klein <uwe_klein_habertw... at t-online.de>
> wrote:
> 
>>gary.limanap... at elisys.co.uk wrote:
>>
>>>Just joining this discussion as we have noticed NTP request from our
>>>Authorised Server every 300ms on our LAN. They occur only between the
>>>Time Server and the WiFi Tablet during a socket connection while there
>>>is a low signal strength. The Tablet sends its own NTP request with a
>>>Poll Interval of 4 (16 seconds). The server returns its response
>>>increasing the Poll Interval to 10 (1024 secs). The server then keeps
>>>sending this same packet every 300-500ms.
>>
>>Does the ntp process submit these packets repeatedly or
>>are you seeing some (uncalled for) "collision/resend" action due to
>>issues with the wlan connection?
>>
>>uwe
> 
> 
> Would it matter if the packet colided? NTP is using UDP and I can't
> see from the packet analyser that it is expects a response back. When
> it does work with a known good machine there is no acknowledgement of
> the packet being sent. Do you think that there another level of
> operation in the network that I am not seeing with the packet analyser?

you usually get retransmission on collision from the hardware ( or the driver ).
( ethernet i am certain about, no firm knowledge about wlan though )
This would be independent of the protocol used.

this might help ( look for collision .. RTS/CTS packet ):
	http://wlan.nat.sdu.dk/802_11standard.htm

 From my side this is an absolutely blind guess. But it could
well be a point to look at before trying to find an app bug
that may not be there.

uwe




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