[ntp:questions] Very rapid polling

Richard B. Gilbert rgilbert88 at comcast.net
Sun Feb 15 18:06:33 UTC 2009

Uwe Klein wrote:
> 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

Remember that NTP uses UDP.  UDP does not guarantee delivery, does not 
resend packets, etc.  It sends a response to a request and doesn't know 
or care if the response was received or not!

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