Richard B. Gilbert wrote: > Uwe Klein wrote: > >> gary.limanap...@elisys.co.uk wrote: >> >>> On Feb 15, 9:15 am, Uwe Klein <uwe_klein_habertw...@t-online.de> >>> wrote: >>> >>>> gary.limanap...@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!
Watch my lips ( or this wrongfull usage of that idiom) : The hardware does automatic resend on collision using an exponential+random backoff algorithm. In Ethernet hardware this is buried in the chipset. Wlan does similar stuff but buried in the driver OS side and/or Firmware side. ( And the newfangled stuff tends to have more and nefarious implementation issues ) It has nothing to do with UDP, TCP or whatever type of protocol you think you are using ( wrong layer ). An eternity ( in internet time ) ago I used to design ethernet interface cards. You could have very subtle errors in the transceiver or cabling where some party on the cable saw a collision while others did not. uwe _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
