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I have a network consisting of

  • a GBit switch
  • a WIFI access point (DLink DWL-G700AP), connected to the switch
  • a Windows XP machine hooked to the WIFI access point
  • a Linux machine with 100 Mbit NIC, connected to the switch
  • a ADSL modem, connected to the switch

The Linux machine runs Samba and a VDR (video disk recorder). The ADSL modem is running a DHCP server.

Overall everything works fine. However, the XP machine occasionally suffers from an unstable network connection. Symptoms:

  • Ping timeouts, both to a well reachable host on the internet and to the Linux machine, typically one to five consecutive timeouts during a ping -t.
  • Hanging web server requests in Firefox, reload usually fixes the problem.
  • A TCP video stream (MPEG-2 SD material, 2 to 5 Mbit/s) from the VDR freezes in the VLC media player, or does not even start properly. VLC reports dropped frames.

I have tested with another XP machine, this one does not show the problems. Therefore I suspect the cause within the problem XP machine.

I have done these things to debug the problem:

  • Restore the TCP stack configuration with netsh: no help
  • Check the network traffic with MS network monitor: no "strange" traffic
  • running iperf between XP and Linux: up to 20 Mbit/s sustainable traffic

During the iperf tests i noted sort of a slow start behaviour, sometimes it took up to 10 sec. to ramp up the traffic.

What else can I do to look for my problem cause?

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A long shot, but this may be related.

  • The XP machine had another preferred WIFI network configured. The problem was fixed with switching that netowrk to "on demand" so that only on preferred WIFI network is available. Now I need to figure out how to tell the machine to switch networks. – Bernd Sep 30 '09 at 12:12

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