[Prism54-users] Sudden loss of connectivity when transferring from NFS mounts

[Jason Tackaberry]

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I just recently picked up a Netgear WG511 based on the success rate
noted on the website.  I previously was using a 3com 16-bit PCMCIA
802.11b card (used atmel_cs) with no problems, except for the fact that
it was slow and used PIO.  My access point is a Belkin 802.11g
F5D7230-4.

I am using Fedora Core Test 3, except I've compiled stock kernel 2.6.5.
I've tried firmwares 1.0.4.0 and 1.0.3.0.

When I transfer (downstream) large files (I've been testing with a 250M
file) from NFS mounts, I will consistently lose connectivity.  iwconfig
still reports that it sees the access point, and displays changing link
quality and signal/noise levels, but I otherwise lose all network
connectivity.  After taking down the interface and bringing it back up
(ifdown/ifup), connectivity is restored, although of course the transfer
operation gets aborted.

The extremely strange part about all this is that if I FTP this file,
everything works fine.  Furthermore, I've not been able to reproduce any
loss of connectivity when copying large files _to_ an NFS mount, only
when downloading.

syslog indicates nothing out of the ordinary.=20

I've tried changing various settings: disabling WEP, changing channels,
forcing a lower bitrate, changing RTS to 250, moving my laptop right
beside the access point, etc.  None of that has any effect; I can still
consistently reproduce connectivity loss when copying a large file from
NFS.

Here is the output from iwconfig when all is fine:

eth1      IEEE 802.11b/g  ESSID:"XXXXXX"  Nickname:"draco.sault.org"
          Mode:Auto  Channel:11  Access Point: 00:30:BD:90:CA:F4
          Bit Rate:54Mb/s   Sensitivity=3D20/200
          Retry min limit:8   RTS thr:2347 B   Fragment thr:2346 B
          Encryption key:XXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XX   Security mode:r=
estricted
          Link Quality:202/0  Signal level:-52 dBm  Noise level:-6 dBm
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

The link quality and signal level remain fairly consistent, but I notice
noise level is all over the map.  It routinely changes from -1 to -20
dBm and then hovers for some time around -250 dBm.

Although this may be a red herring I thought I'd mention it anyway: the
only real difference I can see when copying a file via NFS is that the
latency to the remote server increases to about 30-50ms, whereas with
ftp, it stays about 2-10ms.  This is likely simply due to the nature of
TCP vs. UDP, but my thought is that maybe that little extra push on the
bandwidth causes something to break.

I am otherwise terribly happy with this card, and I'd hate to have to
return it or exchange it.  Can anyone here suggest what the problem
might be?

Thanks,
Jason.

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