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Old 07-08-2009, 06:34 PM   #1
ShadyCraig
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Question very high packet loss on kernel driver, fedora 10


Hello all,

My fedora 10 pc is suffering with very high packet loss, it's typically between 10% and 40%, also some packets have a long rtt (up to 50 seconds).
I hope someone can help me get to the bottom of it.

The device is a linksys wireless pcmcia card. I don't think this is a location/interference problem as other nearby devices are ok and I've tried moving the wireless router to beside the pc without improvement.

I've connected to other wireless routers and have the same problem.

Output of various commands follows:

ifconfig
Quote:
wlan1 Link encap:Ethernet HWaddr 00:16:B6:C3:F6:91
inet addr:192.168.1.100 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::216:b6ff:fec3:f691/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1116 errors:0 dropped:0 overruns:0 frame:0
TX packets:1352 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:342088 (334.0 KiB) TX bytes:245838 (240.0 KiB)

[root@desk ~]# ping -c 1000 -q 192.168.1.254
Quote:
PING 192.168.1.254 (192.168.1.254) 56(84) bytes of data.

--- 192.168.1.254 ping statistics ---
1000 packets transmitted, 908 received, 9% packet loss, time 1011528ms
rtt min/avg/max/mdev = 1.723/129.188/5652.712/500.944 ms, pipe 6
lspci -v
Quote:
02:00.0 Ethernet controller: Atheros Communications Inc. AR2413 802.11bg NIC (rev 01)
Subsystem: Linksys Device 0053
Flags: bus master, medium devsel, latency 168, IRQ 19
Memory at 64000000 (32-bit, non-prefetchable) [size=64K]
Capabilities: [44] Power Management version 2
Kernel driver in use: ath5k_pci
Kernel modules: ath5k
Please let me know any more info is required.

Many Thanks,
ShadyCraig
 
Old 07-08-2009, 08:32 PM   #2
stress_junkie
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Can you temporarily replace the wireless NIC in the computer?
 
Old 07-09-2009, 01:34 AM   #3
ShadyCraig
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I have tried this, however, the 2nd nic doesn't seem to support the features of the 1st as it won't attach to the wireless router. I keep getting the wpa2 passkey box, so it may not support wpa2 (I would have thought that this would be an OS feature rather than a driver or hardware ones though?).

I have also tried the 2nd nic on another wireless router without any security. This worked and gave me a consistent 0% loss. I should mention that this nic uses a different driver (ndiswrapper).

So the problem is either: a faulty nic or a faulty driver.

I will try using a live cd for my distro with the nic to see if this makes any difference.

Thanks!
 
Old 07-09-2009, 08:47 AM   #4
stress_junkie
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I tried researching Linksys PCMCIA Wifi NICS to see what brand of chipset it might have. The brand of chipset is very important in Linux support because some brands are better supported than other. I cannot quickly determine what brand of chipset your NIC has because you did not provide the exact model name/number of this device. You should always provide this kind of detail when you are inquiring about a hardware component.

[QUOTE=ShadyCraig;3601813]I have tried this, however, the 2nd nic doesn't seem to support the features of the 1st as it won't attach to the wireless router. I keep getting the wpa2 passkey box, so it may not support wpa2 (I would have thought that this would be an OS feature rather than a driver or hardware ones though?).
Hardware drivers are often incorporated into the Linux kernel at some point. However hardware support for specific components almost always starts as an independent add-on. Sometimes driver support remains independent of the kernel because the driver developers do not license their driver under open source/GPL terms. (Nvdia, ATI, maybe others)

Quote:
Originally Posted by ShadyCraig View Post
I have also tried the 2nd nic on another wireless router without any security. This worked and gave me a consistent 0% loss. I should mention that this nic uses a different driver (ndiswrapper).
This makes me think that the NIC uses Broadcom chips. The following page mentions in the comments section that Broadcom chips may not work with WPA2 and may have very bad performance. However this applies to the native Linux driver. This does not apply to the Windows driver that is used by means of ndiswrapper.
http://blogs.computerworld.com/new_l...drivers_arrive

Ndiswrapper is a translation layer. It allows you to use Windows drivers for wireless NICs in Linux. Ndiswrapper is not a driver in and of itself.

Quote:
Originally Posted by ShadyCraig View Post
So the problem is either: a faulty nic or a faulty driver.
Yes. If your NIC uses a Broadcom chipset then it most likely is the driver. Best solution: get a wireless NIC that uses some other chipset such as Atheros. Sorry but that's what I would do.

Quote:
Originally Posted by ShadyCraig View Post
I will try using a live cd for my distro with the nic to see if this makes any difference.
That is a very good idea. Good device level troubleshooting technique where in this case the device is the software.

Last edited by stress_junkie; 07-09-2009 at 08:49 AM.
 
Old 07-09-2009, 01:36 PM   #5
ShadyCraig
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Quote:
Originally Posted by stress_junkie View Post
I tried researching Linksys PCMCIA Wifi NICS to see what brand of chipset it might have. The brand of chipset is very important in Linux support because some brands are better supported than other. I cannot quickly determine what brand of chipset your NIC has because you did not provide the exact model name/number of this device. You should always provide this kind of detail when you are inquiring about a hardware component.
I thought I'd provided this in the lspci output in my first post. This this is not the case can you tell me how I can find this out.
 
Old 07-09-2009, 05:27 PM   #6
ShadyCraig
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I found this ticket: http://madwifi-project.org/ticket/2148
In there someone suggested altering the rate down to 24Mbs using 'iwconfig wlan0 rate 24M'. This seems to have done the trick as loss is 0% after 500 pings now.
 
  


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