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Cisco aironet a/b/g doesn't pick the best AP!

Hi I am using Aironet a/b/g (PCI) with the latest driver and firmware. I use it to connect to my school's network which uses WPA/TKIP with server based authentication (EAP-TLS). Based on "Cisco Site Survey Utility" or scan result of Aironet Desktop Utility, there is one access point which has almost 100% (SNR), but the problem is that my card doens't connect to it even half of the time and it always picks up the APs which have really bad signal strength and bit rate. I have tried to enter the MAC address of the good AP in "Prfered Access Point" lists but that doesn't help either. For this last couple of days I know that AP shouldn't have too many clients on it since the school is on break.

Is there anything I can do to ensure that my card gets connected to proper access point at least half of the tim ?

You can see a screenshot of list of available Infrastructure here:

formatting link
As you can see there is about -20db difference between the two AP!

Thanks in advance

Reply to
moushak
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Hm. The CB21AG/PI21AG normally do a pretty good job of picking the best AP, so I'm not sure why yours is choosing the AP on channel 11 with RSSI of -75dBm (call it "AP11") rather than the one on channel 1 ("AP1") with -58.

Can I assume that your PC is staying parked in the same physical location and is not roaming around at this time?

One possible explanation might be that, although the RSSI of AP11 is -17dB better, conceivably its net SNR is actually worse. (From your description, though, it doesn't sound like it.) Also, your site survey shows only one other AP on channel 1, and its RSSI is 23dB lower ... while channel 11 shows 7[!] other APs, one with a 15dB STRONGER signal than AP11s. ALSO you have an AP out there on channel 10 which would definitely impose noise on channel 11 (and,to a lesser extent, on 6), so it sure SEEMS that AP1 is the one we ought to pick.

Another possibility might be that AP1's configuration (SSID? Security settings) is (intermittently??) different from AP11's. This seems a bit far-fetched too ...

There's not really any simple answer here ... to figure out more actually re why your card is picking the AP it's picking, we'd need to put some debugging code onto your PC, and also it would be good to gather concurrent wireless sniffs of channels 1, 6 and 11.

One thing you COULD do would be to go into Device Manager and play around with the card's BSS Aging and Scan Valid timers ... these control how vigorously the card will roam. I have no reason to believe that they will make any difference in your case, but at least they will give you a knob to fiddle with.

Regards,

Aaron

Reply to
Aaron Leonard

Aaron, thanks, I really appreciate your input.

Yes, my pc is not roaming.

SNR and RSSI of the strong channel are always the best, at least when my card picks it up.

As far as I know the security settings of all APs are the same.

Where can i get more info to do this debugging/sniffing ?

I am gonna do this, should I increase or decrease those two values ?

thanks again

Reply to
Moushak

~ > There's not really any simple answer here ... to figure out more ~ > actually re why your card is picking the AP it's picking, we'd need ~ > to put some debugging code onto your PC, and also it would be good ~ > to gather concurrent wireless sniffs of channels 1, 6 and 11. ~ ~ Where can i get more info to do this debugging/sniffing ?

Well, for the wireless sniffing bit, you "just" get three wireless sniffers (@ US$5k or so) and have them sit around your PC.

On the client side, you'd need to open a Cisco TAC case.

~ >

~ > One thing you COULD do would be to go into Device Manager and ~ > play around with the card's BSS Aging and Scan Valid timers ... ~ > these control how vigorously the card will roam. I have no reason ~ > to believe that they will make any difference in your case, but at ~ > least they will give you a knob to fiddle with. ~ ~ I am gonna do this, should I increase or decrease those two values ?

You can try both increasing and decreasing. In general, the BSS Aging value should be greater than the Scan Valid interval value - but no more than twice.

Regards,

Aaron

Reply to
Aaron Leonard

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