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How does a client choose which AP to connect to?

When connecting to the wireless network I have noticed that the clients will often skip an AP 10 feet away and connect to one two floors up and 100+ feet away. That doesn't sound very efficient and data rates are pretty poor.

Can this be fixed?

My test client is a Dell Latitude E6540 laptop running CentOS 6 -- I can get others if necessary. The access points are CAP-3702Es operating in Flex-Connect mode, and the controller is a WC5508.

VIP Advisor

Re: How does a client choose which AP to connect to?


 Clients usually uses RSSI basically to take decision. If you had the chance to look at clients decision algorithm, RSSI is almost everything the worry about. Well, I know this may does not make sense considering that the AP at 10 ft should provide always higher RSSI but this is not that easy. For some reason, i´ve seen poor decision like that all the times. 

 There are some mechanism in order to educate clients but in my opinion, those mechanism all comes with a cost. One of them is RX-SOP. RX-SOP creates an virtual cell boundary, that force Access Point to ignore signal at certain level. This way, if you are far way from AP cell, you can´t connect. But, if you connect and then you move away, RX-SOP does not disconnect you. Stick clients problems remains.

 Another feature, and perhaps better then RX-SOP, is Optimized Roaming. Optimized Roaming works similar but it controls not only the entrance on the AP cell but also the hand off. If you determine that your cell boundary is -67 dBm, AP will permit clients to connect when they reach this signal level and will rip then off if they walk away and reach -68 dBm. 

 However, those features also can create problem considering the signal variation due interference. Some clients may have problems.

The best advise still is try to achieve a better AP position and use smarter clients as possible. Usually, Intel adapters are very good with Cisco AP, although far way from perfect. 

  Flexconnect or Local mode does not play any role on this problem. This is a basic RF problem.


-If I helped you somehow, please, rate it as useful.-

Hall of Fame Community Legend

Re: How does a client choose which AP to connect to?

Each wireless NIC manufacturer have their own definition about how the chips "roam".  

The older the firmware, the worst the roaming "decision" of the wireless NIC.  

Look at Samsung roaming "logic" (LINK):  Don't roam unless the RSSI is -75 dBm (and worst).  

The easiest way to fix this is to upgrade to the latest wireless NIC drivers.  

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