cisco wireless connection problem

Unanswered Question
Oct 9th, 2007


I have a question on the cisco AP,the scenario is like this. I have AP1,AP2,AP3 , The User1 is nearby to the AP1 but it was connected to the AP3. What is the problem actually. thx


I have this problem too.
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john.preves Tue, 10/09/2007 - 13:33

Depends on how close the AP's are, antennas, etc, but many times if you are under an AP you think you should be associated to and you are not, the power is too high on the AP and or the card as well.

A proper site survey will fix this issue. The length and breadth of which is to long for this space but the info is out there.

gilbertthor Tue, 10/09/2007 - 22:40

Now the situation is the user mostly are connected to the AP3 and this cause the imbalance for the bandwidth on the AP3 while the AP 1 is very free. Any Idea for this?



john.preves Wed, 10/10/2007 - 17:26

At some point during startup or maybe through the course of the day, your users associate to AP3. The signal being too strong, the client sees no reason to roam, even as they move out of the area. By using smaller cells at lower power, you can physically load balance the system. If there is weak signal beyond the edge of what you think should be the edge, the clients will roam to the nearest AP.

Previous post still stands.

Scott Fella Mon, 10/15/2007 - 18:37

John is right... users are associating to a certain ap and will not roam unless signal gets poor. Users are on AP3 but move toward AP1 but has a signal strength of -75, user will not roam. Roaming is done via the client card not the ap. What you can do is tweak the power down and or disable the lower data rates below 11mb or 5.5 and see if that helps.

dennischolmes Tue, 10/16/2007 - 14:28

Ok guys. Let's talk RF here. First and foremost, switching APs (roaming) is a function of the client device. Bear in mind that there are varying levels of client devices from retail type broadcom and centrino internal cards to enterprise class cards from Cisco, Proxim, etc. The retail cards have a function built into them that causes them to try at all costs to associate with the same access point that they initially attach to. This is commonly referred to as "parent sticky". In some cases this can be tweaked inside the client driver for these cards but at a much lesser degree than the functionality you get with more expensive enterprise chipsets. It really has nothing to do with your network. The network simply sees the original AP and its driver either doesn't have the ability to roam until complete connection is lost or it has a setting that says if the signal is better than a set signal strength then roam. Quite frequently this is set for a RSSI of -80. If you change the setting to roam when an AP is heard at -75 then that is what the client will do. Enterprise class cards are much more robust in their ability to be controlled. They have the ability in most cases to aggressivley roam. This is a key requirement when being deployed in a Cisco Unified Wireless Network with LWAPP and load balancing enabled. The increased density of APs in such a deployment requires that the client roam faster and more frequent than ever before. Also, be aware that the way you authenticate can also effect your roam times as the credentials on an autonomous deployment will need to be checked everytime you switch APs. In an lwapp environment, with credentials caching enabled, the credentials are stored on neighboring APs so that you only have to reassociate, not reassociate and reauthenticate.

In summary, your network is not your problem. If you are worried about channel overlap, transmission power settings, and proper coverage I would suggest you move to a Cisco Unified Wireless Network from autonomous. This network also enforces load balancing which will assist you with your problem. Insure your clients have enterprise class cards and that the drivers for these cards are configured for faster roam times. Next, remember that the entire network should be symetric. By symetric, I mean that if the client card is set to 15dbm then set your AP transmission power to 15dbm and adjust AP location accordingly. If you were using LWAPP this would be done for you automatically. Lastly, make sure to keep the drivers updated to those that actually work. That's not always the latest ones.

gilbertthor Tue, 10/16/2007 - 19:36

Hi fella5,

Is it any tools that can detect the signal coverage, as u mention before this might be 1 side AP signal strong and another side AP signal weak.



dennischolmes Wed, 10/17/2007 - 03:32

If the deployment were LWAPP you could use Cisco WCS. If it is not you will need to use a good site survey tool such as Ekahau or Airmagnet Survey Pro. If you are looking for just a cheap signal strength reader try a Cisco client card in site survey mode or download and use NetStumbler.


gilbertthor Thu, 10/18/2007 - 18:00

hi dennischolmes,

Thks for your advise,beside that is it any free tools that i can use. i got found the Ekahau seem like need to charge for the site survey tools.



dennischolmes Fri, 10/19/2007 - 07:58

You could use a Cisco wireless card in site survey mode or for really low price go out and download netstumbler.

walterbates Thu, 10/25/2007 - 10:35

Are you running Autonomous or LAN Controller based wireless? Are you designing for coverage area or capacity?

If autonomous (i.e. IOS) you could restrict the speed required to associate to an AP. The IOS command would be speed basic under the radio interface you're working with. By default the AP allows connections as low as 1Mbps (for phones, etc) which could be increased to g rates of 12Mbps or higher. You could also use a lower gain antenna (like a 2.2 dBi). The signal leaves an omnidirectioanl antenna looking like a donut. The hole in the donut has the antenna going through the middle of it. The higher the gain antenna, the bigger the hole in the donut.

Anyway my two cents worth -W


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