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.
