Roaming is mostly a client-side concern, and the access points and vWLAN have little control over where a client will try to attach itself to the network. The client looks for the best signal when it first starts to associate with the network. Afterwards, most devices try to hang onto the original access point as long as possible. Some clients do have roaming settings, so you may want to look into options you have on that side of the equation.
It is important to understand what caching protocols are supported on both sides of the equation though. In particular, Bluesocket Access Points (BSAP's) support Opportunistic Pairwise Master Key (PMK) Caching (OPC or OKC), however, OKC is not supported by all clients. In particular, iOS devices currently only support Pairwise Master Key (PMK) caching. The difference being that OKC is pro-active whereas PMK is not. With PMK, the supplicant (wireless client) must have associated with the authenticator (BSAP) previously. For this reason, PMK is sometimes called Fast Roam Back. OKC on the other hand, allows the authenticators to share information making it faster for supplicants to roam to authenticators they have never associated with. For this reason, OKC is sometimes called Fast Roam Forward.
There is one main setting you can adjust on the access points, however, it currently only applies to 1800 series access points. Take a look at the screen shot below; this is a section of the AP Templates in vWLAN.
What you may want to adjust is the Minimum Transmit Rate (MTR). This value effectively forces a client to maintain a certain signal quality. If the client cannot maintain the MTR, then the AP will force the client to disassociate. Because most wireless clients will try to reattach themselves to the network, and the client looks for the best signal when it initiates a connection, it is likely the client will attach to a different AP.
To answer your questions, DynamicRF Mode does not provide any key caching between access points, but it could help with roaming in a different way. With OKC, adjacencies are important, but it is entirely separate from DynamicRF. The DynamicRF Mode tells the AP how it should treat interference. Set Once and Hold means the AP will only adjust its settings when a DynamicRF Calibration is run (configured separately under Administration> Jobs). Continuous means the AP will constantly adjust its settings as needed.
So, if the AP's are calibrated such that they have little overlap in their coverage areas, clients are more likely to roam. The AP mode is again independent of key caching and DynamicRF. The AP Mode tells the BSAP if it should act as a sensor. Dual Mode actually employs a time-sharing algorithm such that the AP will occasionally act as a sensor. It will only go into Sensor Mode when no clients are associated to it. Sensor Mode allows the AP to scan all the channels as opposed to AP Mode where the AP will only detect co-channel activity.
I hope this helps clarify the difference between key caching and DynamicRF.
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