It is a wireless client that determines when it will roam and to which access point it will roam. All we can do as designers is design and implement WLANs that make the clients’ decisions better. There are also two amendments to 802.11 that aid in this effort.
802.11k and 802.11r (which have been rolled up into 802.11-2012) were both spearheaded to aid clients in making wise roaming choices. If a client can roam faster and roam to the access point that will provide the best performance, all clients in the ESSID (a group of APs that share the same SSIDs and corresponding security) benefit.
802.11r or Fast BSS Transition (FT) is an amendment that provides for continuous connectivity via faster secure roaming. This is achieved in the following manner. Essentially a client completes a portion of the key exchange and that key is cached and waiting for the client should it roam to that particular AP. This reduces the time it takes to complete a secure roam between APs. There is another less-robust method that exists called OKC (Opportunistic Key Caching).
802.11k or Radio Resource Management (sometimes referred to as RRM). The purpose of 802.11k is to help a mobile unit roam to the best possible access point. Wikipedia list 4 steps how RRM achieves this…
- Access point determines that client is moving away from it.
- Informs client to prepare to switch to a new access point.
- Client requests list of nearby access points
- Access point gives site report
- Client moves to best access point based on report
So no Mr. Mobile Client we cannot make you roam, but we can use the recommendations that the IEEE made to give you a strong incentive. There is yet one more amendment which I know little about (802.11v) and it seems not many others know much about. Furthermore it has not received much traction by vendors. There is some interesting info posted on Ben Miller’s blog…