The simplest form of roaming is reassociation. The client always makes the decision to roam based on proprietary criteria that are most often based on RSSI. Part 1 of this series on roaming, describes how reassociation occurs. Other types of roaming will be discussed later in this series.
Once a client has decided that it wants to roam it send a reassociation request to the new AP.
That AP sends an ACK.
The new AP attempts to inform the original AP of the reassociation request and request the STAs buffered data through the DSM (intacontroller or AP to AP - both methods are proprietary).
If this communication is successful the original AP will forward any buffered data through the DSM.
The new AP sends a reassociation response.
The client ACKs the reassociation response to the new AP which confirms the STA’s intent to roam.
If security mechanisms such as 802.1X/EAP are implemented those steps would need to be completed between from start to finish to complete reassociation.
A few things to note:
Roam-back requires a higher SNR than a regular roam. A roam back usually requiqure a RSSI of 10 DB more than a requalr roam.This prevents a ping pong effect.
Roaming thresholds and communications between the original AP and the new AP are not defined in the standard.