Connectivity and Data Protection
Roaming
As a user roams about an area, the mobile station may need to
reassociate with a second access point having the same SSID as the
first in order to maintain a stable connection to the ESS. This may
happen as the user roams out of range of one access point and within
better range of another access point. Although the decision to
reassociate is not specifically defined in the 802.11 standard, mobile
stations typically will reassociate when either frame retransmissions
exceed a specific value or when the received signal strength drops
below a certain value. It can be far more complicated than only taking
into consideration these two variables, but accounting for all of the
proprietary decision-making algorithms used by various manufacturers
is beyond the scope of this book.
When a station reassociates, it first authenticates with the new access
point, and then starts the association process by sending it a
reassociation request frame as shown in Figure 3.5. The reassociation
