Siemens SIMATIC NET System Manual page 65

The figure above shows how a moving node (in this case an automated guided vehicle
system) is handed over between two wireless cells: The client module runs regular scans of
the wireless signals on all the channels stipulated by the standard being used. The client
module then connects to the access point with the channel on which it finds the best
reception. If the limit between wireless cell 1 and wireless cell 2 is reached, the connection to
the access point of wireless cell 1 is terminated. From this time on, the access point of
wireless cell 2 is responsible for the client module.
The time required for the change (handover time) is in the order of 100 ms. A significant
reduction in handover times can be achieved with Rapid Roaming using the iPCF method
("industrial Point Coordination Function"). Both the access point and client must support
rapid roaming.
With some devices, the support of the iPCF method is released by the KEY-PLUG
"iFeatures" (example: SCALANCE W788-x), the SCALANCE W722-1 RJ45 supports this
method already when shipped.
Industrial Ethernet
System Manual, 09/2019, C79000-G8976-C242-10
Basics of communication with Industrial Ethernet
1.5 Wireless LAN
65