Roaming scanning is to scan all APs under the same ESSID (SSID). There is a way to speed up this process, which is to enable 802.11k, which is a radio frequency scanning protocol. Can be used to obtain information about the current environment.
After turning on 802.11k, roaming scanning can get a second-level speed increase.
For example, a user is on the phone and walks from one side of the building to the other, and the WIFI signal is weak. When it reaches -70dBm, the device will start roaming. When 802.11k is turned on, the device will find that APs with the same ESSID are still working on three channels. After that, the device scans these three channels, and if the signal strength is determined to be sufficient, it will perform roaming. If you don't enable 802.11k, you must scan each channel one by one to find an AP that can roam. The speed will be much slower.
802.11k obtains information of surrounding APs through management frame neighbor report/response, including BSSID and channel information.
reuqest is in this format:
Contains: category-5-Radio measurement
action-4- neighbor report request
dialog token-0
SSID parameter - SSID等
The format of a response:
The length of the frame varies with the number of APs included. Each AP corresponds to a Neighbor report of 13 bytes, including BSSID, Operating class, Channel Number and PHY type. You can reduce the amount of scanning during roaming through channels.