To avoid connection disruption due to channel change, the IEEE 802.11h amendment introduced a channel switch announcement information element (CSA IE) in beacons and probe response frames to enable connected clients to seamlessly follow an AP to the new channel.
The CSA IE contains the new channel number along with a channel switch count field that indicates the number of beacon intervals pending for the channel change to occur. The AP should set the channel switch count field to a large enough value to allow all clients in power save state to receive at least one beacon containing CSA IE. The CSA IE can also be sent between beacons using a CSA action frame.
An important point to note is that the AP is expected to beacon in the old channel until the channel switch count field reaches zero, and then transition to the new channel for subsequent beacons. This implicitly means the AP should complete channel switch within one beacon interval (typically 100ms). In some AP implementations, the channel switch time far exceeds one beacon interval. While most client implementations wait a little longer in the new channel till they receive the first beacon, few client implementations give up hope in 2-3 beacon intervals and initiate a full scan assuming the AP has disappeared. This causes a noticeable disruption for that particular client. In an enterprise network, this can cause frequent client roaming events, although the clients are stationary.
Therefore, my recommendation is an AP should change channels less frequently and should do so either for regulatory reasons like DFS radar detection or if there is clear evidence of long term benefits of doing such a channel change.
LinkedIn: 