| | 7 | Among many other enhancements, the [https://en.wikipedia.org/wiki/IEEE_802.11h-2003 2003 802.11h] amendment added the "Channel Switch Announcement" as an optional tagged parameter in management frames (e.g. beacons). Section 8.4.2.21 of 802.11-2012 describes the element. It contains a "New Channel Number" field that describes, as you might expect, the new channel that associated stations should tune to. Additionally, it contains a "Channel Switch Count" which tells STAs when they should tune to the new channel. A value of {{{0}}} informs them that they should tune immediately while any value {{{N}}} for {{{N > 0}}} informs them they should tune immediately before the beacon {{{N}}}th [https://en.wikipedia.org/wiki/Beacon_frame Target Beacon Transmission Time (TBTT)]. Since beacons are multicast and have no error recovery, a large value of {{{N}}} increases the reliability of client stations tuning to the new channel since they only need to overhear one of the {{{N}}} beacons to properly schedule the retuning event. |
