Specifics of client transition between nodes in the Wi-Fi System

In a home network, when organising a Keenetic Mesh Wi-Fi System, you may experience random switching of some Wi-Fi clients between nodes or sub-optimal selection of the access point by clients. The fact is that the Wi-Fi System does not switch clients between nodes and does not manage this process -  Wi-Fi standards do not regulate such a possibility. In Wi-Fi technology, the decision to switch between access points is made solely and exclusively by the client. On the controller side of the Wi-Fi System (on the Main Router), it is possible to enable fast search and informing clients about neighbouring access points, to enable fast client transition, to force the client to limit its choice of nodes and/or to deprive it of choice (for example, to specify only one particular access point). But once a client is left with a choice of nodes to connect to, we can no longer control that choice.

When seamless roaming is enabled, access points do the following:

  • 802.11k informs clients, who support the relevant standards and can accept information, about access points available in the roaming domain;
  • 802.11v recommends a transition to the adjacent band (this is just a recommendation, it is not mandatory for the client).

But this has only an indirect effect on client switching between nodes in a Wi-Fi System. Based on this information, the client makes its own choice of the preferred access point to which it will connect, based on its own supported algorithms and roaming mechanisms.

The quality of seamless roaming is primarily dependent on the capabilities of the Wi-Fi client (the best option is when the client supports the full set of 802.1r/k/v protocols). If a client does not support 802.11k/v protocols, it is not possible to influence its switching algorithm, even by way of information and recommendations. If the client supports 802.11k/v protocols, once the client has selected an access point and started to connect to it, the system further ensures fast switching with the 802.11r protocol (FT; Fast Transition). Once again, please note that the Wi-Fi System only facilitates and speeds up client switching between nodes, but the clients themselves make the decisions and make the connections/transitions.
On devices without 802.11r fast roaming protocol support, Keenetic routers can use PMK cache transition.

Wi-Fi clients usually select an access point with higher signal strength, but not simply by an absolute excess, but only if this excess is greater than a certain value. And the value of this excess depends on the absolute value of the signal strength. An example of one client's passive Wi-Fi roaming table:

Passive roam thresholds:
RSSI > -56: diff 12dBm
RSSI > -62: diff 11dBm
RSSI > -68: diff 10dBm
RSSI > -74: diff 9dBm

If the signal strength from an AP is -62 dBm, the transition to another AP will begin when its signal strength is at least -51 dBm, and if -74 dBm, the transition will occur at -65 dBm.

If a Wi-Fi System has a lot of overlap between nodes, a client may persistently connect to a more distant AP, and we cannot manage this connection from the Main Router and APs.

For seamless roaming to work properly, the coverage areas of different access points should overlap, but it is recommended that this overlap should not exceed 30% (approximately) if possible. In the case of dense access points, try to reduce their signal strength. If there is no overlap, 'blind spots' appear, the client will disconnect from one point when switching to another, and there will be no seamless switching. And if there is too much overlap, the client may constantly switch between different access points, make sub-optimal point selection, or - because the signal sources are too close to each other - switching between adjacent points will not happen.

On the Wi-Fi system side, we can enable 802.11r/k/v protocol support on the Main Router for seamless roaming and also force the client to restrict the choice of certain nodes and bands: 'Wi-Fi seamless roaming'.

 

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