Small Wi-Fi devices, Bar-code scanners and other IOT devices does go for doze state very often to save power. Every Wi-Fi vendor will have some kind of implementations to get attention of those Wi-Fi Client that tend to go silent often.
Traditionally Meru Wi-Fi system have a feature called CLIENT LOCATOR. While after adding the client devices MAC-OUI on the WI-FI System it keeps sending ICMP request and gets an ICMP reply from those silent clients, by this way the clients connection is kept active. Also Wi-Fi system sends out Qos Null frame in earlier days for those Silent clients.
Now in recent Fortinet Infrastructure based AP models there are certain client upstream and downstream silent client feature implemented.
For Active Clients (If Wi-Fi client hasn’t informed about going for a power save but remains silent):
> If the client is silent for more than 2 seconds, silent client polling kicks in from AP every 2 seconds.
> Consider, if no reply from the silent client then the AP tried to send the RTS for 8 – 30 seconds and gives up. Then the AP will update the “coordinator” about the client is been lost now.
station log will look like this:
| 802.11 State | * <AID=31>[abgn](v0) (pre found) lost from assigned <AP=13> ESSID=***** Ch=149 A-BSSID=***** reason=Station lost from AP
>So, Once station is declared lost, TIM bit is enabled in the beacon.
>And if station is back on network, then a found notification will be send. If not found then the system will run the station ideal time out for 33 min(default) and will send out a De-auth.
Power Save Clients (Client informed going for power save)
>Again if client is silent for 2 sec, silent client polling kicks in from AP every 2 sec.
> Silent client polling starts by AP setting TIM vector in beacons.
> However, TIM bit is still set in the beacons for 33 minutes and if no response from client then later TIM bit is reset and De-auth will be sent out.
>Silent client polling starts by AP setting TIM vector in beacons and stations sends PS- POLL frame to AP, AP in turn sends QOS NULL data.
The default silent_client.frame_fail_threshold varies from “8 – 30” depending on the Firmware version on the system and this can be changed with the help of AP Boot script. However, before any changes i would advise you to get some tips from Experts.