D-Link DIR-822 User Manual page 90

Section 4 - Configuration
Specify how often (by the number of beacon frames) that DTIM is
DTIM period (in
transmitted. By default this is set to 1.
beacon frames):
Specify the time interval (in seconds) between keep alive checks of
Station Keep Alive
wireless devices from your WLAN.
(in seconds):
D-Link DIR-822 User Manual 86