traffic indication message (802.11) (TIM)
Each access point of a WLAN s ends a Traffic Indication Message (TIM) in each beacon period. This is a message from the access point for WLAN stations that are in the idle state. With this TIM message, the access point indicates to the WLAN station that it has cached a message for it.
In addition to the actual Traffic Indication Message (TIM), there is also the Delivery Traffic Indication Message( DTIM) and the Announcement Traffic Indication Message( ATIM). The Delivery Traffic Indication Message (DTIM) is a special TIM message that the wireless access point( WAP) sends after a specified number of beacon intervals, informing the WLAN client that it has cached multicast and broadcast messages.
And with the Announcement Traffic Indication Message (ATIM), the access point notifies the peers of an upcoming data transfer. The TIM interval in 802.11ac is the same as the Beacon interval, while the DTIM interval is a multiple of the TIM interval. The TIM message contains a counter that counts down and transmits the DTIM message at zero.