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802.11 – TIM and DTIM Information Elements

In this blog post I investigate 802.11 TIM and DTIM.

Read the entire blog post here:

http://community.arubanetworks.com/t5/Technology-Blog/802-11-TIM-and-DTIM-Information-Elements/ba-p/256997 

Traffic Indication Map (TIM) – 

After reviewing what the 802.11 standard says about TIM. Lets discuss in real world terms what a TIM is and how it works.

You will specifically find TIM in a management frame called a beacon. A beacon is triggered by default on an access point every 102us. Think of a beacon as a network advertisement. The beacon advertises specific <BSSID> wireless network information such as supported PHY rates, security protocols, supported QoS/WMM, vendor specific information and much much more. Included in the beacon is a TIM information element.

Example: BEACON WITH TIM

 

beacon

 

Delivery Traffic Indication Map (DTIM) – 

After reviewing what the 802.11 standard says about DTIM. Lets discuss in real world terms what a DTIM is and how it works.

You will specifically find DTIM in a management frame called a beacon under the TIM information element. DTIM is to broadcast / multicast traffic as TIM is to unicast traffic.

Under the TIM you will see DTIM count and DTIM period.

Example: DTIM COUNT / DTIM PERIOD

 

dtimcount

 

 

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George Stefanick

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