Cisco Wireless LAN Controller Configuration Guide, Release 7.5
Configuring the DTIM Period
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Configuring the DTIM Period

Configuring the DTIM Period

Information About DTIM Period

In the 802.11 networks, lightweight access points broadcast a beacon at regular intervals, which coincides with the Delivery Traffic Indication Map (DTIM). After the access point broadcasts the beacon, it transmits any buffered broadcast and multicast frames based on the value set for the DTIM period. This feature allows power-saving clients to wake up at the appropriate time if they are expecting broadcast or multicast data.

Typically, the DTIM value is set to 1 (to transmit broadcast and multicast frames after every beacon) or 2 (to transmit after every other beacon). For instance, if the beacon period of the 802.11 network is 100 ms and the DTIM value is set to 1, the access point transmits buffered broadcast and multicast frames 10 times per second. If the beacon period is 100 ms and the DTIM value is set to 2, the access point transmits buffered broadcast and multicast frames 5 times per second. Either of these settings are suitable for applications, including Voice Over IP (VoIP), that expect frequent broadcast and multicast frames.

However, the DTIM value can be set as high as 255 (to transmit broadcast and multicast frames after every 255th beacon) if all 802.11 clients have power save enabled. Because the clients have to listen only when the DTIM period is reached, they can be set to listen for broadcasts and multicasts less frequently which results in a longer battery life. For example, if the beacon period is 100 ms and you set the DTIM value to 100, the access point transmits buffered broadcast and multicast frames once every 10 seconds. This rate allows the power-saving clients to sleep longer before they have to wake up and listen for broadcasts and multicasts, which results in a longer battery life.


Note


A beacon period, which is specified in milliseconds on the controller, is converted internally by the software to 802.11 Time Units (TUs), where 1 TU = 1.024 milliseconds. On Cisco’s 802.11n access points, this value is rounded to the nearest multiple of 17 TUs. For example, a configured beacon period of 100 ms results in an actual beacon period of 104 ms.


Many applications cannot tolerate a long time between broadcast and multicast messages, which results in poor protocol and application performance. We recommend that you set a low DTIM value for 802.11 networks that support such clients.

You can configure the DTIM period for the 802.11 radio networks on specific WLANs. For example, you might want to set different DTIM values for voice and data WLANs.

Configuring the DTIM Period (GUI)


    Step 1   Choose WLANs to open the WLANs page.
    Step 2   Click the ID number of the WLAN for which you want to configure the DTIM period.
    Step 3   Unselect the Status check box to disable the WLAN.
    Step 4   Click Apply.
    Step 5   Choose the Advanced tab to open the WLANs > Edit (Advanced) page.
    Step 6   Under DTIM Period, enter a value between 1 and 255 (inclusive) in the 802.11a/n/ac and 802.11b/g/n text boxes. The default value is 1 (transmit broadcast and multicast frames after every beacon).
    Step 7   Click Apply.
    Step 8   Choose the General tab to open the WLANs > Edit (General) page.
    Step 9   Select the Status check box to reenable the WLAN.
    Step 10   Click Save Configuration.

    Configuring the DTIM Period (CLI)


      Step 1   Disable the WLAN by entering this command:

      config wlan disable wlan_id

      Step 2   Configure the DTIM period for a 802.11 radio network on a specific WLAN by entering this command:

      config wlan dtim {802.11a | 802.11b} dtim wlan_id

      where dtim is a value between 1 and 255 (inclusive). The default value is 1 (transmit broadcast and multicast frames after every beacon).

      Step 3   Reenable the WLAN by entering this command:

      config wlan enable wlan_id

      Step 4   Save your changes by entering this command:

      save config

      Step 5   Verify the DTIM period by entering this command:

      show wlan wlan_id