Cisco Air Time Fairness (ATF) for High Density Experience (HDX) allows network administrators to enable some groups to regulate downlink air time and configure some groups to receive traffic from the WLAN, more frequently than other groups. Therefore, some groups are entitled to more air time than other groups.

Cisco ATF establishes air time limits (defined as a percentage of total air time) and to allows administrators to apply those limits on a per SSID basis, where the SSID is used as a parameter to define a client group. Other parameters can be used as well to define groups of clients. Furthermore, a single air time limit (defined as a percentage of total air time) can be applied to individual clients.

If the air time limit for an SSID (or client) is exceeded, the packets that are in the downlink direction are dropped. Dropping downlink packets (AP to client) frees up air time whereas dropping uplink packets (client to AP) does not do anything to free up air time because the packet has already been transmitted over the air by the client.

Only air time in the downlink direction, that is AP to client, can be controlled accurately by the AP. Although air time in the uplink direction, that is client to AP, can be measured, it cannot be strictly controlled. Although the AP can constrain air time for packets that it sends to clients, the AP can only measure air time for packets that it hears from clients because it cannot strictly limit their air time.

Choose the Configuration > Wireless > Air Time Fairness to configure the following:

1. On the Global Config tab, set the Status field to Enabled for the radios that you want.
2. To monitor air time usage statistics such as the air time used by different WLANs, the total air time used by a radio, and the dropped packets, as reported by access points in the AP group, for all AP the transmissions periodically, set the mode to Monitor.
3. To enforce air time usage in the access point group, based on the configured ATF policy, set the Mode field to Enforced. In Enforced mode, statistics such as air time usage per policy, drops due to policy violation, and expected air time usage per measurement interval are reported in addition to the data monitored in Monitor mode.
4. To allow WLANs to share unused air time from other users optimally, use the slider to enable Optimization.

5. Use the slider to enable or disable Bridge Client Access feature.

   The Airtime Allocation value is displayed; which cannot be edited.

6. Click Apply to save your ATF configuration.

1. On the Profiles tab, click Add to create a new ATF policy.

2. Specify a name, ID, and weight to the ATF policy. Weighted ratio is used instead of percentages so that the total can exceed 100. The minimum weight that you can set is 5.

3. Use the slider to enable or disable the Client Sharing feature.
4. Click Apply to Device to save your ATF configuration.

5. To delete a policy, select the check box next to the appropriate policy and click Delete.

6. To edit an existing ATF policy, select the check box next to the policy you want to edit. Details of the policy are displayed in the Edit ATF Policy window. You can modify the weight for the policy and client sharing detail.