Air Time Fairness

Information About Air Time Fairness

Cisco Air Time Fairness (ATF) allows network administrators to group devices of a defined category and enables some groups to receive traffic from the WLAN more frequently than the other groups. Therefore, some groups are entitled to more air time than the other groups.

Cisco ATF has the following capabilities:

  • Allocates Wi-Fi air time for user groups or device categories.

  • Air time fairness is defined by the network administrator and not by the network.

  • Provides a simplified mechanism for allocating air time.

  • Dynamically adapts to changing conditions in a WLAN.

  • Enables a more efficient fulfillment of service-level agreements.

  • Augments standards-based Wi-Fi QoS mechanisms.

By enabling network administrators to define what fairness means in their environments with regards to the amount of air time per client group, the amount of traffic is also controlled.

To control air time on a percentage basis, the air time including both uplink and downlink transmissions of a client or SSID is continuously measured.

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 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.

Cisco ATF establishes air time limits (defined as a percentage of total air time) and applies 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 can be applied to individual clients.

If the air time limit for an SSID (or client) is exceeded, the packets 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.

Client Fair Sharing

Cisco Air Time Fairness can be enforced on clients that are associated with an SSID or WLAN. This ensures that all clients in an SSID or WLAN are treated equally based on their utilization of the radio bandwidth. This feature is useful in scenarios where one or a few clients could use the complete air time allocated for an SSID or WLAN, thereby depriving Wi-Fi experience for other clients associated with the same SSID or WLAN.

  • The percentage of air time to be given to each client is recomputed every time a client connects or disconnects.

  • Client fair sharing is applicable only to downstream traffic.

  • Clients can be categorized into usage groups at the policy level.

  • Client-based ATF metrics accumulation is performed in the transmit complete routine. This allows the air time that is unused by clients in low-usage or medium-usage groups to be accumulated to a common share pool bucket where the high-usage clients can be replenished.

Supported Access Point Platforms

Cisco ATF is supported on the following APs:

  • Cisco Aironet 2700 Series Access Points

  • Cisco Aironet 3700 Series Access Points

  • Cisco Aironet 2800 Series Access Points

  • Cisco Aironet 3800 Series Access Points

  • Cisco Aironet 4800 Series Access Points

  • Cisco Aironet 1540 Series Access Points

  • Cisco Aironet 1560 Series Access Points


Note

Cisco ATF is supported on MESH, if APs support ATF. ATF is supported on FlexConnect mode and the Local mode.

Note

Cisco Catalyst APs offer capabilities that are equivalent to ATF by leveraging the enhancements in the Wi-Fi 6 and 6E protocols. 802.11ax features such as OFDMA, bidirectional MU-MIMO, and BSS coloring, combined with the advanced QoS features in the Cisco Catalyst 9800 Series Wireless Controllers, help resolve scheduling and congestion problems, accommodate multiple users at the same time, and allocate bandwidth more efficiently.

Cisco ATF Modes

Cisco ATF operates in the following modes:

  • Monitor mode in which users can do the following:

    • View the air time

    • Report air time usage for all AP transmissions

    • View reports

      • per SSID or WLAN

      • per site group/tag

    • Report air time usage at periodic intervals

    • No enforcement as part of Monitor mode

  • Enforce Policy mode in which users can do the following:

    • Enforce air time based on configured policy

    • Enforce air time on the following:

      • A WLAN

      • All APs connected in a Cisco Catalyst 9800 Series Wireless Controller network

      • per site group/tag

Restrictions on Cisco Air Time Fairness

  • Cisco ATF can be implemented only on data frames in the downstream direction.

  • When ATF is configured in per-SSID mode, all the WLANs are disabled before you enter any ATF configuration commands. The WLANs are enabled after you enter all the ATF commands.

Cisco Air Time Fairness (ATF) Use Cases

Public Hotspots (Stadium/Airport/Convention Center/Other)

In this instance, a public network is sharing a WLAN between two (or more) service providers and the venue. Subscribers to each service provider can be grouped and allocated a certain percentage of air time.

Education

In this instance, a university is sharing a WLAN between students, faculty, and guests. The guest network can be further partitioned by the service provider, for distribution of bandwidth privileges to the guests. Each group can be assigned a certain percentage of air time.

Enterprise/Hospitality/Retail

In this instance, the venue is sharing a WLAN between employees and guests. The guest network can be further partitioned by service provider. The guests could be sub-grouped by tier of service type with each subgroup being assigned a certain percentage of air time, for example a paid group is entitled for more air time than the free group.

Time Shared Managed Hotspot

In this instance, the business entity managing the hotspot, such as a service provider or an enterprise, can allocate and subsequently lease air time to other business entities.

Configuring Cisco Air Time Fairness (ATF)

Configuring Cisco Air Time Fairness

The following are the high-level steps to configure Cisco ATF:

  1. Enable Monitor mode to determine network usage (optional).

  2. Create Cisco ATF policies.

  3. Add WLAN ATF policies per network or per site group/tag.

  4. Determine, if optimization must be enabled.

  5. Periodically check the Cisco ATF statistics.

Creating a Cisco ATF Profile (GUI)

Procedure

Step 1

Choose Configuration > Wireless > Air Time Fairness.

Step 2

Click the Profiles tab and click the Add button, to create a new ATF policy.

The Add ATF Policy window is displayed.

Step 3

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. For example, if you configure the weight as 50, this means that the air time for this ATF profile is 50% when applied to an policy profile.

Step 4

Use the slider to enable or disable the Client Sharing feature. When you enable this option in the Web UI, the default ATF configuration is set to Enforce and not Monitor.

Step 5

Click Apply to Device.

Creating Cisco ATF Profile (CLI)

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 2

wireless profile airtime-fairness atf-policy-name atf-profile-id

Example:

Device(config)# wireless profile airtime-fairness atf-policy-name 1

Creates a new Cisco ATF policy.

  • atf-policy-name —Enters the ATF profile name.

  • atf-profile-id —Enters the ATF profile ID. Range is from 0 to 511.

Step 3

weight policy-weight

Example:

Device(config-config-atf)# weight 5

Adds a weight to the Cisco ATF policy.

  • policy-weight —Enters the policy weight. Range is from 5 to 100.

Step 4

client-sharing

Example:

Device(config-config-atf)# client-sharing

Enables or disables the client sharing for Cisco ATF policy.

Step 5

end

Example:

Device(config-config-atf)# end

Returns to privileged EXEC mode. Alternatively, you can also press Ctrl-Z to exit global configuration mode.

Attaching Cisco ATF Profile to a Policy Profile (GUI)

Procedure

Step 1

Choose Configuration > Tags & Profiles > Policy. Policy.

Step 2

Click Add.

The Add Policy Profile window is displayed.

Step 3

Click the Advanced tab.

Step 4

Under the Air Time Fairness Policies section, select the required policy for 2.4 GHz and 5 GHz policies.

Step 5

Click Apply to Device.

Attaching Cisco ATF Profile to a Policy Profile (CLI)

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 2

wireless profile policy profile-name

Example:

Device(config)# wireless profile policy profile-name

Creates policy profile for the WLAN.

  • profile-name —Is the profile name of the policy profile.

Step 3

dot11 {24ghz | 5ghz} airtime-fairness atf-policy-name

Example:

Device(config-wireless-policy)# dot11 24ghz airtime-fairness atf-policy-name

Configures air time fairness policy for 2.4- or 5-GHz radio.

  • atf-policy-name —Is the name of the air time fairness policy. For more details on creating Cisco ATF policy, refer to the Creating Cisco ATF Policy.

Note

 

You can assign the same ATF policy to both 2.4-GHz and 5-GHz radios (or) have two different ATF policies as well.

Step 4

end

Example:

Device(config-wireless-policy)# end

Returns to privileged EXEC mode. Alternatively, you can also press Ctrl-Z to exit global configuration mode.

Enabling ATF in the RF Profile (GUI)

Procedure

Step 1

Choose Configuration > Tags & Profiles > RF.

Step 2

Click Add.

The Add RF Profile window is displayed.

Step 3

Click the Advanced tab.

Step 4

Under the ATF Configuration section, complete the following :

  1. Use the slider to enable or disable the Status. The Mode field is displayed.

  2. Click the Monitor mode or Enforced mode radio option. If you enable the Enforced mode, use the slider to enable or disable Optimization.

  3. Use the slider to enable to disable Bridge Client Access. This is applicable for mesh mode APs. Bridge Client Access determines the percentage of the ATF policy weight that is allocated to clients connected to the mesh APs.

Step 5

Specify the Airtime Allocation value between 5 and 90.

Step 6

Click Apply to Device.

Enabling ATF in the RF Profile (CLI)

Cisco ATF must be enabled on 2.4 GHz or 5 GHz radios separately.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 2

ap dot11 {24ghz | 5ghz} rf-profile rf-profile

Example:

Device(config)# ap dot11 24ghz rf-profile rfprof24_1

Configures an RF profile for 2.4- or 5-GHz radio.

Step 3

airtime-fairness mode {enforce-policy | monitor}

Example:

Device(config-rf-profile)# airtime-fairness mode enforce-policy

Configures air time fairness in either of the modes:

  • Enforce-policy—This mode signifies that the ATF is operational.

  • Monitor—This mode gathers information about air time and reports air time usage.

Step 4

airtime-fairness optimization

Example:

Device(config-rf-profile)# airtime-fairness optimization

Enables the air time fairness optimization.

Optimization is effective when the current WLAN reaches the air time limit and the other available WLANs does not use air time to its full extent.

Step 5

end

Example:

Device(config-rf-profile)# end

Returns to privileged EXEC mode. Alternatively, you can also press Ctrl-Z to exit global configuration mode.

Verifying Cisco ATF Configurations

You can verify Cisco ATF configurations using the following commands:

Table 1. Commands for Verifying Cisco ATF Configurations
Commands Description
show wireless profile airtime-fairness summary Displays the summary of air time fairness profiles.
show wireless profile airtime-fairness mapping

Displays the ATF policy mapping with the wireless profiles.
show ap airtime-fairness summary

Displays the ATF configuration summary of all radios.
show ap dot11 24ghz airtime-fairness

Displays the ATF configuration for 2.4-GHz radio.
show ap dot11 5ghz airtime-fairness

Displays the ATF configuration for 5-GHz radio.
show ap name ap-name airtime-fairness

Displays the ATF configuration or statistics for an AP.
show ap name ap-name dot11 {24ghz | 5ghz} airtime-fairness statistics summary

Displays the ATF statistics of 2.4- or 5GHz radio.

Verifying Cisco ATF Statistics

Table 2. ATF Statistics per WLAN
Commands Description
show ap name ap-name dot11 {24ghz | 5ghz} airtime-fairness wlan wlan_name statistics

Displays the ATF statistics related to a WLAN.
Table 3. ATF Statistics per ATF Policy
Commands Description
show ap name ap-name dot11 {24ghz | 5ghz} airtime-fairness policy policy-name statistics

Displays the ATF statistics related to an ATF policy.
Table 4. ATF Statistics per Client
Commands Description
show ap airtime-fairness statistics client mac_address

Displays the ATF statistics related to a client.