Information about BSS Coloring and Spatial Reuse

The 802.11 Wi-Fi standard minimizes the chance of multiple devices interfering with one another by transmitting at the same time. This carrier-sense multiple access with collision avoidance (CSMA/CA) technology was based on static thresholds that allowed Wi-Fi devices to avoid interfering with each other on air. However, with increased density and number of Wi-Fi devices, these static thresholds often lead to CSMA/CA causing devices to defer transmissions unnecessarily.

For example, if two devices associated with different BSSs can hear each transmissions from each other at relatively low signal strengths, each device has to defer its transmission when it receives a transmission from the other. But if both devices were to transmit at the same time, it is likely that neither would cause enough interference at the other BSS's receiver to cause reception failure for either transmission.

Devices today must demodulate packets to look at the MAC header in order to determine whether or not a received packet belongs to their own BSS. This process consumes power, which could have been saved if devices could quickly identify the BSS by looking at the PHY header alone, and subsequently drop packets that are from a different BSS. Prior to Wi-Fi 6, there was no provision for devices to do this.

The new 802.11ax (Wi-Fi 6) standard addresses both of the issues discussed above, through the new BSS Coloring and Spatial Reuse mechanisms. BSS Coloring is a new provision that allows devices operating in the same frequency space to quickly distinguish between packets from their own BSS and packets from an Overlapping BSS (OBSS), by simply looking at the "BSS color" value contained in the HE PHY header. Spatial Reuse allows devices, in certain cases, to transmit at the same time as OBSS packets they receive, instead of having to defer transmissions due to legacy interference thresholds. Since every Wi-Fi 6 device understands the BSS color, it can be leveraged to increase power savings by dropping packets earlier, and to identify spatial reuse opportunities.

BSS Coloring

BSS (Basic Service Set) Coloring is a method to differentiate between BSSs of access points and their clients on the same RF channel. Wi-Fi 6 enables each AP radio to assign a value (from 1 to 63), known as the BSS color, to be included in the PHY header of all HE transmissions from devices in its BSS. With devices of each BSS transmitting a locally-unique color, a device can quickly and easily distinguish transmissions coming from its BSS from those of a neighboring BSS.

The following platforms support this feature:

  • Cisco Catalyst 9800 Series Wireless Controllers

  • Cisco Catalyst 9115 Access Points

  • Cisco Catalyst 9120 Access Points

Configuring BSS Color on AP (GUI)

Procedure

Step 1

Choose Configuration > Wireless > Access Points.

Step 2

Click the 5 GHz Radios section or the 2.4 GHz Radios section.

The list of the AP radios in the band is displayed.
Step 3

Click the required AP name.

The Edit Radios window is displayed.
Step 4

From the Edit Radios window, select the Configure tab.

The general information, Antenna Parameters, RF Channel Assignment, Tx Power Level Assignment, and BSS Color are displayed.
Step 5

In the BSS Color area and from the BSS Color Configuration drop-down list, choose Custom configuration

  • Custom: To manually select the BSS color configuration for the AP radio.

    1. Click the BSS Color Status field to disable or enable the feature.

    2. In the Current BSS Color field, specify a corresponding BSS color for the AP radio. The valid range is between 1 and 63.

Step 6

Click Update & Apply to Device.

Configuring BSS Color in the Privileged EXEC Mode

Procedure

  Command or Action Purpose
Step 1

enable

Example:

Device> enable
Enables privileged EXEC mode. Enter your password if prompted.
Step 2

ap name ap-name dot11 { 24ghz | 5ghz| dual-band [ slot slot-id ] } dot11ax bss-color <1-63>

Example:

Device#ap name apn dot11 24ghz slot 0 dot11ax bss-color 12

Example:

Device#ap name apn no dot11 24ghz slot 0 dot11ax bss-color
Sets the BSS color on the 2.4 GHz, 5 GHz, or dual-band radio, for a specific access point on the following slots:

  • 5 GHz - Slot 1 and 2

  • 2.4 GHz - Slot 0

  • dual-band - Slot 0

Use the no form of the command to disable BSS color.

Configuring BSS Color Globally (GUI)

Procedure

Step 1

Choose Configuration > Radio Configurations > Parameters.

Step 2

In the 11ax Parameters section, enable BSS color globally for the 5 GHz and 2.4 GHz radios by checking the BSS Color check box

Configuring BSS Color in the Configuration Mode

Procedure

  Command or Action Purpose
Step 1

enable

Example:

Device> enable
Enables privileged EXEC mode. Enter your password if prompted.
Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.
Step 3

[no] ap dot11 { 24ghz | 5ghz } dot11ax bss-color

Example:

Device(config)#[no] ap dot11 24ghz dot11ax bss-color

Enables the 802.11ax BSS color on all 2.4GHz or 5GHz radios. Use the no form of the command to disable the BSS color.

Verifying BSS Color

To verify if the global per-band BSS color is enabled, use the following show command:

Device# show ap dot11 24ghz network
802.11b Network                           : Enabled
11gSupport                                : Enabled
11nSupport                                : Enabled
.
.
.
802.11ax                                  : Enabled
  DynamicFrag                             : Enabled
  MultiBssid                              : Enabled
  BSS Color                               : Enabled
802.11ax MCS Settings:
  MCS  7, Spatial Streams = 1             : Supported
.
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To view the BSS color configuration of all the AP radios on the band in the summary list along with Channel, TX Power and so on, use the following show command:
Device# show ap dot11 24ghz summary extended
AP Name                           Mac Address     Slot    Admin State    Oper State    Width  Txpwr           Channel                        BSS Color
------------------------------------------------------------------------------------------------------------------------------------------------------       
Ed2-JFW-AP1                       84b2.61ba.4730  1       Enabled        Up            40     1/6 (17 dBm)    (136,132)*                                        
11AX-9120-AP1                     d4ad.bda2.3fc0  1       Enabled        Up            20     1/8 (23 dBm)    (36)                           30         
Ed2-JFW-AP2                       f8c2.8885.59f0  1       Enabled        Up            20     1/5 (15 dBm)    (40)
To view the BSS color configuration and the capability of the AP radio, use the following show commands: 
Device# show ap name AP7069.5A74.816C config dot11 24ghz
Cisco AP Identifier                             : 502f.a876.1e60
Cisco AP Name                                   : AP7069.5A74.816C
Attributes for Slot 0
  Radio Type                                    : 802.11b
  Radio Mode                                    : REAP
  Radio Role                                    : Auto
  Radio SubType                                 : Main
  Administrative State                          : Enabled
  Operation State                               : Up
  .
  .
  .
Phy OFDM Parameters
    Configuration                               : Automatic
    Current Channel                             : 6
    Channel Width                               : 20 MHz
    TI Threshold                                : 1157693440
    Antenna Type                                : External
    External Antenna Gain (in .5 dBi units)     : 8
    .
    .
    .
  !BSS color details are displayed below:        
  802.11ax Parameters
    HE Capable                                  : Yes
    BSS Color Capable                           : Yes
    BSS Color Configuration                     : Customized
    Current BSS Color                           : 34
Device# show ap name AP7069.5A74.816C config slot 0
Cisco AP Identifier                             : 502f.a876.1e60
Cisco AP Name                                   : AP7069.5A74.816C
Country Code                                    : US
AP Country Code                                 : US  - United States
AP Regulatory Domain                            : -A
MAC Address                                     : 7069.5a74.816c
IP Address Configuration                        : DHCP
IP Address                                      : Disabled
.
.
.
Attributes for Slot 0
  Radio Type                                    : 802.11n - 2.4 GHz
  Radio Role                                    : Auto
  Radio Mode                                    : REAP
  Radio SubType                                 : Main
  Administrative State                          : Enabled
.
.
.
  Phy OFDM Parameters
    Configuration                               : Automatic
    Current Channel                             : 6
    Channel Assigned By                         : DCA
    Extension Channel                           : NONE
    Channel Width                               : 20
    Allowed Channel List                        : 1,2,3,4,5,6,7,8,9,10,11
    TI Threshold                                : 1157693440
    DCA Channel List                            : 
    Antenna Type                                : EXTERNAL_ANTENNA
    External Antenna Gain (in .5 dBi units)     : 8
Diversity                                       : DIVERSITY_ENABLED
    802.11n Antennas
      A                                         : ENABLED
      B                                         : ENABLED
      C                                         : ENABLED
      D                                         : ENABLED
  .
  . 
  . 
  !BSS color details are displayed below:
  802.11ax Parameters
    HE Capable                                  : Yes
    BSS Color Capable                           : Yes
    BSS Color Configuration                     : Customized
    Current BSS Color                           : 34
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