802.11ax BSS Color in a multi-AP roaming environment

I've read some BSS color articles (such as this), and as far as I understand it is used to improve 802.11ax Wi-Fi performance on overlapping access points using the same channel.

However I have some points that are not clear to me. Assuming the following scenarion:

Multiple overlapping APs connected to the same network, sharing the same SSID/credentials for client roaming.

My questions are:

  1. For two overlapping APs (same network, same SSID) using different channels, should the BSS color be the same or different? I guess that since they are using different channels the BSS color this would not matter.

  2. For two non-overlapping APs (same network, same SSID) using the same channel, should the BSS color be the same or different? I guess that they should use different BSS colors, but since they are not overlapping this would not matter.

  3. For two overlapping APs (same network, same SSID) using the same channel, should the BSS color be the same or different? I believe this is the case that BSS color would help, and BSS color should be different for each AP. But since they are part of the same network/SSID, I'm wondering if they should use actually the same BSS color (reading the articles this is not clear).

Any comment to clarify the above questions are appreciated!

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TBF I was surprised that bss color is even a user option. From what I read most of it will be a self configuring protocol (OFDMA just like cell phones) and not as reliant on users entering colors or frequencies. This will be enforced if cell phones share the same "color space" and will not be tinkerer friendly.

It's similar to 802.11ac where a user picks a channel and bandwidth but behind the scenes the system is actually juggling the resource units. Too bad the IEEE stuff is pay walled or user sign up.

it always comes back to the same basic problem, if the vendors released the source code, Openwrt would also perform better.

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OpenWrt already supports BSS color via option he_bss_color:

Thank you, but my question is specifically how to use it in the same network with Wifi roaming across multiple APs sharing the same SSID.

Please consider the text below as pure speculation. It is based only on my recollection of something I read or watched somewhere, possibly something from here: https://www.wirelesstrainingsolutions.com/blog/.

BSS coloring is used when determining if it is OK to transmit.

In 802.11ac and earlier there were two questions asked: Is there already some noise on the channel with signal level > x dBM? Is there already someone else transmitting Wi-Fi with strength > y dBM?

x > y and I believe x=-63 dBm and y=-83 dbM or something like that. We take care not to talk when there's Wi-Fi on the channel, but we don't care as much if we're talking when there's some non-Wi-Fi noise. If the noise is to loud though, we have to wait.

In 802.11ax, Wi-Fi traffic with a different BSS color (6-bit value) is regarded as noise. That means that between x and y dBm the behavior is different from 802.11ac. If we don't want to shout over our own medium-strength traffic, we should use the same color everywhere.

Neither 802.11ax or ac cares about SSID when determining if it is OK to transmit. I guess the BSS color is transmitted much earlier in the frame (in the preamble?) or it is just a shorter value and is therefor better to use for this purpose. I dunno.

Because of this, "overlapping" in your question should probably be defined in terms of signal levels.

Apparently there is overhearing between channels if they are sufficiently close, at least on 2.4 GHz (which ax may use). So "different channels" in your questions should probably be rephrased as "different distant channels" or something to make the questions easier to answer.

If so, I'd say:

  1. Doesn't matter
  2. Doesn't matter if signal level < y dBm for STAs belonging to the other AP and that other AP, seen from all STAs belonging to the AP under consideration and from the AP. But use the same color to be sure not to disturb each other when STAs move around.
  3. Use the same color.

But your preferences may be different. I guess you could make a case for being more aggressive and try to shout louder than distant WLANs. After all, that's what you will do with your neighbors'' traffic that has a different color.


Thank you @KAD. Even if you are speculating, it does make sense.

And yes, by "overlapping APs" I mean a specific region/location where a client gets a medium-strength signal from two different APs in the same network (same or different channels depending on the roaming zone).

Regarding case (3) with a region that gets a medium or strong signals from two APs in the same network and with same channel, you suggested using the same BSS color. This means that in this case the two overlapping APs will not shout over each other, right?

I'm wondering that a general recommendation would be to use the same BSS color ID for all APs in the same network (the same way that all APs should use the same 802.11r mobility domain ID).

In principle, every AP should be a unique BSS color, completely independent of the question if they're part of the same logical network or not. The BSS coloring has been introduced to help all participants ignoring noise they don't care about quickly, even with 802.11r and similar approaches, WLAN connections are always 1:1, client <--> AP - everything else is noise.


Would all the STA connected to a particular AP use the same BSS Color; that of the AP?