What is the BSS color of router WiFi6? The building is full of neighbors. The corridors are crowded into a pot of porridge. This invisible switch is secretly working.

When I moved into this community last year, the first thing I did was tortured by WiFi. The building is as dense as a honeycomb. When scanning with the mobile phone, 23 2.4G signals alone were detected, and there were also more than a dozen 5G signals. My Xiaomi AX3000T can run over 400 Mbit/s during the daytime speed test. At eight or nine o'clock in the evening, it spins in circles while watching videos. I took it at that time The article about channel interference The old method is to scan the channels and move 2.4G to 1 and 5G to 149. It was indeed better for a while.

But after switching to the AX3000T with WiFi 6 last winter, I discovered a strange thing: On the same crowded channel, the new router is actually much more stable during the evening peak hours than the old WiFi5 one. The reason why I can't find it when scrolling through the background is that in addition to OFDMA and MU-MIMO, which I have written about, there is another thing that no one has ever mentioned in the parameter page - BSS color. Some firmwares are called "coloring" and some are called "BSS Coloring". I followed it and found out that this thing is the reason why WiFi6 dares to go sideways in the crowded channel. Let’s explain it clearly today.

Let’s first talk about the color of BSS: Give each WiFi a color stamp

You may have seen the term BSS. A WiFi network created by a router is called a BSS, which is the abbreviation of Basic Service Set. The BSSID article As I mentioned earlier, there may be several BSSs hidden behind a WiFi name. Each node of the Mesh counts as one, and 2.4G and 5G count as two separately. Each router of each neighbor in your building is an independent BSS.

The BSS color is a number assigned to each BSS by WiFi6, from 0 to 63, a total of 64 numbers. The rules are very simple: When sending the packet, the router writes this number into the HE-SIG-A field of the packet header, which is equivalent to stamping a color stamp on the envelope. When you hear someone else sending a package, first look at the color of the seal - the color is the same as mine, which means it's "one of your own" (or a router with a mixed number), and wait honestly. ； Different colors indicate that they are "outsiders." Even if the outsider is on the same channel as me, as long as the conditions are met, I can ignore him and continue to send my own.

This is unthinkable in the WiFi5 era. According to the old rules, whenever you hear someone talking on the channel, no matter whose bag it is, you must shut up and retreat. Your router wants to send a packet. First listen carefully. If you hear the neighbor sending it, wait. ； After the neighbor has finished sending, he still has to wait for a random back-off time to prevent two families from grabbing the microphone at the same time. The 23 signals in the building are so polite to each other that no one can talk happily. This set of queuing rules of "listen first, speak later", I am The article about old equipment slowing down the entire network Calculate the account: The holding time of the microphone is the most precious resource in WiFi. Please come and go, please wait.

Why can the same frequency be transmitted at the same time?: The account of distance and threshold

You may ask, if two people transmit on the same channel at the same time, wouldn’t it cause a collision? The accounts here deserve to be settled clearly.

The key is "the intensity of hearing". When the neighbor's packet reaches your router, it is attenuated. Across a wall and a distance of more than ten meters, the dropped signal may only be -85dBm, which is much weaker than the -50dBm sent by your own device. The spatial reuse rules of WiFi6 are to make a fuss about this difference.: When the outsider signal heard is lower than a threshold (this threshold is called OBSS-PD, the overlapping BSS packet detection threshold, the typical value can be relaxed to -72dBm or even -62dBm, and the old rule is -82dBm), the router determines "This person is far away from me, he sends his, and I send mine, so as not to drown each other's packets."

This is spatial multiplexing - the space of the same channel is multiplexed by several pairs of communications at different distances. Neighbors in the building who were separated by two or three walls used to line up politely with each other on the passage, but now each has his own thing. The WiFi6 router is much more stable during the evening rush hour at your home. Half of the credit is due to OFDMA's ability to connect the packets to the car, and the other half is here.: The "social distance" with neighbors has been relaxed.

Of course it's not magic. If the car really crashes, it will still be retransmitted with error code. That account is The article about signal dropout and network speed drop by half The book talks about it in detail - the noise pushes the constellation points to the next grid, and if you admit your mistake, you have to start over. The bet of spatial reuse is "too far away to push". If the bet is won, the throughput will increase.

What should I do if my number is bumped?: WiFi6 will change the number on its own

64 numbers may sound like a lot, but many routers are randomly selected by default when shipped from the factory, so the probability of number collision is not low. The color of your house is 23, and the one upstairs is also randomly assigned to 23. The two "outsiders" become "internal friends" and politely retreat from each other, which is equivalent to using this function in vain.

WiFi6 also has a plan for this, and the mechanism is called BSS color collision processing. The router will monitor the colors of other BSSs on the same channel. If it finds that it has a different number, it will take the initiative to change it to an unused one. You don’t need to do this work, the firmware does it by itself. Therefore, I never recommend manually nailing the color number in the settings - if you nail it, it will not dare to change it if the number is bumped, and you will do bad things with good intentions. If there is firmware for this setting, just select "Automatic".

By the way, the BSS color belongs to the HEW direction of WiFi6 (high-efficiency wireless), and it also works with the target wake-up time (TWT, the power-saving set, and the door lock notification is also late. Wrote a separate article ) and OFDMA. These are all enabled by default, so you don’t have to go through them one by one.

Old equipment and old routers cannot enjoy this, this is a flaw

Be clear about the limitations and don't expect too much from it.

First, WiFi5 and older devices don’t understand colors at all, and they don’t have that stamp in their bags. Once your old camera or TV box is shipped, the WiFi6 router cannot hear the color and can only retreat according to the old rules. Therefore, for people who have a lot of old equipment at home, most of the space that can be saved by BSS color will be eaten up by the airtime occupied by the old equipment. The principle of this account is the same. Old iPad becomes stuck all over the family continuously It's the same thing. Can we make do with old routes and how can we mix connections? Let’s see. The article about mixing WiFi5 and WiFi6 .

Second, the benefits from 2.4G are very limited. 2.4G only has three channels 1, 6, and 11 that do not fight with each other. There are 23 signals in the building crowded into three channels. The channel itself is already terrible. You can save the color by queuing, but you can't save the noise floor. 2.4G congestion, the fundamental solution is still what I did at the beginning: For large traffic, remove 5G or plug in network cables, give up 2.4G to smart devices, and coexist with Bluetooth microwave ovens. 2.4G garbage dump article It’s all written down. 5G has many channels and relatively few people, so space multiplexing can be used.

Third, this feature is distance sensitive. If you and your neighbor live against the same wall and face the door, the signal will not be attenuated much, and the threshold will not pass the line, so you still have to queue up. Its sweet spot is the combination of "same channel but far apart" - those neighbors in the building who are a few floors or houses away from you on the same channel are exactly this type.

Hand-select channel and BSS color, don’t get confused about division of labor

As I write this, I have to explain an easy confusion.: Some people think that "WiFi6 has colors, you can choose the channel at will, and it will be automatic." Not so.

Color solves the problem of "same channel but far away" multiplexing, and channel selection solves "who squeezes the same channel with whom". The relationship between the two is upstream and downstream.: The channel is to divide the territory, and the color is to increase the tolerance in the divided territory. The territory has not been divided well. Nine of the 23 signals in the building are crowded on channel 1, and five or six of them are still strong signals separated by a wall. At this time, no matter how clever the color is, it cannot save it. Therefore, the order is always to scan first and stagger the channel first. The color is a free bonus given to you by WiFi6, not a death-free gold medal.

I'll give you a division of labor sheet and keep it:

Back to my own AX3000T. I pinned 2.4G to channel 1 and 5G after 149, and left the rest of the optimization to itself.: OFDMA combines small packages, BSS colors maintain social distance with neighbors, and TWT saves power for sensors. I have never touched any of these switches manually, they are all default values ​​- the design concept of the WiFi6 generation is "battlefield state when shipped from the factory". If you get the channel and positioning right, the rest will be more skillful than yours. If the signal coverage is not enough, that is a matter of networking. Read the Mesh articles and don’t let the color matter.