Modulation and channel width when mixing clients of different generations

[negora]

Hi:

Suppose that in an 802.11ax network there is one client connected, which supports 802.11ax, and another one that "only" supports 802.11ac. Does the AP negotiate a specific modulation with each client? Or is it the same for both?: The highest common modulation, I guess.

And what about the channel width? Is it also negotiable per client? For example, Could an 802.11ax client work at 160 MHz and an 802.11ac client at 80 MHz? I doubt it, but just to know...

Thank you.

 

[L&LD]

That's how I've seen it work. I've set 160MHz width mode to see just the AX clients but they all still connected at the speeds they could.

 

[thiggins]

Each station advertises its capabilities when it responds to AP beacons. AP and STA then negotiate the best connection.

That said, a STA with lower bandwidth capability will take more airtime to move a given amount of data. That is a different problem that the AP must deal with. Some use a form of "airtime fairness" that keeps "slower" stations from slowing down "faster" STAs.

 

[negora]

That's how I've seen it work. I've set 160MHz width mode to see just the AX clients but they all still connected at the speeds they could.

Thanks. So, Were there some clients using a band width of 80 MHz whereas others used a width of 160 MHz? Or did they all use a width of 80 MHz (highest common width)?

Each station advertises its capabilities when it responds to AP beacons. AP and STA then negotiate the best connection.

Thanks. I thought it was like that for certain features, but I wasn't sure about the modulation and the band width. So one client can use a width of 40 MHz whereas other can use 80 MHz, Right?

That said, a STA with lower bandwidth capability will take more airtime to move a given amount of data. That is a different problem that the AP must deal with. Some use a form of "airtime fairness" that keeps "slower" stations from slowing down "faster" STAs.

I opened this thread after reading this: 802.11ax backward compatibility performance with mixed clients. It surprised me that each client could negotiate its own features and that the performance loss came only from the airtime that each one uses. I thought that the AP forced the clients to use only the features that were common to all them. I feel better knowing that's not the case.

 

[ColinTaylor]

So one client can use a width of 40 MHz whereas other can use 80 MHz, Right?

Correct.

 

[negora]

Correct.

Great. That changes everything to me. Because I'll be able to do the switch from AC to AX more gradually. Thank you.