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Does a 5.0 40 MHz client affect a 5.0 80 MHz client?

OzarkEdge

Part of the Furniture
Given a router 5.0 WLAN set to 20/40/80 MHz bandwidth, does a client connecting a 40 MHz affect/limit clients that can connect at 80 MHz?

OE
 

ColinTaylor

Part of the Furniture
Given a router 5.0 WLAN set to 20/40/80 MHz bandwidth, does a client connecting a 40 MHz affect/limit clients that can connect at 80 MHz?
No, because each client has to use at least the primary 20 MHz channel and optionally any secondary 20 MHz channels. So as each client has to wait its turn to use the primary channel it makes no difference if the clients are using a bandwidth of 20, 40 or 80 MHz.

Also bear in mind that all the 20/40/80 setting does is allow the router to chose which of those 3 bandwidths it will use at startup. So if it chooses 80 MHz it will stay at 80 MHz (ignoring DFS actions). In other words 20/40/80 isn't some sort of magic mode that lets the router or clients dynamically change their bandwidth settings on the fly.

It looks like 20/40/80 is a type magic mode that allows to router to change its bandwidth (and therefore channel usage) if it detects an access point using overlapping channels (OBSS) within range. See the following discussion and post #19.
 
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OzarkEdge

Part of the Furniture
No, because each client has to use at least the primary 20 MHz channel and optionally any secondary 20 MHz channels. So as each client has to wait its turn to use the primary channel it makes no difference if the clients are using a bandwidth of 20, 40 or 80 MHz.

Also bear in mind that all the 20/40/80 setting does is allow the router to chose which of those 3 bandwidths it will use at startup. So if it chooses 80 MHz it will stay at 80 MHz (ignoring DFS actions). In other words 20/40/80 isn't some sort of magic mode that lets the router or clients dynamically change their bandwidth settings on the fly.
Thanks!

I'm left wondering... when does one set 20 or 40 or 80 MHz vs. 20/40/80 MHz?

OE
 

drabisan

Senior Member
1. Capabilities
2. Number of configured antennas
3. Quality of measured spectrum

Not by the book: bad drivers, bad implementation, bugs
 

ColinTaylor

Part of the Furniture
Good question. I think the answer depends on you knowing exactly what's going on in your WiFi neighbourhood and what your channel plan is.

The bandwidth setting shouldn't really be taken in isolation because it's linked to the channel, which is in turn effected by nearby stations.

Setting the channel to "auto" and the bandwidth to "20/40/80" is the safest out-of-the-box configuration because it's almost certain to find at least one free 20 MHz channel.

Here's quite an old but still quite good explanation of things to consider.

Fortunately where I am there is an 80 MHz block of the spectrum that none of my nearby neighbours are using, so I set that as the fixed channel with the bandwidth at 80 MHz. But if you're in a crowded WiFi environment with volatile channel switching the decision becomes much harder.
 

L&LD

Part of the Furniture
While it may not interfere with the 80MHz width connection directly, it does, in practice.

WiFi being a shared medium will make the nominally faster 80MHz connected device slower when a 20 or 40 MHz connected device is in use. Simply less airtime for a given time slot means less performance/throughput for the fastest device(s) on the network.
 

thiggins

Mr. Easy
Staff member
Also bear in mind that all the 20/40/80 setting does is allow the router to chose which of those 3 bandwidths it will use at startup. So if it chooses 80 MHz it will stay at 80 MHz (ignoring DFS actions). In other words 20/40/80 isn't some sort of magic mode that lets the router or clients dynamically change their bandwidth settings on the fly.
This isn't necessarily true.

From your Revolution WiFi link
So dynamic channel allocation is part of 802.11ac. Whether it is actually implemented in most products is another discussion entirely. I know years ago Qualcomm was touting it in their marketing material. But, again, whether it is used in the real world is another thing. You'd have to do packet sniffing to tell.
 

ColinTaylor

Part of the Furniture
This isn't necessarily true.

From your Revolution WiFi link

So dynamic channel allocation is part of 802.11ac. Whether it is actually implemented in most products is another discussion entirely. I know years ago Qualcomm was touting it in their marketing material. But, again, whether it is used in the real world is another thing. You'd have to do packet sniffing to tell.
I could well be wrong but was interpreting that in a different way. The "20/40/80" setting I was referring to is specifically the option shown in the router's config, which I think is something different than "dynamic per-frame channel width".

Consider this: If I set my router's bandwidth to "80 MHz" that doesn't prevent my client from connecting to it at 40 or 20 MHz (using the dynamic channel width feature). AFAIK the 20/40/80 option is only allowing the router to attempt to determine the maximum bandwidth possible when it is initialised. This is similar to the "auto" channel setting.
 

OzarkEdge

Part of the Furniture
Thanks All, for the feedback! I need to study up. There seem to be many considerations, subject to who implements what with what generation of 802.11.

Since my remote AC86U died and dismantled my AiMesh, I have replaced it with an N66U in Media Bridge Mode connecting at 5.0 ~243 Mbps -73 dBm more or less depending on when and where you look (77' through some brick walls, etc.). Its Wireless Log suggests this link is using 40 MHz bandwidth where as the AC86U main router is set for 20/40/80 MHz. Hence, my bandwidth questions.

I wired an OBi202 ata to the N66U, so that is back in service.

And I wired a dual-band Wireless-N Linksys E3200 router in Bridge Mode (only option) to the N66U, 1 Gbps WAN-to-LAN, to serve as a remote AP. The E3200 WLANs are set for OE-50 40 MHz (max option) and OE-24 20 MHz, same different SSIDs as on the router but on different channels from the router.

If the router is using 5.0 ch 157 at 80 MHz, can the AP use ch 149 at 40 MHz, or should I move the AP off the 149-161 block of channels? I have been preferring these channels for highest power in the US and no DFS disruption (they also gave me the strongest AiMesh backhaul values in the Wireless Log).

For reference:
80211ac channels.png


Now to go out and test it... erector set networking!

OE
 
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ATLga

Regular Contributor
Thanks All, for the feedback! I need to study up. There seem to be many considerations, subject to who implements what with what generation of 802.11.

Since my remote AC86U died and dismantled my AiMesh, I have replaced it with an N66U in Media Bridge Mode connecting at 5.0 ~450 Mbps -73 dBm more or less depending on where you look (77' through some brick walls, etc.). Its Wireless Log suggest this link is using 40 MHz bandwidth where as the AC86U main router is set for 20/40/80 MHz. Hence, my bandwidth questions.

I wired an OBi202 ata to the N66U, so that is back in service.

And I wired a dual-band Wireless-N Linksys E3200 router in Bridge Mode (only option) to the N66U, 1 Gbps WAN-to-LAN, to serve as a remote AP. The E3200 WLANs are set for OE-50 40 MHz (max option) and OE-24 20 MHz, same different SSIDs as on the router but on different channels from the router.

If the router is using 5.0 ch 157 at 80 MHz, can the AP use ch 149 at 40 MHz, or should I move the AP off the 149-161 block of channels?

For reference:
View attachment 25277

Now to go out and test it... erector set networking!

OE
Interesting thread
 

thiggins

Mr. Easy
Staff member
@ColinTaylor The 20/40/80 bandwidth settings determine the maximum bandwidth used when transmitting. Dynamic bandwidth allocation then occurs (or doesn't, depending on what the product supports) within those bounds.

@OzarkEdge As @Pork noted, 5 GHz Tx power limits were changed a few years ago to allow the max power on all channels in the U.S.

@K-2SO Slower devices take more airtime, so can slow down faster ones, yes. Channel bandwidth is only one factor determining Tx airtime. Others are signal level, Wi-Fi standard supported, MU-MIMO and now OFDMA.

That said, routers have gotten better at allocating bandwidth among different "speed" devices. Some implement airtime fairness techniques to prevent slower devices from dominating air time.
 

ATLga

Regular Contributor
@ColinTaylor The 20/40/80 bandwidth settings determine the maximum bandwidth used when transmitting. Dynamic bandwidth allocation then occurs (or doesn't, depending on what the product supports) within those bounds.

@OzarkEdge As @Pork noted, 5 GHz Tx power limits were changed a few years ago to allow the max power on all channels in the U.S.

@K-2SO Slower devices take more airtime, so can slow down faster ones, yes. Channel bandwidth is only one factor determining Tx airtime. Others are signal level, Wi-Fi standard supported, MU-MIMO and now OFDMA.

That said, routers have gotten better at allocating bandwidth among different "speed" devices. Some implement airtime fairness techniques to prevent slower devices from dominating air time.
If I may take this a step further and not off topic, take a N Client that hops on your 5 ghz network cause it’s set to 20/40/80, wouldn’t changing the 5.0 to 80 only force that N Client to the 2.4 network since it can’t use higher than the 40 anymore.
 

K-2SO

Very Senior Member
Others are signal level, Wi-Fi standard supported, MU-MIMO and now OFDMA.
You know some of those are best for marketing purposes only. I've never seen any real life benefits of Beamforming and MU-MIMO. You can only measure small % differences with the pro equipment you test with. Airtime is the most limiting factor even in ideal conditions. Multiple APs come to rescue when many devices compete for airtime.

wouldn’t changing the 5.0 to 80 only force that N Client to the 2.4 network
No. The N client will still connect at 40MHz channel. My network is set to 80MHz channel and I have few N clients on 5GHz, for example.
 

ATLga

Regular Contributor
You know some of those are best for marketing purposes only. I've never seen any real life benefits of Beamforming and MU-MIMO. You can only measure small % differences with the pro equipment you test with. Airtime is the most limiting factor even in ideal conditions. Multiple APs come to rescue when many devices compete for airtime.



No. The N client will still connect at 40MHz channel. My network is set to 80MHz channel and I have few N clients on 5GHz, for example.
How can it connect on the 40 if it is set to 80 only. That’s the point of having that choice isn’t it.
 

K-2SO

Very Senior Member
How can it connect on the 40 if it is set to 80 only. That’s the point of having that choice isn’t it.
Because it's not 80MHz only, but up to 80MHz. @ColinTaylor explained what it means above. If your router is set to 20/40/80 and the router decided 40 is the maximum possible, then you can have 20/40 clients only. When you set it to 80 manually all 20/40/80 clients can connect. I don't like Smart and Auto settings and I set my network on 80 always. I monitor what's happening on the WiFi battlefield around. 80 is possible and working in my area.
 
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ATLga

Regular Contributor
Because it's not 80MHz only, but up to 80MHz. @ColinTaylor explained what it means above.
So setting it to 80 only is the same as 20/40/80 because that’s up to 80 too. I’m so confused hahaha. I thought the point of being able to pick on versus the group was so you could eliminate the slower ones and make them use the high speed and not drop back
 

OzarkEdge

Part of the Furniture
@OzarkEdge As @Pork noted, 5 GHz Tx power limits were changed a few years ago to allow the max power on all channels in the U.S.
Thanks! I'll update my notes... I was not sure of this since it's been influx and varies with dated source.

That leaves the empirical approach of directly observing the channel that gives the best connection... in my case for the AiMesh wireless backhaul.

OE
 

ColinTaylor

Part of the Furniture
@ColinTaylor The 20/40/80 bandwidth settings determine the maximum bandwidth used when transmitting. Dynamic bandwidth allocation then occurs (or doesn't, depending on what the product supports) within those bounds.
Yes that was my understanding. The confusion for Asus users is that in addition to the bandwidth cap settings of "20", "40" and "80" there is another setting called "20/40/80" the effect of which is not obvious.
Code:
Router setting  Broadcom bw_cap value
20              20MHz
40              20/40MHz
80              20/40/80MHz
20/40/80        sets the value to 20/40MHz or 20/40/80MHz depending on capabilities
                of router and turns on OBSS Coexistence.
EDIT: Corrected 20/40/80 behaviour above.

How can it connect on the 40 if it is set to 80 only. That’s the point of having that choice isn’t it.
No that's not the point. As Tim said you are setting a cap on the maximum bandwidth, you're not limiting the minimum bandwidth.
 
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