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Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

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Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#41

Post by cortesoft »

niobe wrote: post #31
anyfoo wrote: post #12

> Wi-Fi signal strength decreases at an exponential rate as you move further away from a router. This is surprising to me. I'd have guessed it decreases quadratically (i.e. due to the inverse square law), not exponentially. The paragraph below seems to contain an explanation, but I don't really understand it (namely because I don't know what that percentage "Coverage" column actually means, or what we mean with "the…

So that table is using distance as a proxy for signal to noise ratio. SNR is what really matters. Each data rate in the standard uses a different encoding technique. "Faster" encoding techniques cram more data into a given transmission interval but require a higher signal to noise ratio to be received without error. Since SNR declines with distance you can have a rough idea at what distance from a transmitter you wil…

There are a lot of people who are the only ones using their Wi-Fi, so they probably don't care about the performance for anyone else

Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#42

Post by bityard »

Normal_gaussian wrote: post #28

Today I set up a NWA210BE (Zyxel) to replace a unifi 6+ AP; I bought it second hand and my key metrics were: 4x4 MIMO, available used/discounted, current gen, fully functional standalone mode. The 4x4 makes all the difference. Sitting in my car the 6+ would fight with my 4G for internet and cause maps to be super slow; now I'm off the property before its unusable. I had intended to put APs in multiple rooms, but ther…

Interesting...

I have a Netgear WAX218, one of the last cheap business-class APs I could find that don't require a cloud service to manage. WAY better than the pro-sumer wifi routers I was running before in access point mode. I'll have to look into Zyxel offerings a bit more when I'm ready to replace my Netgear.

Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#43

Post by 9x39 »

KingMachiavelli wrote: post #4

I'd like to understand why the WiFi spec developed so slowly from G to N and finally to AC but now it's seems like a new version is released every other year yet many of the features/extensions are poorly implemented or have nearly 0 real world improvement.

I'm not a hardware guy, but my guess would be evolution of radio transceiver tech in the cell space drives improvements downstream in wifi. Better transceivers can pull quality signals from what was noise generations past, its not magic of course, but the speed transceivers can run over copper cable goes up similarly. 1Gbps was a fast cable a while ago, and now we're doing hundreds of gigabits commonly.

Another thing is that features like beamforming and higher QAM, let's say, are going to matter more in ideal scenarios where APs are in their sweet spot relative to clients, and you get to take advantage of high SNRs. Is that going to help when someone buys a Netgear Wifi 7 AP only to flip it upside down behind the couch in their apartment in an environment where 2.4 and even 5 ghz are basically gone from all their neighbors' use? Still, faster data rates mean clients get on and off the air quicker overall, saving airspace and battery if applicable. So, I think there's mainstream and highly specialized features rolling out simultaneously.

Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#44

Post by niobe »

rayiner wrote: post #34
niobe wrote: post #14

An impressive attempt to summarise Wi-Fi which is a very deep topic. However I think the executive summary already missed the most critical thing about Wi-Fi: only 1 transmitter at a time per channel - across all WLANs, yours and your neighbours, with no deterministic way to avoid collisions. It's a shared medium and it's not even half duplex, unlike the dedicated full duplex you would typically get with an ethernet…

> only 1 transmitter at a time per channel - across all WLANs, yours and your neighbours, with no deterministic way to avoid collisions. That’s not correct. You and your neighbor can use the same channel at the same time. On your network, the transmissions of the other network appear will appear as noise. As long as the other devices are far enough away, however, your devices will still be able to make out their own…

This is a common misconception.. you and your neighbour can configure the same channel, you cannot successfully transmit at the same time on the same channel within range. Nor can you and your own AP successfully transmit at the same time on the same channel.

When you and your neighbour _appear_ to be transmitting at the same time, each adapter is actually spending most of it's time waiting for a clear medium and for various backoff timers to expire before attempting to transmit.

"Appear as noise" is not defined for Wi-Fi adapters. There is only "I received a frame addressed to me and acknowledged it" or "I sent a frame and either did or didn't get an acknowledgement back from the receiver". Receivers do not know why they didn't receive a frame, or, if they received a corrupted frame, why it was corrupted. They just wait for a retransmit. Senders ordinarily wait a certain time to receive an acknowledgement, and if they don't, the start the transmit wait cycle again. But they often then reduce the data rate to increase the odds of a successful transmission.

I'm glossing over some complexity here, because there's a sender and receiver to consider, and each has a different view of the RF environment, but the point is always correct when all transmitters and receivers (lets say the 2 APs and each has 1 client) are in audible range of each other. And this is most of the time. Note that "audible range" (where the signal is such that the medium is deemed as busy by the adapter) is much larger than the "usable range" (where data can be transmitted at reasonable speeds). So transmitters create interference in a much larger area than they actually operate in.

That means your neighbour transmitting at 6Mbps to his AP will indeed degrade the performance of your client who wants to transmit at 600Mbps because your client has to wait ~100 times longer for a clear medium.

Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#45

Post by niobe »

9x39 wrote: post #38
niobe wrote: post #14

An impressive attempt to summarise Wi-Fi which is a very deep topic. However I think the executive summary already missed the most critical thing about Wi-Fi: only 1 transmitter at a time per channel - across all WLANs, yours and your neighbours, with no deterministic way to avoid collisions. It's a shared medium and it's not even half duplex, unlike the dedicated full duplex you would typically get with an ethernet…

The multi access story is improving, though. OFDMA on wifi7/802.11be: https://blogs.cisco.com/networking/wi-fi-7-mru-ofdma-turning...

Yes, and before that MU-MIMO is also an improvement to the problem. Still only 1 transmitter at a time, but multiple receivers.

Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#46

Post by Jach »

KingMachiavelli wrote: post #4

I'd like to understand why the WiFi spec developed so slowly from G to N and finally to AC but now it's seems like a new version is released every other year yet many of the features/extensions are poorly implemented or have nearly 0 real world improvement.

Speaking just on timelines (rather than actual underlying innovations or improvements), 802.11 was in 1997, next in 1999, G in 2003, then a 6 year gap to N in 2009, 4 year gap to AC in 2013, 8 year gap to wifi 6 in 2021, wifi 7 in 2024 (though apparently buyer beware), and wifi 8 expected (according to the article) in 2028. Doesn't seem too rapid? The 8 year gap is the weird one out.

I think part of it is that if there isn't a regular and practiced process for bumping standards, then gaps between revisions can grow quite large and stagnation can set in, and if there are any significant improvements it'll take longer for them to come to fruition than if there were regular revisions that are only modest most of the time. Looking at a few other things that come to mind: USB had an 8 year gap between 2 and 3 as well, PCIe had a 7 year gap between 3 and 4 (albeit while they only had a 3 year gap between the specification for 5 to 6, it still took 3 more years (2025) for the first pcie6 devices, and I still can't buy a consumer-level pcie6 motherboard, it's a separate mess), C++ had an 8 year gap between C++03 and C++11, Java had a 5 year gap between 6 and 7 (and another 3 years after 7 to get to Java 8); all of these things now have more rapid cycles.

Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#47

Post by niobe »

cortesoft wrote: post #41
niobe wrote: post #31

Earlier quoted context omitted.

So that table is using distance as a proxy for signal to noise ratio. SNR is what really matters. Each data rate in the standard uses a different encoding technique. "Faster" encoding techniques cram more data into a given transmission interval but require a higher signal to noise ratio to be received without error. Since SNR declines with distance you can have a rough idea at what distance from a transmitter you wil…

There are a lot of people who are the only ones using their Wi-Fi, so they probably don't care about the performance for anyone else

But this is the point. What your neighbour's are doing greatly affects the performance of your network.

If you have a good connection and are successfully able to transmit packets to your AP at 600Mbps, and your neighbour has a poor connection and is transmitting at 6Mbps to his AP at that moment, you literally have to wait ~100 times as long for a free medium before you can attempt to transmit. And that's for every single frame. Then you have to hope his client is well-behaved enough not to transmit while you are transmitting. Otherwise you end up having to wait again and retransmit anyway.

You might not notice this with only 2 clients. It might be the difference between a 80MBps and a 50MBps download for example. But it decays exponentially with the number of clients.

Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#48

Post by xuki »

Onavo wrote: post #22
niobe wrote: post #14

An impressive attempt to summarise Wi-Fi which is a very deep topic. However I think the executive summary already missed the most critical thing about Wi-Fi: only 1 transmitter at a time per channel - across all WLANs, yours and your neighbours, with no deterministic way to avoid collisions. It's a shared medium and it's not even half duplex, unlike the dedicated full duplex you would typically get with an ethernet…

Well the newer WiFi standards on 6Ghz support a lot more channels. Not a perfect work around by any means but it does significantly reduce congestion.

Yeah 6Ghz freq doesn't have DFS channels which remove a lot of usable channels for 5Ghz. Unfortunately it'll be a while until most devices support 6Ghz.

Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#49

Post by toast0 »

jauntywundrkind wrote: post #33
blindriver wrote: post #32

One thing that wasn't mentioned is that the more APs you have, the worst off your life gets. That's because the way clients connect to a particular AP is done client-side and you have no control over it or visibility. So, no matter how you fiddle with it, your client may connect to the AP that is 40 feet away and on another floor rather than the one that is 10 feet away with a perfect line of sight. And you won't kno…

There's band steering. You absolutely do have control, if you opt to do so. On openwrt, DAWN or usteer can both help your APs to get sounding maps from clients and to tell them which AP to join. Looking at the sounding maps is very fun data to see: highly tecommend! The settings aren't the world's greatest but they are pretty good starts! https://github.com/berlin-open-wireless-lab/DAWN https://openwrt.org/docs/guide…

My experience with DAWN wasn't great. Some of my clients don't like the extensions you need, so I had to go back to no roaming extensions and just hoping clients make good decisions and tuning ap power levels to help.

Might try it again though, I'd love for it to work. And I was also dealing with some baseline wifi instability that I think firmware updates has resolved.

Re: Wi is Fi: Understanding Wi-Fi 4/5/6/6E/7/8 (802.11 n/AC/ax/be/bn)

#50

Post by lake_trade »

monk_grilla wrote: post #29

Anyone know of a similarly excellent resource for understanding wired networking? CAT specifications, how to pick high quality switches/routers etc.?

Beej's guide will help you with understanding networking overall, I don't think it would help you choosing switches/routers specifically.
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