[Make-wifi-fast] Real-world testing: wifi8 and 802.11 wg

[Sebastian Moeller]

@David,

did you ever give a talk about this, and if so is that available somewhere? And if not, maybe you should ;) 


Regards
	Sebastian


> On 2. Sep 2024, at 17:04, Rich Brown via Make-wifi-fast <make-wifi-fast at lists.bufferbloat.net> wrote:
> 
> 
> How can this message be flagged as an important "stake in the ground" re: testing of Wi-Fi for common/useful situations? Thanks, David...
> 
>> On Sep 2, 2024, at 1:05 AM, David Lang via Starlink <starlink at lists.bufferbloat.net> wrote:
>> 
>> 
>> I'll start off by saying that my experience is from practical in-the-field uses, deploying wifi to support thousands of users in a conference setting. It's possible that some people are doing the tests I describe below in their labs, but from the way routers and wifi standards are advertised and the guides to deploy them are written, it doesn't seem like they are.
>> 
>> My belief is that most of the tests are done in relatively clean RF environments where only the devices on the test network exist, and they can always hear everyone on the network. In such environments, everything about existing wifi standards and the push for higher bandwidth channels makes a lot of sense (there are still some latency problems)
>> 
>> But the world outside the lab is far more complex
>> 
>> you need to simulate a dispursed, congested RF environment. This includes hidden transmitters (stations A-B-C where B can hear A and C but A and C cannot hear each other), dealing with weak signals (already covered), interactions of independent networks on the same channels (a-b and c-d that cannot talk to each other), legacy equipment on the network (as slow as 802.11g at least, if not 802.11b to simulate old IoT devices), and a mix of bulk-transfers (download/uploads), buffered streaming (constant traffic, but buffered so not super-sentitive to latency), unbuffered streaming (low bandwidth, but sensitive to latency), and short, latency sensitive traffic (things that block other traffic until they are answered, like DNS, http cache checks, http main pages that they pull lots of other URLs, etc)
>> 
>> test large number of people in a given area (start with an all wireless office, then move on to classroom density), test not just one room, but multiple rooms that partially hear each other (the amount of attenuation or reflection between the rooms needs to vary). The ultimate density test would be a stadium-type setting where you have rows of chairs, but not tables and everyone is trying to livestream (or view a livestream) at once.
>> 
>> Test not just the ultra-wide bandwidth with a single AP in the rooms, but narrower channels with multiple APs distributed around the rooms. Test APs positioned high, and set to high power to have large coverage areas against APs positioned low (signals get absorbed by people, so channels can be reused at shorter distances) and set to low power (microcell approach). Test APs overhead with directional antennas so they cover a small footprint.
>> 
>> Test with different types of walls around/between the rooms, metal studs and sheetrock of a modern office have very little affect on signals, stone/brick walls of old buildings (and concrete walls in some areas of new buildings) absorb the signal, the metal grid in movable air walls blocks and reflects signals
>> 
>> Remember that these are operating in 'unlicensed' spectrum, and so you can have other devices operating here as well causing periodic interference (which could show up as short segments of corruption or just an increased noise floor). Current wifi standards interpret any failed signals as a weak signal, so they drop down to a slower modulation or increasing power in the hope of getting the signal through. If the problem is actually interference from other devices (especially other APs that it can't decipher), the result is that all stations end up yelling slowly to try and get through and the result is very high levels of noise and no messages getting through. Somehow, the systems should detect that the noise floor is high and/or that there is other stuff happening on the network that they can hear, but not necessarily decipher and switch away from the 'weak signal' mode of operation (which is appropriate in sparse environments), and instead work to talk faster and at lower power to try and reduce the overall interference while still getting their signal through. (it does no good for one station to be transmitting at 3w while the station it's talking to is transmitting at 50mw). As far as I know, there is currently no way for stations to signal what power they are using (and the effective power would be modified by the antenna system, both transmitted and received), so this may be that something like 'I'm transmitting at 50% of my max and I hear you at 30% with noise at 10%' <-> 'I'm transmitting at 100% of my max and I hear you at 80% woth noise at 30%' could cause the first station to cut down on it's power until the two are hearing each other at similar levels (pure speculation here, suggestion for research ideas)
>> 
>>> How many different tests would it take to give reasonable coverage?
>> 
>> That's hard for me to say, and not every device needs to go through every test. But when working on a new standard, it needs to go through a lot of these tests, the most important ones IMHO are how they work with a high density of users accessing multiple routers which are distributed so there is overlapping coverage and include a mix of network traffic.
>> 
>> David Lang
>> _________________________________
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