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Author Topic: WLAN selection  (Read 485 times)

Weaver

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WLAN selection
« on: April 16, 2021, 02:02:10 PM »

(I wasnít sure whether or not to put this question under ĎAppleí as it could be considered an iOS question.)

How do operating systems choose which WLAN / SSID to connect to when they have several available? Is it down to signal strength only ? What about the speed of the networks ? Say you have one that offers 300Mbps max and another that offer 150 mbps max? (Or we could consider current actual speeds at the particular signal strength available right now.)

Iím thinking about having a 20 MHz wide 2.4 GHz channel and a 40 MHz wide 5 GHz channel and am wondering what clients will do. This is instead of the current situation where there is a choice between 2.4 and 5 GHz channels that are both 40 MHz and so both 300 Mbps max at the current MIMO settings that are the same. In practice 2.4 GHz can be faster at certain times because of better penetration of (lightweight) internal walls.
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meritez

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Re: WLAN selection
« Reply #1 on: April 16, 2021, 04:18:04 PM »



Hi Weaver, is there any chance of knowing the devices in question?
From the above chart, if you are limiting both your 2.4ghz and 5ghz networks to 40mhz 802.11n and two spatial streams, the maximum sync rate is 300, though if your 5ghz network supports 802.11ac and 256-QAM modulation and two spatial streams, the maximum throughput for 5ghz at 40mhz is 400.

Do both of your SSIDS share the same SSID name, or are they named separately?
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DaveC

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Re: WLAN selection
« Reply #2 on: April 16, 2021, 06:14:18 PM »

Apple have a page where they describe their algorithm:

https://support.apple.com/en-gb/HT202831
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burakkucat

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Re: WLAN selection
« Reply #3 on: April 16, 2021, 08:43:27 PM »

How do operating systems choose which WLAN / SSID to connect to when they have several available?

In my experience, it is down to a combination of the end-user and the OS.
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Weaver

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Re: WLAN selection
« Reply #4 on: April 17, 2021, 12:43:52 AM »

Hi Meritez. I have three SSID names; a general one, a one for guests, and one that I alone use. The general one and the guest one have different SSIDs obviously but the same SSID name is used for 2.4 and 5 GHz. Guests and standard users are allowed to use both bands. The WAPs are ancient ZYXEL 802.1n (not ac) WMA-3560n devices, two in use and one in a box not deployed yet, for some reason. Over ten years old! Their PSUs are new though, they have DC UPS Ďplugí-type PSUs. Iím thinking they are using 2x2 MIMO, anyway, two spatial streams, 40ns 40 MHz wide channel and 64-QAM which give a max of 300 Mbps according to your excellent chart. When going through wooden walls, the indicated data rate in one of the directions goes down to 6 MHz !

The WAPs contain two radios each and each of the radios can be set to either 2.4 GHz or 5 GHz. So in fact it is possible to have a WAP on 2.4 and 5 GHz and that is how WAP1 is set up, but WAP2 has two SSIDs, one assigned to each radio, with distinct names set to two different channels both on 5GHz. This is done mainly to make full use of both of the radios in this WAP. I am the only user of the distinctly named SSID on WAP2 radio:2 and this is done so that Janet and I get distinct twin lots of 300 Mbps when weíre both working.
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meritez

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Re: WLAN selection
« Reply #5 on: April 19, 2021, 11:49:19 PM »

Hi Weaver,

Due to signal penetration, operating systems should prefer the 2.4 signal.
When a device connects to an access point, the access point will ask the device what do you support, and if a device states 802.11b at 1mb, the ap will happily serve that believing it has done its job.

So I take it from your reply that you are broadcasting 802.11n only in both 2.4 and 5 bands, and 802.11a, b and g are disabled?

I have a dozen of those particular access points in the office from a Unifi install, I may go and pick up one to see if there is anything different in its protocols, I think it has a interfere mode with other access points
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Weaver

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Re: WLAN selection
« Reply #6 on: April 21, 2021, 12:08:35 AM »

> 802.11a, b and g are disabled?

Correct.
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Alex Atkin UK

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Re: WLAN selection
« Reply #7 on: April 21, 2021, 01:13:05 AM »

Due to signal penetration, operating systems should prefer the 2.4 signal.

Thing is though AFAIK these days they don't.  Its either enforced by the Access Points (even Unifi its experimental) especially on mesh networks, or the drivers have a "prefer this frequency" option on say Windows.

You don't want to favour 2.4 as a weak 5 signal often achieves much higher throughput than a strong 2.4.
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Weaver

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Re: WLAN selection
« Reply #8 on: April 21, 2021, 06:56:55 AM »

Meritez asked me about what devices Iím using: All iPads.

Alex wrote:
> a weak 5 signal often achieves much higher throughput than a strong 2.4.

Exactly. One of my concerns when starting this thread.

My WAP #2 is just outside the bedroom, through a wooden wall, approx 5 m away from me. I donít get max speed from it on my iPad Pro though because of the wall and the fact that Iím using 5 GHz - Iím assuming thatís the cause. It seems to me that 2.4 GHz is far better as long as you donít have any neighbours and youíre on the same channel width.

That WAP (#2) has two 5GHz radios in it and radio #2 is for my use only. Privileged users such as Janet can use WAP2 #2 Radio 1 (5GHz) or either of the radios in WAP #1 : WAP #1 radio 1 is 40MHz wide 2.4 GHz, and WAP #1 radio 2 is 5GHz. Guests can use 2.4 GHz on WAP #1 radio 1 and also iirc WAP #1 radio 2. I forget the exact security and SSID assignments.

One of my SSIDs is available on both radios and in both bands, so the o/s has maximum freedom of choice. Given that the downstairs WAP #1 is very close to the bedroom, and very high up, if Janet has associated with WAP#1 and then brings her device up to the bedroom, it wonít be the end of the world if it remains on WAP #1 especially if it is on WAP #1 radio #1 which is 2.4 GHz and 40 MHz wide.

* Another question: I have left a ~20MHz wide band free on 2.4GHz; am using channels 1 and 6 bonded on WAP #1 radio 1. I am wondering if this free space is beneficial for Bluetooth? Does Bluetooth search for a free channel?
« Last Edit: April 21, 2021, 07:09:16 AM by Weaver »
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meritez

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Re: WLAN selection
« Reply #9 on: April 21, 2021, 09:19:47 AM »

@Weaver,

All Apple devices changes this, as Apple has a recommended wireless setup page: https://support.apple.com/en-gb/HT202068
Quote
All devices, including older devices, can then connect using the fastest radio mode they support

So Apple has a 5ghz preference set in their operating system, there's also stuff about bluetooth interference and location services interfering.
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Alex Atkin UK

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Re: WLAN selection
« Reply #10 on: April 21, 2021, 11:43:55 AM »

I can't take any guide very seriously when they recommend Auto for the channel.
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Weaver

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Re: WLAN selection
« Reply #11 on: April 21, 2021, 04:24:22 PM »

> when they recommend Auto for the channel.

Absolutely. Itís asking for an amount of intelligence that most systems simply donít have. And I worry about multiple systems using auto, chasing each other round the frequency space as one updates to get out of the way of the other(s). One ought to have an algorithm to detect that kind of instability. If you have near-AI type of algorithmic power in your o/s and the system is tested in competition with like-minded systems, at a bare minimum, then maybe, otherwise itís really iffy somehow.
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Alex Atkin UK

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Re: WLAN selection
« Reply #12 on: April 21, 2021, 07:08:42 PM »

It may work in commercial installations, not sure, but definitely residential hardware is too half-assed.  Seen too many cases of them putting 2.4Ghz on none-standard channels causing clashes across multiple channels.
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Weaver

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Re: WLAN selection
« Reply #13 on: April 22, 2021, 02:05:18 AM »

The auto feature in my ZyXEL WAPs can be told which channel numbers are allowed to be used in the auto mode, so for example you can tell it whether you and your neighbours have the three-channel 2.4GHz 1, 6, 11 allocation scheme or the four-channel scheme (1, 5, 9, 13 - is that right?).
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Alex Atkin UK

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Re: WLAN selection
« Reply #14 on: April 22, 2021, 03:04:18 AM »

Correct, although if I recall correctly 802.11b used to be 22Mhz wide which is why 1, 6, 11 became the standard.
Once 802.11n reduced it to 20Mhz there were too many APs still using 1, 6, 11 and by the time everyone had capable hardware, most manufacturers never bothered to adjust the allocation so we lost the use of channel 13 as unless everyone uses the UK scheme, nobody can. :(
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