How does a mesh network work from a technical perspective?

[Eanhernandez]

I have an asus GT-AXE16000 and two rpax-58s with wired backhauls. The two rpax's occasionally decide to switch to a wireless backhaul for a while as well. I was wondering what is going on at a networking and radio level on this network when a wireless client (my iphone for example) moves through the house and goes from from being connected to one rpax to being connected to another rpax, or just ends up connecting to the gt-axe. I thought I understood it reading about channels, where multiple 2.4ghz or 5ghz devices on the same network will occupy different channels to avoid overlap, but then I downloaded wifi analyzer and noticed that all the 2.5ghz traffic (20+ devices) is on channel 8! I've read that nodes on a mesh networks use the same channel, and this seems strange, like there would be a lot of overlap and errors in transmission, plus I can't see how one node would know if the client was talking to it or another node, and I cant see how the clients would know either. Mysterious!

Can anyone suggest some reading on how this all works at a technicsl level? Or if you have an answer in mind, I'd love to read that as well. The network works great, but I just can't picture HOW it works. I find the idea of all these little conversations and calculations and exchanges taking place in my house to be very interesting, and would enjoy knowing how they work.

Thanks

 

[Tech Junky]

Well, if it were designed and not automagically configured the 3 devices would use different channels to handoff properly as signal decreases. However since most people aren't network engineers and don't setup their gear properly and let the vendor do it for them this is what happens. This also is what causes issues in a sense setting where your neighbors do the same thing and cause more channel hopping due to interfering with each other.

Ideally you would set them to opposing channels to make a honeycomb type of setup. Why they're switching between wired and wireless backhaul is a different story though as the wired connection should be preferred in most cases. In a traditional router and AP setup this would be the case since you'd have to manually change the AP mode to root/repeater modes to allow a wireless backhaul.

With networking though there's no one way to do things though so, you end up with weird setups sometimes.

 

[tgl]

Can anyone suggest some reading on how this all works at a technicsl level? Or if you have an answer in mind, I'd love to read that as well. The network works great, but I just can't picture HOW it works.

Bearing in mind that I know just enough to be dangerous ... I believe the way that this kind of setup works at a low level is that the clients perceive each AP as a separate device identified by its MAC address. The SSID name acts more like an authentication credential than anything else. If various nearby APs are sending beacon frames that say that they serve SSID "foo", and the client has been told that it should try to connect to "foo", then it will pick the "foo" AP with strongest signal and try to connect to that. If the password it has works, it's in. (The potential for abuse by hostile APs is obvious. I'm not sure how much the more-recent wifi security standards mitigate that, but I think that WPA3 provides at least some defense against connecting to fraudulent APs.)

"Mesh" networks are about 80% marketing, because what I said above is inherent in the wifi standards and has nothing to do with exactly which APs or clients you use. The value-add that a typical "mesh" system brings falls into two classes:

* Easier configuration/administration of multiple APs. Usually you only directly configure the primary node, and the secondary ones are given compatible settings automatically. This works great until it doesn't (and when it doesn't, troubleshooting is typically a real PITA for lack of visibility into what the secondary nodes' settings actually are).

* Assisted roaming. The 802.11k/v wifi standards permit cooperating APs to nudge clients to connect to the AP that would be best according to what the APs measure rather than what the client can see. Sadly, this bit is frequently mostly snake-oil, because (a) no "mesh" AP manufacturer will tell you exactly what they are actually doing in this area, and there's often a lot of nonstandard secret sauce involved; (b) a lot of client hardware still doesn't implement 802.11k/v very well or at all, and the extent to which specific clients react well to nonstandard AP roaming hacks is anyone's guess. When it works, though, a moving client will reconnect to the now-best AP in a seamless fashion, where it might not if the APs involved are independent.

I agree with @Tech Junky 's comment that a well-designed multi-AP setup will put nearby APs on different channels to minimize airtime conflicts. The mesh systems I've used don't do that, which does not give them sterling marks for engineering IMHO. Still, it will more or less work as long as you're not saturating the channel.

If you have wired backhaul available, using wireless backhaul instead seems utterly flat out broken from where I sit. You should be able to configure the system to not do that.