I've noticed that a lot of modern devices have USB 3.0 port. Would it be reasonable to use a USB wifi adapter to create a mesh? There are a limited number of triband devices so it would be nice to be able to turn a regular wifi router into a mesh device. With a dedicated USB for the backhaul you could take full advantage of the build in radios. Additionally the wireless adapters tend to support multiple bands so the mesh could be much more dynamic.
No, there is a lot of prior discussion about using USB wireless cards for continuous operations or AP mode found via the forum search. In almost all cases the internal radios would wipe the floor with any USB WLAN card and even the repeater effect ends up being small in comparison.
So are you saying that the performance of the USB radios would end up being a limiting factor? From my understanding 802.11s based mesh doesn't need anything like MU-MIMO or other advanced features.
I have read previous posts and I didn't see anything where someone actually tested this.
The most obvious limit for USB adapters is the number of clients on AP Mode. (7-16 clients on BCM43143, 32 clients on all rtw88 devices). I don't know how these limits will interact with 802.11s, though.
After that, it should be noted that the Linux drivers for almost all USB adapters do not act on their own, but rely on a small firmware binary that depends on the manufacturer, and unless they are the latest model, this firmware is not updated.
Manufacturers usually test only the station mode, and AP mode testing is very little, if any. If you want to use an adapter with 802.11s, you would have to test it yourself being aware that it might not work and no one will be able to help you, especially if it is a bug in this binary firmware.
That said, I think the “workload” for Mesh (802.11s) or a pseudo mesh (WDS Station mode) would be less than that of an AP and I think it would be good to try to set up a mesh that way. If you can buy an adapter, it would be good to write your experience. Maybe I will try it with my routers.
You do not need a triband device for mesh, in fact it is of little use as the third radio is usually 5GHz and in most locations non-DFS channels are very limited and you cannot reliably run a mesh on a DFS channel. On many, it is also intended only for passive scanning use in a proprietary Easymesh type system (a vendor specific closed source WDS type system).
Most usb wireless dongles are very limited and intended for STA mode only. Those that do support mesh (or AP) mode are still not designed for the continuous traffic those modes produce and tend to overheat and shut down or even burn out when things get busy.
Finally, by its very nature, a mesh backhaul requires greater penetration/range than an AP does as it is generally used for connecting APs together. The limited power availability and limited (or almost non-existent) antennas on a dongle are a great disadvantage in a mesh environment.
Yes
Your understanding is incorrect. Where did you read that?
Given that the primary usage of a mesh backhaul is to connect APs together, this is clearly not the case. In fact the workload is usually much higher.
Yes, that's true. I have not explained myself well.
In other words, a good/expensive Wi-Fi adapter should have no problem with high traffic throughput if it is connected as an STA.
The problems I have encountered with USB adapters were:
- don't work well as an AP regardless of traffic, especially if there are many clients connected.
- bad drivers. This is common in Realtek, but I have backported mainline drivers from the rtw88 maintainer and they work fine now. Mediatek based USBs are well supported on standard Linux, apparently.
- Stability. The cheaper adapters really hate to operate 24/7 and get unstable, I imagine because of....
- Temperature. The adapters heat up easily. One of the adapters that has served me best (one with an old rtl8812au chip) has a heatsink.
- flaky or underpowered USB ports on the routers
That is the use case the manufacturers primarily aim to satisfy whilst keeping costs down.
Yes indeed.
Occasionally true, but the most common reason for designing in a usb port into a router is to support 4g cellular dongles and they are more power hungry than most other things.
This is very true and your backporting is very interesting. But does it actually support mesh mode?
Can you run the following:
iw list
Then look for the usb dongle phy and show the 2 or 3 lines from valid interface combinations onwards.
Typically, an embedded wireless in a router you will see something like:
valid interface combinations:
* #{ IBSS } <= 1, #{ AP, mesh point } <= 16, #{ managed } <= 19,
total <= 19, #channels <= 1, STA/AP BI must match, radar detect widths: { 20 MHz (no HT), 20 MHz, 40 MHz, 80 MHz, 160 MHz }
On generic Linux, most MediaTek dongles are supported, but I have found very often the support is only STA mode or very limited AP mode (only very small numbers of connections and no support for simultaneous STA and AP modes) and no mesh mode.
So using one of these for connecting to a "hotspot" is quite useful, or replacing a failed built-in wireless module in a laptop for example.
Good point, a cheap rtl8821cu adapter with rtw88 driver doesn't support 802.11s
Supported interface modes:
* IBSS
* managed
* AP
* AP/VLAN
* monitor
* P2P-client
* P2P-GO
...
valid interface combinations:
* #{ managed } <= 1, #{ AP, P2P-client, P2P-GO } <= 1,
total <= 2, #channels <= 1
Yes, it's a problem. Your rtl8821cu example can do STA (managed) at the same time as AP, but pretty much no other useful combinations.
If it stays cool and stable under load it could be used as a wan uplink, aka a "hotspot" scenario....
You can already, you don't need triband either.
There are packages specifically to manage a mesh backhaul as well, eg batman and mesh11sd.
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