I'm looking for an OpenWRT router under €100, and I see that many of them advertise mesh functionality. I was wondering if these routers differ from non-mesh routers in terms of hardware, or if it's just a software thing.
I'm talking about low-end devices such as the Linksys MX4200 or the Mercusys MR70X.
Let's take the latter, for example:
In many cases, the difference is just the features included in the vendor firmware and not necessarily any hardware changes of consequence. Sometimes they'll use an updated a radio chip that is a bit more capable, but still leverage a standard dual band radio setup (1x 5G and 1x 2.4G).
Higher end mesh devices tend to have a dedicated backhaul radio for the mesh to use so that the same radio doesn't need to be shared between mesh and standard AP modes. For example, a dual band setup with 2x 5G and 1x 2.4G radios will dedicate the 2nd 5G radio to the backhaul.
YMMV, of course, depending on the brand/model.
I'll answer by posing a question.
What do you mean by mesh?
In terms of open source, a mesh is a layer 2 backhaul based on 802.11s wireless frames.
Mesh nodes can join the mesh backhaul, forming literally a 3D "mesh" of interconnected nodes. Normal user/client devices cannot connect to this backhaul. Instead, they must connect to a special type of node called a mesh gate.
All of this is what OpenWrt supports.
Most routers that can run mainstream OpenWrt can be used as meshnodes.
There is a proprietary, closed source system called "EasyMesh". This is something else entirely, allowing for example three special types of "router like" devices to interconnect using a nonstandard proprietary WDS.
EasyMesh is unlikely, because of its closed nature, ever to be incorporated into OpenWrt.
Is there a way to tell which of the two cases it is?
The generic feature that allows you to "combine" multiple routers. I know the definition is very vague, but so is the advertising for various routers.
Each brand seems to have a different name for it; for example, ASUS calls it AIMesh.
You need to look at the detailed specifications. Sometimes the manufacturer will state it in the published specs, other times you need to do further research based on tear downs and the like.
Each ecosystem / brand uses their own special sauce and are almost always incompatible with others. It is how they attempt to build “lock-in” and sell more devices, but also can allow them to develop features and interfaces to simplify the setup of multiple devices (theoretically providing a competitive edge against their rival manufacturers).
These proprietary mesh(-ish) technologies at the firmware level are not compatible with OpenWrt’s standards based approach. However, for devices that can run official OpenWry, once installed you can setup a proper 802.11s mesh across multiple hardware brands/models without issue (when all of them are using openwrt).
Understood, thanks a lot!
The only hardware-side difference you may see, is between devices with 3 radios (2.4+5+5 GHz, one 5 GHz radio for a dedicated backhaul) or cheaper 2 radio (2.4+5 GHz) devcies; respectively 4 radios (2.4+5+5+6 GHz) for devcies with 6 GHz support. The number of 'good' (~= 4x4 or better) radios contributes significantly to the purchasing price (and power consumption), but the dedicated backhaul is beneficial for maximum performance.
It is worth noting that many 2.4+5+5 devices are built for the EasyNet approach where the second 5GHz radio is only intended for the Easynet "scanning" ie receive only, used in the proprietary WDS-like protocol to search for other EasyNet devices to connect to.
These radios rarely have the proper antennas required for transmitting, even though OpenWrt can set them up that way.
The problem with two 5GHz radios is that in most regions it is very difficult, or even impossible to find two separated channels - a true mesh will have great problems if trying to use DFS, TPC or fixed very low power - and that is without mentioning that outdoor use may be prohibited.
A mesh has to have a fixed and reliable channel to operate on - all nodes on the same channel, so DFS is a non-starter - your backhaul could go down every time a plane flew over at 30,000ft - in a large mesh, any particular node might get a false positive radar detection from remote nodes of its own mesh!
In summary, a three radio device can be of less use than you might expect at first thought.
Interesting, I haven't seen any devices like those, yet (apart from the xiaomi ax3600/ ax9000, where a 1x1 radio is intended for Xiaomi's IoT ecosystem or the linksys wrt3200acm/ wrt32x where it's unused, but originally intended fir DFS scanning).
The ac/ ax/ be devices I had in mind all have full-featured radios. One 5 GHz radio serving ch36-64, the other ch100-144, with the wireless 'mesh' backhaul usually on ch100-144 (with DFS). The ipq40xx based options often reserve the better 4x4 radio for the backhaul, while ipq807x+ ones tend to be 4x4 throughout (with 12- (2.4+5+5) or 16 (2.4+5+5+6) antennas).
E.g. ASUS map-ac2200 (2.4 GHz 2x2 qca4019 + 5 GHz (ch36-64) 2x2 qca4019 + 5 GHz (ch100-144) qca9886 2x2).
In a large 802.11s mesh network, false positive DFS detection caused by remote nodes in the same channel is very likely, causing at best, a storm of mesh path changes as nodes stop transmitting, at worst a complete collapse of the backhaul for minutes at a time.
Likewise, a real DFS event causes a domino effect collapse, with time in minutes after event close before backhaul recovery.
Note on remote mesh node "out of range" signals: multipath interference - from environmental reflections - results in decorrelation of the remote signals in the time domain, effectively scrambling them. Constructive interference can result in surprisingly strong pulses. The net result is something that without detailed analysis is very like a stream of radar pulses.
With just 2 or 3 nodes, you would not expect distant uncorrelated signals from the same mesh, so false positives are much less likely, but collapse due to real events is still an issue.
With the oem firmware, these use the third radio when EasyNet is enabled to scan for other EasyNet devices - never transmitting, or at least that is what seemed to be happening on close inspection. This allows new nodes to change channel to get the required EasyNet-WDS connection.
Yes indeed some more up to date models do have full featured radios, but do they have "full featured" antennas? Not always. Regardless, the same mesh problems exist ie lack of non-DFS/non-restricted channels.
But the incoming 802.11be tri-radio devices are a different beast entirely, allowing 2.4/5/6 GHz simultaneously.
Currently, you can configure a simple 802.11s mesh with OpenWrt, and anything goes - no safeguards. The result is potential non-functionality with no errors.
The Mesh11sd package blocks the selection of DFS channels on startup, giving a clear warning.
I don't know what Batman does, I have not tried a DFS channel there....