Zigbee routing and 20 devices (directly connected) hardware limit

Like @Sharkys says: it’s a hardware limitation, specifically a RAM limitation of the Zigbee SoC. There is some room to squeeze out a few more additional devices, but not a lot. But AFAIK, the Zigbee rewrite doesn’t include a new SoC-firmware.

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These 20 device limit that we are talking about, I guess this refers to devices that runs on batteries, not routers?

It refers to any type of directly connected device.

Oh, I always thought it was referred to battery powered devices. Will the mesh network force devices to connect via routers when the limit is reached?
Otherwise, this is a greater limitation than I thought. But hey, this is not really connected to Aqara, but Zigbee as a whole

It applies to all devices. That’s why it’s typically advised to add router devices to Homey first, end devices later (when a decent mesh has established itself).

No, that’s not how Zigbee works.

Or rather, Homey’s Zigbee hardware. Othert projects using the same hardware have the same limitation.

You were wrong!
Ted has already updated the app so it works.

Yeah, but in theory it might not matter, I guess. If all devices, battery powered or not, decide to connect directly to Homey it doesn’t matter in which order they are connected. Maybe I am totally wrong here. But I understand the purpose of at least starting with routers.

Unfortunately, I have had my Homey since mid 2017, at the time I wasn’t aware of this, so I started off with a mix of routers and end devices and I haven’t had the patience to remove old end devices in order to rearrange the mesh network.

Really appreciate your input @robertklep

Devices don’t really decide this, they just look around for a router (including the controller, aka Homey) close by that will provide them with a connection. So if you have a nice mesh with routers spread around the house, the chance that a new device will be closer to a router than to Homey will be bigger.

Yes, that is true. The probability that a new battery powered device will connect via a router is greater in this case. It would be nice to govern/control this to a larger extent

I just transfered my zigbee devices back from deCONZ to Homey. In total ~30 devices of which only 4 are direct connected. All others, including routers are being routed, some with 4 hops. So this makes me believe if there is a healthy zigbee network in place, the 20 devices limitation only becomes a limitation with a huge network.

The purpose of adding your routers first, is that your theoretical device limitation is increased.

For example. If you only have Homey and start adding battery powered devices, you can’t add more than 20 devices. Trying to a add a router after you’ve reached the limit, will mean it cant connect since Homey’s limit is reached. It will not ‘push out’ a battery powered device.

If you first add 6 routers, you’ll have a theoretical limit of (Homey + 6 routers = 7 devices * 20) = 140 devices. Minus the 6 routers you’ve added, it’s 134 devices. Adding an end device after this means it has 7 options to connect to Homey. The 140 devices is purely theoretical. If Homey is ‘full’ and other routers are out of reach, you’ll still be unable to add it. So you’ll probably won’t hit 140 devices in total. But it will help you add devices more easily.

This is only when you take into consideration if all devices also have a limit of 20, I can assume some device have less space, or in the other part of the spectrum more space to store in other device data.

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True, the 20 device limit is ‘more or less’ from my experience. But as a rule of thumb, it works

Why have you done this?

I still to seem have issues adding new devices.
Should I remove some of my direct connected devices to allow more new ones? I have 20+ routers in my house so that shouldn’t be the issue.

Just afraid if I remove some devices I cannot add them later.

Second question, should I while I add a device hold it close to homey, or close to a router? Will the last option work at all and improve the chance of having it use a router?

I’ve had about 34 devices connected to Homey with 4 Innr smartplugs routers. Somehow every router only accepted 4 devices and it became impossible to add more devices. So I probably needed to add more routers. But since Homey didn’t accept new Zigbee devices, you need to reset the Zigbee network and add all devices again. And after that fix all the flows with missing devices… Total nightmare. Now I use the Deconz solution on my Synology NAS and it’s working great. I have 6 router devices in the network, but most devices are directly connected to the Conbee II stick.

Thanks @Neuron44, it makes sense and I get how this works, in theory. I have my Homey in the centre of my house, and more or less all my routers seem to connect directly to Homey. Maybe it might be good to move the Homey a bit to “force” this kind of routing. I don’t know, maybe it is better to remove my end devices and start all over with them and let Honey build a better mesh than the one I have now.

To be honest, I have no issues what so ever now. But I have maybe 25 devices in total, most of them connect directly. I am afraid that I can’t add so many more since the quota has been reached.

If you have routers, the qouta isn’t 20 devices in total. When Homey is ‘full’, e.g. when Homey is connected to 20 devices directly, new devices will connect to a router, as long as they are in range.

But let’s say that I have 20 devices that connect directly to Homey.
If I need to add another device (router or end device), will that be rejected by Homey or will that device be pushed downstream and connected via a router? Many devices are a bit cranky and needs to be close to Homey to be able to connect to the network

It won’t be rejected. Many users have more than 20 devices. I have 40 devices. It’ll just try to find a router connected to Homey. If there is a router in range which has ‘room’ for the device, it’ll connect to that router. It wouldn’t be wrong to say that it’s pushed downstream. A device will simply search for the best way to connect, if Homey itself has no more space, it’ll find the next best thing in Homey’s mesh, which is one of your routers.

I think it’s also possible that a device connects to a router rather than Homey directly, even if Homey still has space for it. This will happen when the router is close by and Homey isnt.