I have several Philips Hue Downlights which I have grouped together in groups using Zigbee ZHA Groups. I decided to use Zigbee groups over the HA Helper Light Groups to limit the Zigbee traffic and to have the lights turn on/off simultaneously.
However, they function very unreliably. Both turning on and off is hit and miss. Sometimes I have to try 5 times before it works. When it fails, none of the lights in the target group exhibit any physical behaviour. See example below where I am trying to turn on the ‘Living Room Lights’ but it fails twice in a row.
Outside of the groups, the lights work very reliably. I tried recreating the same groups as helper light groups. Stress testing those shows very reliable behaviour. I know that can be a good workaround instead of ZHA Groups but I want to figure out why it is failing.
I believe that Zigbee groups actually increase traffic considerably, particularly if lights are turned on and off rapidly (by an automation, for example). This is because messages don’t go directly to each target device, but bounce around the mesh, which gets flooded with requests. When a message fails it’s repeated, which makes matters worse. (This is Zigbee thing, incidentally, not just ZHA.)
The main advantage of Zigbee groups is that the lights go on and off together, whereas lights in HA groups change one at a time.
I am not entirely sure about Zigbee groups, but my guess is that they either use a multicast feaute, so only one message go around or that the devices are having attached a group address that can then be called with only one message.
It does not make sense to send multiple messages with Zigbee groups, since it would be no benefit over normal operations then.
From what I can gather, group commands are ‘broadcast’ and routers can re-broadcast it. Considering I have a lot of mains powered devices, there are a lot of routers, and the message might get re-broadcast a lot. I do assume that each router is smart enough to only re-broadcast once. Each device has knowledge of which group it belongs to and will only respond if the broadcast is aimed at its group.
I do not know what happens if it receives the original broadcast from the controller, and then another 15 broadcasts from the re-broadcast by routers. It is strange to me that when it fails, none of the devices within the group respond. Given the broadcast principle and each device individually decided if it is going to respond or not I would expect to see some difference between lights in the same group.
When I do look for suggestions on using ZHA Groups vs HA Groups most posts seem to suggest it greatly reduces traffic in your network.
A broadcast and a unicast message would generate the same amount of traffic. That is the benefit of the group broadcast.
I agree with that.
It looks like either the broadcast is never done or the broadcast is somehow corrupted at the source, so no device respond to it.
It will.
A Zigbee group will send one message and “should” hit all devices in the group.
HA groups will send one message per device in the group, which in larger groups can cause saturation of the RF spectrum and then either retransmits or lost packets.
Thanks for your thoughts! I have rolled back to helper groups in all my automations now but would really like to see if I can fix this ZHA group issue.
Will see if there is some way to monitor what is being sent/broadcast when targeting the ZHA Groups. Whether it is an issue in the communication between the SLZB-06M and HA or if it happens in the zigbee network.
