Hello everyone,
is there an posibillity to reduce KNX bustraffic at startup of home assistent?
In the start up procedure I have to sync a lot of KNX adresses and that floods the bus and so the traffic is very high with the result that not all adresses could be synced.
So I’m looking for a solution that limits the groupvalueread_requests from HomeAssistant.
For me it is not a problem wenn it tooks some seconds longer to get al values from the bus.
Hi 
!
It’s unlikely that bus traffic is too high to be handled by the Knx bus. Xknx does its syncing very gently 
(there is no user available setting about this).
The errors you see can be caused by (very old) devices that react slowly to a read request (>1 second iirc), and / or have multiple hops (routers, line couplers, etc). Usually they do react though and the answer is processed normally.
If you have devices that can’t be synced at all, even by a manual single read request, this has different causes.
There is no setting from the KNX bus itself - right.
To avoid high traffic during the startup of the KNX bus (inkluding all KNX devices) there is a posibillity to define a individual startup time for each bus device. That is in my point of view a posibillity to reduce traffic.
But during the startup of home assistent the bus traffic jumps to high values around 100 % or maybe more (normal is 1 - 8 % in my setup)
And I thought this was caused by the startup of home assistent.
In the start up time of home assistent around 1000 KNX group adresses need to be sinced and I have read somewere that KNX bus can handle 40 telegrams per second.
1000 group adresses are implemented maybe not all are synced during startup.
after some time all devices are sinced so it is not a reali big issue.
The Knx integration works this way: Only _state addresses are read. On startup it sends 2 read telegrams and waits for an answer. If one of the reads was answered, or timed out (2 seconds), it sends the next. So there is no need to delay certain entities (like startup time) as they never send parallel reads anyway.
In a typical installation this results in ~15 reads per second (30 telegrams including answers). A Knx TP bus can handle up to 50 Telegrams per second.
All of this is additionally rate limited by your Knx Ip interface. So if another device sends a lot at the same time, the interface would throttle HA.
thank you @farmio for explaining.
then there are not so much read requests as first expected.
Then maybe the KNX to IP Router could be the limiting component.
Have to think about filter tables…
Are you using routing? The rate limiting thing only applies to tunnelling. In routing it works quite differently - the receiving routers should take care of not flooding the bus and should send a busy signal eventually … but maybe not all of them do - especially non-certified / software routers.
But the basic 2 parallel request limitation applies to any connection method anyway, so in theory it should be fine.
Im not realy shure what I use in detail.
It is an KNX IP Router with 4(?) tunelling adresses.
But I think it should use 1 tunnel adress.
The KNX information in home assistent shows a physical adress
Most likely tunneling then. You can see this at the diagnostic entities of the “Knx Interface” device.