Question about the KNX architecture

[Warichet]

Hi,

From the KNX architecture, I understand that a Line can be composed of 4 segments, with 3 repeaters,
for segment 1, devices are numbered from 0-63
for segment 2, devices are numbered from 64-127
etc
0, 64 etc are reserved for couplers/repeaters

Is it so that the repeater has no "intelligence" besides "repeating" and galvanic isolation ?

hence all traffic flows on all 4 segments
hence on segment 1, I could have a device 1.1.200 ? (which theorically belongs to segment 4).

The doc shows the devices cleanly organized, but I guess it is for clarity only ? no other implications ?

What would be the benefit of an architecture with a main Line 1.0.x and a secondary Line 1.1.x and a LC for a EFH where the traffic is obviosly low, versus an architecture with a single line with 2 segments and a repeater ?

Thank you for your comments.

[MatthiasS]

- Only 0 is reserved.

- no intelligence

- of course, 1.1.1 to 1.1.255

- 1.1.200 can be anywhere, it is not necessary to sort your devices within the 4 segments

- no benefit
(iin case that Line 2 is outside of the house, security reasons could make a line coupler with address filter necessary instead of a stupid repeater)

[domoticom]

in Your case a line coupler could lower the impact in case of a short circuit in the bus, and better spread load over 2 power supplies

[MatthiasS]

No!

Why?

There is no physical differnce between repeater and line coupler. It is the same device! In case of shortened circuit, the segment will be dead or the line. In both cases the numer of devices is the same.

[domoticom]

you are right, I did not read the question good enough

[Warichet]

Hi Matthias,

Thank you for this right-to-the-point answer

(in case that Line 2 is outside of the house, security reasons could make a line coupler with address filter necessary

Indeed, I forgot to mention the fact that one wire segment is outside the house, which originally led me to the 2 lines design.

a line coupler with address filter necessary instead of a stupid repeater)

I would love to have a "stupid repeater" for the moment I've got a "stupid line coupler" which I can't convince to act as a repeater. If he persists, he will end up on eBay

This address filter topic is not clear to me.
Although I understand the basic principle, analogy with the network counterpart.
I understand that if all senders & receivers on 1.1.x are on one side of the "bridge" and all senders & receivers on 1.0.x are on the other side of the "bridge", no problem, no one crosses the bridge (if filtering is enabled).
Imho, it wouldn't be very clever to mess around, i.e. all sensors on one side and all actuators on the other side.
Can you please provide me with a practical example, where the situation requires filtering or where it really makes sense ?

And what about the HS ? where should we place it ? as he obviously has to "know" everything, should be able to query the status of any device, should be able to trigger any actuator, wherever it is residing ?

My intuition would place it on line 1.0.x, but ... doesn't this lead to a passthrough set-up of the LC ? hence defeating argument #1 of a LC ?
Thank you for sheding some light in my darkness

[MatthiasS]

Very delicate topic.

The reason for address filtering comes IMHO from installations in office buildings. There is a need to reduce traffic, otherwise knx would work. Imagine having an office building with 20 floors and every telegram from every floor goes everywhere.

So normally one complete floor is one one line, sebnsors and actuators. The line would work standalone.

If there is a central device ("Visu"), this device would only have summary messages passed through coupler, this device (Hs) would sit on the top level line. It would receive only a very small set of the existing telegrams.

Please remember: couplers work on group address filtering, not on pysical addresses.

I think, having a private home with a "HS" is a special application and KNX was not designed for it basically ;-) Filtering in a private house where you want to see everything makes no big sense.

A real example for filtering I do not have. I could imagine not to let go through group telegrams from the outer line to my knx burgalar alarm device.

[Warichet]

Thank you very much.

[Gamma]

Hello Warichet,
I'm sorry but you're still mixing up some things...
1) your stupid LC should get an stupid repeater if you assign a physical address x.x.y, y must be nonzero.
2) the filtering is done on Group addresses, not on a physical base.
that means your analogon to Ethernet "Subnetting" is wrong - sorry.
Ethernet subnetting "can" be coarsly compared with the physical addresses on KNX, but the KNX GA filtering scheme would fit much better into an
Ethernet switch setup to route an multicast packet or not.

btw: the ETS checks whether GA's are "used" in the different Lines/areas and generates the filter tables accordingly for download into the area/line couplers.
3) the GA filtering is needed in KNX setups where several thousands
of devices are installed. So just as Matthias mentioned there will be no need
to use it in home appliances.

best regards, Gamma

[Warichet]

I'm sorry but you're still mixing up some things...

I'm very good at that

1) your stupid LC should get an stupid repeater if you assign a physical address x.x.y, y must be nonzero.

ûûh, point taken

2) the filtering is done on Group addresses, not on a physical base.
that means your analogon to Ethernet "Subnetting" is wrong -

ûûh, yet another point taken

ETS checks whether GA's are "used" in the different Lines/areas and generates the filter tables accordingly for download into the area/line couplers.

OK, this brings up a related question: as this data is written into the device at programming time, how long should ETS wait & listen in order to build a representative table ? as some GA are only present a couple of times /day ?

3) the GA filtering is needed in KNX setups where several thousands
of devices are installed. So just as Matthias mentioned there will be no need to use it in home appliances.

OK, this was already clear to me, heck, I don't mix everything

As an aside;
if on a wire segment, I change all devices PA, i.e. from 1.1.x to 1.0.x, without touching their GA, simply re-programming their PA, and physically move that segment to line 1.0.x, will it work ? Don't know if such a trick is allowed without re-programming everything.

Thank you very much for putting me right
( but you still have plenty of work to do in that area )

[MatthiasS]

OK, this brings up a related question: as this data is written into the device at programming time, how long should ETS wait & listen in order to build a representative table ? as some GA are only present a couple of times /day ?

Wrong again

The filter table is not generatetd by listening to the real traffic, it is generated by entries made in ETS. You tell ETS, which addresses to filter!

[Warichet]

Wrong again !

Ouups

The filter table is not generatetd by listening to the real traffic, it is generated by entries made in ETS. You tell ETS, which addresses to filter!

Thank you.

With all the smashes I've recently collected, I'll hide away, deep in rural France for a week or two.

[swenga]

Hello Warichet,

if on a wire segment, I change all devices PA, i.e. from 1.1.x to 1.0.x, without touching their GA, simply re-programming their PA, and physically move that segment to line 1.0.x, will it work ? Don't know if such a trick is allowed without re-programming everything.

I have exactly done that last time when one of my lines exceeded the number of devices/current. It worked. However dont forget to program the LC, only when it is programmed, it will have a filter table and forward data. BTW: this also works with "Overwrite existing adress", it saves the time running to all devices and pushing program buttons

When you have LC's, it is a good idea to have a ETS dummy device with the adress of the homeserver in the according segment. You can assign all the GA's you need to have in the homeserver to this dummy device. Now the ETS knows, that a GA is in two lines and will generate the filter table for the LC approprietly.

According to your other problem: In my opinion a Line coupler's behaviour is derived from its adress: Does it have a 0 at the end, it is a LC, otherwise it will work as a Repeater. Dont take it for sure, i do not use repeaters, but it's worth trying.

Best regards, Swen

[Warichet]

Hi Swen,

I have exactly done that last time when one of my lines exceeded the number of devices/current.

I'm triggered by exactly the same motivation.
Although my installation with 66 devices works OK, I fear an overload.
More than often, we have a power outage, when the power comes back, all EMO do a recalibrate (all 4 at the same time, no fun when it happens at 3 o'clock at night, nothing to do about it, merci EDF)

However dont forget to program the LC, only when it is programmed, it will have a filter table and forward data.

According to above arguments, it makes little/no sense to enable filtering in a EFH. So I wan't enable filtering.

this also works with "Overwrite existing adress",

Yes, thank you, it was my intention to do it that way.

When you have LC's, it is a good idea to have a ETS dummy device with the adress of the homeserver in the according segment. You can assign all the GA's you need to have in the homeserver to this dummy device. Now the ETS knows, that a GA is in two lines and will generate the filter table for the LC approprietly.

Hé, hé, clever trick where have you got that one ?

a Line coupler's behaviour is derived from its adress

That's what I learned from master Matthias & Gamma . They are really good at teaching dummies
I must admit I've completely missed this topic, based on the fact that I've seen applicaions for repeater and LC. I stand corrected now .

btw, you are very good at teaching dummies as well

Thank you very much

[swenga]

Hi Warichet,

More than often, we have a power outage, when the power comes back, all EMO do a recalibrate (all 4 at the same time, no fun when it happens at 3 o'clock at night, nothing to do about it, merci EDF)

I can only recommend an UPS for the KNX power supplies. As all my power supplies are in one cabinet, it was easy to put one (really cheap standard APC device) in between the power connection. We also moved from urban to rural with the new house. In the city i had at most 3 power outages in 10 years, here in the countryside already about 6 in a year, although some are very short (<10 seconds).

Youre welcome,

Salut, Swen.