BACnet Gateway

[Diggerz]

Hi,

Im planning a large KNX project that requires BACnet interfacing. The project consists of 10 floors, each floor with 7 KNX IP routers. Im planning to place 1 logic machine per floor to act as a BACnet gateway and Visu for each floor.

My question is will the logic machine work in this scenario to serve BACnet objects for the 7 KNX IP lines and Visu? 

I'm yet to use a logic machine in this way on a large project, is there a particular setting I should use? Previously on smaller projects i have used TP Couplers and connected the logic machine to the TP Backbone.

[admin]

How many objects will you have per floor? If possible, use different multicast addresses for each floor to separate them if they are all on the same network.

[Diggerz]

They will all be on the same network, Each network will have 50-80 objects to pass over BACnet, so the LM will be handling 350-560 Bacnet objects.

If using different multicast address's would it still be possible to have communication between floors? This is really just for common functions such as time schedule signals and PE cell.

Would it be better in this scenario to use TP Line Couplers on each floor, and use the LM as an ethernet Area coupler on each level? The reason for using Ethernet couplers was redundancy, so each line was independent, however in each scenario the LM with BACnet is still a central point, so it may not make a big difference to use TP couplers and LM as Ethernet area coupler.

1.0.0 - LM ETHERNET
1.1.0 - TP
1.2.0 - TP
1.3.0 - TP
1.4.0 - TP
1.5.0 - TP
1.6.0 - TP
1.7.0 - TP

2.0.0 - LM ETHERNET
2.1.0 - TP
2.2.0 - TP
2.3.0 - TP
2.4.0 - TP
2.5.0 - TP
2.6.0 - TP
2.7.0 - TP

[admin]

You should use IP routers as TP is too slow for large lines. You can have common multicast address for all devices but then you will have to setup filtering table correctly otherwise TP lines will be overloaded with unnecessary telegrams and possibly LM can be overloaded as well.

[Daniel]

You can always communicate between LMs by using different protocol like MQTT, modbus, web services. Plenty to choose from.

[Diggerz]

Thanks, I'll stick with using the same multi cast address for the entire network and be selective with the objects we pass through the ip routers. Would there be any issue with using the logic machine as one of the 7 ip routers for a KNX line as well as providing BACnet, visuals etc for the floor. So 6 ip routers and 1 LM, or would it be better to use 7 ip routers and set the LM aside to perform just the BACnet, and visuals only for each floor?  

I'm planning to structure the project as 1 main line per floor, each with 7 sub lines. so 1.1.x -- 1.7.x, 2.1.x -- 2.7.x, 3.1.x -- 3.7.x etc etc

[Diggerz]

Sorry after re-reading Daniel's reply I had another thought with regards to using a different multicast address per floor. If using a different multicast address per floor will aid in reducing traffic / load I may be able to use one additional logic machine as a BACnet client, and use BACnet to control the common functions such as time schedules, PE Signals etc. This LM can iframe to the other LM's for the building Visual's too.

Would this be a better approach than using 1 multi cast address for the entire network? I'm not familiar with how the multi cast traffic works so apologies for all the questions!

[Daniel]

Our bacnet client is not meant to be used with big amount of objects, you would be better in using different protocol.
It may actually work on single multicast if you implement correct filtering policy.