BACnet is a communication protocol for Building Automation and Control (BAC). All FS20 within a gateway communicate through BACnet. In the following the BACnet configuration is explained for FS20.

For further information on BACnet integration refer to: BACnet CL Integration with OIS MP 3.0, document ID A6V101121669.

Configuring the Device Identifier

The device identifiers of all FS20 in different networks need to be different or BACnet UDP ports need to have different port numbers, for example 47808 and 47809.

BBMD Configuration

If a BACnet network comprises two or more subnetworks, messages need to be distributed to all networks using the BACnet broadcast address. Since standard IP routers do not forward such local broadcasts, an additional device called BBMD (BACnet Broadcast Management Device) is required. Using only one active BBMD per BACnet network is recommended. The BBMD configuration is required to ensure that the Who-Is I-Am communication works properly. Each BACnet network that the Cu-Handler communicates with needs to be entered in the BBMD list. To avoid an immense flow of broadcast messages if several Cu-Handlers are connected in a network, then activate a BBMD only for one Cu-Handler.

For the Who-Is I-Am services, the UDP broadcast packets are not blocked. If this is not possible, the foreign device functionality needs to be activated. For more information refer to: Specific FS20 Attributes.

The communication process is as follows:

  1. A BACnet device sends a Who-Is broadcast message in its network.
  1. The BBMD in this network receives this telegram and forwards it to all its BBMD partners in the BBMD list.
  1. A BBMD that receives a telegram from another BBMD sends a local broadcast message to all BACnet devices in its network.
  1. The FS20 whose device identifier is in the specified range answers with I-Am.


Example of a Configuration with BBMD

The following two FS20 with BBMD in two separate networks are available:

  • The first FS20 has the IP address
  • The second FS20 has the IP address

The BFP stack (BACnet stack) is configured using the bbs_interface and bbs_bbmd attributes in the BACnet Cu-Handler unit. Since a different naming scheme is often used during a new installation of the Debian 11 system, the values of the bbs_interface attribute can vary. You then have to adjust it accordingly, for example:

  • bbs_interface: eth0 or ens32
  • bbs_bbmd:,