How to fix broken BACnet subnet to subnet communications

March 20, 2019

Broken BACnet network is a problem often experienced by our product users, analytics or consultative clients. It happens more times than you think— it is usually about customers trying to get from TCP/IP subnet to subnet without (the usually banned) global broadcasts between subnets.

Often there is a Broadcast Management Device (BBMD) or Foreign Device (FD) are involved and often communication is broken.

“Broken” can mean some or all devices involved:

Support only a “local” mode. While they can do global broadcasts, they themselves do not support directing those broadcasts. They need external BBMD support.
Have FD or BBMD support - but status and administrative access do not allow one to see or configure said FD or BBMD.
Claim to be a BBMD or FD but it does not actually function as such. Sometimes because of a complex configuration process – or simply the type of broadcast transport is broken.
Function fine as a BBMD or FD but have obscure or complex UI, or deliver no status information in real-time.
Are mixed in capabilities A-D in a complex array of different devices. Though some or all might work, they are very complex to manage – due to a different function, interfaces and nomenclature.

Note that software BACnet network devices can add another layer of complexity where execution privileges, network access and OS firewall issues can cause difficulties. The solution to this problem will be a standalone BBMD – e.g. Cimetrics B3060 - running on an embedded hardware platform with a network OS. Just turn off or remove all your problem BBMDs, and place the standalone BBMD in each and every isolated subnet. B3060 Configuration steps involved:

- Open up Foreign Device (FD) on each form allowed remote access (allow FD and get status via Foreign Device Table (FDT).

- Point each unit at all other units with which you wish to share broadcasts. (Fill the BDT with a mesh of your design in your control).

BBMD Broadcast Management Device Cimetrics B3060