BBMDs & Foreign Device Registration

In small, simple networks, the Mapped gateway scans the subnet it's assigned to in order to find devices and extract time series data. Many networks, however, are more complex and may have multiple independent segments. In these situations, there is typically one ore more BBMDs (BACnet Broadcast Management Devices) we typically need to interact with to find all the devices across multiple segments.

What is a BBMD

BBMDs are specialized network devices that ensure communication between different segments of a larger network, especially when those segments are separated by different subnets. Normally, devices on separate subnets can't directly broadcast messages to each other. A BBMD facilitates that communication, acting as an intermediary, forwarding broadcast messages from one network segment to another.

BDTs (Broadcast Distribution Table)

For a BBMD to know where to forward these messages, it relies on a Broadcast Distribution Table (BDT). The BDT is essentially a directory that lists all the other BBMDs in different network segments.

Registering as a Foreign Device

In order for Mapped to see all the devices across all the different network segments, our gateway needs to register as a foreign device with at least one of the BBMDs in a BDT. The registration involves an initial message to the BBMD, the "Foreign Device Registration Request", which is validated by the BBMD and confirmed. Once registered, our gateway is officially part of the network and can now receive broadcast messages from the network as if it were a local device.

Periodically, the Mapped gateway will send a new registration request to stay connected and receiving packets.