BACnet over the Internet

In general, BACnet is a broadcast network protocol. For this reason it is not well suited to use over a wide area network, or the Internet. To facilitate the transport of BACnet information over a WAN the BBMD (BACnet Broadcast Management Device) was introduced.

I like to compare the operation of BBMDs with the operation of a CB radio. On the local network all controllers can "hear" each other talking as would everyone in the cab of a truck when one person talks into their CB. The communications are then sent to other BBMDs over the wide area network that are aware of each other (each BBMD must be aware of every other BBMD, like being on the same CB channel). On the receiving end, all controllers "hear" the remote device's broadcast on their local network as would everyone sitting in the cab of a truck receiving a CB transmission.

That said, the use of BBMDs makes BACnet over a wide area network possible. At each site a BBMD is needed. Each BBMD must be programmed to know about every other BBMD that will be part of the system. The front end must have either a local BBMD or act as a foreign device to at least one of the remote BBMDs.