40 Network Guide
BACnet/IP Broadcast Management Device Service
Though BACnet/IP or FOX uses IP protocol to communicate, a standard IP router does not
forward broadcast messages which are important in BACnet to identify services that are avail-
able within the BACnet internetwork.
When two Building Controllers communicate to each other over a standard IP connection that
is separated by an IP router, both Building Controllers need the BACnet/IP Broadcast Man-
agement Device (BBMD) service to be configured and operational.
The BBMD service identifies BACnet messages on the BACnet MS/TP network that are
intended for a device located on another BACnet network. The BBMD service encapsulates
these messages into an IP message to the appropriate BBMD service of the other BACnet
MS/TP network(s). The BBMD service on these networks strips out the encapsulation and
sends the BACnet message on to the appropriate devices.
When sending BACnet messages across a standard IP connection that has an IP router, there
must be one BBMD service running on each BACnet MS/TP network.
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