BACnet/IP networks can be more involved, with devices designated as BBMDs and “foreign devices”, plus standard TCP/IP (IP) routers. Note that BBMDs are used to avoid having separate B/IP networks for each subnet—this would require a BACnet/IP router to exist on each subnet (yet even more complexity).
Figure C.9 shows an example internetwork that includes an Ethernet/IP backbone.
Figure C.9. Internetwork that includes single B/IP network spanning multiple IP subnets, plus other BACnet networks
The B/IP network shown in Figure C.9 spans multiple IP subnets. Use of BBMDs provides BACnet broadcast message delivery through IP routers
Note that on subnet 192.168.1, there is no BBMD. Both BACnet/IP nodes on that subnet (Device IDs 7, 8) are registered as a “foreign device” with a remote BBMD.
Note also that on the physical Ethernet segment used by subnet 192.168.7, there are both BACnet/IP devices (Device IDs 2 and 3) and BACnet over Ethernet devices (Device IDs 4, 5, and 9). Router “C” provides communications between these two BACnet networks.
With the exception of router “B” (B/IP to B/ARCNET), all BACnet routing and BBMD functions can be performed by Niagara stations.
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On subnet 192.168.3, router A functions (B/IP to MS/TP) and BBMD functions can be performed by a QNX-based JACE with two MSTP trunks and BACnet/IP enabled.
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On subnet 192.168.5, BBMD functions can be performed by any Niagara station with BACnet/IP enabled.
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On subnet 192.168.7, router C functions (B/IP to B/Eth) and BBMD functions can be performed by any Niagara station with both B/Ethernet and BACnet/IP enabled.
Figure C.10 shows an a similar internetwork with these functions provided by Niagara stations, as described above.
In the internetwork above, the station operating as BACnet device (node) 6 could be hosted either by either a JACE controller, or a BACnet (OWS or AWS) Supervisor.