Example BACnet/Ip diagrams

BACnet/IP networks can be complex, with devices designated as BBMDs and foreign devices, plus standard TCP/IP (IP) routers. BBMDs are used to avoid having separate B/IP networks for each subnet, which would require a BACnet/IP router to exist on each subnet (yet even more complexity).

Internetwork that includes a single Bacnet/IP network spanning multiple IP subnets, plus other BACnet networks

A Bacnet/IP network may span multiple IP subnets. Use of BBMDs provides BACnet broadcast message delivery through IP routers.

Figure 16. Multiple networks

On subnet 192.168.1, there is no BBMD. Both BACnet/IP nodes on that subnet (Device IDs 7, 8) are registered as foreign devices with a remote BBMD.

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 host stations.

On subnet 192.168.3, a QNX-based host with two MSTP trunks and BACnet/IP enabled perform router A functions (B/IP to MS/TP) and BBMD functions.
On subnet 192.168.5, BBMD a host station performs functions with BACnet/IP enabled.
On subnet 192.168.7, any host station with both B/Ethernet and BACnet/IP enabled can perform router C functions (B/IP to B/Eth) and BBMD functions.

A similar internetwork with stations providing BBMD and routing functions

The figure shows a similar internetwork with functions provided by Framework stations.

Figure 17. Framework station provide internetwork functions

In the internetwork above, the station operating as BACnet device (node) 6 could be hosted by either a remote controller or a BACnet (OWS or AWS) Supervisor.