Obvius BACnet - Manual (Page 37)

BACnet Server for AcquiSuite Page 37 of 52
CVS:bacnet/Documentation/BACnet_Users_Guide.doc
“BBMD” stands for BACnet Broadcast Management Device, a service which forwards BACnet
broadcast messages from the local IP subnet to one or more remote IP subnets.
The BACnet Server for AcquiSuite is able to act as a full BBMD, to provide flexibility in placing the
AcquiSuite on remote IP subnets.
BACnet/IP relies on broadcast messages (Who-Is, I-am) to discover devices. These broadcasts are
usually blocked by IP routers.
When a BACnet network spans multiple IP subnets, a BBMD should be configured on each subnet with
the IP addresses of all other BBMDs.
For example, in the following diagram, the BACnet network consists of two IP subnets (in orange),
separated by an IP router.
The two BBMD’s forward BACnet/IP broadcasts between the two IP-subnets, allowing devices on each
side of the router to discover devices on the other.
Note 1: BBMD’s only forward broadcasts. BACnet services such as ReadProperty or
WriteProperty, which are never broadcast, pass though the IP-routers without any help.
Note 2: The BBMD feature is not needed if your BACnet network is contained in a single IP
subnet, or if the subnet already has a BBMD.