| BACnet driver uses BACnet dynamic device binding to discover available BACnet
devices and to define their IP addresses and other device attributes.
BACnet driver periodically sends Who-Is broadcast message and receives I-Am
responses from BACnet devices. Also the driver allows a Unit to go online only
if I-Am message from a BACnet device has been received.
IP broadcasts are not routed but some of BACnet capabilities, such as dynamic
name binding and unsolicitied change-of-value notification need broadcast
messages. Therefore BACnet specification defines two ways how a broadcast
message can be sent between different IP subnets (BACnet spec, Annex J). The
first one is to configure a "BACnet/IP Broadcast Management Device" (BBMD) on
each IP subnet and the second one is to use IP multicasting.
Reference:
https://bacnet.org/bibliography/
BACnet driver is using Cimetrics BACnet protocol stack which includes BACstac
service. This service can be confugured to be a BBMD device and send broadcast
messages to other subnets. Alternatevely it can be configured as a foreign
device and subscribe to broadcast messages through specified BBMD.
So currently to make BACnet driver to communicate to other IP subnets either
BBMD or IP multicasting should be used. (ie. Currently only a hardware solution is available, meaning a
BACnet router will be needed to cross subnets)
Modificaton of the driver to use a specified IP address instead of relying on
Who-Is, I-Am broadcast messages is currently being investigated by the
Schneider Electric SCADA Activity Driver Development Team.
Please contact Support for futher information.
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