| Applies To: |
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| Summary: |
| The BACnet driver does not seem to
have the capability to allow Citect to talk to a BACNET device when
both are on a different subnet. |
| Solution: |
| 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: http://www.bacnet.org/Bibliography/ES-7-99/IPPART2.HTM 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. Author: Alexander Meshcheryakov & Nathan Slider |
| Keywords: |
| BACnet Speciality Driver gateway BACNET/IP |
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