All BACnet drivers support more than one link layer type using multiple network ports under the BACnet network’s child container. A new BACnet network defaults to BACnet/IP (Ip Port). The other port types (EthernetPort, MstpPort) are available in the bacnet palette. The MstpPort component, which supports a BACnet MS/TP device trunk, requires a station hosted by a QNX-based host.
Each port must reference a unique BACnet network number across an internetwork. The range for BACnet network numbers is 1-65535.
You define this Network Number property in each port component’s Property Sheet. This property defaults to -1, which means that it is undefined or inactive.
If you are installing a station on an existing BACnet internetwork, where one or more BACnet routers already exist, you need to know the assigned network number(s), and enter them, as appropriate, in the network port(s) under the container. You can find the existing network number information in the configuration setup of the BACnet routers.
A station’s BACnet network is not limited to only BACnet networks defined by its own network ports. The BACnet network automatically learns other remote networks, from global BACnet I-Am messages received from the devices (and routers) on other remote networks. The station maintains a table of known BACnet networks under the network’s child in a Router Table component.
By default, the station automatically performs BACnet router functions across multiple BACnet networks. Often this is the
desired behavior, especially when there are MS/TP trunks that attach to RS-485 ports on a remote controller. However, multiple
BACnet routes to the same network segment result in message flood issues, and are considered a mis–configuration. If the driver
detects this configuration, it automatically disables BACnet routing by setting the Routing Enabled property (found in the BACnet network’s component slot) to false.
The BACnet network maintains a table of BACnet routers in the component. Included is the ability to modify, add, and remove entries that represent BACnet routers.
A full listing of all BACnet router functions is extensive—refer to the BACnet specification for complete details on routers. From a general perspective, BACnet routers pass BACnet messages among BACnet networks. This applies to all directed messages as well as broadcast messages.
Usually, a BACnet router joins networks of different media/link-layer types, for example a router with RS-485 MS/TP port(s) and an Ethernet-BACnet/IP port.