The router and gateway play key roles in your BACnet network, and are often easily mixed up. It’s important to understand how these disparate parts communicate with one another.
The BACnet router transmits messages between BACnet networks. It might connect a BACnet/IP system to an MS/TP system, for example. This is important on mixed MS/TP and IP networks, as Control Solutions Minnesota explains, because the wiring and network packets are different. So, a router might change the packaging of the message but, as the BACnet website explains, the “form or content of the message” doesn’t change. With a router, different BACnet devices can communicate with one another between networks, sending Who-Is and I-Am messages.
A BACnet gateway, on the other hand, connects devices between different network protocols. This allows users to internetwork various protocols (like LonWorks or Modbus, for example) with BACnet, as Kele explains. It essentially plays the role of translator, relaying messages in a totally different protocol. This is different from a router, which again, doesn’t change the content of the messages it forwards.
These diagrams from David Fisher from PolarSoft’s description of routers and gateways help to illustrate their differences. Note that you can have an integrated router and gateway in one, and that some controllers can have added router or gateway functionality.
Figure 1: The router here connects the Ethernet and MS/TP networks, repeating messages between A and B.
Figure 2: The gateway connects two different networks, and transmits messages in the appropriate protocol.