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What is A BACnet Router and Gateway?

Two sets of colorful electrical wires on a white background
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 concept of “routers” and “gateways” for BACnet management has morphed a lot over time: A BACnet router and a BACnet gateway can be the same thing, but they don’t have to be. You may need both of them to maintain communications across your networks, but you’ll probably have them both already. And don’t forget about your BACnet Broadcast Management Devices (BBMDs), you’ll need those too!

Confused yet? Don’t be. When it comes to creating and connecting BACnet-compatible networks, routers, gateways, and BBMDs are clever solutions that have been developed to overcome some basic limitations in the way different networks function and communicate. Let’s briefly define each one of these critical devices and how they work together to connect protocols like MS/TP, BACnet IP, Ethernet, and more. 

 

What is a BACnet Router?

In the simplest terms, a BACnet router transmits (routes) messages between BACnet networks. Because they speak the same protocol and occupy the same OSI layer (we don’t need to dive into that now, but here’s a great primer), it’s simply a matter of passing the message along. The BACnet networks can be BACnet/IP, BACnet/Ethernet, BACnet/MSTP, BACnet/Arcnet, and more. Most commonly, a BACnet router is used to connect mixed networks – like a more capable BACnet/IP network to an older BACnet MS/TP system. 

A simple diagram of a BACnet router connecting an MS/TP network and a BACnet IP network. Since they are both based in BACnet, only the router is needed. Source: Intesis.com
A simple diagram of a router connecting an MS/TP network and a BACnet IP network. Since they are both based in BACnet, only the router is needed. Source: Intesis.com

This is important because the router might need to change the packaging around the message to cross networks, but preserve the message itself so it’s understood at both the source and destination.

With a router, different BACnet devices can communicate with one another between networks, like through Who-Is and I-Am messages. If you have more than one set of devices networked together, you’ll likely have at least one router enabling communication between BACnet devices.

 

What is a BACnet Gateway?

A BACnet gateway functions a lot like a router but works to connect networks that use different protocols. For example, a gateway allows users to link LonWorks or Modbus-based systems, – with a BACnet IP or MS/TP system. It essentially plays the role of translator, relaying messages between two languages. 

A simple diagram showing a Gateway connecting three networks with two different protocols, LON and BACnet (IP & MS/TP). Source: Intesis.com
A simple diagram showing a Gateway connecting three networks with two different protocols, LON and BACnet (IP & MS/TP). Source: Intesis.com

 

This is different from a router, which again, doesn’t change the content of the messages it forwards. 

This diagram from PolarSoft’s David Fisher illustrates how gateways function a lot like routers, but connect non-compatible protocol networks.
This diagram from PolarSoft’s David Fisher illustrates how gateways function a lot like routers, but connect non-compatible protocol networks.

Remember when we said, “A BACnet router and a BACnet gateway can be the same thing?” That’s because most modern BACnet routers now contain an integrated gateway in one. In fact, there is now an entirely new class of Versatile Building Automation Appliances that, depending on your configuration, can play the role of BACnet controller, router, gateway, or expansion I/O device. 

 

A Quick Note About BBMDs

BACnet Broadcast Management Devices (BBMDs) are another key component to enabling communications across your network. To put it simply, BBMDs act as a sort of forwarding service. BACnet systems work primarily by broadcasting messages, meaning every device on the network receives the same message from a singular device elsewhere on the network. On smaller networks, this isn’t a problem. On big systems, though, you can’t have every device on every network sending and responding to broadcasts – the traffic flood would bring the whole building network down. That’s why IP routers by their nature block broadcast messages. 

Instead, we send broadcast messages between networks through BBMDs. There are a few cool tricks a BBMD performs – like transforming broadcast messages to unicast messages to punch through an IP block – but for this article, we can simplify: A BBMD forwards messages from one subnetwork to another, so communications can be broadcast locally—no overwhelming the network with broadcast messages, and no convoluted one-to-one command instructions.  

And these days, you don’t even need a dedicated BBMD device either! Many routers and controllers can act as the BBMD on a network.

Messages move from BBMD 1 on the source network to BBMD 3 on the destination network, passing through the IP routers, for rebroadcast. Source: Controls Course
Messages move from BBMD 1 on the source network to BBMD 3 on the destination network, passing through the IP routers, for rebroadcast. Source: Controls Course

As OT/IT convergence continues to foster more multi-use devices for BAS networks, it’s still important to understand the fundamentals, and the core functions of your network hardware to properly configure, monitor, and troubleshoot. Get the edge with OptigoVN’s cloud-based BAS troubleshooting and monitoring software solution. Sign up for free today.

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