What B-RTR Is
A BACnet device profile is a standardized capability level: a checklist of things a device must be able to do before it can wear the label. B-RTR (BACnet Router) is defined in Annex L of ANSI/ASHRAE 135-2024 (clause L.7.1) as a device that forwards BACnet messages between two or more BACnet networks, for example between a BACnet/IP network and a BACnet MS/TP (Master-Slave/Token-Passing) trunk.
It is a Miscellaneous-family profile, so a device can claim it alongside a profile from another family: a controller that also routes between its IP and MS/TP ports claims both B-BC and B-RTR. The checklist items are BACnet Interoperability Building Blocks (BIBBs); a device documents its claim in its PICS (Protocol Implementation Conformance Statement).
Where It’s Used
B-RTR is the device that joins BACnet networks of different types or numbers into one internetwork.
- IP-to-MS/TP routing. The most common case: a router bridging an Ethernet BACnet/IP backbone to one or more RS-485 MS/TP controller trunks.
- Joining network numbers. Connecting separately numbered BACnet networks so devices on each can address the other.
- A router built into a controller or gateway. A supervisory device that carries the routing function in addition to its main role.
Required Services
The table below is the service set required by the B-RTR BIBBs, including the network-layer messages that make routing work. Initiates means the device sends the message; Executes means it receives and acts on it. BIBB codes encode the same split: a -A BIBB is the initiating side, a -B BIBB the executing side. A - means the profile does not require that direction; a device may still support it.
| Capability area | Service | Required by BIBB | Initiates | Executes |
|---|---|---|---|---|
| Data sharing | ReadProperty | DS-RP-B | - | Yes |
| Data sharing | WriteProperty | DS-WP-B | - | Yes |
| Device and network management | Who-Is | DM-DDB-A | Yes | - |
| Device and network management | I-Am | DM-DDB-A | - | Yes |
| Device and network management | Who-Has | DM-DOB-B | - | Yes |
| Device and network management | I-Have | DM-DOB-B | Yes | - |
| Device and network management | AddListElement | DM-LM-B | - | Yes |
| Device and network management | RemoveListElement | DM-LM-B | - | Yes |
| Network layer | Who-Is-Router-To-Network | NM-RC-B | Yes | Yes |
| Network layer | I-Am-Router-To-Network | NM-RC-B | Yes | Yes |
| Network layer | Reject-Message-To-Network | NM-RC-B | Yes | Yes |
| Network layer | Router-Busy-To-Network | NM-RC-B | Yes | Yes |
| Network layer | Router-Available-To-Network | NM-RC-B | Yes | Yes |
| Network layer | Network-Number-Is | NM-RC-B | Yes | Yes |
The DM-LM-B list-manipulation rows let a management tool edit the router’s configuration lists (such as its routing table) with AddListElement and RemoveListElement. The network-layer messages are the BACnet routing protocol itself: a router answers Who-Is-Router-To-Network with I-Am-Router-To-Network, and uses the busy and available messages to manage congestion.
Related Profiles
| Profile | How it relates to B-RTR |
|---|---|
| B-BBMD | Broadcast Management Device: forwards broadcasts across IP subnets, a different job from routing between networks |
| B-GW | Gateway: presents non-BACnet devices as BACnet, whereas a router forwards native BACnet traffic |
| B-BC | Building Controller: a common base profile to stack the routing function onto |
What Chipkin Provides
The CAS BACnet Stack implements the router configuration function (NM-RC-B) and the data-sharing and list-management services the profile requires. Talk to us about building or integrating a B-RTR device on the stack.