What B-BBMD 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-BBMD (BACnet Broadcast Management Device) is defined in Annex L of ANSI/ASHRAE 135-2024 (clause L.7.3) as a device that transports BACnet broadcasts between different IP subnets, the BACnet BBMD function defined in Annex J.
It is a Miscellaneous-family profile, so a device can claim it alongside a profile from another family: a building controller that also forwards broadcasts claims both B-BC and B-BBMD. The spec requires that a device providing BBMD functionality be reconfigurable as a non-BBMD. 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-BBMD is the profile for the device that lets BACnet/IP discovery cross subnet boundaries.
- Per-subnet broadcast forwarding. One BBMD on each routed subnet, forwarding Who-Is and other broadcasts to its peers so devices on different subnets can discover each other.
- A BBMD built into a controller or gateway. A device carrying the BBMD function in addition to its main role, common on supervisory gateways.
- Foreign-device registration. A BBMD accepting registrations from remote devices that are not on any BBMD’s local subnet.
Required Services
The table below is the application-service set required by the B-BBMD BIBBs. Executes means the device receives and acts on it (responding, for confirmed services); Initiates means it sends the request or notification. 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-B | - | Yes |
| Device and network management | I-Am | DM-DDB-B | 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 | DeviceCommunicationControl | DM-DCC-B | - | Yes |
The defining requirement is not an application service. B-BBMD additionally requires the BACnet BBMD configuration function, NM-BBMDC-B, which operates at the BACnet Virtual Link Layer (BVLL): maintaining the Broadcast Distribution Table (BDT) and Foreign Device Table (FDT), and forwarding broadcasts between subnets. The application services above are the ordinary device surface; the BACnet BBMD page covers the broadcast-forwarding mechanism itself.
Related Profiles
| Profile | How it relates to B-BBMD |
|---|---|
| B-SCHUB | Secure Connect Hub: the BACnet SC hub-and-spoke model that removes the BBMD broadcast layer entirely |
| B-RTR | Router: forwards traffic between BACnet networks, a different network-infrastructure role |
| B-BC | Building Controller: a common base profile to stack the BBMD function onto |
What Chipkin Provides
The CAS BACnet Stack implements the BACnet BBMD configuration function (NM-BBMDC-B), including BDT and FDT management and foreign-device registration, along with the device-management services the profile requires. Talk to us about building or integrating a B-BBMD device on the stack.