What NM-BBMDC-B Is
NM-BBMDC-B (Network Management-BBMD Configuration-B) is the BACnet Interoperability Building Block (BIBB) for a device acting as a BACnet BBMD that accepts reads and writes of its own Broadcast Distribution Table (BDT) and reads of its Foreign Device Table (FDT) through the NetworkPort object. A device claiming NM-BBMDC-B is the B-side, the BBMD itself being configured, not the tool doing the configuring.
What It Requires
| Piece | What it does |
|---|---|
BBMD_Broadcast_Distribution_Table | Readable and writable list of peer BBMD entries this device forwards directed broadcasts to |
BBMD_Foreign_Device_Table | Readable list of currently-registered foreign devices, maintained by the BBMD as registrations arrive and expire |
| Capacity | The BTL checklist specifies a minimum BDT and FDT size; a real campus deployment can push that minimum hard |
Where You Meet It in the Field
Any device acting as a BACnet BBMD in a multi-subnet deployment is claiming NM-BBMDC-B. It matters most on a campus or enterprise site where the BDT changes regularly, adding a building, replacing a peer, adjusting a foreign-device timeout, since a device that only supports NM-BBMDC-B at read means every one of those changes still needs a vendor tool.
A device that claims NM-BBMDC-B at read only is a common, and easy to miss, half-claim: it can tell you what its BDT currently holds, which is genuinely useful for diagnosing a broadcast-forwarding problem, but every actual change still routes through whatever proprietary tool the vendor shipped. The BIBB is only doing its full job once BDT writes land through WriteProperty the same way any other property write does.
[!NOTE]
BBMD_Broadcast_Distribution_TableandBBMD_Foreign_Device_Tableare not symmetric. The BDT is an administrator-maintained list, readable and writable. The FDT is populated by the dynamic foreign-device-registration process itself, readable but not a WriteProperty target; a device does not need write access to its own FDT to claim NM-BBMDC-B correctly, because nothing external is supposed to write it directly.
What Chipkin Provides
The CAS BACnet Stack supports NM-BBMDC-B today, evidenced by a dedicated test panel including a capacity test that verifies the stack accepts and serves a BDT and FDT of at least the BTL minimum size. This is test-panel evidence, not a BTL profile run. Talk to us about your specific BDT/FDT capacity needs.