BacNet Terminology

APDU Application (layer) protocol data unit. Basically, a BACnet message—that is, a unit of data specified

within any of the BACnet link-layer protocols, consisting of protocol control information and possibly

application user data.

BACnet Building Automation and Control NETworking protocol (ANSI/ASHRAE Standard 135-

2004). An open communication protocol standard conceived by a consortium of manufacturers and system

users under the auspices of ASHRAE. Data is modeled as a common set of “objects”, which can be

accessed using a standard set of “services.” See “Bacnet FAQs” about the spelling variation “Bacnet.”

BACnet client Operation mode for a BACnet system or device, where it makes use of a BACnet device

for some particular purpose via a service request instance.

BACnet server Operation mode for a BACnet system or device, where it provides a service to a requesting


BACnet/Ethernet Or B/ETH. BACnet over Ethernet, one of the original BACnet link-layer types.

Since the introduction of BACnet/IP, its usage has become less common.

BACnet/IP Or B/IP. BACnet over Ethernet IP. Introduced in “Annex J” of the BACnet standard, it has

become the most popular BACnet link-layer protocol (except in lowest-cost devices, where MS/TP is


BACnet MS/TP Or MSTP. BACnet link-layer protocol used by lower-cost devices, using master slave

/ token passing over RS-485 multidrop networks. QNX-based JACEs support direct MS/TP (network)

trunks, one per RS-485 port (if licensed for MS/TP). See “Bacnet MS/TP licensing” on page 1-2.

BBMD BACnet/IP Broadcast Management Device. A device that receives and redistributes broadcasttype

BACnet messages (Who-Is, I-Am, etc.) to other B/IP devices on its own subnet, and sends broadcasttype

messages to BBMDs on other subnets. By having one BBMD on each subnet, a B/IP network can

span subnets (between IP routers, which otherwise typically block broadcast type messages). A Niagara

station supports operation as a BBMD. See “About BBMDs” on page C-3 for more details.

BTL BACnet Testing Laboratories, established by BACnet International to support compliance testing

and interoperability testing of BACnet products. The BACnet AWS Supervisor and BACnet OWS

Supervisor are each BTL-certified. See “BACnet AWS and OWS Supervisors” on page A-1.

Config object NiagaraAX can model BACnet objects in a client BACnet device as “Config” objects,

where you can see all properties of the object together. For details, see “About Bacnet Config objects” on

page 3-28.

COV Change-of-Value. BACnet provides services for COV reporting, on both the client and server

sides. NiagaraAX supports COV reporting services on both sides.

Device object Or device component. In general NiagaraAX terms, any component representing an external

device. Specific to a BacnetNetwork, each BacnetDevice is a container that represents a particular

BACnet device. It has several device extensions, one being the Config Device Ext. By default, this Config

extension contains a (frozen) Device Object component, which represents the single BACnet Device Object

in that device. This component cannot be deleted, but other Config objects can be added and deleted

as needed.

On the BACnet server side, a station’s Device Object is represented by the configuration of its single Local

Device component under its BacnetNetwork. See “Local Device notes” on page 4-72.

foreign device A BACnet/IP term for a BACnet device that exists on an IP subnet without a BBMD,

where the device can “register” with a BBMD on another (remote) subnet as a “foreign device” to explicitly

receive BACnet broadcast messages. In no way does it imply any reduced functionality. For more details,

see “About BBMDs” on page C-3.

internetwork Two or more BACnet networks connected by a BACnet router, or essentially “everything

on your site that can be accessed via BACnet”, or whatever you can get to with a BACnet request.


BACnet Guide


Preface Document Change Log

December 5, 2011

The single BacnetNetwork in a station often represents an internetwork, for example if any external

BACnet routers exist, or if the BacnetNetwork has multiple ports under its BacnetComm, Network component.

If the latter, the station can act as a BACnet router between its local networks.

In a BACnet internetwork, each network must have a unique Network_Number, from 0 to 65534. Each

BACnet device must have a Device object with a unique Object_ID, from 0 to 4194302.

For more details, see “Internetworks and BACnet/IP” on page C-1.

MS/TP Master Slave / Token Passing. See BACnet MS/TP.

object identifier Or object ID. A BACnet method to identify a particular object within a device, using

a combination of its object type and an instance number (unique for that type, within that device). In the

case of the single Device Object (type) per BACnet device, it must have a unique instance number across

the BACnet internetwork on which it is installed.