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BACnet Glossary



AcronyfoAmerican National StandardInstitute


AcronyfoAmerican Societof HeatingRefrigeratinganAir ConditioninEngineers


variable number used tmeasure a continuously varying entitysuch as pressure or temperature.


Acronyfo“BuildinAutomation ControNetworkAlsANSI/ASHRAStandar135-2012BACnet is an ASHRAE anANSstandarprotocol, whicis a protocodesignefothe building automatioindustryThiis also an international standard known as IS16484-5ThtestinoBACnet ibased on a companiostandarANSI/ASHRA135.1-2011.

BACneBroadcast ManagemenDevic(BBMD)

Some BACnet operations such as dynamic device binding rely on broadcast messages that are received by every BACnet device on a local segment, and in some cases across segments or globally within the whole BACnet internetwork. Because of how IP handles routing, broadcasts cannot cross IP subnets. In situations when there are multiple IP subnets with BACnet/IP devices, a special device functionality is required to deliver broadcasts to all members of a multi-subnet community. BBMDs fill this role. The functionality of BBMDs is often built in to larger controllers or routers, but not always.


BACneInterest Group (BIG)

Associations formed by BACnet users for the benefit of BACnet users. BIGs enable individuals to exchange information and share experiences about the implementation and application of BACnet. Many BACnet Interest Groups have formed around the world to support BACnet users. There is BACnet International, BIG-EU Europe, BIG-CA China/Asia, BIG-FI Finland, BIG-ME Middle East, BIG-PL Poland, BIG-RU Russia, BIG-SE Sweden and BIG-AA AustralAsia.



BACnet International is the international organization that encourages the successful use of BACnet in building automation and control systems through interoperability testing, educational programs and promotional activities. BACnet International complements the work of other BACnet-related groups whose charters limit their commercial activities.


BACnet International community membership includes a who's who list of top tier companies involved in the design, manufacture, installation, commission and maintenance of control and other equipment that use BACnet for communication.  

(More Information on BACnet International)


BACnet International was formed from the merger of the BACnet Manufacturers' Association (BMA) and BIG-NA North America. 



Collections of one or more BACnet services that function to define the interoperational capabilities of a BACnet device. Certain BIBBs may also be predicated on the support of certain, otherwise optional, BACnet objects or properties. BIBBs may also constrain allowable values of specific properties or service parameters. 


BACneTestinLaboratories™ (BTL)

BACnet Testing Laboratories was established by BACnet International to support conformance testing and interoperability testing activities and consists of the BTL Manager and the BTL-WG (BTL Working Group). (More BTL Information)


BACnet/Ior B/IP

BACnet/IP or B/IP refers to the BACnet MAC layer that uses UDP/IP messaging to transport BACnet messages across IP infrastructures. 



In BACnet, binary generally refers to discrete two-state values. See also Digital.



A device that connects two datalinks together. A bridge can connect a wired Ethernet and fiber-optic Ethernet, for example. Unlike routers, bridges are protocol-independent. They forward messages without analyzing their content. 



In networked systems, an application or device acting as a requestor or consumer of data. A client makes requests to a server device for data resident in the server or for the server to perform actions on its behalf.



The datalink layer as defined in the OSI (Open Systems Interconnection) model. The datalink organizes a package of data into a structure and manages the delivery of that data to a specific destination. In BACnet ANSI/ASHRAE Standard 135-2012, there are seven distinct datalink network types:

  • BACnet/IP  

  • BACnet ARCNET  

  • BACnet Ethernet 8802-3  

  • MS/TP (master-slave/token passing)  

  • BACnet over LonTalk Foreign Frames  

  • BACnet PTP (point-to-point)  

  • BACnet over ZigBee



The instance portion of the Object_Identifier of a given device’s Device object. Unlike all other object types, each device may contain only one Device object. The instance number of this Device object must be field-configurable so that it may be assigned a unique instance number among all of the Device objects of all of the devices on a given BACnet internetwork.



Discretely valued entities represented by two states, such as an on/off switch. See also Binary.  



A high-speed MAC layer also known as ISO 8802-3. 


Extensible MarkuLanguag(XML)

XML is a worldwide standard for defining documents and data structure that has many applications. In the context of BACnet, XML is used with BACnet/WS web services to facilitate the exchange of data and requests with enterprise application programs. 



In BACnet, a device that can participate as one partner in a point-to-point (PTP) connection. Two half-routers form an active PTP connection and act as a single router. 



HyperText Markup Language is a worldwide standard for defining and identifying format and grouping information (“markup”) within text documents. Characteristic styling such as bold, italic, font, color and so forth are indicated by the tagging of words or sections of documents. Most commonly used in web pages. 



The HyperText Transport Protocol is carried over TCP and is used to facilitate exchange of information typically encoded using text, HTML or XML. Most commonly used in web pages and web services. 


ID (Identifier)

BACnet defines three important IDs used to identify BACnet devices, objects, and properties. An Object ID identifies an object’s type and instance number. A Vendor ID defines the vendor who manufactured a device. A Property ID identifies a property by a code. 


IP (Internet Protocol)

IP handles the breaking up of data messages into packets (also called datagrams), the routing of the packets from their origin to the destination network and node, and the reassembling of the packets into the data message at the destination. IP operates at the internetwork layer of the TCP/IP model, which is equivalent to the network layer of the ISO/OSI reference model.


ISO/OSI ReferencModel

Short for International Organization for Standardization/Open Systems


Interconnection ReferencModel

The model is the foundation of most network standards. It breaks down network communications into seven conceptual levels, each concerned with a specific aspect of network communications. The seven layers are Application, Presentation, Session, Transport, Network, Data Link and Physical.



In BACnet, a number that uniquely identifies an object within a device or a device on a BACnet internetwork. See also Device Instance.



A set of two or more networks interconnected by routers.


LAN (Local Area Network)

A single network providing the physical infrastructure for device communication based on a common MAC layer datalink.



A device that uses BACnet as its principal, if not only, means of communication.


Medium AccesControl (MAC)

The part of a network that handles access to the physical network (medium) for a particular datalink. In BACnet, each device has a unique MAC Address/Network Number combination that identifies it on the BACnet internetwork. 


MSTP (Master-Slave/Token Passing)

It is a type of MAC layer implemented using the EIA-485 signaling standard. This LAN type is suitable for unitary controller and terminal control communications. To initiate communications on the network, a node must receive a "token" (actually a small message), that is passed from one node to another around the network. Master devices are allowed to have and manage the token, whereas slave devices are allowed only to respond to requests from master devices. 


National Institute of Standards and Technology (NIST)

An agency of the U.S. Department of Commerce. The NIST charter is to strengthen the U.S. economy and improve the quality of life by working with industry to develop and apply technology, measurements, and standards. NIST has played an integral role in the development of BACnet. 



A collection of information in a BACnet system, described by its properties. An object might represent information about a physical input or output, or it may represent a logical grouping of points that perform some function, such as a setpoint. Every object has an identifier (such as AI-1) that allows the BACnet system to identify it. An object is a collection of data points that contain additional information other than present value. An object is monitored and controlled through its properties. 



A type of network in which messages are passed between each node, and each node is an equal peer on the network that may act as a client or server or both.



Every year BACnet International sponsors an event called PlugFest. BIG-EU sponsors a similar event in Europe. Interested manufacturers and developers of BACnet products get together in host locations (locations vary from year to year), to have a multi-day interoperability test. Groups of vendors with common interests connect their equipment together and do performance and interoperability tests with each other; first testing in small focus groups, and then in a larger network. The results of these tests are confidential to encourage a collegial and interactive event where the whole point is to discover issues and failures without concern or embarrassment.



A type of network in which disconnection is the normal status, but when messages are to be passed between nodes, and the nodes are on different networks, then network routers make a temporary connection. Used primarily for dial-up telephone connections.



An individual data element of an object. Every object may contain an arbitrary number of properties that define aspects of the object’s operation or knowledge. Properties may act as indicators of information known to the object or as “setpoints” or receivers of information from outside of the object. BACnet specifies over 350 standardized properties for objects. Three properties (Object_Identifier, Object_Name, and Object_Type) must be present in every object. BACnet also requires that certain objects support specific additional properties. The type of object and the type of device in which that object resides determine which properties are present. Some properties can accept writes, and others can only be read.


Protocol Implementation Conformance Statement (PICS)

A document that details the particular BACnet objects, services and capabilities supported by a type of BACnet device. Every BACnet-conforming device has an associated PICS published by the manufacturer. 



A device that connects two or more, usually different, MAC layers together. Routers are similar to bridges, but provide additional functions, such as message routing and forwarding based on various criteria.



Refers to the standardized definition of specific XML tags that make them suitable for a particular application. BACnet/WS defines an explicit schema for information sharing and interoperability. 



In electronic networked systems, an application or device acting as a provider of data, responding to a request from a client. 



How one BACnet device gets information from another device, or commands a device to perform certain actions (through its objects and properties, of course), or lets other devices know that something has happened. The only service required by all devices is the ReadProperty service. There are 41 standard services in the 135-2012 standard. 


TCP/IP (Transmission Control Protocol/Internet Protocol)

TCP/IP is one of several protocol standards used by the public Internet and IP-centric infrastructures in general. IP deals only with packet transmission and routing and is analogous to BACnet’s Network Layer. TCP provides a connection-oriented delivery mechanism that can multiplex between multiple destination and source “ports” maintained by a target destination IP address. TCP/IP is a stream-oriented protocol that enables two hosts to establish a connection and exchange streams of data. Although TCP/IP is used extensively in Internet communications, it is not used by BACnet except in BACnet/WS which can exchange messages using HTTP over TCP/IP. 

UDP/IP (User Datagram Protocol/Internet Protocol)

UDP/IP is one of several protocol standards used by the public Internet and IP-centric infrastructures in general. IP deals only with packet transmission and routing and is analogous to BACnet’s Network Layer. UDP provides a connectionless delivery mechanism that can multiplex between multiple destination and source “ports” maintained by a target destination IP address. This should not be confused with TCP/IP. BACnet/IP uses the combination of IP address and UDP port as a pseudo-MAC address in combination with a BACnet Virtual Link Layer (BVLL). This combination acts like a MAC layer in its own right for conveying BACnet datagrams over UDP/IP.



See Extensible Markup Language


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