BACnet^® > Definitions

10BASET, 10BASE2, 10BASEF, 100BASET

See Ethernet.

American National Standards Institute (ANSI)

Founded in 1918, ANSI is administrator and coordinator of the United States private sector voluntary standardization system. ANSI facilitates development of American National Standards, such as BACnet, by establishing consensus among qualified groups. The Institute ensures that its guiding principles-consensus, due process and openness-are followed by the more than 175 distinct entities that it accredits (organizations, committees, and canvasses).

American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)

An organization with chapters throughout the world, ASHRAE advances the arts and sciences of heating, ventilation, air conditioning, and refrigeration for the public's benefit through research, standards writing, continuing education, and publications. Through its membership, ASHRAE writes standards that set uniform methods of testing and rating equipment and establish accepted practices for the industry worldwide.

ARCNET

Short for Attached Resources Computer NETwork (ANSI/ATA 878.1). ARCNET is one of the oldest, simplest, and least expensive types of local area network (LAN). Datapoint Corporation introduced ARCNET in 1968. It uses a token-ring architecture, supports data rates up to 2.5 Mbps, connects up to 255 devices, and runs on a variety of media, including twisted-pair, coaxial cable, and fiber-optic cable.

BACNET®

Short for the Building Automation and Control networking protocol (ANSI/ASHRAE Standard 135-1995). BACnet is a non-proprietary communication protocol standard conceived by a consortium of building managers, system users, and manufacturers under the auspices of ASHRAE.

BACnet Interest 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 BIG-NA, North America (www.big-na.org); BIG-EU, Europe (www.big-eu.org), and BIG-AA, AustralAsia (www.big-aa.org).

BACnet Interoperability Building Blocks (BIBBS)

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.

BACnet Manufacturers Association^TM (BMA)

An organization of companies that design, market, and install BACnet-based building automation products.

BACnet Testing Laboratories^TM (BTL)

The BACnet Manufacturers Association formed the BACnet Testing Laboratories to test building automation products and certify them as BACnet compliant.

Bridge

A device that connects two LANs or two segments of the same LAN. The LANs can be alike or different. A bridge can connect an Ethernet and token-ring network, for example. Unlike routers, bridges are protocol independent. They forward messages without analyzing or rerouting them.

Client/Server

A network architecture in which each computer or device on the network is either a client or a server. Occasionally called a two-tier architecture. Clients rely on servers for resources, such as files, devices, and processing power. Servers are usually more powerful computers or processors.

Coaxial Cable

A round, flexible, two-conductor cable that consists of a copper wire (at the center), a layer of protective insulation, a braided mesh sleeve, and an outer shield, or jacket. Coaxial cable is used in 10Base2 Ethernet applications and in some ARCNET applications.

Conformance Class

Like BIBBs, conformance classes provide a method of describing various capabilities of a device for communicating data and interoperating with other BACnet devices. A device's protocol implementation conformance statement (PICS) details its conformance class.

Device, BACnet

Any equipment that supports digital communication using the BACnet protocol.

Ethernet

The IEEE 802.3 standard for contention networks. Ethernet is one of the most widely implemented LAN standards in the world. It is based on a local area network (LAN) protocol developed by Xerox Corporation in cooperation with DEC and Intel in 1976. Ethernet networks have a bus or star topology, provide for baseband data transmission at 10 Mbps, and use a variety of physical media: twisted pair (10BaseT), fiber-optic cabling (10BaseF) and coaxial cable (10Base2). To regulate communications on the network, Ethernet uses a form of access known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD). The Ethernet standard continues to develop and evolve, with the emergence of 100BaseT (or Fast Ethernet, which operates at 100 Mbps) and Gigabit Ethernet (IEEE 802.3z, which operates at 1000 Mbps, or 1 Gbps).

Extranet

An intranet that is partially accessible, with restricted access, to authorized outsiders. You can access an extranet only if you have a valid username and password. Your identity determines which parts of the extranet you can view.

Fiber Optics

Optical technology that transmits data using radiant light through fibers made of transparent materials such as glass, fused (vitreous) silica, or plastic. Fiber-optic cable can transmit signals at speeds up to 2 Gbps and is immune to eavesdropping and electromagnetic interference. Fiber-optic systems are either single-mode or multimode. Multimode is most often encountered in site LAN applications, while single-mode is mostly employed by Telcos.

Firewall

A security mechanism, or combination of mechanisms, designed for network access control and authentication. Firewalls detect and prevent unauthorized or unwanted traffic from a protected network. Mechanisms, functions, configurations, and effectiveness of firewalls vary widely.

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Gateway

In networking, a device (usually a combination of software and hardware) that connects networks using different communication protocols so that information can be passed from devices on one network to the other.

Half-router

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.

Hub

A common connection point for nodes on a network. Hubs connect segments of a LAN and contain multiple ports. When a packet (message) arrives at one port, it is copied to all other ports. A passive hub is simply a conduit for data, much like a repeater. An intelligent hub (also called a manageable hub) offers features that enable an administrator to monitor traffic and configure ports.

Instance

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

Internetwork

A network made up of smaller, interconnected networks. Internetwork often refers to communication between one LAN and another over the Internet or another wide-area network (WAN).

Intranet

A network based on TCP/IP (an Internet) belonging to an organization and accessible only to members of that organization. Intranets appear just as any other web site, but are surrounded by a firewall that fends off unauthorized access.

IP

Acronym for 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 Reference Model

Short for International Standards Organization Open Systems Interconnection reference model. The model is the foundation of most network standards. It breaks down network communications into seven manageable, conceptual levels, each concerned with a specific aspect of network communications. The seven layers are Application, Presentation, Session, Transport, Network, Data Link, and Physical.

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LAN

Acronym for Local Area Network. A distance-limited network for transferring data between computers or other digital devices. BACnet supports four types of LANs-Ethernet, ARCNET, MS/TP, and LonTalk.

LONTALK®

One of the LAN types BACnet devices may use. Like Ethernet and ARCNET, LonTalk uses a chipset for communications. However, unlike these network types, special development environments and tools available only from the Echelon Corporation are required to develop applications and nodes for it. LonTalk, like the other LAN types, is simply used to transmit BACnet messages from one device to another. LonTalk is often confused with LonMark and LonWorks, and all are often confused as being BACnet-compliant. An Ethernet device is not BACnet-compliant simply by virtue of using Ethernet, nor is a LonWorks or LonMark device BACnet-compliant simply by virtue of using LonTalk. LonMark products are not BACnet-compliant and require a gateway to interoperate.

Media Access Control (MAC)

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

Metropolitan Area Network (MAN)

A data network designed for a town or city. In terms of geographic size, MANs are larger than LANs, but smaller than WANs. MANs usually employ high-speed fiber-optic cabling and public networks.

MS/TP LAN

Acronym for Master-Slave/Token Passing Local Area Network, a LAN developed by the BACnet committee specifically for use on BACnet. MS/TP is a twisted-pair LAN based on the Electronic Industries Association (EIA) RS-485 signaling standard. It uses a token passing scheme for network communications. To initiate communications on the network, a node must have an electronic "token" (actually a small packet), which is passed from one node to another around the network. Master devices are allowed to have the token, whereas slaves are allowed only to respond to requests from masters.

National Institute of Standards and Technology (NIST)

An agency of the U.S. Department of Commerce's Technology Administration. 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.

Network

A group of devices (computers, controllers, or other digital units) that are connected by communication facilities, such as twisted-pair cabling, coaxial cable, fiber-optic cable, or wireless means.

Network Interface Card (NIC)

Also called a network adapter, network card or expansion card. A device that connects a computer or other device to a LAN. For computers, the NIC is usually installed in an expansion slot and has a chip that handles the physical and data-link layers of network communications.

Node

A device (such as a computer or a controller) on a network that is capable of communicating with other network devices.

Objects, Object Model

Representing data in a defined data structures called objects. Each object has a set of properties and a group of functions that can be applied to them. BACnet defines objects to represent control system data. BACnet objects can represent information about a physical input or output, a file or a logical grouping of data that performs some function (a setpoint or schedule, for example). By prescribing an object-model method to represent all control system data, BACnet facilitates interoperability and extensibility.

Peer-to-Peer

A type of network in which each node has equivalent capabilities and responsibilities.

Point-to-Point (PTP)

A method of data transmission developed by the BACnet committee to provide serial communications between BACnet devices. Typically used for remote and roaming access to BACnet systems-dial-up communications over modems or a portable computer connection to a controller, for example.

Property

In object-oriented systems, a characteristic or parameter of an object. Properties of a file object in BACnet, for example, may include file size, type, and modification date. In BACnet, certain properties of an object may be required, while others may be optional.

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-compliant device has an associated PICS published by the manufacturer.

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Repeater

A network device that regenerates or replicates a signal. Repeaters are used in transmission systems to regenerate analog or digital signals distorted by transmission loss. A hub can operate as a repeater by relaying messages to all connected computers. A repeater cannot perform the intelligent routing performed by bridges and routers.

Router

A device that connects two LANs. Routers are similar to bridges, but provide additional functions, such as message filtering and forwarding based on various criteria.

Services, BACnet

Services control the transfer of information such as scheduled commands and alarms between BACnet devices. The services provided by a BACnet device are generally described by the device's Conformance Class and detailed in its PICS.

Switching Hub (SWITCH)

In networking, a special type of hub that forwards packets to the appropriate port based on the packet's address. Switching hubs offer better performance than conventional hubs. Most switching hubs also support load balancing, which dynamically reassigns ports to LAN segments based on traffic patterns.

TCP/IP

Acronym for Transmission Control Protocol/Internet Protocol. TCP/IP is the de facto protocol standard used by the Internet. Whereas IP deals only with packet transmission, TCP enables two hosts to establish a connection and exchange streams of data. TCP handles delivery and order of data streams.

Wide Area Network (WAN)

A geographically widespread network, usually comprising one or more LANs. WANs are often connected through public networks, leased lines, and satellite or microwave communications.

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