Introduction to BACnetPresented by Jianqing Zhang

OverviewBACnet: Building Automation and Control NetworksSupported by SPC of ASHRAE since 1987Standard Project Committee (SPC) 135P American Society of Heating, Refrigerating and Air-Conditioning EngineersPosition:American national standardEuropean pre-standardISO global standard

Benefits of BACnetSingle point of controlCompetitive system expansionEliminate fear of being locked inPossibility of integrating all BAC functionsLow costInteroperabilityData sharingAlarm and event managementTrendingSchedulingRemote device and network management

BACnet ApplicationScopeScalable from small to large installationsMainly for large installationDifferent buildings using equipments from different manufacturesEquipmentsHVAC control (Heating, Ventilation and Air-Conditioning, i.e. Climate Control)Fire detection and alarmLighting controlSecuritySmart elevatorsUtility company interface

BACnet ProtocolSet of Hardware + Software of RulesApply toElectrical SignalingAddressingNetwork Access (Master/Slave, Peer-to-Peer)Error CheckingFlow ControlMessage Sequencing, Segmentation, Check pointingPresentation Format (Compression, Encryption)Message Format

ObjectsDefinition Collection of information related to a particular function that can be uniquely identified and accessed over a network in a standardized way.Objects representPhysical inputsPhysical outputsSoftware processes

Objects exampleEach object is characterized by a set of properties that describe its behavior or govern its operation

Objects Summary 23 standard object typesBinary Input/Output/ValueAnalog Input/Output/ValueMulti-state Input/Output/ValueLoopFile/Program/Device

BACnet DeviceA collection of objects that represents the functions actually present in a given real deviceDeviceLoopScheduleGroupBI/BOAI/AO/AV

CommunicationClient-Server modelApplication ServicesAlarm and Event ServicesFile Access ServicesObject Access ServicesRead/Write the properties of an objectManage objectsRemote Device Management ServicesVirtual Terminal Services

LAN Options

Native BACnetNative BACnet devices provide BACnet communications directly, device to device

Interconnect Multiple LANsRe-package BACnet messages and re-transmit them unchanged

Gateways

Working over IP internetIP Message TunnelingBACnet devices don't know, or need to know, anything at all about IP

BACnet/IPBACnet device is actually a full-fledged IP node, complete with its own IP address and IP protocol stack

IP Message TunnelingAnnex HRouterBACnetDeviceBACnetDeviceBACnetDeviceAAnnex HRouterBACnetDeviceBACnetDeviceBACnetDeviceBInternetNet 1Net 212345

BACnet/IPBACnet + Intrinsic IPBACnet devices access the IP infrastructure as if it were just a different kind of LAN or virtual data linkA devices IP address serves the same purpose as a devices MAC or physical LANBACnet Virtual Link Layer (BVLL)Deals with specific idiosyncrasies of IP networks, such as broadcastEncompass virtually any kind of new network technology or other micro protocolATM, SONE, ISDN, etc.Data encryption, data compressionEnhanced security and efficiency measures

BACnet/IP-UnicastBBMDBACnetDeviceBACnetDeviceBACnetDeviceBBMDBACnetDeviceBACnetDeviceBACnetDeviceInternetNet 1Net 2BACnet Broadcast Mngt. Device AB

BACnet/IP-BroadcastBBMDBACnetDeviceBACnetDeviceBACnetDeviceBBMDBACnetDeviceBACnetDeviceBACnetDeviceInternetNet 1Net 2BACnet Broadcast Mngt. Device 1234A

BACnet/IP-Foreign DeviceBBMDBACnetDeviceBACnetDeviceBACnetDeviceBBMDBACnetDeviceBACnetDeviceBACnetDeviceInternetNet 1Net 2BACnet Broadcast Mngt. Device Foreign DevicesForeign devices can register with certain BBMDs to receive forward broadcast message

Application Example:BACnet-Compliant Lighting A Lighting Applications Group, Jan. 2001Different vendors provides different productsGateway, Controller, SoftwareExample: Synergy Lighting Control System

Competitor: LonTalkOpen protocol offered by EchelonPart of LonWorksA LAN specificationDifferent control communicationDifferent aligned manufacturesRapid increase in BACnet installationsa promising indicator of market penetration?

SummaryBACnetBAC Model and Message + Network Layer + LANsObjects: Representing informationServices: Making requests and interoperatingLANs: Transport systemFeaturesNo fixed architectureObject model is easily extendedDoesnt depend on current technologyBroad participation in its developmentMany vendors are committed to itGlobal interest

Supporting VendorTotally nearly 70 by 2/4/06Controller: BACnet-capable sensors and actuatorsGatewayRouterWorkstationWeb serverTools: Protocol analyzer

Smart elevators: A new elevator system developed by Fujitec America Inc. alleviates passenger bottlenecks in lobbies and in other high-traffic areas. minimizes stops by grouping together passengers with common destinations. This is accomplished by introducing "objects." An object is simply a collection of information related to a particular function that can be uniquely identified and accessed over a network in a standardized way. All information in a BACnet system is represented by such data structures. The object concept allows us to talk about and organize information relating to physical inputs and and outputs, as well as non-physical concepts like software, or calculations. Objects may represent single physical points, or logical groupings of points that perform a specific function. Objects meet the design requirement of providing each device with a common "network view," i.e., all objects, regardless of the machine in which they reside, look alike!

Although there are thousands of potentially useful object types which might be found in building automation, BACnet defines 23 standard object types in some detail. A BACnet standard object is one whose behavior, in terms of which properties it provides and what they do, is defined in the BACnet standard.This set of standard objects represents much of the functionality found in typical building automation and controls systems today. BACnet devices are only required to implement the Device object. Other objects are included as appropriate to the devices functions. A "BACnet Device" is simply a collection of objects that represents the functions actually present in a given real device. While the slide shows only one instance of each kind of object in the example device, a more typical BACnet device might have 16 BI and BO objects, 2 or 3 Schedule objects, and so on. The second part of the development challenge was to agree on what kinds of messages building automation and control devices might want to send to each other. Because BACnet is based on a "Client-Server" communication model, these messages are called "services" which are carried out by the server on behalf of the client. ARCNET (also CamelCased as ARCnet, an acronym from Attached Resource Computer NETwork) is a local area network (LAN) protocol, similar in purpose to Ethernet or Token Ring. ARCNET was the first widely available networking system for microcomputers and became popular in the 1980s for office automation tasks. It has since gained a following in the embedded systems market, where certain features of the protocol are especially useful.

Finally, the committee had to decide which networking technologies should be selected out of the dozens available. This was done simply by looking at the cost/benefit aspects of each candidate, the experience the various vendors had had with each one, and the realities of the marketplace. The set of technologies specified in BACnet was chosen because it seemed to span the real-world requirements of building control systems in terms of speed, throughput, cost, familiarity, etc. Also, Ethernet, ARCNET, and LonTalk are off-the-shelf LANs, requiring minimal work on the part of the committee to specify how BACnet messages are to be transported on them. For low-cost EIA-485 and dial-up communications we had to "roll our own" protocols in the form of the BACnet "Master-Slave/Token-Passing" protocol and the "Point-to-Point" protocol. The development of BACnet/IP was exciting because it provided not only the specification for transporting BACnet messages between IP devices but also the framework for embracing other new networking technologies with a minimal impact on existing BACnet technology

"Native" BACnet implies that the devices only speak and understand BACnet. The devices may be interconnected using any of the approved LAN technologies. More and more vendors are considering replacing their legacy protocols with native BACnet implementations. The two routers shown above implement the BACnet network layer protocol and allow devices on disparate networks to communicate. Messages between the ARCNET and MS/TP LANs pass through both routers via the Ethernet segment in the middle. Gateways have a much tougher job. They have to be "multilingual" and do bi-directional, simultaneous translations! Sometimes, as is the case with human languages, things can get "lost in the translation" if the two protocols don't support the same modeling and messaging concepts

A gateway is different from a router in that it doesnt simply transfer messages; it also translates them into each networks local language. This device can also be used to exchange messages with a LonWorks network. BACnet gateways are special items and can add significant cost and complexity to a project. They also present a single point of failure. Beside using the LANs referred to previously, BACnet messages can travel over networks that use the Internet Protocol (IP) as their networking protocol. The major distinction between the two ways that BACnet can work over an IP internet can be summarized as follows: In IP message tunneling, the BACnet devices don't know, or need to know, anything at all about IP. In BACnet/IP, each BACnet device is actually a full-fledged IP node, complete with its own IP address and IP protocol stack.

In IP tunneling, Device A on Network 1 addresses a message to Device B on Network 2 using the BACnet network layer protocol. It sends the message to the Annex H router on its local network. (The router is called an "Annex H" router because Annex H is the place in the standard where this process is defined.) The Annex H router knows how to send IP messages over the Internet (or an "Intranet" based on IP) to its peer device on Network 2. It encapsulates the BACnet message (in a User Datagram Protocol frame) and sends it via IP to the Annex H router on Network 2. Note that both networks are connected via a standard IP router to the Internet at large. When the Annex H router on Network 2 receives the IP message from its peer, it removes the encapsulated BACnet message and sends it on to its final destination, Device B. The only downside to this is that each message shows up twice on each network - once as a pure BACnet message and once as an IP message.BACnet/IP is a different beast entirely. BACnet/IP devices view the IP internet as if it were a local area network. A device's IP address (a 4-octet number like 128.253.245.74) serves the same purpose as a device's MAC or physical LAN address in other BACnet networks (and in the BACnet network layer protocol control information). In order to control all of the functions that the SSPC wanted BACnet/IP to provide, the committee came up with the idea of a "BACnet Virtual Link Layer" or BVLL. The BVLL provides a set of messages that are used to deal, among other things, with specific idiosyncrasies of IP networks, such as the way broadcasts are handled. More on this in a moment. The committee soon recognized another great, and initially unsuspected, benefit of the BVLL concept: the BVLL control information can be easily extended to encompass virtually any kind of new network technology or other "microprotocol" that might come along. (A microprotocol is a set of rules that provide a "value-added" function like data encryption or data compression on packets that are otherwise ready for transport.) This means that with a minimum of fuss a specification could be developed to run BACnet directly over Asynchronous Transfer Mode (ATM) networks, Synchronous Optical Networks (SONET), Frame Relay networks, Integrated Services Digital Networks (ISDN), etc., and to provide for enhanced security and efficiency measures, all without touching BACnet's existing application and network layer protocols

BACnet/IP devices don't need Annex H routers and can talk with each other directly over the Internet. The only hitch is that IP routers don't normally pass along "broadcast" messages, i.e., messages intended for all devices on a BACnet internetwork. Enter the "BACnet Broadcast Management Device" (BBMD). BBMDs act similarly to the Annex H routers previously described except that they only handle the forwarding of broadcasted IP messages. Since broadcasts are generally used very infrequently in BACnet, their propagation should not cause any problems. Wouldn't it be great if you could access a particular BACnet network over the phone from anywhere? That is the purpose behind "foreign device registration" which can be carried out through any internet connection, static or dynamic.

By registering with a BBMD, the workstation above becomes a member of the BACnet/IP network and will receive forwarded broadcast messages from the BBMD when they are available and can request that messages be broadcast by the BBMD on its behalf. The foreign device can, of course, talk with any BACnet device directly without registration but will only receive broadcasts if the registration procedure is followed.