A Performance Analysis of BACnet[R] local area networks.INTRODUCTION Advanced building automation systems require real-time monitoring and control of building facilities. In order to manage building systems efficiently, a wide variety of building-related information needs to be collected, stored, and analyzed an·a·lyze tr.v. an·a·lyzed, an·a·lyz·ing, an·a·lyz·es 1. To examine methodically by separating into parts and studying their interrelations. 2. Chemistry To make a chemical analysis of. 3. . As the demands on building facilities and services have increased, the use of distributed, microprocessor-based control systems has become widespread (Newman 1994). Digital communication networks have become a core technology in advanced building automation systems. In a networked building automation system, many kinds of monitoring, control, maintenance, and management data are transmitted through the network. If network-induced delay of the delivery of these data exceeds practical limits, building automation systems that require real-time control Real-time control is a popular term for a certain class of digital controllers. For effective digital control, it is critical that sample time be constant. Real-time control achieves nearly constant sample time. See also
(specification) functional requirements - What a system should be able to do, the functions it should perform. . Thus, building automation system designers benefit from understanding the performance characteristics of the networks installed in their buildings. BACnet[R] (Building Automation and Control networks) is a data communication protocol standard designed specifically for building automation and control systems (ASHRAE ASHRAE American Society of Heating, Refrigerating & Air Conditioning Engineers 2004). BACnet defines an object-based model of the information that may be exchanged between components of the building automation system and an application layer protocol that is used to access and manipulate this information. It also provides a way to convey the information across a variety of local and wide-area networks Wide-area networks Communication networks that are regional, nationwide, or worldwide in geographic area, with a minimum distance typical of that between major metropolitan areas. Smaller networks include metropolitan and local-area networks. that may be interconnected to form an internetwork (1) To go between one network and another. (2) A large network made up of a number of smaller networks. Same as "internet" (lower case "i"), not the "Internet" (upper case "I"). See internet. . In this study, simulation models of the three most commonly used BACnet local area networks (LANs) were developed. Those LANs are Master-Slave/Token-Passing (MS/TP), ANSI/ATA 878.1 (ARCNET (Attached Resource Computer NETwork) The first local area network (LAN) introduced in 1968 by Datapoint Corporation. It connects up to 255 nodes in a star topology at 2.5 Mbits/sec over twisted pair or coax. A 20 Mbits/sec version was introduced in 1989. ), and ISO- iso- or is- pref. 1. Equal; uniform: isobar. 2. Isomeric: isopropyl. 3. 8802-3 (commonly referred-to as "Ethernet"). Using the simulation models, the performance characteristics of each of these BACnet LANs were investigated. A BRIEF DESCRIPTION OF BACnet Historically, building automation and control systems have used proprietary communication networks. In this kind of closed system, building automation equipment supplied from different manufacturers could not communicate with each other. Building owners and facility managers were forced to rely on products from a single vendor. Modern building automation and control systems provide a variety of building services, such as heating, ventilating ventilating Natural or mechanically induced movement of fresh air into or through an enclosed space. The hazards of poor ventilation were not clearly understood until the early 20th century. Expired air may be laden with odors, heat, gases, or dust. , and air conditioning air conditioning, mechanical process for controlling the humidity, temperature, cleanliness, and circulation of air in buildings and rooms. Indoor air is conditioned and regulated to maintain the temperature-humidity ratio that is most comfortable and healthful. (HVAC (Heating Ventilation Air Conditioning) In the home or small office with a handful of computers, HVAC is more for human comfort than the machines. In large datacenters, a humidity-free room with a steady, cool temperature is essential for the trouble-free ); lighting; fire and life safety systems; security; and vertical transportation. There can be significant safety and operational advantages to integrating these building services through integrated control networks. Closed network systems provide a major barrier to integrated building facilities with the kind of flexibility and expandability that building owners want. In order to solve these problems, ASHRAE developed BACnet. BACnet defines an object-oriented framework for representing the information that may need to be exchanged between components of the building automation system, and an application layer protocol that is used to access and manipulate this information. It also provides a way to convey the information across a variety of local and wide-area networks that may be interconnected to form an internetwork. BACnet has a layered protocol In computer science a layered protocol is a system where one or more programs act as interfaces between two end systems. The end systems and programs can be thought of much like a layer cake, where there is a top layer and a bottom layer with several layers in-between. architecture based on a collapsed version of the Open Systems Interconnection (networking) Open Systems Interconnection - (OSI-RM, OSI Reference Model, seven layer model) A model of network architecture and a suite of protocols (a protocol stack) to implement it, developed by ISO in 1978 as a framework for international standards in heterogeneous computer (OSI (1) (Open System Interconnection) An ISO standard for worldwide communications that defines a framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the ) Basic Reference Model (ISO (1) See ISO speed. (2) (International Organization for Standardization, Geneva, Switzerland, www.iso.ch) An organization that sets international standards, founded in 1946. The U.S. member body is ANSI. 7498 [1984]). Layers 1, 2, 3, and 7 of the OSI model Following is a diagram and description of all the layers in the ISO standard for communications. For more on the purpose of this model, see OSI. For comparisons between the OSI model and other protocol stacks, see TCP/IP, NetWare, ATM, SNA and SS7. are used as shown in Figure 1. The common object model and application layer protocol can be used with any of four LAN (Local Area Network) A communications network that serves users within a confined geographical area. The "clients" are the user's workstations typically running Windows, although Mac and Linux clients are also used. technologies or a point-to-point (PTP (1) See peer-to-peer. (2) (Picture Transfer Protocol) An ISO standard for transferring photos from a digital camera to a computer or photo printer. ) protocol suitable for dial-up telephone communications. BACnet also provides wide-area networking capability (not shown in Figure 1) by using Internet protocols Refers to all the standards that keep the Internet running. The foundation protocol is TCP/IP, which provides the basic communications mechanism as well as ways to copy files (FTP) and send e-mail (SMTP). (IP). The network layer provides a way to combine BACnet networks into an internetwork of arbitrary size and complexity. This allows flexibility in configuring various kinds of network systems, and satisfies real-world requirements of building control systems in terms of speed, throughput, and cost (Bushby 1997). [FIGURE 1 OMITTED] BACnet has been adopted as an international standard by the International Organization for Standardization International Organization for Standardization (ISO) Organization for determining standards in most technical and nontechnical fields. Founded in Geneva in 1947, its membership includes more than 100 countries. (ISO) and by the European Community European Community: see European Union. European Community (EC) Organization formed in 1967 with the merger of the European Economic Community, European Coal and Steel Community, and European Atomic Energy Community. (EN ISO 16484-5 [2003]). Many countries in Europe and Asia have also adopted BACnet as a national standard. DEVELOPMENT OF BACnet SIMULATION MODELS The most commonly used LANs in BACnet systems are Ethernet, ARCNET, and MS/TP. They were selected for this study because of their popularity. Ethernet is now the most widely used LAN technology in the world and is typically used as a high-speed backbone in building automation systems. ARCNET is also a widely known networking technology. In BACnet systems it is typically used over twisted pair A thin-diameter wire (22 to 26 gauge) commonly used for telephone and network cabling. The wires are twisted around each other to minimize interference from other twisted pairs in the cable (Alexander Graham Bell invented this and was awarded a patent for it in 1881). networks with EIA-485 (EIA (Electronic Industries Alliance, Arlington, VA, www.eia.org) A membership organization founded in 1924 as the Radio Manufacturing Association. It sets standards for consumer products and electronic components. 1988) signaling. MS/TP is the only networking option that was developed specifically for BACnet. The name comes from the fact that it can be configured con·fig·ure tr.v. con·fig·ured, con·fig·ur·ing, con·fig·ures To design, arrange, set up, or shape with a view to specific applications or uses: as a master/slave network, a peer-to-peer token-passing network, or a mixture of the two. Communication networks such as MS/TP, ARCNET, and Ethernet can be categorized cat·e·go·rize tr.v. cat·e·go·rized, cat·e·go·riz·ing, cat·e·go·riz·es To put into a category or categories; classify. cat as discrete-event dynamic systems (DEDS DEDS Discrete Event Dynamic System DEDS Data Entry Display System DEDS Digital Error Detection System DEDS Digital Error Detection Subsystem DEDS Data Exchange and Distribution System ) (Casandras and Lafortune 1999). In a DEDS, the state of a system is changed whenever an event occurs, and events occur at random. Some examples of events that can occur in a communication network system include message generation, message transmission, message reception, and many other protocol-specific events, such as message collision, token delivery, polling, etc. In this study, the simulation models were developed using ARENA (Kelton et al. 2001), a tool for developing simulation models of various kinds of DEDS systems. ARENA provides basic templates for the modeling of DEDS systems. Using the basic templates as a starting point Noun 1. starting point - earliest limiting point terminus a quo commencement, get-go, offset, outset, showtime, starting time, beginning, start, kickoff, first - the time at which something is supposed to begin; "they got an early start"; "she knew from the , BACnet-specific LAN models were developed. Figure 2 shows the structure of the simulation models developed in this study. As shown in the figure, the simulation model has three independent modules: the common module, the application layer module, and the LAN protocol module. Users need not modify the whole simulation model when they make a new model for a specific process. Only the modules corresponding to the specific process need to be modified. [FIGURE 2 OMITTED] Table 1 shows a brief description of the modules developed for modeling BACnet LANs. The common module provides an interface for users to set the values of all of the simulation parameters. The application layer module generates the request and reply messages of BACnet application services See ASP and Web services. . The messages received by the destination node are used to collect and analyze the statistical information of network-induced delay. Three independent LAN protocol modules were developed, one each for Ethernet, ARCNET, and MS/TP. More details of the simulation model are described in Song et al. (2003).
Table 1. ARENA Modules Developed for Modeling BACnet LANs
Module Function Description
Simulation Set the simulation time
environment and the number of
replications
Common module Ethernet environment Set the simulation
parameters for Ethernet
ARCNET environment Set the simulation
parameters for ARCNET
MSTP environment Set the simulation
parameters for MS/TP
Application layer Message generation Schedule the generation
module of BACnet messages
Statistical analysis Collect and analyze
statistical information
Ethernet node Ethernet node model
Hub Ethernet hub model
LAN protocol module ARCNET node ARCNET node model
Master node MS/TP master node model
Slave node MS/TP slave node model
Figure 3 shows a screen capture of the window of an MS/TP protocol simulation model that consists of five nodes. The left pane A rectangular area within an on-screen window that contains information for the user. A window may have many panes. See menu pane. shows basic templates provided by ARENA. The middle pane shows a simulation model for MS/TP. Using the MSTP (MultiService Transport Platform) A high-end Cisco router that is geared for optical connections to metropolitan area networks (MANs). MSTPs include the functionality of MultiService Provisioning Platform (MSSP) routers. See MSSP and MSPP. _ENVIRONMENT dialog box A movable window that is displayed on screen in response to the user selecting a menu option. It provides the current status and available options for a particular feature in the program. , various network parameters, such as data rate, propagation delay The time it takes to transmit a signal from one place to another. Propagation delay is dependent solely on distance and two thirds the speed of light. Signals going through a wire or fiber generally travel at two thirds the speed of light. Contrast with nodal processing delay. , timer timer, n radiographic timing device that functions as an automatic exposure timer and a switch to control the current to the high-tension transformer and filament transformer. The face of the timer is calibrated in seconds and fractions of seconds. values, and message length can be set. The dialog window in the figure shows how the simulation parameters are set. The SIMULATION_ENVIRONMENT module is used to set the simulation-related parameters, such as simulation time and the number of replications. [FIGURE 3 OMITTED] In the system model, the block named MASTER is a master node model. Node address The identification of a host, workstation, server, printer or other device in a network. See physical address and Internet address. and the value of some network parameters, such as Nmax_info_frames and Max_Master, can be set using this model. The block named "MASTER_APP See application. app - application program " is the application layer model of an MS/TP node. This block generates request and reply messages and calculates statistical information. The block named "M_PACKET" converts the basic ARENA entity to an MS/TP message. Using the M_PACKET module, a user can generate ReadProperty, WriteProperty, ReadPropertyMultiple, UnconfirmedCOVNotification, ConfirmedCOVNotification, or any other BACnet message. The simulation models for ARCNET and Ethernet have a structure similar to the one shown in Figure 3. PERFORMANCE ANALYSIS OF BACnet LANs In this section, the performance of MS/TP, ARCNET, and Ethernet is analyzed using their simulation models. In this study, we quantify Quantify - A performance analysis tool from Pure Software. the offered traffic load of a network as G. The physical meaning of G is defined as a fraction of medium utilization of offered traffic per medium capacity. The variable G includes the frame overhead of the network protocol (i.e., header and trailer in a message frame) but excludes the overhead for medium access management (i.e., token circulation overhead in MS/TP and ARCNET protocols, and message collision overhead in Ethernet). The variable G is expressed as G = 1/B [N.summation summation n. the final argument of an attorney at the close of a trial in which he/she attempts to convince the judge and/or jury of the virtues of the client's case. (See: closing argument) over (I = 1)][[L.sub.i]/[T.sub.i]], where B is a data transmission rate (bits/s), N is the number of nodes that generate messages in the medium, [T.sub.i] is an average interval of message generation at node i in seconds, and [L.sub.i] is an average message length in bits generated at node i. The variable G has a value between 0 and 1; G approaches 1 as the traffic load offered to the network increases. The delay characteristics of BACnet LANs show different pattern as the network parameters, B, N, [T.sub.i], and [L.sub.i], change. This is because their medium access control algorithms are affected differently by network-induced delay. The variable G is a dimensionless characteristic of the network traffic, and the simulation results can be generalized gen·er·al·ized adj. 1. Involving an entire organ, as when an epileptic seizure involves all parts of the brain. 2. Not specifically adapted to a particular environment or function; not specialized. 3. to other combinations of parameters that result in the same G (see Song et al. 2003). In this study, we analyzed the performance of BACnet LANs with respect to the change of offered traffic load G. The performance of BACnet LANs is evaluated in terms of service (networking) Terms Of Service - (TOS) The rules laid down by an on-line service provider such as AOL that members must obey or risk being "TOS-sed" (disconnected). delay. Service delay is defined as the elapsed time e·lapsed time n. The measured duration of an event. Noun 1. elapsed time - the time that elapses while some event is occurring to complete one transaction of a BACnet service. For a BACnet confirmed service, the service delay is defined from the instant a request message arrives at the transmitter A device that generates signals. Contrast with receiver. queue of a client to the instant when a reply message transmitted by its server has completely arrived at the receiver queue of the client. For a BACnet unconfirmed service, the service delay is defined from the instant when a message arrives at the transmitter queue of a sender to the instant when the same message has completely arrived at the receiver queue of a receiver. Figure 4 shows the structure of client and server nodes in the simulation model. Each node has two processes that run concurrently. A control application process (which is modeled as "MASTER_APP" and "M_PACKET" blocks in Figure 3) generates request messages at time intervals related to the control functionality. A communication process (which is modeled as "RMASTERW" block in Figure 3) that has transmitter queue (Tx Q) and receiver queue (Rx Q) handles frame transmission and reception. A control application process generates its request messages with an average interval of [T.sub.i]. In the ARENA tool described in the previous section, request messages are randomly generated as we specify the corresponding parameters. In Figure 3, messages are generated in the "Create" block, where we specified the corresponding parameters using EXPO(MEAN_TIME). This means that the message generation interval has the exponential distribution In probability theory and statistics, the exponential distributions are a class of continuous probability distribution. They are often used to model the time between independent events that happen at a constant average rate. (i.e., message generation has the Poisson process A Poisson process, named after the French mathematician Siméon-Denis Poisson (1781 - 1840), is a stochastic process which is used for modeling random events in time that occur to a large extent independently of one another (the word event ) and the value of an average interval of [T.sub.i] is specified in the parameter MEAN_TIME. Figure 4 also shows a sequence of request and reply message transmissions between client and server nodes in a BACnet confirmed service. In a BACnet unconfirmed service, no reply message is transmitted. [FIGURE 4 OMITTED] MS/TP NETWORKS Summary of MS/TP Features The Master-Slave/Token-Passing (MS/TP) protocol was designed to be implemented using a single-chip microprocessor with a universal asynchronous receiver/transmitter (communications, hardware) Universal Asynchronous Receiver/Transmitter - (UART) An integrated circuit used for serial communications, containing a transmitter (parallel-to-serial converter) and a receiver (serial-to-parallel converter), each clocked separately. (UART (Universal Asynchronous Receiver Transmitter) The electronic circuit that makes up the serial port. Also known as "universal serial asynchronous receiver transmitter" (USART), it converts parallel bytes from the CPU into serial bits for transmission, and vice ). It uses EIA-485 signaling over a twisted-pair line and is the lowest cost LAN option in BACnet. The name reflects the fact that a MS/TP network can be configured as a master/slave network, a peer-to-peer token passing A communications network access method that uses a continuously repeating frame (the token) that is transmitted onto the network by the controlling computer. When a terminal or computer wants to send a message, it waits for an empty token. network, or a mixture of the two. MS/TP supports transmission rates of 9.6, 19.2, 38.4, and 76.8 Kbps. MS/TP master nodes maintain a cooperative token-passing scheme that regulates access to the medium. The token is circulated from one master node to another, according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. a predetermined pre·de·ter·mine v. pre·de·ter·mined, pre·de·ter·min·ing, pre·de·ter·mines v.tr. 1. To determine, decide, or establish in advance: order based on addresses. A master node that holds the token can transmit up to [N.sub.max_info_frames] messages to either other masters or to slaves before passing the token. [N.sub.max_info_frames] is a network parameter that can be set by the system designer. If there are no more messages to transmit, the node immediately passes the token to the next master node in the token circulation sequence (as we mentioned earlier, this overhead for token circulation is not counted when calculating the offered traffic G). After receiving the token 50 times, a master node transmits a Poll_For_Master frame in order to discover the presence of other master nodes on the network that wish to join the ring. If one is found, it becomes the new successor node in the token ring A local area network (LAN) access method developed by IBM. Conforming to the IEEE 802.5 standard, Token Ring uses a token ring access method and connects up to 255 nodes in a star topology at 4, 16 or 100 Mbps. . If the successor is already the next available address, then this step is omitted. Slave nodes never hold the token. Slave nodes return a reply only when they receive a request from a master node. A master node that receives a request returns the reply immediately or it may return a Reply_Postponed frame, indicating that the actual reply will be returned at some future time when it holds the token. Performance Analysis of BACnet Services in MS/TP Networks This section evaluates the performance of BACnet services over MS/TP networks. Four representative BACnet services, ReadProperty, ReadPropertyMultiple, UnconfirmedCOV-Notification and ConfirmedCOVNotification, were considered, and their average service delays were measured. In this study, the MS/TP network consists of all master nodes because most of the MS/TP networks currently operated in real buildings are all-master systems. In this analysis, we assume the default transmission rate of MS/TP to be 76.8 Kbps because many MS/TP devices are currently implemented with that speed. In the ReadProperty service case, the network consists of [N.sub.m] master nodes. We model one node acting as a central controller. The controller node sends a ReadProperty request message one by one in turn to all the other ([N.sub.m] - 1) master nodes. Upon receiving the request message, each master node immediately returns a reply message. In this analysis, the value of [N.sub.max_info_frames] in the central controller was set to 120. Other master nodes do not generate their own message; they just return a reply message. But the token is circulated along other ([N.sub.m] - 1) master nodes before it comes back to the central controller node, and this causes the token circulation overhead. Message length of request and reply frames is 23 bytes and 29 bytes, respectively, including frame overhead of the MS/TP protocol. Figure 5 shows the resulting average service delays for ReadProperty service requests with respect to the change in the number of nodes [N.sub.m]. As shown in Figure 5, average service delay is sensitive to the number of nodes. This is because the overhead of token circulation is increased as the number of nodes in the medium is increased. [FIGURE 5 OMITTED] When the traffic load is low to medium (less than G = 0.7), delay of ReadProperty service is small. This is because the number of messages built up in the transmitter queue of the central controller during one circulation of token along [N.sub.m] nodes is smaller than the value of [N.sub.max_info_frames], and all of them are transmitted when the token arrives. When the traffic load is high, the number of messages built up in the transmitter queue of the central controller exceeds the value of [N.sub.max_info_frames], and the service delay is abruptly a·brupt adj. 1. Unexpectedly sudden: an abrupt change in the weather. 2. Surprisingly curt; brusque: an abrupt answer made in anger. 3. increased. In the analysis of the ReadPropertyMultiple service, the controller node sends a ReadPropertyMultiple request message to all the other nodes. Upon receiving the request message, each node immediately returns a reply message with ten real values. Ten real values were chosen in order to have a message length that would be representative of typical ReadPropertyMultiple requests in operating systems Operating systems can be categorized by technology, ownership, licensing, working state, usage, and by many other characteristics. In practice, many of these groupings may overlap. . The message length of request and reply frames is 106 bytes and 175 bytes, respectively, including frame overhead. The simulation results are shown in Figure 6. Compared to the ReadProperty service results in Figure 5, network resources for the ReadPropertyMultiple service are saturated at higher traffic load; thus, the throughput performance is increased. [FIGURE 6 OMITTED] Because the message length of request and reply frames is increased in the ReadPropertyMultiple service, for a given G, the message generation interval is reduced. Thus, during one circulation of a token along [N.sub.m] master nodes, fewer messages are built up in the transmitter queue of the central controller compared to the case of the ReadProperty service. The transmitter queue of the central controller is saturated at higher traffic load G. The service delay, however, is slightly higher for the ReadPropertyMultiple service because of the effect of increased message length on transmission time. In the UnconfirmedCOVNotification service case, one node is designated as a central controller node. All of the other nodes transmit change-of-value (COV COV Composés Organiques Volatiles (French) COV Compuestos Orgánicos Volátiles (Spanish: Volatile Organic Compounds) COV Coefficient of Variation COV City of Villians (game) ) notification messages to the central controller node when a COV occurs. The central controller node does not transmit a reply message. In this simulation analysis (language, simulation) SIMulation ANalysis - (SIMAN) A simulation language, especially for manufacturing systems, developed by C. Dennis Pegden in 1983. ["Introduction to Simulation using SIMAN", C.D. Pegden et al, McGraw-Hill 1990]. , the network also consists of [N.sub.m] master nodes. The token is circulated along the [N.sub.m] master nodes. Because the central controller node does not generate its message, it does not transmit a message even if it captures the token. The other ([N.sub.m] - 1) master nodes transmit their COV notification messages when the token arrives. This causes the token circulation overhead. In this analysis, the value of [N.sub.max_info_frames] in ([N.sub.m] - 1) master nodes was set to 120. Message length of the UnconfirmedCOVNotification service is 46 bytes including frame overhead. Figure 7 shows the simulation results. The average service delay for Unconfirmed-COVNotification requests is also affected by the number of master nodes because of the token circulation overhead. In contrast with the previous cases of ReadProperty and ReadProperty- Multiple services, the number of master nodes that generate these messages is increased to ([N.sub.m] - 1). The service delay is more severely affected by the token circulation overhead, and the effect of the increment To add a number to another number. Incrementing a counter means adding 1 to its current value. of service delay with respect to the increment of [N.sub.m] becomes greater. [FIGURE 7 OMITTED] Like the UnconfirmedCOVNotification case, in the ConfirmedCOVNotification service case, a central controller node receives all of the COV notifications, which are transmitted by the other nodes when a COV occurs. Upon receiving the COV notification message, the central controller node immediately transmits a reply message. Message length of request and reply frames is 48 bytes and 15 bytes, respectively, including frame overhead. Figure 8 shows the simulation results. Comparison with Figure 7 shows that, in an all-master MS/TP network, the difference in service delay between the unconfirmed service and the confirmed service is not significant. The only additional delay for the confirmed service is the transmission delay of the reply message. This is because, in MS/TP networks, the reply is transmitted immediately instead of waiting for the next time the responding node has the token. As expected, network saturation saturation, of an organic compound saturation, of an organic compound, condition occurring when its molecules contain no double or triple bonds and thus cannot undergo addition reactions. occurs slightly earlier in the ConvfirmedCOVNotification case because of the reply messages. [FIGURE 8 OMITTED] Song et al. (2003) investigated the impact of other MS/TP characteristics that cannot typically be changed in an operating system operating system (OS) Software that controls the operation of a computer, directs the input and output of data, keeps track of files, and controls the processing of computer programs. but do have significant implications for product developers. ARCNET NETWORKS Summary of ARCNET Features ARCNET (ATA (1) (AT Attachment) The specification for IDE drives. See IDE. (2) See analog telephone adapter. ATA - Advanced Technology Attachment 1992) is a token passing protocol that supports a range of data transmission rates (156.25 Kbps to 2.5 Mbps) and a variety of network media, including twisted pair, coaxial co·ax·i·al adj. Having or mounted on a common axis. coaxial Adjective 1. Electronics (of a cable) transmitting by means of two concentric conductors separated by an insulator cable, and fiber optic cable Noun 1. fiber optic cable - a cable made of optical fibers that can transmit large amounts of information at the speed of light fibre optic cable transmission line, cable, line - a conductor for transmitting electrical or optical signals or electric power . ARCNET provides faster transmission speeds and more media options than MS/TP. Unlike MS/TP, ARCNET permits a node to transmit only one message when it receives the token even if there is more than one message available in the transmitter queue. Upon receipt of a confirmed request, an ARCNET node must wait for the token before transmitting a reply. Performance Analysis of BACnet Services in ARCNET Networks This section evaluates the performance of BACnet services over ARCNET networks. In a manner similar to the analysis described for MS/TP networks, four representative BACnet services, ReadProperty, ReadPropertyMultiple, UnconfirmedCOVNotification, and Confirmed-COVNotification, were considered, and their average service delays were measured. In BACnet systems it is more common to use 156.25 Kbps because it makes use of low-cost twisted pair wiring. In this simulation analysis, a transmission rate of 156.25 Kbps was considered. In the ReadProperty service case, one node acts as a central controller. Upon capturing the token, the controller node sends a request message to one of the other nodes on the network. A node that receives a request message returns a reply message to the controller node when the receiving node subsequently captures the token. Message length of request and reply frames is 25 bytes and 30 bytes, respectively, including frame overhead of the ARCNET protocol. The simulation results are shown in Figure 9. Due to the effect of token circulation overhead, service delay is sensitive to the number of nodes in the network. By comparing the ARCNET results in Figure 9 with the MS/TP results in Figure 5, it can be seen that the network resource in ARCNET networks saturates at a much lower traffic load G. When the number of nodes in the network is 90, the network becomes saturated even when G is less than 0.07. This indicates that the effect of token circulation overhead in ARCNET networks is greater than in MS/TP networks. This is because ARCNET nodes must always wait for the token before transmitting a reply and only a single message can be transmitted when holding the token. [FIGURE 9 OMITTED] The simulation results for ReadPropertyMultiple service requests with ten real values are shown in Figure 10. Message length of request and reply frames is 108 bytes and 177 bytes, respectively, including frame overhead. Comparison with the ReadProperty service delay in Figure 9 indicates that using the ReadPropertyMultiple service increases the throughput of the network because of the reduced effect of token circulation overhead. The performance improvement for ARCNET is much more significant than it was for MS/TP networks (compare Figures 9 and 10 with Figures 5 and 6). Thus, when using ARCNET networks, it is particularly desirable to use the ReadProperty-Multiple service rather than several repetitions of the ReadProperty service. [FIGURE 10 OMITTED] Figure 11 shows the simulation results for UnconfirmedCOVNotification service requests. One node is designated as a central controller node. All of the other nodes transmit COV notification messages to the central controller node when a COV occurs. Message length of the UnconfirmedCOVNotification service is 48 bytes, including frame overhead. This service is completed in one token circulation because an unconfirmed service does not require a reply. Because unconfirmed services require only one token circulation, their performance is less affected by the change in the number of nodes. The average service delay is increased abruptly around G = 0.6, and the network resource for UnconfirmedCOVNotification service becomes saturated. [FIGURE 11 OMITTED] Figure 12 shows the simulation results for ConfirmedCOVNotification service requests. Like the UnconfirmedCOVNotification case, a central controller node receives all of the COV notifications, which are transmitted by the other nodes when a COV occurs. Upon receiving the COV notification message, the central controller node transmits a reply message. Message lengths of request and reply frames are 50 bytes and 17 bytes, respectively, including frame overhead. A comparison of Figures 11 and 12 shows a significant difference in performance between ConfirmedCOVNotification and UnconfirmedCOVNotification in ARCNET networks. This is because ARCNET nodes must wait for the token before transmitting a reply. In addition, because the central controller node can transmit only one reply message when it captures the token, the reply messages are built up in the transmitter queue of the central controller node, and the service delay increases rapidly. Since most BACnet services are confirmed, ARCNET networks will tend to degrade TO DEGRADE, DEGRADING. To, sink or lower a person in the estimation of the public. 2. As a man's character is of great importance to him, and it is his interest to retain the good opinion of all mankind, when he is a witness, he cannot be compelled to disclose in throughput more quickly as the number of nodes increase when traffic is high. [FIGURE 12 OMITTED] ETHERNET NETWORKS Summary of Ethernet Features Ethernet is the most widely used LAN technology in the world (Buchanan 1999). Ethernet uses carrier sense multiple access with collision detection In computer networking, Carrier Sense Multiple Access With Collision Detection (CSMA/CD) is a network control protocol in which
Performance Analysis of BACnet Services in Ethernet Networks This section evaluates the performance of BACnet services over Ethernet networks. In real applications, traffic generation patterns in Ethernet can be different from that in MS/TP or ARCNET. This is because it is more common for building automation devices on a backbone Ethernet network to generate their own traffic independently rather than having communication with a supervisory controller dominate the traffic, as often happens on other LANs. However, the objective of this study is to investigate and compare the characteristics of network-induced delay in each BACnet LAN protocol. The same four representative BACnet services used with the other network technologies were simulated: ReadProperty, ReadPropertyMultiple, UnconfirmedCOVNotification, and ConfirmedCOV-Notification. In addition, the average service delay of the AtomicWriteFile service was measured because Ethernet is often used as a backbone network A backbone network provides a path for the exchange of information between different LANs or subnetworks.[1] A backbone can tie together diverse networks in the same building, in different buildings in a campus environment, or over wide areas. . The data rate used in these Ethernet simulations was 10 Mbps. In the ReadProperty service simulation, one node acts as a central controller node. The node sends a request message to the other nodes in the network whenever it is ready in the transmitter queue. The message may experience a collision before being delivered to its destination node. A node that receives a request message returns a reply message. It may also experience collision. Message length of request and reply frames is 72 bytes, including the Ethernet frame overhead. The simulation results are shown in Figure 13. In Ethernet networks, the number of message collisions increases as the traffic load is increased. Figure 13 shows that the service delay suddenly begins to increase when traffic load G crosses over 0.3. Comparison with the results in Figure 9 shows that ARCNET networks saturate sat·u·rate v. Abbr. sat. 1. To imbue or impregnate thoroughly. 2. To soak, fill, or load to capacity. 3. To cause a substance to unite with the greatest possible amount of another substance. at a lower value of G than Ethernet networks when the number of nodes increases. This is because token overhead increases with the number of nodes in ARCNET, but collisions are a function of message generation rate instead of the number of nodes. [FIGURE 13 OMITTED] Figure 14 shows the simulation results for ReadPropertyMultiple service requests with ten Real values. Message length of request and reply frames is 121 bytes and 190 bytes, respectively, including frame overhead. Compared to the ReadProperty service in Figure 13, the Read-PropertyMultiple service increases the throughput of the network system just as it did for the other network technologies. Comparison with the results from ARCNET in Figure 10 shows that the average service delay for Ethernet networks is smaller at light traffic loads, but that Ethernet is saturated at a lower value of G. This illustrates that CMSA/CD is faster at low traffic loads because it does not have token management overhead. As the traffic load increases, collisions cause the network to reach saturation earlier than with token passing networks. [FIGURE 14 OMITTED] Figure 15 shows the simulation results for UnconfirmedCOVNotification service requests. Message length for the UnconfirmedCOVNotification service is 72 bytes, including frame overhead. Similar to the MS/TP and ARCNET networks, all the nodes in the medium transmit COV notification messages to a central controller node when a COV occurs. Service delay begins to increase when G is greater than 0.4. [FIGURE 15 OMITTED] Figure 16 shows the simulation results for the ConfirmedCOVNotification service. Like the UnconfirmedCOVNotification case, a central controller node receives all of the COV notifications, which are transmitted by the other nodes when a COV occurs. Upon receiving the COV notification message, the central controller node transmits a reply message. The message length of request and reply frames is 72 bytes, including frame overhead. Compared with the unconfirmed service in Figure 15, the service delay for the confirmed service is larger, and it increases more abruptly. Comparison with the results from ARCNET in Figure 12 shows, once again, that the network resource for ConfirmedCOVNotification service in Ethernet is saturated at higher values of G when the number of nodes increases. [FIGURE 16 OMITTED] Most building automation and control system architectures use Ethernet as a backbone network. In this section, performance of the service delay for AtomicWriteFile service on Ethernet networks is investigated. AtomicWriteFile was chosen as a way to represent the impact of large message sizes. In this simulation, the message length for a file is assumed to be the maximum length of an Ethernet packet. The message length of request and reply frames is 1503 bytes and 72 bytes, respectively, including frame overhead. Figure 17 shows the simulation result and that the service delay increases exponentially ex·po·nen·tial adj. 1. Of or relating to an exponent. 2. Mathematics a. Containing, involving, or expressed as an exponent. b. as the traffic load is increased. The AtomicWriteFile service delay is not significantly affected by a change in the number of nodes. [FIGURE 17 OMITTED] CONCLUSIONS A building automation system cannot satisfy the requirement of real-time operation Noun 1. real-time operation - data processing fast enough to keep up with an outside process real-time processing data processing - (computer science) a series of operations on data by a computer in order to retrieve or transform or classify information if the network-induced delay exceeds the application requirements. This study examined the delay characteristics of three popular BACnet LANs: MS/TP, ARCNET, and Ethernet. Simulations were made using a selection of BACnet messages that represent confirmed and unconfirmed services, and offered traffic load that varies from low to high. The main criteria to evaluate the performance of LANs are delay and throughput. Throughput is identical to the offered traffic G when the network system is not saturated. The simulation results presented in this paper also should be interpreted in terms of delay and throughput. The reader should keep in mind that the fact that one LAN saturates at higher G does not imply that the LAN is better than others. Service delay and other factors can also be important and should be considered along with throughput. MS/TP provides simple and low-cost means of communication. Using the ReadPropertyMultiple service to retrieve multiple data values instead of repeated use of the ReadProperty service significantly increases throughput performance but slightly increases the service delay. In all-master MS/TP networks, the difference in service delay between the UnconfirmedCOVNotification and ConfirmedCOVNotification was found to be negligible. Even though MS/TP networks are relatively slow, they are quite efficient for BACnet application services. This is because a capability of immediate reply to confirmed services and the ability to transmit more than one message when holding the token are features well suited to the client/server communication nature of building automation systems. ARCNET provides faster communication speeds than MS/TP. For ReadProperty service requests, the network resource in ARCNET networks saturates at a much lower traffic load than in MS/TP when MaxInfoFrames for MS/TP is larger than the rate of packet generation. With ARCNET, using the ReadPropertyMultiple service rather than several repetitions of the Read- Property service can significantly increase network utilization. The delay for Unconfirmed-COVNotification in ARCNET is less affected by the token overhead. The delay for the ConfirmedCOVNotification service, in ARCNET, is significantly affected by the token overhead, and the performance is degraded de·grad·ed adj. 1. Reduced in rank, dignity, or esteem. 2. Having been corrupted or depraved. 3. Having been reduced in quality or value. compared to the UnconfirmedCOVNotification service. ARCNET is faster than MS/TP but, because the effect of token circulation overhead is greater for ARCNET, the network performance degrades at lower traffic levels than MS/TP. Both MS/TP and ARCNET are suitable for a LAN that requires real-time communication because they are operated on token-passing discipline. Because of its cost, Ethernet is usually only used as a backbone LAN in building automation systems. Its high data transmission rate makes it well suited for that application. Compared to ARCNET, the service delay in Ethernet is less affected by the change of the number of nodes. Compared to ARCNET, the delay characteristics of Ethernet are more randomized ran·dom·ize tr.v. ran·dom·ized, ran·dom·iz·ing, ran·dom·iz·es To make random in arrangement, especially in order to control the variables in an experiment. with respect to the traffic change. Compared to ARCNET, the network resource for ReadProperty service in Ethernet is saturated at higher traffic load, especially when the number of nodes in the network is larger. Using the ReadPropertyMultiple service in Ethernet increases the throughput of the network system just as it did for the other network technologies. The network resource for UnconfirmedCOVNotification and ConfirmedCOVNotification services in Ethernet begins to saturate as G > 0.4. The rate of the increase in service delay for ConfirmedCOVNotification is higher than that for UnconfirmedCOVNotification. Although Ethernet is very efficient at low traffic load, protocol overhead caused by contention is increased as the traffic load is increased. At a heavy traffic load, it may not be able to guarantee the real-time requirements. This is an important consideration if the network is also used to serve business applications or carry other traffic unrelated to the building automation system. However these collision effects might be largely mitigated by the use of Ethernet switches A device that connects clients and servers to each other in an Ethernet network. See switched Ethernet. rather than hubs. This paper presents the characteristics of the service delay of MS/TP, ARCNET, and Ethernet when they deliver BACnet services. In Song et al. (2003), more details of the performance characteristics of three representative BACnet LANs are described. The report includes the effect of the change of MS/TP network parameters on the performance of single-master and multi-master MS/TP networks. It also presents the performance characteristics of transmission delay in ARC- NET and Ethernet. The effect of processing time for BACnet application services in the application and user layers on the performance of service delay is also reported. The simulation results obtained from this study can provide some guidelines guidelines, n.pl a set of standards, criteria, or specifications to be used or followed in the performance of certain tasks. for designing BACnet networks used in building automation systems. In particular, the results provide insight into characteristics that can be used to help select the appropriate LAN and operating constraints that must be met to remain within acceptable service delay limits. ACKNOWLEDGMENT acknowledgment, in law, formal declaration or admission by a person who executed an instrument (e.g., a will or a deed) that the instrument is his. The acknowledgment is made before a court, a notary public, or any other authorized person. This work was partially supported by the grant from the Basic Research Program of the Ubiquitous Sensor Network A low-speed industrial network that is used to connect sensors to actuators. A sensor network implies limited or no controller functions. Multiple sensor networks may be coupled to form device networks. See industrial control network. Research Center (USNRC USNRC United States Nuclear Regulatory Commission ) funded by the Gyeounggi Regional Research Center (GRRC GRRC Ground Radio Repair Course ) plan. REFERENCES ASHRAE. 2004. ANSI/ASHRAE Standard 135-2004, BACnet: A Data Communication Protocol for Building Automation and Control Networks. Atlanta: American Society of Heating, Refrigerating re·frig·er·ate tr.v. re·frig·er·at·ed, re·frig·er·at·ing, re·frig·er·ates 1. To cool or chill (a substance). 2. To preserve (food) by chilling. and Air-Conditioning Engineers, Inc. ATA. 1992. ANSI/ATA 878.1-1992, Local Area Network: Token Bus (networking) token bus - (IEEE 802.4) A networking protocol which mediates access to a bus topology network as though it were a token ring. This eliminates the collisions found in carrier sense collision detect protocols. (2.5 MBPS). ARCNET Trade Association. Buchanan, B. 1999. Handbook of Data Communication and Networks, pp. 497. Boston: Kluwer Academic Publishers. Bushby, S.T. 1997. BACnet: A standard communication infrastructure for intelligent buildings. Automation in Construction 6(5-6):529-40. Casandras, C.G., and S. Lafortune. 1999. Introduction to Discrete Event Systems. Boston: Kluwer Academic Publishers. EIA. 2003. ANSI/EIA/TIA-485-A-1998 (R2003), Standard for Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems. Arlington, VA: Electronic Industries Alliance. EN ISO. 2003. EN ISO 16484-5, Building Automation and Control Systems--Part 5 Data Communication Protocol. Geneva Geneva, canton and city, Switzerland Geneva (jənē`və), Fr. Genève, canton (1990 pop. 373,019), 109 sq mi (282 sq km), SW Switzerland, surrounding the southwest tip of the Lake of Geneva. : International Organization for Standardization. IEEE. 1998. ANSI/IEEE 802.3-1998, Local Area Networks--Carrier Sense Multiple Access With Collision Detection See CSMA/CD and collision avoidance system. (networking) collision detection - A class of methods for sharing a data transmission medium in which hosts transmit as soon as they have data to send and then check to see whether their transmission has suffered a collision with (CSMA/CD) Access Method and Physical Layer Specifications. Piscataway, NJ: Institute of Electrical and Electronic Engineers. ISO. 1984. ISO 7498, Information processing information processing: see data processing. information processing Acquisition, recording, organization, retrieval, display, and dissemination of information. Today the term usually refers to computer-based operations. systems--Open Systems Interconnection--Basic Reference Model. International Organization for Standardization. Kelton, W.D., R.P. Sadowski, and D.A. Sadowski. 2001. Simulation with ARENA. Boston: McGraw Hill. Newman, H.M.1994. Direct Digital Control of Building Systems: Theory and Practice. New York New York, state, United States New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of : John Wiley John Wiley may refer to:
Song, W.S., S.H. Hong, and S.T. Bushby. 2003. A simulation analysis of BACnet local area networks. NISTIR NISTIR National Institute of Standards and Technology Interagency Report NISTIR National Institute of Standards and Technology Internal Report 7038. National Institute of Standards and Technology National Institute of Standards and Technology, governmental agency within the U.S. Dept. of Commerce with the mission of "working with industry to develop and apply technology, measurements, and standards" in the national interest. , Gaithersburg, MD. Received May 10, 2006; accepted July 17, 2007 Won Seok Song, PhD Seung Ho Hong, PhD Steven T. Bushby Member ASHRAE Won Seok Song is a senior researcher in the R&D Center, I-Controls, Inc., Seongnam, Korea. Seung Ho Hong is a professor in the School of Electrical and Computer Engineering, Hanyang University Hanyang University is a large university in South Korea. It is located in Seoul, with a second campus in the suburban city of Ansan. Love in Truth in Deed is the founding principle and educational philosophy of Hanyang University. It is located in South Korea. , Ansan, Korea. Steven T. Bushby is a leader in the Mechanical Systems and Controls Group, Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD. |
|
||||||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion