Building Management System to Save Energy
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1. Introduction of BMS
Building Management System (BMS) is to control and monitor building services systems in an efficient way by centralizing the control of individual systems ( 1.1). The systems include HVAC, Fire Services Lift, Escalator, Lighting, Electrical Distribution, Steam & Hot Water, and Plumbing & Drainage.
The main function of BMS is centralized control & monitoring and fault management. So it has another name call Central Control and Monitoring System (CCMS). The other functions are enhance interface & connectivity between systems, service response to customer, operator control of systems and graphical display to make the control of system more users friendly. Improve energy efficiency and operational efficiency. Allow capacity for future upgrades & expansions and automation. And related system Building Automation System (BAS) will be use on BMS.
2. Basic BMS Design
3-Levels BMS Architecture ( 2.1):
l Management Level - User can configure and monitor plant performance. Anticipate future trends, improve efficiency, and analyze management report.
l Automation / Controller Level - The location with greatest technical control requirement, and differentiate one from others. Controllers automatically perform their tasks from I/P and to O/P. Controllers can communicate with each other (Peer-to-Peer). Event based operation. The devices can function at the highest efficiency and no repetitive information is transmitted. Controllers only react with the Management Level when plant goes out of limits, and adjustments are made through a user interface.
l Field / Floor Level - Information is gathered through sensors and other intelligent devices. The information will be sent back to the controllers.
Third party equipment is integrated into the Automation and Field levels with control at the Management level.
Centrally controlled system ( 2.5) - A control system in which transmission is to a central computer and the reliance of all controls on a central computer.
Distributed control ( 2.6) - A control system in which control computations and intelligence are made at different locations and the result coordinated.
The constraints of BMS are network expansion, the limited variety of topologies and transmission media. The solutions are mixing of communication media (twisted pair, power line, radio, infra-red, fibre optics, coaxial). Complete implementation of OSI model. Using free topology, user-friendly software and development cost.
Topology affects system redundancy, communication protocol and system response time. The common system topologies such as: Bus, Star, Tree, Ring and Mesh.
Bus Topology ( 2.7) - All devices are connected to a central cable, call the bus or backbone. The advantage is much less cabling requirements. The brands using include Ethernet, Profitbus, ControlNet, LonWorks.
Star Topology ( 2.8) - All devices are conned to a central hub. Star networks are relatively easy to install and manage, but bottlenecks can occur because all data must pass through the hub. Cable fault affects one device only. But communication hub fault affects all devices. The brands using include Ethernet, Profitbus, ControlNet, LonWorks.
Tree Topology ( 2.9) - The topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs. Device at the highest point in the hierarchy controls the network. The brands using include Ethernet, Profitbus, ControlNet, LonWorks.
Ring Topology ( 2.10) - All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. Same as bus network with both edges connect. The brands using include Token Ring, FDDI, Profitbus.
Mesh Topology (Fig 2.11) - Network topology which combines more than one basic topology such as bus, ring, or star. Good for redundancy. It will use lots of cable to connect every device with every device.
Considerations in Topology Layout for automating building with vast amount of points require well-designed network segmentation, in order to achieve a good performance & infrastructure. Well designed structured network by using repeaters, bridges or even better using routers to improve network reliability and simplify network troubleshooting. Some reasons why segmenting a network is important: Isolation of individual network segments in order to limit the propagation of a single fault to one segment and prevent this single fault from spreading out over the entire network. Different nodes demand different communication media and different network speeds but they all need to communicate with each other, which requires and interconnection between the different networking media. Increase the number of possible nodes in a single network and increase the number of possible nodes in a single network. Keep local traffic within one segment in order to avoid network traffic overload conditions which will make service like HVAC, lighting ... malfunction.
There are three types' configurations using in BMS:
1. Conventional configuration - Server workstations daisy chained with DDCs (usually using RS-485). Typical RS-485 Controller Level network ( 2.14) relatively low bandwidth (around 9600 bps). The limited nodes around 100, and the distance is lower than 1200m. Only for data transmission.
Controller Level Network
2. Ethernet-Based configuration - Use Ethernet as transmission media. Servers, Workstations and DDCs on the same Ethernet platform. Typical Ethernet-Based Network ( 2.15) with high bandwidth (typical 1Gbps backbone). Use IP Technology means open platform for various applications. Virtually no distance limitation. Always use for data, voice & video systems.
3. Hybrid configuration ( 2.16) - Non-hierarchy architecture with combination of different independent networks and interfaces. Various network topologies.
Networking - Protocol
Protocol ( 2.17) is a set of rules, which allows computer/controllers/devices to communicate from one to another. Proprietary Protocols developed by systems or computer manufacture to communicate to their OWN hardware and software over a recommended network. Open Protocols opening up protocols means disclosing procedures, structures, and codes and allowing other system developers to write interfaces and share data on their network. Acceptance of an open protocol depends on its quality, features, and services provided.
The OSI Seven Layer Model ( 2.18)
Each layer has a defined set of functions. The model provides a useful common reference to communicate protocol. Most communication protocols including those used in our field today use either all or some of the seven layers of the OSI model.
1. Network-capable Applications produce DATA.
2. Each protocol layer adds a header to the data it receives from the layer above it. This is called encapsulation. Encapsulated data is transmitted in Protocol Data Units (PDUs). There are Presentation PDU's, Session PDU's, Transport PDU's etc.
3. PDU's are passed down through the stack of layers (called the stack for short) until they can be transmitted over the Physical layer.
4. Any layer on one machine speaks the same language as the same layer on any other machine, and therefore can communicate via the Physical layer.
5. Data passed upwards is unencapsulated before being passed farther up.
6. All information is passed down through all layers until it reaches the Physical layer.
7. The Physical layer chops up the PDU's and transmits the PDU's over the wire. The Physical layer provides the real physical connectivity between machines over which all communication occurs.
2.18 OSI Seven Layer Model
The Physical layer provides for physical connectivity between networked devices. Transmission and receipt of data from the physical medium is managed at this layer. The Physical layer receives data from the Data Link Layer, and transmits it to the wire. The Physical layer controls frequency, amplitude, phase and modulation of the signal used for transmitting data, and performs demodulation and decoding upon receipt. Note that for two devices to communicate, they must be connected to the same type of physical medium (wiring). Ether to Ether, FDDI to FDDI etc. Two end stations using different protocols can only communicate through a multi-protocol bridge or a router. The physical layer is responsible for two jobs:
1. Communication with the Data link layer.
2. Transmission and receipt of data.
The Datalink Layer is the second layer of the OSI model. The datalink layer performs various functions depending upon the hardware protocol used, but has four primary functions:
1. COMMUNICATION with the Network layer above.
2. SEGMENTATION of upper layer datagrams (also called packets) into frames in sizes that can be handled by the communications hardware.
3. BIT ORDERING. Organizing the pattern of data bits before transmission (packet formatting)
4. COMMUNICATION with the Physical layer below.
This layer provides reliable transit of data across a physical link. The datalink layer is concerned with physical addressing, network topology, physical link management, error notification, ordered delivery of frames, and flow control.
Network Layer establishes and terminates connections between the originator and recipient of information over the network. Assign unique addresses to each node on the network. The addresses identify the beginning and end of the data transmission packets. Outbound data is passed down from the Transport layer, is encapsulated in the Network layer's protocol and then sent to the Datalink layer for segmentation and transmission. Inbound data is de-fragmented in the correct order, the IP headers are removed and then the assembled datagram is passed to the Transport layer. The Network layer is concerned with the following primary functions:
1. Communication with the Transport layer above.
2. Management of connectivity and routing between hosts or networks.
3. Communication with the Datalink layer below.
Transport Layer maintain reliability on the network and enhances data integrity by delivering error-free data in the proper sequence. It may use a variety of techniques such as a Cyclic Redundancy Check, windowing and acknowledgements. If data is lost or damaged it is the Transport layer's responsibility to recover from that error. Functions:
1. Communicate with the Session layer above.
2. Detect errors and lost data, retransmit data, reassemble datagrams into datastreams
3. Communicate with the Network layer below.
The session layer tracks connections, also called 'sessions'. For example: keep track of multiple file downloads requested by a particular FTP application, or multiple telnet connections from a single terminal client, or web page retrievals from a Web server. In the World of TCP/IP this is handled by application software addressing a connection to a remote machine and using a different local port number for each connection. The session performs the following functions:
1. Communication with the Presentation layer above.
2. Organize and manage one or more connections per application, between hosts.
3. Communication with the Transport layer below.
The Presentation layer handles the conversion of data formats so that machines can 'present'
data created on other systems. For example: handle the conversion of data in JPG/JPEG format to Sun Raster format so that a Sun machine can display a JPG/JPEG image. The Presentation layer performs the following functions:
1. Communication with the Application layer above.
2. Translation of standard data formats to formats understood by the local machine.
3. Communication with the Session layer below.
The application layer is the application in use by the user. For example: a web browser, an FTP, IRC, Telnet client other TCP/IP based application like the network version of Doom, Quake, or Unreal. The Application layer provides the user interface, and is responsible for displaying data and images to the user in a recognizable format. The application layers job is to organize and display data in a human compatible format, and to interface with the Presentation layer.
Utilities Power Generation
DNP3 Users Group
EIB - European Installation Bus
OPC - OLE for Process Control
Microsoft and other companies
ABB, Siemens, Honeywell
Message Frame Format
Fig 2.19 Message Frame Format
Master-Slave Protocol (2.20) - The control station is called "master device". Only master device can control the communication. It may transmit messages without a remote request. No slave device can communicate directly with another slave device.
2.20 Master-Slave Protocol
Peer-to-Peer Protocol (2.21) - All workstations are loaded with the same peer-to-peer network operating system. Each workstation configured as service requester (client), service provide (server), or even BOTH.
2.21 Peer-to-Peer Protocol
Client-Server Protocol (2.22) - Client workstation are loaded with specialized client software. Server computers are loaded with specialized server software designed to be compatible with client software.
2.22 Client-Server Protocol
The CSMA/CE Protocol is designed to provide fair access to the shared channel so that all stations get a chance to use the network. After every packet transmission all stations use the CSMA/CD protocol to determine which station gets to use the Ethernet channel next. CSMA/CD likes a dinner party in a dark room: Everyone around the table must listen for a period of quiet before speaking (Carrier Sense). Once a space occurs everyone has an equal chance to say something (Multiple Access). If two people start talking at the same instant they detect that fact, and quit speaking (Collision Detection). IEEE 802.3 standard covers CSMA/CD.
Switched Ethernet - nodes are connected to a switch using point-to-point connections, When a frame arrives at the switch, the control logic determines the transmit port. If the transmit port is busy, the received frame is stored in the queue which is a First-in First-out (FIFO) queue. The memory to store pending frames is obtained from a shared memory pool. In case the memory is full, the received frame is dropped.
Networking - Cables
Copper wire pairs are the most basic of the data media.
• Two wire untwisted pair
The insulated wire conductors run in parallel, often in a moulded, flat cable. Normally used over short distances or at low bit rates, due to problems with crosstalk and spurious noise pickup. Performance in multiple conductor cables is enhanced by dedicating every second cable as a ground (zero volt reference), and by the use of electrically
1. A single wire is used for the signal transmission/reception
2. A common reference level/point is existed between the transmitter and receiver
3. It is the simplest connection technique but it is sensitive to noise, interference, loss, and signal reflection
4. It is suitable for short distance and low data rate application (Normally less than 200Kb-meter/s)
• Twisted Pair
The insulated conductors are twisted together, leading to better electrical performance and significantly higher bit rates than untwisted pairs. UTP is unshielded, like telephone cable, whilst STP is shielded and capable of higher bit rates. Systems using banetworkced signals obtain the highest bit rates.
1. Twisting or wrapping the two wires around each other reduces induction of outside interference
2. 1 to 5 twists per inch is quite typical • Cheap and moderate bit rate applications
3. For a few km distance the bit rate can be up to 10Mb/s, and 100Mb/s can be achievable for short distance applications like 100m
2.23 Two wire untwisted pair and Twisted Pair
Unshielded Twisted Pair (UTP):
•Composed of two of more pairs of wires twisted together
•Signal protected by twisting of wires
•Impedance of 100W
•Recommended conductor size of 24 AWG
2.24 Unshielded Twisted Pair
Cat5e: 100MHz ANSI/TIA/EIA-568-B.1
•Susceptibility to damage
•Limited flexibility for MACs (move, add and change)
•Distance limit of 10m
•Avoid in high traffic areas, heavy furniture locations, cross undercarpet power on top at 90 degrees
2.25 Cat3, Cat5e and Cat6 Cable
Screened Twisted-Pair (ScTP):
•Characteristic impedance of 100 W
•Four pair 22-24 AWG solid conductors
•Mylar/aluminum sheath around all conductors
•Drain wire that must be grounded
2.26 Screened Twisted-Pair
Shielded Twisted Pair (STP):
•Composed of two pairs of wires
•Metal braid or sheathing that reduce electromagnetic interference (EMI)
•Must be grounded
•Characteristic impedance of 150 W
•Conductor size is 22 AWG
•Electrical performance is better than UTP (300MHz bandwidth)
•Harder to handle - thick and heavy
2.27 Shielded Twisted Pair
Coaxial Cable (Coax): Composed of insulated center conductor with braided shied. It provides high degree of protection against EMI.
•Because the electrical field associated with conduction is entirely carried inside the cable; problems with signal radiation are minimized very little energy escapes, even at high frequency.
•There is little noise pick up from external sources. Thus, higher bit rates can be used over longer distances than with twisted pairs
2.28 Coaxial Cable
Series 6 (Video):
•Characteristic impedance of 75 ohms
•Mylar/aluminum sheath over the dielectric
•Braided shield over the mylar
•18 AGW solid-center conductor
2.29 Series 6
Series 11U (Video):
•Characteristic impedance of 75ohms
•Mylar/aluminum sheath over the dielectric
•Braided shield over the mylar
•14 AWG solid-center conductor or 18 AWG stranded-center conductor
2.30 Series 11U
•50 ohms characteristic impedance
•Multiple mylar/aluminum sheath over the dielectric
•Multiple braided shield over the mylar
•11 AWG solid-center conductor
2.31 Series 8
Series 58 A/U:
•50 ohms characteristic impedance
•Mylar/aluminum sheath over the dielectric
•Braided shield over the mylar
•20 AWG solid-center conductor
2.32 Series 58 A/U
Fibre Optics: Higher bandwidth and much lower signal loss than copper conductors. It used in the backbone or in horizontal runs of huge control network.
•The data is carried as pulses of light from a laser or high-power LED.
•Optical fibre is non-electrical, hence is completely immune from electrical radiation and interference problems. It has the highest bit rate of all media.
•The fibre consists of an inner glass filament, contained inside a glass cladding of lower refractive index, with an outer protective coating. In a step index fibre, there is a sudden transition in refractive index. A graded index fibre has a gradual transition from high to low index, and much higher performance.
•Most common fibres are multimode, where the inner fibre is larger than the wavelength of the light signal, allowing multiple paths to exist, and some dispersion to limit the obtainable bit rate. In single mode fibres, the inner fibre is very thin, and extremely high bit rates (several Gbps) can be achieved over long distances.
2.33 Fibre Optics
Multimode Fibre: Composed of a 50 or 62.5 micron core and 125 micron cladding. It commonly used in horizontal and intrabuilding backbones. It has distance limitation of 2000m. Often uses a light-emitting diode (LED) light source.
•The center core is much larger and allows more light to enter the fiber
•Since there are many paths that a light ray may follow as it propagates down the fiber, large time dispersion may occur which results in short distance applications or bandwidth reduction
•Because of the large central core, it is easy to couple light into and out of the this type of fiber
•It is inexpensive and simple to manufacture
•Typical value: 62.5/125
Multi-Mode Graded Index
•It is characterized by a center core that has non-uniform refractive index
•The refractive index is maximum at the center and decreases gradually towards the outer edge
•The performance is a compromise between single-mode step index fiber and multi-mode step index fiber
2.34 Multi-Mode Fibre
Singlemode Fibre: It composed of a 6 or 9 micron core and 125 micron cladding (say8/125 or 9/125). It used for distances up to 3000m. It uses a laser light source.
•Small core diameter so that there is essentially only one path that light may Take care,as it propagates down the fiber
• There is minimum time dispersion because all rays propagating down the fiber with the same delay time and results in wider bandwidth (i.e. high bit rate)
• Because of the small central core, it is difficult to couple light into and out of the this type of fiber
• It is expensive and difficult to manufacture
• Typical value: 9/125
2.35 Singlemode Fibre
4-wire phone station wire
Flat Gray Modular
Flat Satin, tele. cable
RJ-11 / RJ-45
Short data cables
*Twist prevent interference
*Voice grade usually not for data
RJ-45 / IBM data connector
*Shielding reduces interference
Frozen yellow garden hose
Original Ethemet cabling
*Looks like cable TV
*Easier to work with than thick coax.
BNC or IBM data connector
Similar to RG-58, but not interchangeable
SI / ST / SMA905 / SMA906
*Difficult to install
*Virtually error free
2.36 LAN Media Technology Analysis
The definition of open system is that system implements sufficient open standards for interfaces and services. It is supporting formats to enable properly engineered components to be utilized across a wide range of systems and to interoperate with other components. And that system in which products and services can be mixed and matched from set of suppliers; and supports free exchange of information/data between different systems without inserting gateways or proprietary tools. Some benefits from Interoperability:
•Devices can be shared among different subsystems.
•Reduce cost, shorten installation time, and reduce complexity as parts are being reduced.
•Devices in different subsystems can interact with each other; therefore, new breed of applications can be created easily.
•Owners can choose the best-of-breed products from different manufacture.
•Elimination of gateway dependency, especially during system upgrade.
•Allow move-add-change relatively easy, hence lower life-cycle costs.
The characteristics of open system are well defined, widely used, preferably nonproprietary interfaces/protocols; Use of standards which are developed/adopted by recognized standards bodies or the commercial market place; and definition of all aspects of system interfaces to facilitate new or additional systems capabilities for a wide range of applications.
The different between proprietary protocols and open protocols; For Proprietary protocols, most manufactures have their own proprietary protocols within their systems, so no communication between Systems unless a gateway is deployed. For open protocols, it allows systems of different manufacturers to communicate. Systems communicate with each other.
2.1 BMS - Open System - Modbus:
A high-level protocol for industrial networks developed in 1979 by Modicon (now Schneider Automation Inc.) for use with its PLCs. It is providing services at layer 7 of the OSI model. Modbus defines a request/response message structure for a client/server environment. It is the most commonly available means of connecting industrial electronic devices. Several common types of Modbus:
l Modbus RTU
n A compact, binary representation of the data.
l Modbus ASSII
n Human readable & more verbose.
n Very similar to Modbus RTU but is transmitted within TCP/IP data packets.
2.2 BMS - Open System - ARCent:
Attached Resource Computer NETwork (ARCnet) was founded by the Data point Corporation in late 1970s. ARCnet was one of the topologies used early on networking and is rarely used as the topology of choice in current LAN environments. ARCnet, however, still is a solid, functional and cost effective means of networking. Each device on an ARCnet network is assigned a node number. This number must be unique on each network and in the range of 1 to 255. ARCnet manages network access with a token passing bus mechanism. The token (permission to speak on the network) is passed from the lowest number node to higher number nodes in ascending order. Lower numbered addresses get the token before the higher numbered addresses. Network traffic is made more efficient by assigning sequential numbers to nodes using the same order in which they are cabled. Choosing random numbers can create a situation in which a node numbered 23 can be a whole building away from the next number, 46, but in the same room as numbers 112 and 142. The token has to travel in a haphazard manner that is less effective than if you numbered the three workstations in the same office sequentially, 46, 47, and 48, and the workstation in the other building 112. With this configuration, the packet stays within the office before venturing on to other stations. A maximum time limit of 31 microseconds is allotted for an ARCnet signal. This is also called a time-out setting. Signals on an ARCnet can travel up to 20,000 feet during the 31-microsecond default time-out period. You can sometimes extend the range of an ARCnet by increasing the time out value. However, 20,000 feet is the distance at which ARCnet signals begin to seriously degrade. Extending the network beyond that distance can result in unreliable or failed communication. Therefore, the time-out parameter and cabling distance recommendations should be increased only with great caution.
An ARCnet network is used primarily with either coax or twisted pair cable. Most older ARCnet installations are coax and use RG-62 A/U type cable terminated with 93 Ohm terminators. Twisted pair (UTP) installations are newer and use stranded 24 or 26 gauge wire, or solid core 22, 24, or 26 gauge type cable terminated with 100-Ohm terminators. Many ARCnet networks use a mix of both coax and UTP cabling. UTP cable is simple to install and provides a reliable connection to the devices, whereas coax provides a means to span longer distances. Typical ARCnet installations are wired as a star. ARCnet can run off a linear bus topology using coax or twisted pair as long as the cards specifically support BUS. The most popular star-wired installations of ARCnet run off two types of hubs:
1. Passive hubs cannot amplify signals. Each hub has four connectors. Because of the characteristics of passive hubs, unused ports must be equipped with a terminator, a connector containing a resistor that matches the ARCnet cabling characteristics. A port on a passive hub can only connect to an active device (an active hub or an ARCnet device). Passive hubs can never be connected to passive hubs.
2. Active hubs have active electronics that amplify signals and split them to multiple ports. The number of ports on an active hub varies with the manufacturer, but eight is typical. A port on an active hub can be connected to a port on another active device (such as another active hub or an ARCnet device) or to a passive hub.
One of the greatest flexibilities of ARCnet is that you can integrate connections from active hubs to a linear bus connection as long as you terminate at the last connection point.
2.38 Standard ARCnet Connection
• In cabling ARCnet networks with coax cable, you must follow several rules:
1. Never connect a passive hub to another passive hub directly.
2. Passive hubs should never be used to connect two active hubs.
3. Passive hubs are only used to connect an active hub and a node.
4. Unused connectors on active hubs do not need to be terminated.
5. Unused connectors on passive hubs must be terminated using a 93 Ohm terminator.
• The Fig 2.39 shows an ARCnet configuration using active and passive hubs. Active hubs are required to extend the network for long distances and to configure networks that have more than four nodes. Passive hubs are used as an economical means of splitting a port on an active hub to support three devices.
2.39 ARCnet Network with Coax
2.40 ARCnet Cable Distance
The trouble shooting of ARCnet:
•Duplicate addresses: No more than one node can have a given node address on the same network. If two or more nodes share an address, one of the two workstations will either lose its network connection or will not be able to find a network.
•Missing terminators: Missing terminators may not present visible problems on a small network. Missing terminators cause data retransmits on smaller systems, eventually appearing as transmit time out errors or network errors.
•Using a terminator with an incorrect rating: Coax uses 93 Ohm; UTP must use 100 Ohm terminators. A terminator's value in ohms depends on the impedance of the cable. The cable's impedance and the terminator's value should always match.
•Failed network interface
•Failed active hubs (or a port on that hub)
•Cable lengths that exceed specifications: Twisted pair, cabled in a bus rather than a star, cannot have more than ten devices per segment. This number varies with different manufacturers. ARCnet UTP installed in a bus configuration is generally used only in very small networks of six nodes or less. This configuration has the major drawback of halting the network if a single cable is disconnected. In an ARCnet bus configuration, the network must be brought down to make any changes or service to the ARCnet interface cards.
•Coax connector not built and/or crimped correctly: Twist-on connectors are responsible for more intermittent errors on a network than most other failures because of their design.
ARCnet use as an office automation has diminished; however, ARCnet continues to find success in the field level automation industry because its robustness, deterministic performance and long cable distances.
• ARCnet ANSI/ATA 878.1 standard was developed by the ARCnet Trade Association (ATA) and approved by the American National Standards Institute (ANSI) in 1992.
• ARCnet Standard:
1. ANSI/ATA 878.1 - This standard defines the frame format, medium access, services, active hub operation, and the physical layer functions and connectors for a token bus LAN operating at 2.5 Mbps.
2. ANSI/ATA 878.1-1999 - Broaden the 878.1 standard to include alternate physical layers such as fiber optics and EIA-485 communications as well as alternate data rates.
3. ATA 878.2 (Draft) - This standard defines the method and the frame formats by which a block of data can be transferred utilizing ARCNET independent of the number of octets in the block of data. The standard defines a protocol by which data can be fragmented into one or more ARCNET frames and re-assembled at the receiving station.
4. ATA 878.3 (Draft) - This protocol encapsulation standard defines a method to embed or encapsulate an existing protocol onto an ATA 878 (ARCNET) network. This standard allows devices using RS-232, RS-422/485 point to point standards to migrate upward to a high-speed network with multi-master capabilities.
• Over the years, ARCnet has developed a large customer base for smaller LAN real-time automation systems, including building automation and industrial controls systems. Its success can be attributed to its high speed deterministic nature and its high reliability.
• ARCnet is a data-link layer technology with no defined application layer (i.e., defines two lower layers of the OSI model: data link and physical layers)
• The token-passing MAC defines five transmission types:
1. Invitation to transmit (ITT): the token
2. Free buffer enquiry (FBE): a query from the transmitting node to destination node to check buffer availability
3. Data packet (PAC): the data transmitted between nodes (8 to 516 characters)
4. Positive acknowledgement (ACK): acknowledgement of recipient
5. Negative acknowledgement (NAK): of FBE and PAC from the destination node
• Basic Symbol Units are the elements used to construct basic frames and reconfiguration bursts:
1. <SD>Starting Delimiter (all ARCnet frames begin with this symbol unit)
1 1 1 1 1 1 (6 symbols)
2. <RSU>Reconfiguration Symbol Unit
1 1 1 1 1 1 1 1 0 (9 symbols)
3. <ISU>Information Symbol Unit (each information unit contains 8 bits of data and 3-bit preamble)
1 1 0 d0 d1 d2 d3 d4 d5 d6 d7 (11 symbols)
• The data in <ISU> can be:
1. <SOU>Start of Header 0x01 (used to identify a packet)
2. <ENQ>Enquiry 0x85 (used to identify a request for a free buffer)
3. <ACK>Acknowledgement 0x86 (used to identify acceptance)
4. <NAK>Negative Acknowledgement 0x15 (used to identify non-acceptance)
5. <EOT>End of Transmission 0x04 (used to identify a token pass to the logical neighbor)
6. <NID>Next Node Identification 0x01 to 0xff (used to identify the next node in the token loop)
7. <SID>Source Node Identification 0x01 to 0xff (used to identify the source node of a packet transmission)
8. <DID>Destination Node Identification 0x000 to 0xff (used to identify the destination node of a transmission request or a packet transmission)
9. <CP>Continuation Pointer 0x03 to 0xff (used to identify the length of packet.)
In short packet mode (0 to 252 bytes), the CP requires only one <ISU>.
In long packet mode (256 to 507 bytes), the CP requires two <ISU>.)
10. <SC>System Code 0x00 to 0xff (used to identify a high level protocol, the ATA has a list of SC assignments)
11. <...DATA...>Data (the user data) Packet with size of 253, 254 or 255 ISUs are called exception packets and must be padded with null data and sent as a long packet
12. <FCS>Frame Check Sequence 0x00 to 0xffff (cyclic redundancy check CRC-16)
• A token is passed in an orderly fashion among all the active nodes in the network
• For example:
1. A network consisting of four active nodes addressed 6, 109, 122 and 255, connected in a star topology as shown above
2. Once the network is configured, the token is passed from one node to the node with the next highest node address even though another node is physically closer
3. All nodes have a logical neighbor and will continue to pass the token to their neighbor in a logical ring fashion regardless of the physical topology of the network, e.g., 6 - 109 - 122 - 255 - 6 - ...
• Directed Messages:
1. Source node, which has grabbed the token to talk, inquires if the destination node is in a position to accept a transmission by sending out a FBE.
2. The destination node responds by returning an ACK meaning that a buffer is available or by returning a NAK meaning that no buffer is available.
3. Upon an ACK, the source node sends out a PAC with either 0 to 507 bytes of data
4. If the data was properly received by the destination node, the destination node sends another ACK. If the transmission was unsuccessful, the destination node does nothing, causing the source node to timeout. The source node will infer that transmission failed and will retry after it receives the token on the next token pass
5. The token is passed to the next node
• If the desired message exceeds 507 bytes, the message is sent as a series of packets - one packet every token pass. This is called a fragmented message. The packets are recombined at the destination node to form the entire message.
•ARCnet supports a broadcast message, which is an unacknowledged message to all nodes.
•Nodes that have been enabled to received broadcast messages will receive a message that specifies node 0 as the destination address.
•Node 0 does not exist on the network and is reserved for broadcast function
•No ACKs or NAKs are sent during a broadcast message making broadcast messaging fast
•ARCnet is able to reconfigure the network automatically if a node is either added to or deleted from the network. This reconfiguration process is automatic and quick without any software intervention.
•If a node joins the network, it does not automatically participate in the token-passing sequence. Once a node notices that it is never granted the token, it will jam the network with a reconfiguration burst that destroys the token-passing sequence. Once the token is lost, all nodes will cease transmitting and begin a timeout sequence based upon their own node address. The node with the highest address will timeout first and begin a token pass sequence to the node with the next highest address. If that node does not respond, it is assumed not to exist. The destination node address is incremented and the token resent. This process is repeated until a node responds. At that time, the token is released to the responding node and the address of the responding node is noted as the logical neighbor of the originating node. The process is repeated by all nodes until each node learns its logical neighbor. At that time the token passes from neighbor to neighbor without wasting time on absent addresses.
•RECON - Reconfiguration Burst <RSU><RSU>...<RSU> 765 RSUs
•If a node is unplugged from the network the reconfiguration sequence is slightly different. When a node releases the token to its logical neighbor, it continues to monitor network activity to ensure that the logical neighbor responded with either a token pass or a start of a transmission sequence. If no activity was sensed, the node that passed the token infers that its logical neighbor has left the network and immediately begins a search for a new logical neighbor by incrementing the node address of its logical neighbor and initiating a token pass. Network activity is again monitored and the incrementing process and resending of the token continues until a new logical neighbor is found. Once found, the network returns to the normal logical ring routine of passing tokens to logical neighbors.
2.3 BMS - Open System - EIB:
EIB concentrates on home and/or building automation and management.
Europe: European Installation Bus
Asia: Electrical Installation Bus
The protocol standards of EIB are ANSI/EIA 766 and ENV 13154-2.
• The EIB Device Network protocol defines:
1. Physical Layer
2. Data Link Layer
3. Network Layer
4. Transport Layer
5. Application Layer
• EIB goes on to specify (mandatory!) standard datapoint formats and their semantics in various applications.
The EIB Device Network Protocol supports the following media:
1. Twisted Pair (9600 bps)
• STP with 30Vdc
• Balanced, baseband, asynchronous (UART) transmission with even parity (range 1 km)
• Data packet size of 14 bytes (extension to 230 is currently under consideration)
• CSMA with bit-wise Collision Avoidance (dominant 0)
2. Powerline Carrier (1200 bps)
• Currently 230V 50Hz mains only
• Spread-spectrum FSK
• Maximum distance between 2 devices (without repeater): 600 m. (Communication is influenced by electromagnetic pollution conditions in the installation.)
3. Radio Frequency
• Under development
• In free field conditions, the transmission distance is about 300 m.
• Under development
• No other information on this media.
The physical network topology of EIB.TP:
•The electrical segments can have an arbitrary topology (i.e. linear, star, tree, loop or combinations of them) consisting of individual wiring sections as long as the electrical requirements (resistive and capacitive length) are not exceeded.
•Terminating resistors are not required in EIB.
•Up to 64 bus devices may be connected to each lines, allowing a total of 64.000 components to be connected.
•The total cable length shall not exceed 1000 m per electrical segment. The maximum length allowed is 700 m between two devices and 350m between a power supply unit and a device. In certain cases the connection of more than 64 devices to the same line may be required. The system allows two segments to be connected via a bridge, mostly named "repeater". The connection capacity of the line may thus be doubled. In principle, a line may include up to 4 electrical segments connected together via repeaters, thus taking the capacity of the line to 256 devices. However, more than one electrical segment shall only be used for extension of existing installation but not for a new (initial) installation. A maximum of 6 Line Controllers (i.e. Line Couplers, Backbone Couplers and Repeaters) are allowed in one transmission path. The logical segments themselves are connected together by line couplers (LC) via a single logical segment. A maximum of 16 logical segments is allowed. Up to 15 zones can be federated by using the Bus itself. This can be also achieved by higher level bus systems like ISDN or Profibus, requiring appropriated gateways.
•The first character of each frame is the control field.
•The control field contains the information about the layer-2 service, its class and a flag containing the information whether the LPDU is a repeated one.
•The control field indicates the type of the request frame, L_Data-, L_Poll_Data request frame or Acknowledgment frame. The two class-bits of the control field control the priority of the frame, if two devices start transmission simultaneously.
•Repeated format 1 frames have the repeat_flag set to zero, non-repeated ones have it set to one.
•The last character of a frame is the check byte which makes an odd parity over the set of corresponding bits belonging to the preceding bytes of the frame. This represents a logical NOT XOR function over the individual bits of the preceding bytes of the frame.
•EIB is a fully peer-to-peer network, which accommodates up to 65536 devices.
•The logical topology allows 256 devices on one line: 15 lines may be grouped together with a main line into an area
•An entire domain is formed by 15 areas together with a backbone line.
•On open media, nearby domains are logically separated with a 16-bit SystemID.
•Without the addresses reserved for couplers, (255 x 16) x 15 + 255 = 61'455 end devices may be joined by an EIB network.
•Installation restrictions may depend on implementation (medium, transceiver types, power supply capacity) and environmental (electromagnetic noise, ...) factors. Installation and product guidelines should be taken into account. Couplers connect lines or segments, e.g. within the Twisted Pair (TP) medium, or different media; their functionality may be (some combination of) repeater, bridge, router, package filter (for traffic optimisation), firewall protection etc. EIB defines various standard coupler profiles.
• Physical Address
1. Each device, i.e. a router or an EIB end device shall have a unique physical address in an EIB network. The physical address is a two-octet value that consists of an 8-bit device number, a 4-bit line number and a 4-bit area number.
2. The device number shall be unique within a line. Routers shall always have the device number zero; i.e. EIB end devices may have the device numbers 1-255. See also paragraph 1.3.3 "Router, Sub-line, Main Line and Zone" for details.
3. The line number shall be unique within an area (0-15). The devices in the main line of an area shall always have the line number zero.
4. The area number shall be unique within an EIB network (0-15). The devices in the inner area shall always have the area number zero.
• Group Address
1. The group address is a two-octet value that doesn't need to be unique. An EIB end device may have more than one group address.
2. Each EIB end device belongs to group zero, i.e. request frames with destination group address zero are broadcasts.
3. Functions of EIB Bus devices belonging to the same group, may be controlled by only one message sent by a "source" EIB Bus device.
• The source address field always contains the physical address. The physical address is only used as destination address for initialization, programming and diagnostic operations (connection oriented transmission).
Transport Layer Services - EIB layer-4 provides four different types of communication relationships:
•(T_Groupdata) A multicast communication relationship connects group-objects that belong to the same group. Group-objects may be distributed to a number of EIB end devices. Each EIB end device may be a transmitter. More than one group-object may exist in an EIB end device. The group-objects of an EIB end device may belong to the same or to different groups.
•(T_Broadcast) The broadcast communication relationship connects a single EIB end device with all communication partners. The single EIB end device is always a transmitter, the communication partners are always receiver.
•(T_Data_Unack) Every EIB end device has a one-to-one connection-less communication relationship with every other EIB end device. A one-to-one connection-less communication relationships shall not be used if the connection-oriented communication relationship is established to the same partner at the same time.
•(T_Connect, T_Data, T_Disconnect) An EIB end device only has a single one-to-one connection-oriented communication relationship.
The destination address (octets three and four) defines the EIB end device(s) that shall receive the frame. The destination address can be either a physical address (DAF=0) or a group address (DAF=1), depending on the destination address flag (DAF) of octet five.
The APDU corresponds to the TPDU, but reduced by the transport control field. The application control field is encoded and decoded by layer-7 and contains the layer-7 service codes. The application control field has a length of 4 or 10 bits, depending on the layer-7 service. The codes for the application control field are shown in 3/3/7-3. The complete PDU for each service primitive is shown in the description of every service. Not defined and not supported application layer services are ignored by the layer-7.
•4 bits in octet 5 indicate the length of data, the maximum length is 14
•Through the Network Protocol Control Information (NPCI), the Network Layer controls the hop count; for devices other than routers or bridges,
•Every message passing require acknowledgement from the receiving device(s)
Two vendor-independent EIB Tool Software (ETS) suites for Windows:
1. ETS End-User's Edition: A project engineer or electrical contractor can import the Component Description into the ETS Project Edition. All device instances can be customized to the needs of the project and logically linked by assigning Group Addresses.
2. ETS Developer's Edition (ETS+): With the ETS Developer's Edition, the manufacturer encapsulates the remotely loadable applets in a series of abstract representations, which hide all implementation details. The resulting Component Description can be exported.
•1 bus line with up to 64 bus devices (max 1km)
•1 main line (function area) with up 16 bus line by line couplers
•1 area line (bus system) with up to 15 main lines by backbone couplers
•Total available bus devices in an EIB system is 11,520
EIB.net - Automation Network specification realizes EIB on all media with a logical link layer according to ISO/IEC 802-2, including Ethernet and Arcnet. Not limited to highspeed backbones, EIB.net also allows management or automation level devices to be directly connected. An enhanced specification catering for routing based on the Internet Protocol (IP) is being reviewed. In this way, EIB.net allows transparent usage of existing LAN infrastructure, and is intrinsically Internet and Intranet enabled.
Advantages of EIB:
• For manufacturers and vendors:
1. EIB's compact communication stack allows for small footprint implementations (< 5 kB); requirements are such, that the system may be realized easily on an 8-bit microprocessor.
2. Kick-start building blocks are available through standard EIB system implementations from major manufacturers.
3. Any product from any manufacturer can be imported as a template into the common ETS binding tool, without any need for PC software development by the product manufacturer.
4. An open software engineering Component Architecture for PC tools and implementations.
5. Tens of thousands of trained installation professionals.
• For installers and system integrators:
1. A synonym for unrivaled multi-vendor flexibility, guaranteed by certified EIB logo.
2. Neutral ETS tool platform for project design and commissioning.
3. Off-the-shelf training from dozens of training centers.
4. Wide spectrum of available products and solutions.
5. Robust installation technology.
• For owner, occupant and Facility Manager:
1. Minimal cost of ownership, as shown by 10 years of experience.
2. High electrical and functional safety of each individual device and of the system as a whole.
3. Long-term availability of extension and replacement technology and components.
• For all:
1. Standard Win32 API's, including OPC server etc.
2. IP connectivity ensured through EIB ANubis.
The Limitations of EIB is 64 thousand devices with 32 thousand individually addressable, shared datapoints or subnetwork..
2.4 BMS - Open System - OPC:
OPC (OLE for Process Control) originally based on Microsoft's OLE COM (Component Object Model) and DCOM (Distributed Component Object Model) technologies, the specification defined a standard set of objects, interfaces and methods for use in process control and manufacturing automation applications to facilitate interoperability.
OPC is a standard interface for factory automation application. It allows every system and communication drive program to connect and communication freely, therefore, OPC is a software interface definition.
OPC is not a new bus standard or a general communication protocol.
2.41 OPC Specification
2.4 BMS - Open System - LonWork:
LonWorks technology, brought on the market by the Echelon Corporation, is a complete platform for implementing control network systems, these networks consist of intelligent devices or nodes that interact with their environment, and communicate with one another over a variety of communications media using a common, message-based (information-based) control protocol, called LonTalk. LONs stand for local operating networks.
•The LonWorks protocol is also known as the LonTalk protocol and ANSI/EIA
•The LonTalk protocol is a layered, packet-based, peer-to-peer communications protocol
•It is designed for the specific requirements of control systems, rather than data processing systems
•The LonTalk tailors the protocol for control at each of the OSI seven layers to ensure a reliable and robust communications for control applications
•LONWORKS technology provides many different communications media options including 1.25 Mbps twisted pair, power line, fiber optic, coax, IR and RF transceivers. This media-independent feature provides the designer and end-user with a wide range of choices for communicating your data.
•The bit rate of a channel depends upon the properties of the medium and the transceiver design. In addition, the transceiver determines transmission distance, data throughput, node power consumption and node cost.
•For TP channels, 22- or 24- AWG cables should be used.
•For PL channel, the frequency range of transceivers is 100kHz to 450kHz.
•For RF channel, the currently approved transceiver is for a transmission speed of 4.883 kbps and frequency ranges conforming to the standard of region, e.g., ETS 300220 for European standard, MPT 1329 for UK standard, RCL 1993/1 for Australian standard, and FCC Part 90 for USA.
For data encoding methods, multiple data encoding methods are used in the LonTalk. Each encoding scheme is media dependent.
•Differential Manchester Coding used in direct mode:
•A transition at the beginning of every bit period provides a signal for synchronizing the receiver clock
•The presence of a second transition halfway between clock transitions indicates a zero data
•A "1" data is indicated by absence of a second transition in a bit period
•Non Return to Zero Coding (NRZ) used in special purpose mode:
•"1" is high and "0" is low
• The LonWorks modified the CSMA protocol for multiple communication media, sustained performance during heavy loads, and support large networks
• If the devices wait for the same duration after backoff and before retry sending data, repeated collisions will result. Thus, randomizing the access delay reduces collisions
• LonWorks devices randomize over a minimum of 16 different levels of delay
• For example, 16 slots reduce the probability of two packets colliding to 1/16 = 0.0625
• A unique feature of the LonTalk protocol is that the number of available time slots is dynamically adjusted by every device, based on an estimate of expected network loading maintained by each device and hence number of randomization slots is increased as traffic increases (predicting the channel load)
• The number of randomizing slots = n * 16, where n = 1 to 63, the estimated channel backlog
• Each node that requires priority access is allocated a unique slot number on its Priority Channel
1. Linearly increasing response time, up to 99 % of the bandwidth
2. Supports open transmission media
3. Adding and removing of devices does not disturb data transmission
•Preamble is a sequence of "1" bits that allows the other nodes to synchronize their receiver clocks. The length of it must be long enough for synchronization. It is user-selectable, but at least six bits long.
•Byte sync is a single "0" bit that marks the end of preamble and indicates the beginning of a frame
•Followed by up to 256 bytes of L2 data (MSB first)
•Packet ends with Manchester code violation
•Delta backlog field in Layer 2 header updates offered traffic estimate on receiving nodes
•For example: For acknowledged message to a group of nodes, the expected traffic = 1 ACK from each receiver
•Packets can be addressed to a single device, to any group of devices, or to all devices.
•A LonTalk address is hierarchical structured as shown in the diagram above.
•Physical Address: Every LonWorks device includes a uniquie 48-bit identifier called the Neuron ID. The Neuron ID is typically assigned when a device is manufactured, and does not change during the lifetime of the device.
•Device Address: A LonWorks device is assigned a device address when it is installed into a particular network. Device addresses are used instead of physical addresses because they support more efficient routing of messages, and they simplify replacing failed devices. Device addresses consists of three components: a domain ID, subnet ID, and node ID. Devices must be in the same domain to exchange packets. The subnet ID identifies a collection of devices that are on a single channel, or a set of channels connected by repeaters. Subnet Ids are used to support efficient routing of packets in large networks. A node ID identifies an individual device within a subnet.
•Group Address: A group is a logical collection of devices within a domain. Groups are limited to 64 devices if acknowledged messaging is used; whereas any number of devices if unacknowledged messaging is used. A device is allowed to configure to be a member of up to 15 groups.
•Broadcast Address: It identifies all devices with a subnet, or all devices within a domain.
•An address is assigned to a node during installation process. It is said that the node is configured.
•The total address size is computed by adding the appropriate number of bytes indicated in the table above.
•Every LonTalk packet contains the address of transmitting device (the source address) and the address of receiving devices (destination address) that can either be a physical address, a device address, a group address, or a broadcast address.
•Devices respond only to those packets corresponding to their domain ID and their own physical address, which is usually known only to the corresponding network installation tools.
There are four different message services on LonWorks: Acknowledged, Repeated, Unacknowledged and Authenticated.
•Acknowledged Messaging: Acknowledgements are expected from each receiving device. If the sender do not receive acknowledgements, it times out and retries the transaction. The number of retries and timeout are both configurable.
•Repeated Messaging: A message is sent to a device or group devices multiple times. This messaging service does not incur the overhead and delay of waiting for acknowledgements. This is especially important when broadcasting information to a large group of devices.
•Unacknowledged Messaging: A message is sent once and no response is expected. This messaging service has the lowest overhead.
•Authenticated Service: Allows the receivers to determine if the sender is authorized to send that message. This messaging service prevents unauthorized access to devices and is implemented by distributing 48-bit keys to the devices at installation time.
A number of tradeoffs between efficiency, response time, security and reliability must be taken into account when using these message services.
• Authentication prevents unauthorized access to nodes and their applications, e.g., a junior technician cannot operate on a security device if he is not authorized.
• Sender and receiver possess the same 48-bit encryption key.
• Authentication is set by a network management command at installation time.
• Authentication process:
1. A receiver receives an authorized message
2. The receiver sends a random number to the sender and challenges the sender to provide authentication
3. The sender then uses the 48-bit encryption key, the data from the ori
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