Introduction to communication networks for electrical distribution
This chapter will introduce the fundamentals of network communication and provide a more detailed description of typical applications relevant to Electrical Installations.
A network is a group of devices connected to share data. Connecting and sharing is commonly referred to as communication. Devices can be components directly in the electrical network such as circuit breakers, sensors associated with the application, communication network infrastructure such as Ethernet switches or controllers automating the system i.e.. Computers or PLC’s.
Device functions can be categorized into the following:
1.Sensor – “read-only” data measured. Ex: discrete inputs, 4-20mA analog signals, transducer signals
2.Actuator – changing the state of the process or system via some control mechanism. Ex: Open/Close circuit breaker, contactor, relay, discrete output, varying frequency.
3.Infrastructure – support and manage the network. Ex: router, switch, media converter, protocol converter, datalogger.
4.Controller – Logic or decision. Ex: Alarms, software code / applications.
In electrical installation applications, many devices can perform many functions. For example, advanced electronic circuit breakers can meter the circuit, remotely operate, alarm on defined logic and log their own data as well as for other devices. On the other extreme, simple single purpose sensors may have only the ability to measure and communicate.
A “technical network” is a generic term to describe a communication infrastructure for specific technical applications, i.e. Building Automation, Industrial Networks and Power System automation. This terminology is to distinguish from common networks found in buildings connecting office computers, printers, telephone, etc.
Technical network design is application specific to handle real-time control and data integrity in harsh environments over large installations. This is accomplished by proper selection of key attributes of the network, including, but not limited to, Protocols, Media and Topology. In most instance these 3 attributes are interdependent meaning a particular protocol may require a specific media and only allow for limited topology options, for example the Zigbee protocol is based on wireless media and generally a mesh topology.
Communication protocol is a system of rules that allow devices in a network to transmit information. Protocols have well-defined formats, in many cases formal Technical Standards.
Communication protocols are a vast and complex topic as many aspects can be layered together. Regarding Electrical Installation, we can take a simplified view and consider protocols in 2 categories, language and services. Protocols that define properties of the message and how it is communicated can be thought of as a language some examples are Modbus, Profibus, DeviceNet.
Other protocols that can provide additional values to a network such as device time synchronization, file transfer, redundancy, email, etc can be considered as services on the network, for example SNTP, FTP, RSTP, SMTP. Most importantly when compatible, multiple protocols can be layered together, allowing for a network to utilize multiple language and multiple service protocols.
Industrial Ethernet is a particularly interesting and growing category of communication protocols. It is the use of Ethernet in an industrial environment with protocols that provide determinism and real-time control. Some examples of protocols for Industrial Ethernet include EtherNet/IP, PROFINET, and Modbus/TCP. Industrial Ethernet can also refer to the use of standard Ethernet protocols with rugged connectors and extended temperature switches in an industrial environment, for automation or process control. Components used in plant process areas must be designed to work in harsh environments of temperature extremes, humidity, and vibration that exceed the ranges for information technology equipment intended for installation in controlled environments.
- Increased speed, up to 1 Gbit/s
- Increased distance
- Ability to use standard access points, routers, switches, and cables
- Peer-to-peer architectures may replace master-slave ones
- Better interoperability
- Migrating existing systems to a new protocol
- Real-time uses may suffer for protocols using TCP
- The minimum Ethernet frame size is 64 bytes, while typical industrial communication data sizes can be closer to 1–8 bytes. This protocol overhead affects data transmission efficiency.
A wide range of communication media solutions exist and are determined by application and expertise, as well as dependent on protocols and topology requirements.
Wired media defines any physical connection between devices on a network. Wired media includes the properties of the cable as well as the end device connectors and any required infrastructure.
Single twisted pair cables are common in serial communication commonly used for fieldbus, connected many devices and sensors involved in a building or process located “in the field”. This type of solution provides simple relatively inexpensive cabling for long distances, however the amount of data and speed of communication is relatively low.
In contrast Ethernet defined cabling implements 4 twisted pairs enabling parallel communication. Ethernet based solutions historically were reserved for connections between networks, and in higher levels of a control system, where more data and present and speed was required.
Recently with advances in protocols and media enabling Industrial Ethernet, it is increasingly common to apply Ethernet based cabling solutions at lower and lower levels of the control system, specifically into the fieldbus area direct to field devices and field sensors.
A specific cable type typically utilized in Ethernet applications is Fiber Optic. Fiber optic cable is a glass fiber. It carries pulses of light that represent data. Some advantages over metal wires are very low transmission loss and immunity from electrical interference. Optic fibers can be used for long runs of cable carrying very high data rates.
Wireless networks include a wide range of solutions in size and application, from satellite cellular 4G/5G, local WIFI, to line of sight such as Bluetooth. These networks can be defined by their size, application, technology and application, each with advantages and disadvantages.
Wireless personal area networks (WPANs) connect devices within a relatively small area, that is generally within a person's reach. Bluetooth is an example.
Local Area Networks are often used for connecting to local resources and to the Internet A wireless local area network (WLAN) links two or more devices over a short distance using a wireless distribution method, usually providing a connection through an access point.
Mesh network is a wireless ad hoc network made up of radio nodes organized in a mesh topology. Each node forwards messages on behalf of the other nodes and each node performs routing. Ad hoc networks can "self-heal", automatically re-routing around a node that has lost power.
A cellular network or mobile network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver, known as a cell site or base station.
Each standard varies in geographical range, thus making one standard more ideal than the next depending on what it is one is trying to accomplish with a wireless network. The performance of wireless networks satisfies a variety of applications. As wireless networking has become commonplace, sophistication increases through configuration of network hardware and software, and greater capacity to send and receive larger amounts of data, faster, is achieved.
Wireless networks offer many advantages when it comes to difficult-to-wire areas trying to communicate but are physically separated but operate as one. Wireless networks allow for users to designate a certain space which the network will be able to communicate with other devices through that network.
Compared to wired systems, wireless networks are frequently subject to electromagnetic interference. This can be caused by other networks or other types of equipment that generate radio waves that are within, or close, to the radio bands used for communication. Interference can degrade the signal or cause the system to fail.
Some materials cause absorption of electromagnetic waves, preventing it from reaching the receiver, in other cases, particularly with metallic or conductive materials reflection occurs. This can cause dead zones where no reception is available.
The wireless spectrum is a limited resource and shared by all nodes in the range of its transmitters. Bandwidth allocation becomes complex with multiple participating users.
Network topology is the arrangement of the various devices of a network, the structure of a network and may be depicted physically or logically. Physical topology is the placement of the various components of a network, including device location and cable installation, while logical topology illustrates how data flows within a network, regardless of its physical design. Distances between nodes, physical interconnections, transmission rates, or signal types may differ between two networks, yet their topologies may be identical.
The cabling layout used to link devices is the physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling. The physical topology of a network is determined by the capabilities of the network devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.
Logical topology is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices. A network's logical topology is not necessarily the same as its physical topology.
Daisy chain topology
Daisy chain topology is defined by simply connecting each device in series to the next. If a message is intended for a device partway down the line, each system bounces it along in sequence until it reaches the destination. Except for star-based networks, the easiest way to add more computers into a network is by daisy-chaining.
A daisy-chained network can take two basic forms: linear and ring. A linear topology puts a two-way link between one device and the next. Each device requires 2 hardware connections or ports, which can be costly. By connecting the devices at each end, a ring topology can be formed.
A Ring topology is a bus topology in a closed loop. Data travels around the ring in one direction. When one node sends data to another, the data passes through each intermediate node on the ring until it reaches its destination. The intermediate nodes repeat the data to keep the signal strong. Every node is a peer; there is no hierarchical relationship of clients and servers. If one node is unable to re transmit data, it severs communication between the nodes before and after it in the bus. Ring topology performance scales better than a bus topology. However one negative is that the aggregate network bandwidth is bottlenecked by the weakest link.
Bus topology is defined where each node is connected to a single cable, by interface connectors. This central cable is the backbone of the network and is known as the bus. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted. Because the bus topology consists of only one cable, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, because only one cable is utilized, it can be the single point of failure.
In mesh topology each node relays data for the network. All mesh nodes cooperate in the distribution of data in the network. Mesh networks can relay messages using either a flooding technique or a routing technique.
With routing, the message is propagated along a path by hopping from node to node until it reaches its destination. To ensure that all its paths are available, the network must allow for continuous connections and must reconfigure itself around broken paths. Self-healing allows a routing-based network to operate when a node breaks down or when a connection becomes unreliable. The network is typically quite reliable, as there is often more than one path between a source and a destination in the network. Although mostly used in wireless situations, this concept can also apply to wired networks and to software interaction.
A mesh network whose nodes are all connected to each other is a fully connected network. Fully connected wired networks have the advantages of security and reliability: problems in a cable affect only the two nodes attached to it. However, in such networks, the number of cables, and therefore the cost, goes up rapidly as the number of nodes increases.
In star topology, each network host is connected to a central hub (router, switch) with a point-to-point connection. All traffic that traverses the network passes through the central hub. The hub acts as a signal repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure. Since all peripheral communication must flow through the central hub, the aggregate central bandwidth forms a network bottleneck for large clusters.
Tree topology (or star-bus topology) is a hybrid topology in which star networks are interconnected via bus networks. Hybrid networks combine two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies.
Automation is the use of various control systems for operating equipment such as machinery, processes in factories, pumps, HVAC, Lighting with minimal or reduced human intervention, with some processes have been completely automated.
Automation and Control practices originated in industries with highly critical and continuous processes, however overtime with many technological developments, similar but scaled solutions are common in smaller, simpler, less critical applications where an ROI exists, for example non-critical commercial buildings and residential smart homes.
Common fundamental building blocks of an Automation system:
A programmable logic controller (PLC) is an industrial digital computer which has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability control and ease of programming and process fault diagnosis.
PLCs can range from small "building brick" devices with tens of inputs and outputs (I/O), in a housing integral with the processor, to large rack-mounted modular devices with a count of thousands of I/O, and which are often networked to other PLC and SCADA systems.
Based on digital computers, PLC’s were developed with several key attributes.
- stringent operating environmental control for temperature, cleanliness, and power quality
- support discrete (bit-form) input and output in an easily extensible manner,
- not require years of training to use, and
- permit its operation to be monitored.
Since many industrial processes have timescales easily addressed by millisecond response times, modern (fast, small, reliable) electronics greatly facilitate building reliable controllers, and performance could be traded off for reliability.
A distributed control system (DCS) is a computerized control system for any process, in which autonomous controllers are distributed throughout the system, but there is central operator supervisory control. This is in contrast to non-distributed control systems that use centralized controllers; either discrete controllers located at a central control room or within a central computer. The DCS concept increases reliability and reduces installation costs by localizing control functions near the process, but enables monitoring and supervisory control of the process remotely.
Distributed control systems first emerged in large, high value, safety critical process industries, and were attractive because the DCS manufacturer would supply both the local control level and central supervisory equipment as an integrated package, thus reducing design integration risk. Today the functionality of SCADA and DCS systems are very similar, but DCS tends to be used on large continuous process plants where high reliability and security is important, and the control room is not geographically remote.
The key attribute of a DCS is its reliability due to the distribution of the control processing around nodes in the system. This mitigates a single processor failure. If a processor fails, it will only affect one section of the plant process, as opposed to a failure of a central computer which would affect the whole process. This distribution of computing power local to the field Input/Output (I/O) field connection racks also ensures fast controller processing times by removing possible network and central processing delays.
Supervisory control and data acquisition (SCADA) is a control system architecture that uses computers, networked data communications and graphical user interfaces for high-level process supervisory management, but uses devices such as PLC’s to interface to the downstream device or machine. The operator interfaces which enable monitoring and the issuing of process commands, such as controller set point changes, are handled through the SCADA supervisory computer system. However, the real-time control logic or controller calculations are performed by networked modules which connect to the field sensors and actuators.
The SCADA concept was developed as a universal means of remote access to a variety of local control modules, which could be from different manufacturers allowing access through standard automation protocols. In practice, large SCADA systems have grown to become very similar to distributed control systems in function, but using multiple means of interfacing with the plant. They can control large-scale processes that can include multiple sites, and work over large distances.
Building automation is the automatic control of a building's heating, ventilation and air conditioning, lighting and other systems through a building management system or building automation system (BAS). The objectives of building automation are improved occupant comfort, efficient operation of building systems, reduction in energy consumption and operating costs, and improved life cycle of utilities.
Building automation is an example of a distributed control system – the computer networking of electronic devices designed to monitor and control the mechanical, security, fire and flood safety, lighting (especially emergency lighting), HVAC and humidity control and ventilation systems in a building.
A building management system (BMS), or building automation system (BAS), is a computer-based control system installed in buildings that controls and monitors the building’s mechanical and electrical equipment such as ventilation, lighting, power systems, fire systems, and security systems.
Building management systems are most commonly implemented in large projects with extensive mechanical, HVAC, and electrical systems. Systems linked to a BMS typically represent 40% of a building's energy usage; if lighting is included, this number approaches to 70%. BMS systems are a critical component to managing energy demand.
The communication protocols most commonly used in Building applications are detailed below.
BACnet – communications protocol for Building Automation and Control network, that leverage the ASHRAE, ANSI, and ISO 16484-5 standard protocol.
The BACnet protocol defines a number of services that are used to communicate between building devices. The protocol services include Who-Is, I-Am, Who-Has, I-Have, which are used for Device and Object discovery. Services such as Read-Property and Write-Property are used for data sharing. As of ANSI/ASHRAE 135-2016, the BACnet protocol defines 59 object types that are acted upon by the services. The BACnet protocol defines a number of data link / physical layers, including BACnet/IP.
C-Bus (Clipsal) is a communications protocol for home and building automation that can handle cable lengths up to 1000 meters using Cat-5 cable.
It is used in Australia, New Zealand, Asia, the Middle East, Russia, United States, South Africa, the UK and other parts of Europe including Greece and Romania. C-Bus was created by Clipsal Australia's Clipsal Integrated System division (now part of Schneider Electric) for use with its brand of home automation and building lighting control system. C-Bus has been briefly available in the United States but Schneider Electric has now discontinued sales in the United States C-Bus is used in home automation systems, as well as commercial building lighting control systems. Unlike the more common X10 protocol which uses a signal imposed upon the AC power line, C-Bus uses a dedicated low-voltage cable or two-way wireless network to carry command and control signals. This improves the reliability of command transmission and makes C-Bus far more suitable for large, commercial applications than X10.
Digital Addressable Lighting Interface (DALI)
Digital Addressable Lighting Interface (DALI) is a trademark for network-based systems that control lighting in building automation.
The underlying technology was established by a consortium of lighting equipment manufacturers as a successor for 0-10 V lighting control systems, and as an open standard alternative to Digital Signal Interface (DSI), on which it is based.
DALI is specified by technical standards IEC 62386 and IEC 60929.
EnOcean: an energy harvesting wireless technology used primarily in building automation systems, and is also applied to other applications in industry, transportation, logistics and smart homes.
Modules based on EnOcean technology combine micro energy converters with ultra-low power electronics, and enable wireless communications between batteryless wireless sensors, switches, controllers and gateways.
The radio signals from these sensors and switches can be transmitted wirelessly over a distance of up to 300 meters in the open and up to 30 meters inside buildings.
KNX – Common Home and Building protocol in Europe and China. Supports media (twisted pair, radio frequency, power line or IP/Ethernet), they can exchange information.
Bus devices can either be sensors or actuators needed for the control of building management equipment such as: lighting, blinds / shutters, security systems, energy management, heating, ventilation and air-conditioning systems, signaling and monitoring systems, interfaces to service and building control systems, remote control, metering, audio / video control, white goods, etc.
All these functions can be controlled, monitored and signaled via a uniform system without the need for extra control centers.
LonWorks (local operating network) is a networking platform specifically created to address the needs of control applications. The platform is built on a protocol created by Echelon Corporation for networking devices over media such as twisted pair, powerlines, fiber optics, and RF.
It is used for the automation of various functions within buildings such as lighting and HVAC.
Modbus is a serial communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Simple and robust, it has since become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices.
The main reasons for the use of Modbus in the industrial environment are:
- developed with industrial applications in mind
- openly published and royalty-free
- easy to deploy and maintain
- moves raw bits or words without placing many restrictions on vendors
Modbus enables communication among many devices connected to the same network, for example, a system that measures temperature and humidity and communicates the results to a computer. Modbus is often used to connect a supervisory computer with a remote terminal unit (RTU) in supervisory control and data acquisition (SCADA) systems. Many of the data types are named from its use in driving relays: a single-bit physical output is called a coil, and a single-bit physical input is called a discrete input or a contact.
- Modbus RTU — This is used in serial communication and makes use of a compact, binary representation of the data for protocol communication. Modbus RTU is the most common implementation available for Modbus.
- Modbus TCP/IP or Modbus TCP — This is a Modbus variant used for communications over TCP/IP networks, connecting over port 502.
- Modbus over TCP/IP or Modbus over TCP or Modbus RTU/IP — This is a Modbus variant that differs from Modbus TCP in that a checksum is included in the payload as with Modbus RTU.
oBIX (for Open Building Information Exchange)
oBIX (for Open Building Information Exchange) is a standard for RESTful Web Services-based interfaces to building control systems. oBIX is about reading and writing data over a network of devices, within a framework specifically designed for building automation.
Building control systems include those electrical and mechanical systems that operate inside a building, including Heating and Cooling (HVAC), Security, Power Management, and Life/Safety alarms that are in nearly all buildings.
oBIX is a web services interface because it does not necessarily allow deep interactions with the underlying control systems. This interface can enable communications between enterprise applications and embedded building systems as well as between two embedded building systems. Facilities and their operations to be managed as full participants in knowledge-based businesses.
Zigbee is a low-cost, low-power, wireless mesh network standard targeted at the wide development of long battery life devices in wireless control and monitoring applications. Zigbee devices have low latency, which further reduces average current. The zigbee network layer natively supports both star and tree networks, and generic mesh networking. Every network must have one coordinator device, tasked with its creation, the control of its parameters and basic maintenance. Within star networks, the coordinator must be the central node. Both trees and meshes allow the use of zigbee routers to extend communication at the network level. Zigbee provides the ability to run for years on inexpensive batteries for a host of monitoring and control applications. Communication security is one of Zigbee’s strengths.
Industrial control system is a general term that encompasses several types of control systems and associated instrumentation used in industrial production technology, including supervisory control and data acquisition (SCADA) systems, distributed control systems (DCS), and other smaller control system configurations such as programmable logic controllers (PLC) often found in the industrial sectors and critical infrastructures.
Industrial control systems are typically used in industries such as electrical, water, oil, gas and data.
Based on data received from remote stations, automated or operator-driven supervisory commands can be pushed to remote station control devices, which are often referred to as field devices. Field devices control local operations such as opening and closing valves and breakers, collecting data from sensor systems, and monitoring the local environment for alarm conditions.
The most common protocols used in Industrial Applications are listed below.
AS-Interface (Actuator Sensor Interface, AS-i) is an industrial networking solution designed for connecting simple field I/O in discrete manufacturing and process applications using a single 2-conductor cable. AS-Interface is an 'open' technology supported by a multitude of automation equipment vendors. AS-Interface is a networking alternative to the hard wiring of field devices. It can be used as a partner network for higher level fieldbus networks ie, Profibus, DeviceNet, Interbus and Industrial Ethernet, a low-cost remote I/O solution.
DeviceNet – an implementation of CIP, originally by Allen-Bradley
EtherNet/IP is an industrial network protocol that adapts the Common Industrial Protocol to standard Ethernet. EtherNet/IP is one of the leading industrial protocols in the United States and is widely used in a range of industries including factory, hybrid and process. EtherNet/IP uses both of the most widely deployed collections of Ethernet standards –the Internet Protocol suite and IEEE 802 project. CIP uses its object-oriented design to provide EtherNet/IP with the services and device profiles needed for real-time control applications and to promote consistent implementation of automation functions across a diverse ecosystem of products
Modbus RTU or TCP
Profibus, there are two variations of PROFIBUS in use today; the most commonly used PROFIBUS DP, and the lesser used, application specific, PROFIBUS PA:
PROFIBUS DP (Decentralized Peripherals) is used to operate sensors and actuators via a centralized controller in production (factory) automation applications.
PROFIBUS PA (Process Automation) is used to monitor measuring equipment via a process control system in process automation applications. PA uses the same protocol as DP, and can be linked to a DP network using a coupler device. The much faster DP acts as a backbone network for transmitting process signals to the controller. This means that DP and PA can work tightly together, especially in hybrid applications where process and factory automation networks operate side by side.
PROFINET IO is an industry technical standard for data communication over Industrial Ethernet, designed for collecting data from, and controlling, equipment in industrial systems, with a strength in delivering data under tight time constraints (on the order of 1ms or less)
Power system automation
Power-system automation includes processes to monitor, control, and protect the physical systems that generate, transmit, and distribute power. Monitoring and control of power delivery systems in the substation and on the pole, reduce the occurrence of outages and shorten the duration of outages that do occur. The Intelligent electronic devices (IED), communications protocols, and communications methods, work together as a system to perform power-system automation.
The most common protocols used in Power system automation are listed below.
DNP3 (Distributed Network Protocol) is a set of communications protocols used between components in process automation systems. Its main use is in utilities such as electric and water companies. It was developed for communications between various types of data acquisition and control equipment. It plays a crucial role in SCADA systems, where it is used by SCADA Master Stations (a.k.a. Control Centers), Remote Terminal Units (RTUs), and Intelligent Electronic Devices(IEDs). It is primarily used for communications between a master station and RTUs or IEDs. ICCP, the Inter-Control Center Communications Protocol (a part of IEC 60870-6), is used for inter-master station communications. Competing standards include the older Modbus protocol and the newer IEC 61850 protocol.
IEC 61850 is a standard for vendor-agnostic engineering of the configuration of Intelligent Electronic Devices for electrical substation automation systems to be able to communicate with each other. The abstract data models defined in IEC 61850 can be mapped to several protocols. Current mappings in the standard are to MMS (Manufacturing Message Specification), GOOSE (Generic Object Oriented Substation Event), SMV (Sampled Measured Values and Web Services. These protocols can run over TCP/IP networks or substation LANs using high speed switched Ethernet to obtain the necessary response times below four milliseconds for protective relaying. IEC 61850 features include: Data Modeling, Reporting, Fast Transfer of events , Setting Groups, Sampled Data Transfer, Commands, Data Storage
Open Automated Demand Response (OpenADR) is a research and standards development effort for energy management led by North American research labs and companies. The typical use is to send information and signals to cause electrical power-using devices to be turned off during periods of high demand. Automated demand response consists of fully automated signaling from a utility, ISO/RTO or other appropriate entity to provide automated connectivity to customer end-use control systems and strategies. OpenADR provides a foundation for interoperable information exchange to facilitate automated demand response.
Automatic meter reading (AMR) is the technology of automatically collecting consumption, diagnostic, and status data from water meter or energy metering devices (gas, electric) and transferring that data to a central database for billing, troubleshooting, and analyzing.
The most common protocols used in meter applications are listed below.
ANSI C12.18 & C12.21 is an ANSI standard that describes a protocol used for two-way communications with a meter, mostly used in North American markets. The C12.18 standard is written specifically for meter communications via an ANSI Type 2 Optical Port, and specifies lower-level protocol details. ANSI C12.19 specifies the data tables that will be used. ANSI C12.21 is an extension of C12.18 written for modem instead of optical communications, so it is better suited to automatic meter reading.
IEC 61107 is a communication protocol for smart meters published by the IEC that is widely used for utility meters in the European Union. It is superseded by IEC 62056, but remains in wide use because it is simple and well-accepted.
M-Bus (Meter-Bus) is a European standard for the remote reading of gas or electricity meters and other types of consumption meters. The M-Bus interface is made for communication on two wires, making it very cost effective. A radio variant of M-Bus (Wireless M-Bus) is also specified in EN 13757-4.
Rapid Spanning Tree Protocol (RSTP) is a network protocol that builds a logical loop-free topology for Ethernet networks. Spanning tree allows a network design to include spare (redundant) links to provide automatic backup paths if an active link fails. RSTP creates a spanning tree within a network of connected layer-2 bridges, and disables those links that are not part of the spanning tree, leaving a single active path between any two network nodes. RSTP is typically able to respond to changes within a few milliseconds of a physical link failure.
Media Redundancy Protocol (MRP) allows rings of Ethernet switches to overcome any single failure with recovery time much faster than achievable with Spanning Tree Protocol. During normal operation one of the Manager ring ports is blocked, while the other is forwarding. Conversely, both ring ports of all Clients are forwarding. In case of failure of a link connecting two Clients both ring ports of the Manager are forwarding; the Clients adjacent to the failure have a blocked and a forwarding ring port; the other Clients have both ring ports forwarding.
Parallel Redundancy Protocol (PRP) is a network protocol standard for Ethernet that provides seamless failover against failure of any network component. PRP and HSR (High-availability Seamless Redundancy) are suited for applications that request high availability and short switchover time, such as: protection for electrical substation, or high power inverters, where the recovery time of commonly used protocols such as the Rapid Spanning Tree Protocol (RSTP) is too long.
Each PRP network device has two Ethernet ports attached to two separate networks. A device sends simultaneously two copies of a message, one over each port. The two messages travel through their respective networks until they reach a destination device with a certain time difference. The destination device accepts the first frame of a pair and discards the second (if it arrives). Therefore, if one LAN is operational, the destination application always receives one frame. PRP provides zero-time recovery and allows to check the redundancy continuously to detect lurking failures.
FTP (File Transfer Protocol) is a standard network protocol used for the transfer of computer files between a client and server on a computer network. FTP is built on a client-server model architecture and uses separate control and data connections between the client and the server. FTP users may authenticate themselves with a clear-text sign-in protocol, normally in the form of a username and password, but can connect anonymously if the server is configured to allow it.
SMTP (Simple Mail Transfer Protocol) is an Internet standard for electronic mail (email) transmission. First defined by RFC 821 in 1982, it was last updated in 2008 with Extended SMTP additions by RFC 5321, which is the protocol in widespread use today.
Although electronic mail servers and other mail transfer agents use SMTP to send and receive mail messages, user-level client mail applications typically use SMTP only for sending messages to a mail server for relaying.
SNMP (Simple Network Management Protocol) is an Internet-standard protocol for collecting and organizing information about managed devices on IP networks and for modifying that information to change device behavior. Devices that typically support SNMP include cable modems, routers, switches, servers, workstations, printers, and more.
SNMP is widely used in network management for network monitoring. SNMP exposes management data in the form of variables on the managed systems organized in a management information base (MIB) which describe the system status and configuration. These variables can then be remotely queried (and, in some circumstances, manipulated) by managing applications.
SNTP (Simple Network Time Protocol) A less complex implementation of NTP, a networking protocol for clock synchronization between computer systems, variable-latency data networks, it is used in some embedded devices and in applications where high accuracy timing is not required.
Other important terms
Serial communication is the process of sending data one bit at a time, sequentially, over a communication channel. In contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels. Serial communication is used for all long-haul communication, where the cost of cable and synchronization difficulties make parallel communication impractical.
RS-485, is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems. Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Multiple receivers may be connected to such a network in a linear, multi-drop configuration. These characteristics make such networks useful in industrial environments and similar applications.
RS-485 supports inexpensive local networks and multidrop communications links. It is generally accepted that RS-485 can be used with data rates up to 10 Mbit/s and distances up to 1,200 m (4,000 ft), but not at the same time. The recommended topology is a line or bus.
RS-485 only specifies electrical characteristics of the generator and the receiver. It does not specify or recommend any communications protocol, only the physical layer. Other standards define the protocols for communication over an RS-485 link.
Master/slave is a model of communication where one device or process has unidirectional control over one or more other devices. In some systems, a master is selected from a group of eligible devices, with the other devices acting in the role of slaves.
Fieldbus is the name of a family of industrial computer network protocols used for real-time distributed control, standardized as IEC 61158. Fieldbus is an industrial network system for real-time distributed control. It is a way to connect instruments in a manufacturing plant. Fieldbus works on a network structure which typically allows daisy-chain, star, ring, branch, and tree network topologies. Fieldbus is the equivalent of the current LAN-type connections, which require only one communication point at the controller level and allow multiple (hundreds) of analog and digital points to be connected at the same time. This reduces both the length of the cable required and the number of cables required.