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Nowadays information technology (IT) is increasingly determining the growth in the world of automation. After it changed hierarchies, structures and flows in the entire office world, it now covers all the sectors from the process and manufacturing industries to logistics and building automation. The technological problems are shifting from measurement and control to information management and connectivity, leading to widespread use of networking.
The communication capability of devices and continuous, transparent information rules are indispensable components of future-oriented automation concepts. The 1980’s saw the beginning of the network in Industrial Automation and the 1990’s saw plants turn to standardized bus architectures. At the turn of the 21st century, we can expect the wireless connectivity to dominate. It’s a foregone conclusion that communication will shape the factory of tomorrow, as it will be faster, more efficient and reliable, work areas will be safer and productivity will increase. The future of the automation industry lies in the hand of internet based advanced networking and connectivity, utilizing the standard and proven
bus architecture and protocols. Also over the past several years the advancement in the windows operating systems have provided new mechanisms for the exchange of information among various desktop application at a relatively low cost.
The technical paper gives the reader a basic understanding of how industrial networking can be used in various applications.
Introduction
What Is Networking?
“ Networking are collection of computer which are communicate with each other over a shared medium ” OR“ it is a process in which two or more computers inter connected to share the resources available at different computers.”
Over the past 50 years, the field of computer networking has grown in bits and pieces. Networking allows people to share resources such as printers, large hard drives, host computers such as mainframe, mini-computers, workstations, modems, servers like database servers, electronic-mail, world wide web servers, search engines etc. and it means less hardware investment. In computers networking rules are usually referred to as protocols.
There are over 100 industrial networks and identifying the right one for the right application becomes a tricky issue. This technical paper will discuss many of such issue that need to be considered when selecting industrial network. The network should allow us to communicate with all the interconnected devices without concerns about the loss or corruption of the data and getting the right information to the right user.
One of the first networks, modbus, which almost become extinct, but is now reborn on Ethernet.
History of Networking
Diagram:-
In the time-sharing, there are terminals with which the user access and share the central computer system. Time-sharing allows multiple users use the computer at the same time.
The terminal is basically a remote interactive peripheral device supporting two-way communication. A computer can be connected to another (local or remote) computer through the communication controller.A communication controller is nothing but an I/O controller for data communication.
Network Elements
• Network services provided by the computer system.
• Transmission media connecting the computers.
• Protocols specifying the rules of communication.
Server:
“A server is a computer system that provides services to other computers.”
Client:
“A client is a system that requires services from the server”
Node:
“Each device on a network that is accessed directly by network is a node. Any computer or any peripheral device can become a node. A node a unique name or IP address.”
Network Services
File Services
This involves storing, retrieving and transferring data files.
Print Services
This enables sharing of printers
Message Services
This involves storing, reading and delivering of messages.
Application Services
It involves running of application programs of client by application servers.
Database services
It support centralized database for the network clients.
Why To Use Networking?
• To connect I/O back to the controller
• Connect PLCs and operator interface together
• Link manufacturing computers together
• Link manufacturing with the rest of the company
• Link manufacturing with other plants that supply row materials or consumes the products manufactured
• Linkage the inventory with manufacturing
• Promote enterprise management solution
Types Of Networking
Local Area Network (LAN)
These are those networks usually confined to a small geographic area such as a room, within a building, inside a campus etc. It may consist of workstations, printers, modems and mainframe computers. The development of various standards for networking protocols and media has made possible proliferation of LANs world wide for business and educational applications. LANs are connected by dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links etc. In a typical LAN, one computer works as the file server and other computers are termed as workstations.
Wide Area Network (WAN)
It combines multiple LANs that are geographically separated. Often a network is located in multiple physical places. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links, and data packets carrier services. WAN can be simple as modem and remote access server for employees to dial into, or it can be as complex as hundreds of branch offices globally linked using special routing protocols and filters to minimize the expense of sending data sent over vast distances.
Metropolitan Area Network (MAN)
A metropolitan area network (MAN) connects computers placed across a big city or nearby cities.
Internet
Systems of Worldwide Linked Networks are worldwide in scope and facilitate data communication services such as remote login, file transfer,
electronic mail, the World Wide Web and newsgroups with the meteoric rise in demand for millions of users.
Intranet
Private network using internet- type tools available in limited area like within a given organization, building, and location etc. for large organization, an intranet provides an easy access mode to corporate information.
Protocols
Network protocols are standards that allow computers to communicate. A protocol defines hoe computers identify one another on a network, the form that the data should take in transit, and how this information is processed once it reaches its final destination. Protocols also define procedures for handling lost or damaged transmission or “packets”.
Although each network protocol is different, they all share the same physical cabling. This common method of accessing the physical network allows multiple protocols to peaceful coexist over the network media and allows the builder of a network to use common hardware for a variety of protocols.
Principle roles of protocols
• Node must be adhere to the same standards if they are to communicate.
• Define how computers identify each other on a network.
• How data is transmitted
• How received information is processed
• Message error handling
• TCP/IP- (Transmission control protocol / Internet protocol)
• Standards that define the data link and network protocols.
Network characteristics
To correct analyze and evaluate industrial networks, we need to define and analyze several characteristics and most of the below mentioned characteristics are interrelated.
1) Response time and variance
• What is the typical response required on the network?
• Are some message high priority and some low priority?
• Are the messages continuous or intermittent?
• How fast do the device need to respond to each other?
• What happens if the devices communicate at different intervals?
2) Bandwidth
What is the row speed that the data travels: bandwidth is the ability to pump data through the communication links. Think of it how big are the pipes and pumps to pump the data.
3) Efficiency
It is the measure of how much additional work has to be done to send a message.
• How much overhead is required to send a message.
• How many message need to be sent to read and write data to a device.
• How much the host computer has to do.
4) Access method
• Deterministic means that given the number of devices on the network we can calculate what the maximum response time will be. Response time tends to vary less than networks based on collision network. Typically master-slave networks operate in a deterministic manner where the master sends data to each data back to the master. Most industrial I/O networks are deterministic.
• Collision Detection is where a device listens before it starts talking. If the device dose not hare anything then it starts talking. If someone else starts talking at the same time, then each device stops for a random amount of time and then starts listening for silence again.
5) Distance
Each type of network has distance and speed limitations that are related. The most common characteristic to all network is that the longer the distance – the slower the speed. Repeaters, bridges, gateways, hubs, switches are way to get around these limitations. There is limit to how many repeaters you can use on one cable to extent the cables.
6) Capabilities
We need to determine what the communication capabilities of each device are.
7) Length of message
Theoretically it is ideal to have similar sized message on the same network.
Networking Topology
A network topology defines the physical connectivity if the network. The basic refers to how cables are run can all cables run back to hub or do you “daisy- chain”?
Bus
E.g. Ethernet (10 Base 5, 10 Base 2) Token-Bus
Diagram: -
Star
ARC net, 10 Base T
Diagram: -
Broadcast: -
The hub resends the received signal to all the nodes.
Switched: -
The hub sends the message to the destination node only.
Ring
E.g.
IBM Token-ring, Fiber distributed data interface (FDDI)
Diagram: -
Mesh
Diagram: -
Mesh Topology
Networking Architecture
The international standards organization (ISO) formulated the OSI model for standardizing the network architecture and enable easy interconnectivity. The OSI model defines seven layers of network services each “wraps” the preceding layer’s data and header with its own header. On the receiving end, each layer strips off the header that corresponds to its respective layer.
Diagram: -
OSI Model
This provides an entire point for the application software to access network.
• Presentation layer
This layer’s main function is translation of the syntax and semantics of the data transmission. On sending side, it converts computers data representation into a standard network format. On the receiving side, it translate the network format into the receiving end computers format.
• Session layer
There are about 22 services provided by this layer. The main services are dialogue control and dialogue separation.
• Transport layer
It contains protocols and takes care of reliable transmission of data. Two major transport protocols are the TCP (transmission control protocol) and the UDP (user detagram protocol)
• Network layer
Take care of the routing of data (packets) to a system on the network, handles the addressing and delivery of data.
• Data-link layer
Tales care of reliable delivery of data across a physical network by packaging, addressing and transmitting. It ensures that the information has been delivered.
• Physical layer
It handles the electrical / light communication across the network media. This deals with mechanical, electrical, functional and procedural aspects. It also defines the hardware characteristics such as voltage / current levels, signal strength, connector, and media.
Industrial Ethernet
It is the latest hyped technology. Earlier the Ethernet was not a consideration, since it was slow and not deterministic with the development switching technology, Ethernet is emerging as a good alternative.
• Ethernet is a Local Area Network (LAN) technology that transmits information between computers at speed of 10 and 100 mbps.
• The ability to link a wide range of computers using a Neural Network Technology is an essential feature for today’s market. Most LANs must support a wide variety of computer purchased from different manufactures, which requires a high degree of network interoperability of the sort that Ethernet provides.
• Ethernet is simply a way to transport data between two devices – it does not guarantee that the device receiving the data will know how to interpret the data. The protocol is at the highest OSI model layer.
• All devices attached to an Ethernet are connected to a shared signaling system, also called the medium. Ethernet signals are transmitted serially, one bit at a time, over the shared signal channel to every attached device. This ensures that access to the network channel is fair and that no signal device can lock out the other device.
• Access to the shared channel is determining by the medium access control (MAC) mechanism embedded the Ethernet interface located in each of the device. The medium access control mechanism is based on the system called sense multiple access with Direct Collision (CSMA / CD).
• Ethernet is the most popular LAN technology in the use today. Other LAN technology includes Token-Ring, Fast Ethernet, Fiber Distributed Data Interface (FDDI), Asynchronous transfer mode (ATM) and Local talk. Ethernet is popular because it strikes a good balance between speed, cost and ease of installation.
• These benefits combined with wide acceptance in the computer marketplace and the ability to support virtually all popular network protocols, make Ethernet an ideal networking technology for most computer users today.
CSMA / CD protocols
The CSMA / CD protocols functions somewhat like a dinner party in a dark room.
• To translate this into Ethernet terms, each interface must wait until there is no signal on the channel, then it transmitting there will be a signal on the channel, which is called carrier sense
• All Ethernet interface are equal in their ability to send frames onto the network. No one gets a higher priority than anyone else, and democracy reigns. This is what is meant by multiple accesses.
• Since signals take a finite time to travel from one end of an Ethernet system to the other, the first bits of a transmitted frame do not reach all parts of the network simultaneously. Therefore, it’s possible for two interfaces to sense that the network is ideal and to start transmitting their frames simultaneously. When this happen, the Ethernet system has a way to sense the “collision” of signals and to stop the transmission and re-send the frames. This is called collision detect.
• The CSMA / CD 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 get to use the Ethernet channel next.
• The carrier sense part of the protocol CSMA / CD means that before transmitting data, a stations listens to see if any other stations is already sending something. In spite if all this, there exit a few nanoseconds of time where it is possible that two stations could see the network is available and send the data exactly at the sometime.
• This is where collision detection comes in. when such collision occur both the stations stops transmitting, “ back off” and try again after a randomly chosen delay period.
Half Duplex Or Full Duplex
Full duplex links are the key to extending the maximum network diameter of fast (1000mbps) Ethernet. Full duplex requires separate receive and transmit paths. These devices can be Ethernet adapters or switching hub ports. A repeating hub is a part of the collision domain and reinforces collision receives on any of its other ports. Ethernet adapters configured for full duplex, expansion beyond two adapters require a switching hub capable of supporting full duplex operation.
Half duplex means transmitting and receiving over the same medium but not at the same time.
• Full duplex allows for simultaneous sending and receiving.
• It is important to configure full duplex correctly. If this is configured for half duplex it will incorrectly detect collision and take action that could cause late collision (which are not automatically re-sent) and CRC errors. This result is a slowdown of the network negating the benefits of migrating to fast Ethernet.
• As mentioned above, at 100 Mbps the maximum network diameter is short because if limited collision domain at this speed. This not a problem with twisted pair link segments and switch ports because the maximum twisted pair segment length is 100 m, which is within the collision domain time.
• With fast Ethernet, use of switch technology is recommended and when using
Fast Ethernet over fiber optic cabling full duplex operation is recommended.
Wireless networking
There are a lot of different ways to wireless network including infrared, radio frequency, cellular, and satellite. A lot of advances are being made in these areas for Personal Area Networks (Pans), Local Area Networks (LANs), and Wide Area Networks (WANs).
Prominent among them is the blue tooth; a radio communication protocol getting set to dominant the world of networking. The blue tooth technology was initially developed and promoted by Swedish telecommunication giant Ericson in the mid 1990’s. Bluetooth is an industry developed standard intended to allow a broad range of electronic devices to communicate wirelessly. Bluetooth is Radio frequency specification for short range, point to point and point to multi-point voice and data transfer. It consist of a small expensive computer chip that carries a two way, speed spectrum radio that can be installed into virtually any electronic device. Consisting of a low power transmitter and receiver that operate in the 2.4 gigaherts range over a distance of approximate 10 meters. It communicates and exchange information with any similarly equipped device using protocols. By eliminating cables and providing common communication protocol, Bluetooth makes possible the creation of an infinite series of networks.
Wireless LAN
A wireless local area network (WLAN) is a flexible data communication system implemented as an extension to, the wired LAN. Using Radio Frequency Technology, wireless LAN’s transmit / receive data. Wireless LAN standard is not sufficiently rigid to guaranty interoperability. The IEEE 802.1 if standard is suppose to solve this problem by defining a set of interoperability standards but only for direct sequence spread spectrum. The designated purpose for a WLAN is to correct mobile computers and handheld devices directly in to the corporate LAN, which in turn will provide real time data interchange.
Network interface card (NIC)
Location of LAN Board
The major functions of NIC are,
1) Translating the digital signal from the computers into electrical / optical signals.
2) Translating the electrical / optical signals from the cable into digital signals.
3) Transferring the data between the computer memory and the NIC.
The NICs are classified on the basis of bus type and the network type. The common NIC bus type is either ISA or PCI. The ISA bus gives 8.33 MHz speed and 16- bit bus width. The PCI bus gives 33 MHz speed and 32-bit bus width.
Diagram:-
Conclusion:-
For Productivity Improvements-Vary Your Diet: the man-can not-live-on- bread-alone axiom is directly parallel to manufacturing and network. Most manufacturing facilities cannot “live” on one network. The reason is simple: different networks are designed to support the needs of distinctly different applications.
Given that a variety of buses are almost a necessity, the one problem that currently exits is the lack of integration between each, even though several organization are working for unifying and standardizing it.
To increase productivity and decrees cost, however, manufacturers must be able to see, analyze and adjust what is happening on plant floor as a whole. Some control suppliers have recognized this need and are offering products to seamlessly couple networks thought the entire facility.
The bottom line is the ultimate benefit of integrating process and discrete applications is that end users can take full advantage of networks benefits and strengths, with lower cost. Since data can be shared across the plant floor, engineers can easily gather and compare information for on-going productivity improvements, while the management can analyze the performance and productivity.
Each network function in its optimal environments, and manufactures feast from the resulting continues boost in efficiency and reliability. This soon has to be resolved and uniform standards to be developed which will benefit both the manufactures and the users.
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