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Distributed Communication Architecture

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Distributed Communication Architecture

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Hirschmann's long-term communications strategy is based around the complementary strands of industrial automation & control communication and enterprise-wide communications, managed by a common management application, HiVision.The Distributed Communication Architecture (DCA) describes a robust standards-based Ethernet solution for all levels of the industrial automation and control environment, managing and handling information from instruments and sensors to control devices which intercommunicate with plant computer equipment....

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  1. . . . . . . . . . . Hirschmann Network Systems . . . . . . . . . . Distributed Communication Architecture Industrial networking solutions with a future
  2. Hirschmann Boiler plate ..................................................................................................... 5 Section 1 ........................................................................................................................6 Industrial Communications Systems............................................................................6 Introduction.......................................................................................................................... 6 Hirschmann DCA - a strategy for the next millennium ....................................................................6 Strategic direction.............................................................................................................................6 Why do you need a network architecture?........................................................................................7 Flexibility for the future ...................................................................................................................7 The lack of a single transparent automation and control network ................................................7 The network is a long-term major asset........................................................................................7 Principles for industrial network architecture.................................................................. 8 Industry trends..................................................................................................................... 8 The need for high performance Industrial networks ..................................................... 10 Distributed Communication Architecture – DCA ............................................................ 11 A statement of direction for industrial networks ............................................................................11 Real time.....................................................................................................................................11 Migration ....................................................................................................................................11 Topology & Resilience ...............................................................................................................12 Management ...............................................................................................................................12 Performance................................................................................................................................12 Cost.............................................................................................................................................12 A blueprint for future industrial network growth ...........................................................................12 Section 2 ......................................................................................................................13 An industrial networking architecture for the next millennium...............................13 The future of automation .................................................................................................. 13 The Vision........................................................................................................................... 14 Criteria for network evaluation........................................................................................ 16 REAL-TIME...................................................................................................................................16 Ethernet ..........................................................................................................................................16 Legacy Fieldbus..............................................................................................................................16 MIGRATION .................................................................................................................................16 Ethernet ..........................................................................................................................................16 Legacy Fieldbus..............................................................................................................................16 TOPOLOGY & RESILIENCE.......................................................................................................16 Ethernet ..........................................................................................................................................16 Legacy Fieldbus..............................................................................................................................16 Continued… ...................................................................................................................................17 Ethernet ..........................................................................................................................................17 Legacy Fieldbus..............................................................................................................................17 MANAGEMENT ...........................................................................................................................17 Ethernet ..........................................................................................................................................17 Legacy Fieldbus..............................................................................................................................17 PERFORMANCE...........................................................................................................................17 Ethernet ..........................................................................................................................................17 Legacy Fieldbus..............................................................................................................................17 COST..............................................................................................................................................17 Ethernet ..........................................................................................................................................17 Legacy Fieldbus..............................................................................................................................17 2
  3. Section 3 ......................................................................................................................18 The Ethernet Evolution ..............................................................................................18 A brief history .................................................................................................................... 19 The road to deterministic Ethernet .................................................................................. 19 Ethernet developments over the past decade ..................................................................................20 Evolving standards ............................................................................................................ 21 Section 4 ......................................................................................................................22 A time for change........................................................................................................22 Market dynamics ............................................................................................................... 22 Vendor opportunities......................................................................................................... 23 Section 5 ......................................................................................................................24 Hirschmann’s DCA.....................................................................................................24 A blueprint for future industrial growth ......................................................................... 24 The Hirschmann Ethernet Fieldbus Approach................................................................................24 Real-time ....................................................................................................................................25 Migration. ...................................................................................................................................26 Topology & Resilience. ..............................................................................................................26 Management. ..............................................................................................................................28 Performance................................................................................................................................28 Cost.............................................................................................................................................28 Benefits...........................................................................................................................................29 What Hirschmann offers.................................................................................................................29 Summary ........................................................................................................................................29 3
  4. . . . . . . . . . Hirschmann Network Systems Communications Strategy Hirschmann's long-term communications strategy is based around the complementary strands of industrial automation & control communication and enterprise-wide communications, managed by a common management application, HiVision. The Distributed Communication Architecture (DCA) describes a robust standards-based Ethernet solution for all levels of the industrial automation and control environment, managing and handling information from instruments and sensors to control devices which intercommunicate with plant computer equipment. DCA can be deployed throughout the wide spectrum of industrial applications. Factory automation, traffic management and process control are typical environments where Hirschmann’s industrial network solutions are being used. With intranet/Internet access to the control network managers are able to view the shopfloor, data and activities easily and cost-effectively. Industrial networks need to provide two views of the factory or process - a view of operations and a view of configuration/management/diagnostics. Both require traffic management capabilities in the network to prioritize traffic and minimize congestion, which DCA provides. The Scalable Ethernet Architecture (SEA) is a strategic framework for scalable Ethernet throughout the enterprise, from the workgroup to the enterprise backbone, comprising advanced network devices and management software. 4
  5. Hirschmann Boiler plate Hirschmann Network Systems, a division of Richard Hirschmann GmbH & co, is the leading manufacturer of robust system solutions, designed specifically for industrial networking requirements. Part of Rheinmetall Elektronik AG, the highly successful German industrial conglomerate, Hirschmann Network Systems have ambitious growth plans and aim to become the number one supplier of industrial strength networking solutions within the next three years. With a broad spectrum of products, Hirschmann provides a complete range of Ethernet solutions for industrial and corporate end users. Customers come from all enterprises, industrial and public sectors, including chemical and automotive industries, finance and banking, local government, education, the media and health care. Hirschmann has performed particularly well in harsh industrial environments where the emphasis is placed on “super-resilient”, deterministic networks. The industrial product portfolio, IndustrialLine, developed specifically for the challenging conditions of the industrial world, include maintenance free, long-lived, standards compliant products that are easily installed within a plug and play architecture. Consisting of hubs, concentrators and switches, the IndustrialLine includes four product families: ASGE, MC, MR and the second generation DIN Rail family of products all designed to address the specific requirements of mission-critical industrial networking. Steeped in a tradition of technological innovation, the first milestone for the company was back in 1984 with the installation of the world’s first Ethernet network, employing Fibre Optics at the University of Stuttgart. Today, Hirschmann has 100,000 hubs and switches installed in over 15,000 networks world-wide while domestically; Hirschmann is the prime network supplier to 150 of Germany’s Top 500 companies. Hirschmann continues to develop innovative, high quality network systems with 15% of its annual revenues invested back into R&D. Hirschmann is ISO9001 certified and belongs to all the predominant standardisation bodies. These include the IEEE, Gigabit Ethernet Alliance and ATM Forum, Open DeviceNET Vendor Association (ODVA), Profibus Trade Organisation (PTO) and the Fieldbus Foundation. 5
  6. . . . . . . . . . . Section 1 Industrial Communications Systems Networks exist to support the needs of the factory and are the lifeblood of the manufacturing process. However, it seems all this transferring data around between the different layers of the current factory floor network is becoming too complex. Hirschmann solves this dilemma. Instead of viewing factory networks as independent layers, they are viewed as a single resource for data streams prioritised by application needs. By viewing factory traffic as layered data streams, it is possible to forward data using a set of rules that applies to all layers. Instead of compromising between the different capabilities of the different layers of today's factory network, managers can use them fully. Introduction Most factory floor networks are not ready to take manufacturing into the next millenium. The DCA product line from Hirschmann provides manufacturers with a practical high- performance answer with the ability to operate distributed high-bandwidth networks, delivering unmatched performance through sophisticated robust design Hirschmann DCA - a strategy for the next millennium The industry is dominated by legacy fieldbus solutions. So-called fast control networks generally operate at a meagre 1 or 2Mbps and lack the ability to scale to multi-megabit speeds and support thousands of devices. Newer fieldbuses like 12Mbps Profibus promise higher performance, but with an accompanying expensive price-tag. Foundation Fieldbus are now committed to using 100Mbps Fast Ethernet for the long awaited H2 specification. Of these alternatives, it is only Fieldbus Foundation with the H2 standard that has the potential to provide an optimal solution for Industrial automation networks. This is the market opportunity targeted by Hirschmann's Distributed Communication Architecture. Designed to meet the demands of the most mission-critical application, DCA is optimised to deliver the deterministic performance, scalability and high resilience required by these applications at price-points far below those of today's fieldbus solution. Hirschmann's Distributed Communication Architecture describes a control network strategy for the next millennium. Strategic direction Simply, Hirschmann's DCA network architecture defines the strategic direction for its next generation Ethernet fieldbus products - IndustrialLine. The combination of new demands on the factory floor network and the emergence of the intranet/Internet technologies has pushed current-generation fieldbus designs to their architectural limits. Although elegantly simple in concept, DCA is a radical rethinking of the control network architecture - and also defines the strategic direction for the development of the Hirschmann IndustrialLine products. The DCA architecture is the means by which 6
  7. Hirschmann will deliver high performance and guaranteed quality of service for real-time processes as well as easy, low-cost deployment, thanks to its compatibility with legacy fieldbus solutions. Why do you need a network architecture? Users are going to be spending large amounts of money on new automation and control networks to meet the forthcoming bandwidth and performance crisis, so it makes sense to do it right first time. A well thought-out network architecture outlines the solution to this crisis and gives customers confidence about a vendors capability to answer both current and future needs. Flexibility for the future As the automation and control infrastructure changes over time, the network architecture must incorporate the necessary flexibility to accommodate evolving user needs. Investing in the network today will buy flexibility for tomorrow. The lack of a single transparent automation and control network The past lack of an appropriate automation and control network architecture coupled with the lack of standardisation of vendor offerings has prevented the rapid development of new products and new vendor services. The subsequent lack of competitiveness (or dominance of any single vendor-driven set of "standards") and the complexity of current three-tier control networks has opened a new window of opportunity for vendors who want to embrace a new architecture. The diagram below shows how and when Ethernet is going to push down from the information level all the way to intelligent devices at the instrumentation level. The network is a long-term major asset For users, the deployment of an automation and control network and related equipment is a major expense and as a long-term major corporate asset and utility, a coherent network architecture justifies the spending of funds. Network architecture identifies the major components of a network and how they relate to one another. Since it is strategic in definition, individual components or devices may not be currently available, but available in a time-scale of about 18 months. In essence, it defines the ideal state of an actual implementation of a network. However, an architecture does not specify the exact sizing and placement of its components. 7
  8. Principles for industrial network architecture Although hardware and software implementation differs, the underlying standards for open, production management systems are the same as can be found in today’s business systems. That means freedom from the expense of maintaining specialized, one-of-a-kind systems to run their plants. Further, open systems unchain live manufacturing data, enabling companies to distribute it freely across enterprise networks in real-time to people who can use it to make a whole company run more effectively. Changing manufacturing practices are leading towards a new industrial automation and control infrastructure. As firms move into the global marketplace and implement advanced production processes, new technologies - such as Internet, wireless communications, graphical client/server applications, smart devices and decision support systems - are being deployed to reduce costs and streamline operations. However, these new tools and business processes create significant data distribution problems from the device level to the back office. Companies employing the latest automation and control techniques can expect a steep rise in bandwidth requirements, along with multiple challenges as they embrace technology to improve vendors' and customers' role in production. Emerging production processes, integrated systems and control/communications technology offer significant competitive advantages. For many years, the drive in manufacturing has been towards streamlined operations, improved response time to production schedule changes and the use of electronics to price and fill orders. Industry trends The Internet, and its associated technologies, has radically changed the way people go about their business today. It has improved communications throughout society and is now ubiquitous on a global scale. During the 1990’s the main user of the Internet has been people as they provide the intelligence to filter and sort the fast amounts of material available into useable information. This model is changing. In the world of office automation Internet technology has been designed into the devices that support the business and its infrastructure. Example of this evolutionary process can be seen in products as diverse as photocopiers and printers to LAN routers and voice PBXs. So why is this happening? The answer is simple - it makes sense! Giving intelligent devices the ability to communicate with the outside world is a good thing. 8
  9. In the case of the printer & copier automated ordering of consumables such as paper or toner, either to the office administrator or the supplier by email both saves time, money and increases availability of the device. As for the PBX, the ability for a device to inform the maintenance company when tolerances are exceeded and things start to go wrong, rather than wait for a complete system failure, saves time and money for all concerned. The additional benefit is that the technology differentiates the supplier through improved customer service & support. This value proposition, “to save time and money whilst offering increased service and support” has great worth in Industrial application where vast sums of money can be lost in a relatively short time when production or processes are halted. For the process and manufacturing industries, this is the year of change and a shift to new technologies. Underpinning all technological trends is the move towards open, transparent commercial installations based on intranet/Internet and away from legacy, vendor driven systems. Every part of the process control and automation industry - from embedded systems to the Fieldbus Foundation - has recognised the importance of Ethernet and TCP/IP. Ethernet has become the dominant network technology at the controller supervisory level. Every Controller, PLC and DCS vendor has an Ethernet interface and it is now moving downwards towards device and the I/O level. 9
  10. The need for high performance Industrial networks Adding these new processes, systems and technologies to today's automation and control communication infrastructure will stress it unbearably. Bottlenecks caused by, typically three, discrete networks (Plant, Control & Device) will need to be removed before networks become a transparent and plant wide utility. Over the past five years there have been many enhancements to the Ethernet standards, especially in areas of determinism, speed and prioritisation. There is no longer any reason why Ethernet cannot be used to build deterministic fieldbus solutions that are cost- effective and open. Since Ethernet is already the network choice for business computing, its presence at the control level will make sensor to boardroom integration a reality rather than a goal for manufacturers. With the physical bottlenecks removed raw transmission speed needs to be increased and management policies implemented to allow the various traffic types to be prioritised according to needs. The initial impact of adding new, bandwidth hungry applications will be on factory floor network, followed by WANs, should a manufacturer want to make key manufacturing data available to customers and other partners in its supply chain. Distributing manufacturing data is also a bandwidth intensive proposition. Over the next four years, manufacturing plant information generated by DCS equipment is expected to increase by 20 or 30 times the current level. Similarly, a 10 or 20 times increase is expected in PLC equipment collecting information from the factory floor. 10
  11. Distributed control systems (DCS), Controllers and programmable logic controllers (PLCs) also eat up bandwidth. These enabling technologies facilitate smart sensors and devices on the factory floor. Smart sensors mounted on process equipment are now capable of network connectivity throughout the factory; and each sensor being individually addressable and intelligent. Distributed Communication Architecture – DCA The Hirschmann Distributed Communication Architecture provides suppliers and end users with: a statement of direction for industrial networks a blueprint for future industrial network growth A statement of direction for industrial networks To meet the demands of the next generation of automation and control system, the network will require a new architecture comprising six key dimensions: real time, migration from legacy systems, resilience, management, performance and cost. Real time Whether you are designing a small, medium or large control network, Hirschmann networks are designed to grow as end user needs grow and to meet the needs of higher bandwidth real-time applications smoothly. With Hirschmann's Distributed Communication Architecture, its policy-based QoS makes sure high-priority traffic for certain messages always gets through. Migration Hirschmann integrates legacy devices, instrumentation and I/O through gateways supporting existing control and device networks. These gateways also aid smooth migration of installed control networks to Ethernet. 11
  12. Topology & Resilience Ethernet and TCP/IP based networks are inherently scalable by design. The Internet, with its millions of end stations is testament to this. On a local level, single mode fibre optics can move data at rates of 10, 100 or 1000Mbps over distances exceeding 20km with a single hop. Multiple hops and differing topologies (bus, star or ring) extend this even further. Created from the start as mission-critical products, Hirschmann's IndustrialLine offers no single point of failure in a network, either physically or logically Management Hirschmann's Distributed Communication Architecture (DCA) offers comprehensive management capabilities via Web browser, SNMP and priority-based VLANs. Performance Because of DCA's scalability, Hirschmann can give all level of the control and automation network the bandwidth it needs at the level of the network which makes most sense. Ethernet transmission speeds from 10Mbps to 1000Mbps are all fully standardised. Cost. Today, nothing can compare with Ethernet as the lowest cost implementation for a control network. The ability to take advantage of the existing support infrastructure for Ethernet is a major benefit to suppliers and dramatically reduces the total cost of ownership. Cost is also a factor from a development perspective, TCP/IP communications software and the underlying ASIC chips are commodity, mass market items and priced accordingly. A blueprint for future industrial network growth Greater openness/interoperability with other devices, management software and control platforms. Hirschmann DCA provides an open communication architecture compared to legacy control networking and connectivity. Vendors want openness to reduce client software expense and increase access to devices and other products. Reduced dependence on costly, highly skilled field installation and support functions - through automatic Internet Web connection and services. Greater partnership with end users offering open independent solutions with superior support services. 12
  13. Section 2 An industrial networking architecture for the next millennium The demand for ‘open’ industrial communication systems is being driven by end users' desire to move away from older, centralised plant control strategies to distributed control in the field. End users want an enabling technology that provides true device inter- operability, enhanced field-level control, simplified maintenance and reduced installation costs. The only network architecture capable of delivering against these requirements will offer deterministic high performance, be standards based and non-vendor specific. The future of automation New approaches to process and manufacturing automation, which will have a tremendous impact on the design of control networks, include: Manufacturing execution systems (MES). Computer-based information and command for managing production resources, processes, costs, labour, data collection, documentation, and work-in-progress, etc. Data collection. New technologies for traditional functions such as time and attendance recording, labour reporting, and materials tracking. Computerised maintenance management systems (CMMS). Graphical views of process equipment and processes accessed by multiple users to pinpoint faults and failures, order design fixes and accelerate repairs and changes. CCTV for monitoring Data warehouses. Quality information systems. For tracking compliance with ISO9000 and industry-specific benchmarks. Decision support systems. Product data management. Electronic forms. Data support for control and automation processes. These new applications will demand higher bandwidth than ever before from plant, control and fieldbus networks. This increased bandwidth is simply not available from low speed fieldbus systems. 13
  14. The Vision Most plant data collection applications use a batch approach, where data is transmitted at the end of the shift or other low usage times of day. New networking technologies will change this model to real-time, with plant information being continually and automatically collected and analysed - without operator intervention. Plant operations will increasingly be directly connected in a client/server model to host computers and servers. Controllers, PLCs and Enterprise Resource Planning (ERP) systems will be able to access any sensor connected to the control and device network. The result will be better information on manufacturing processes. Imagine the impact of every shopfloor worker having the equivalent of a handheld, possibly wireless network browser at his or her disposal. In real time, process operators will be able to monitor and fine tune system performance, access plant information and communicate directly with their production line managers. These operational online continuous nodes will be another bandwidth consumer, raising traffic levels significantly. And the network will not only supply information internally. Trends towards quick-response, vendor-managed inventory and electronic commerce, are demanding that manufacturing at the centre of the supply chain be brought online. Customers and suppliers need to be able to look at all points in the supply chain, from initial order placement to raw material consumption to assembly to shipment and delivery. Decision support systems and data warehousing applications will soon be able to "mine" massive amounts of data for correlation and trends that can lead to operational improvements. With manufacturing equipment and personnel on the network, higher management can have access to the operational data on the factory floor in unprecedented detail. The new factory floor network will also affect network capacity planning in the same way as switched networks impacted on traditional shared LAN designs. In future, IT/network managers will also need to be aware of developments on the factory floor generating additional traffic which will impact office LANs and servers and, eventually, WAN traffic. Another way of looking at this is of office users extending their reach towards the factory floor. Table 1 shows how key business line functions correspond to plant information sharing and data communication requirements. Table 1 Function Information sharing / Data requirements Operations Detail scheduling Sequencing, priorities, routings, shape, fit, setup, alternative / overlapping / parallel operations, equipment loading, shift patterns Dispatching Production units Flow, jobs, orders, batches, lots,work orders, sequences, changes,events, schedules, controls, buffers Process Monitor, control, correct, decision support, tracking, alarms, management tolerances Product tracking Visibility, status, who is working on what components, suppliers, lots, and genealogy serial numbers, environments, alarms, rework steps, exceptions, history, tracing, usage 14
  15. Performance Up-to-the-minute status, results, history, measurements, utilisation, analysis availability, cycle time, conformance to schedule, performance to standards, parameters, reports Quality Analysis, measurement, collecting, quality control, identifying management problems, correlation, symptoms, actions, results, tracking, inspection Document control Forms, instructions, recipes, drawings, standard procedures, programs, batch records, EC notices, as planned" and "as built" Data collection/ Interfaces, links, production/parametric data, forms, scanned acquisition transaction records, other collected data. Complimentary technologies that support such network related business functions are many and varied. They include: smart sensors and fieldbus devices. Electrical panels and intelligent circuitry in specialised local factory networks which enable multiple performance measurements on production line equipment, operations and materials. high bandwidth devices. Ethernet interfaces, data collection terminals, radiofrequency (RF) devices/transmitters and programmable controllers. traceability. RF tags, barcodes and smart cards. client/server installations & thin clients Internet access As these technologies mature over the next couple of years, current bandwidth levels are expected to hit their ceilings and new network solutions will be required. For control systems, the immediate focus is the factory floor network. Today, many devices are connected to a control network through proprietary serial cabling and protocols. Information is then consolidated from the control network running at speeds typically under 2Mbps. For this information to reach the corporate systems it must cross the divide between the control network and the information network with its links back into the enterprise office automation (OA) network. Typically this function is carried out by a PC based gateway or HMI workstation. With interfaces to the proprietary control network on the one side and the Ethernet/TCP/IP based information network on the other, the gateway provides a route, albeit restricted, across the divide. In the majority of cases today, the information network utilises 10Mbps shared Ethernet. The first casualty of the information explosion will be the legacy fieldbus system with 2Mbps as its upper limit. Shared 10Mbps Ethernet will also be replaced initially by 10Mbps switched increasing to 100Mbps as need dictates. Ethernet will also extend its reach, driving the technology closer to intelligent devices and remote I/O. The Internet and modern networking designs will enable four major functions to be radically improved. Easier product installation for remote or local personnel using HTTP server and browser technology set up, re-configuration and status monitoring Diagnostics/repair help find and solve problems with device or devices' mission using SNMP, FTP, peer-to-peer or HTTP technology and memory dumps to host for analysis, download programs to RAM or flash memory Use the HTTP server to gather a wealth of information from a device Management reporting and network capacity planning 15
  16. Criteria for network evaluation REAL-TIME Ethernet Legacy Fieldbus Application target ALL ALL Determinism YES YES Response time 4ms or less 5ms or less Message size ALL SIZES LIMITED MIGRATION Ethernet Legacy Fieldbus Geography WORLD-WIDE REGIONAL Backwards compatibility HIGH LOW Degree of openness HIGH LOW Interoperability HIGH LOW Standardisation IEEE 802.3 EN 50170 / Fieldbus Foundation Network Security HIGH HIGH Protocol TCP/IP PROPRIETARY TOPOLOGY & Ethernet Legacy Fieldbus RESILIENCE Automation level Business YES NO Control YES YES Device YES YES Bit-sensor GATEWAY YES Physical Connectivity Media TP, FIBER, COAX, AUI, COPPER, FIBER WIRELESS Devices connected CONTROLLERS, FIELD CONTROLLERS, FIELD DEVICES, REMOTE I/O DEVICES, REMOTE I/O Max no of nodes 64000 500 Nodes per segment 1-256 (APPLICATION DEPENDANT) 48 Distance between nodes Up to 40Km Up to 20Km 16
  17. Continued… Ethernet Legacy Fieldbus Repeaters for longer YES YES distances Logical Connectivity Communication modes VARIED VARIED Internet/intranet YES NO Resilience Reliability HIGH HIGH Scalability HIGH MEDIUM Redundancy YES YES Hot insertion of devices YES SOME MANAGEMENT Ethernet Legacy Fieldbus Plug'n'play support YES NO Network topology BUS, STAR, RING BUS, STAR,RING VLANs YES NO HTTP / WWW YES NO SNMP YES NO ISO Levels supported 1, 2, 3, 4, 5, 6, 7 1, 2, 7, User Layer PERFORMANCE Ethernet Legacy Fieldbus Data transfer rate HIGH LOW Speed 10 / 100 / 1000 Mbps 1-12 Mbps Scalability HIGH MEDIUM COST Ethernet Legacy Fieldbus Cost LOW HIGH Cost per connection LOW HIGH Cost of Ownership LOW HIGH Sourcing MULTIPLE SINGLE VENDOR 17
  18. Section 3 The Ethernet Evolution Advances in commercial networking technology have been coming so fast that it has grown difficult for automation and controls suppliers to keep comparable elements of their legacy systems abreast with state-of-the-art network developments. With the networking industry offering dramatically increased bandwidth, commercially available Ethernet equipment is now beyond what suppliers can hope to develop in-house in terms of fieldbus and control networks. For vendors, in-house development of computer hardware, operating systems and networking elements, which can be purchased cost-effectively on the open market, exacts a fierce toll. It is very expensive for suppliers to support 20 year old, proprietary systems. Originally ignored by the Automation industry because of its perceived lack of determinism and robustness, Ethernet has evolved into a technology which the automation and control industry is swiftly adopting. Ethernet TCP/IP is a widespread network technology, with users exceeding 100 million world-wide. Ethernet PC boards sell for sub $30 compared to the $900 or more for a control or device network PC board. In addition, the growing acceptance of Microsoft Windows NT and its incorporation of Ethernet drivers into the operating system enhance Ethernet as the backbone of high-speed control and device networks. Further, Windows CE is being considered as an embedded operating system for devices and controllers, leveraging Windows NT capabilities. Many PCs include an Ethernet network interface card at little or no cost. Ethernet TCP/IP also offers easy connection to the Internet, which is gradually filtering its way into the world of industrial automation and control systems. Devices sitting on an Ethernet TCP/IP network need only be assigned an IP address for Internet connectivity. In addition, a complimentary Internet technology – Java, is already being used in applications from automation and control suppliers. To meet the demands of industrial control networks, Ethernet architecture must be based on six main criteria: real-time capabilities, migration, topology & resilience, management, performance and cost. 18
  19. A brief history The history of local area networking is relatively short - Ethernet was the first working LAN. It was developed at the Xerox Palo Alto Research Park, beginning in 1973, by a team headed by Dr Robert Metcalfe. Ethernet was first widely employed commercially to network terminals to minicomputer systems - more specifically, to network Digital Equipment Corp terminals to its VAX line of minis. Unix-based workstations and scientific workstations were also connected by Ethernet early on. The original published specifications were known as DIX (Digital, Intel, Xerox) Ethernet Specifications Versions 1.0 and 2.0. The IEEE adopted, improved and modified the DIX Version 2.0 specification. This became the IEEE 802.3 standard, which is equivalent to the ISO 8802/3 standard. The first IEEE Ethernet standard was published in 1983, defining what we know today as 10Base5 or thick Ethernet. The earliest commercial network, Ethernet, used a bus - a single data path to which all workstations attach and on which all transmissions are available to every workstation. Only the workstation to which the transmission is addressed can actually read it, however. A bus cable must be terminated at both ends to present a specified impedance to the network workstations. The road to deterministic Ethernet How can only one computer at a time be allowed to transmit on the network? Access to the network - the right to transmit - can be allocated in one of two ways: randomly or in a deterministic order. In a random access method, any station can initiate a transmission at any time - unless another station is already transmitting. In a deterministic access method, each station must wait its turn to transmit. Carrier-Sense Multiple Access / Collision Detect (CSMA/CD) is the random access method used for bus arbitration within the original shared Ethernet standard of IEEE802.3. CSMA/CD and random access are best suited where network traffic is unpredictable and bursty, consisting of many short transmissions. Since industrial networks are characterised by their deterministic nature, consistent low latencies and low jitter, it is hardly surprising that the leading Automation vendors regarded early Ethernet as unsuitable and developed their own networking solutions. However, rapid developments in Ethernet switching technology in the early 1990s’ have eliminated what were once barriers to the adoption of Ethernet as the control network of choice. With its speed, robust performance, low cost of deployment and constantly updated technology, Ethernet is a natural fit into the automation and control hierarchy. Ethernet is typically used in manufacturing operations for communication both between 19
  20. business system components and plant networks. Ethernet's capability to easily communicate with multiple devices and manage the traffic to the information level of the plant make it an ideal candidate for use at the control & device level. Ethernet developments over the past decade A new version of Ethernet, 10BaseT, appeared in the late 1980s. It uses twisted pair (TP) wiring and is arranged in a star topology. Yet the network acts as a logical bus. That is to say, signals transmitted by any workstation are available on the network to all workstations. Only the station for which the transmission is destined can read it. Ethernet switching arrived on the scene during 1992. The best analogy to switched Ethernet is switched voice and the PBX voice switch. Ethernet switches also support multiple simultaneous communications between many devices without collisions. Using addressing information contained in each Ethernet frame a switch forwards data to a switch port to where the destination equipment can be reached. The ability to switch an Ethernet frame to a specific destination based upon information in the Ethernet frame rather than broadcast the frame everywhere was the first step in making Ethernet deterministic. Ethernet switching has since revolutionised the business of networking, originally demanding a premium switched ports are now priced at a level where it makes good sense to deploy them widely. IEEE 802.3x brought with it standardised full-duplex operation and link based flow control. Full duplex working in point-to-point mode, further overcame the issue of determinism by giving a single station full wire rate connection, with no risk of data collisions. It is collisions caused by two devices attempting to transmit at the same instant that made Ethernet unpredictable when loaded. Where contention is a network issue, flow control provides a means whereby an Ethernet switch can indicate to transmitting stations that congestion exists in the network and that they should pause transmission. The next evolution was Fast Ethernet (IEEE 802.3u), which is nearly identical to 10Mbps Ethernet. The packet length, packet format, error control and management information are identical to 10BaseT, but the speed is increased by a factor of 10. It is implemented as a star topology. IEEE 802.3ac, supporting the work carried out by the 802.1 p & Q IEEE working groups, added frame tagging for priority (8 levels) and VLAN identification which, when combined with Ethernet switching, delivers deterministic performance. Recently, Gigabit Ethernet (IEEE 802.3z) has been ratified, combining Fibre Channel technology with Ethernet media access, running at 1000Mbps (1Gbps) over fibre optic cabling. Hirschmann has specifically addressed current concerns about Ethernet's lack of determinism and redundancy using the standards described above and adding further, complimentary features that are specific to building industrial networks. The result is that Ethernet can now be adopted as the control & device network of choice. Several 20
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