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（完整版）_毕业设计外⽂翻译_外⽂原⽂Annual Reviews in Control 31 (2007) 211⼀20Future trends in process automation Helsinki University of Technology, Laboratory of Process Control and Automation, Kemistintie 1, FI Espoo, FinlandReceived 27 April 2007Accepted 29 August 2007Available online 29 October 2007AbstractThe importance of automation in the process industries recent years. In the serves to enhance product quality, master the whole range of products, improve process safety and plant availability, efficiently utilize resources and lower emissions. In the rapidly developing countries, mass production is the main motivation for applying process automation. The greatest demand for process automation is in the chemical industry, power generating industry, and petrochemical industry; the fastest growing demand for is in the pharmaceutical industry.The importance of automation technology continues to increase in the process industries. The traditional barriers between information, communication and automation technology are, in the operational context, gradually disappearing. The latest technologies, including wireless networks, field bus systems and asset management systems, boost the efficiency of process systems. New application fields like biotechnology and microtechnology pose challenges for future theoretical work in the modeling, analysis and design of control systems. In this paper the industry trends that are shaping current automation requirements, as well as the future trends in process automation, are presented and discussed.KeywordsProcess automation;Future trends1. IntroductionThe starting points in assessing the future needs for automation are, on the one the other, the way in which they are reflected in the development of society and the economy. Global risk management willattain ever greater importance in the future. In particular, better control and anticipation is needed in order to contain the risks related to the economy, environment, energy and infrastructure. Faced with climate change and a growing scarcity of raw materials, the world needs to find and develop new environmental and energy solutions. The world's water supply is also in need of development. International competition and global business environments reach everywhere. Business operations and capital markets are dynamic; they seek environments that offer the best opportunities for success in open competition. In addition to business and production, also R&D seeks the best possible operational environments. Economic, organizational and technological trends will cause significant changes in automation technology during the next few years.By developing technologies, it is possible to find solutions to the basic needs of society and the industry. The development of technology all of the current competitive advantages and to create new ones in many new fields, thus further improving prosperity and well-being. The development of of new cooperation models: networking among business companies, universities and research institutes, as well asdecision-makers in the public sector. A trans-disciplinary approach e.g. in materials development requires expertise in physics, chemistry, biomaterials, electronics, communications, programming and automation.Globalization along brings with it social challenges and problems in the interaction between different population groups and cultures. The growth of multiculturalism requires new management practices, knowledge of foreign cultures, and the ability to support and take advantage of the existence of minorities and difference. The management and development of skills and competences in a decentralized organization is becoming increasingly important.The importance of automation in the process industry recent years. It the entire chemical, oil, gas and biotechnology industries. Innovative instrumentation systems now control complex processes, ensuring process reliability and safety, and provide a basis for advanced maintenance strategies. Incessant cost pressures in the chemical and bioindustries leave no alternative to improved productivity. Companies need to take a engineering will play a central role. Process controlensures that the plant assets continuously operate predictably within the most profitable range, leading to a greater output of consistent products, reliability, yield and quality using less energy. This technology will and retrofitting activity designed to increase flexibility.In this paper the industry trends that are shaping current automation requirements, as well as the future trends in process automation, are presented and discussed. The paper is structured as follows: In Section 2 development of the automation market for the process industries up until 2010 is presented: market developments by industries, regions and product and services. In Section 3 future automation technology trends, like the integration of production and business operations and industrial communication technologies, are discussed. The paper ends with recent accomplishments and future application trends in process automation.2. Development of the automation market for the process industries up until 20102.1. Market developments by industriesAccording to the report by Intechno Consulting (Basel, Switzerland), the world market for process automation will grow at an average annualrate of 5.1% between 2005 and 2010 to reach 94.2 billion $ in 2010. The greatest demand for process automation is in the chemical industry, power generating industry, and petrochemical industry; the fastest growing demand for is in the pharmaceutical industry. The share of in individual application sectors.Fig.1. Development of the world market for process automation up until2010—segmentation by industries2.2. Market development by regionsNorth America is the leading market for process automation.Asia-Pacific and Eastern Europe are winning market shares from Western Europe and North America. China is a growing engine for automation in Asia, in spite of its lower levels of plant automation. India, too, is gaining market shares worldwide. In the serves to enhance product quality, master the whole range of products, improve process safety and plant availability, efficiently utilize resources and lower emissions. In the rapidly developing countries, mastering mass production is the main motivation for applying process automation. Quality and environmental aspects are, 2000 were for the process control level, and 60.7% for the field level, including all sensors, measurement equipment, and actuators integrated in the various process technological machines. By 2010, the share of control level in field bus communication and EthernetTCP-IP components. The former is expected to grow at a rate of 8.2%year, and that of the latter should be around 17%.The share of external engineering demand will keep increasing worldwide. It is expected to rise from 13.9% in 2000 to 15.5% in 2010. Engineering expenditures are expected to further increase, especially inthose industries with prototype plants. The trend towards rationalization and plant optimization, accompanied by increased integration of automation systems with the information systems of the production site and the enterprise level, will further addto the engineering share out of the total plant project costs.3. Future technology trends in automation3.1. Current status of the industrial communication technologiesEvolution of communication technologies changes in the structure of industrial automation systems. Up until now, communication support in plant automation systems defined according to the computer integrated manufacturing (CIM) concept. In this such a way that each device is designed for a specific task, and specific networks are used to interconnect devices at the same level, i.e. those running the same task.However, the devices one function, or module, which increases the intelligence level of the equipment automation. Devices like sensors that used for measurement now architecture. Nevertheless, themost of the process control strategies.A brief survey of the most important industrial, low-layer protocols(referring to the ISO model) is given in the following. In addition, some currently essential or emerging protocolsThe most widely available industrial networks at the present time can be classified into three main categories: traditional fieldbusses, Ethernet-based networks and wireless networks.The worldwide leaders within the automation domain with respect to the number of installed Fieldbus nodes are nodes) and Interbus (about 7 million nodes). A good commercial position is also Fieldbus. Fieldbus technology industrial automation, and fulfills the current technical requirements of local industrial communications at the field level of an enterprise.HART and Foundation Fieldbus this diagnostic capability to the process surrounding the instrument. As this trend continues, we will benefit from predictive intelligence. We will know more about the of potential problems and profit-draining inefficiencies. We will move from abnormal situation management to abnormal situation prevention.The increased data transfer needs of the currently popular office network technology – Ethernet-based networks – into industrialenvironments. Several organizations (e.g. IAONA (Industrial Automation Networking Alliance)) are promoting the use of Ethernet in industrial automation. In these applications, the fieldbus standards also include Ethernet-based networks, which implement the Ethernet protocol in low layers. The main development area is the real-time requirements of these networks. Currently, the working group IEC (International Electrotechnical Commission) WG11 is refining the RTE requirements. The Ethernet-based industrial networks included in the IEC 61784 standard are: EthernetIP, Profinet, Interbus, VnetIP, TCnet, EtherCAT, Powerlink, Modbus TCP and Sercos III.In the same way as for Ethernet, the wireless architectures , 2000) and the network currently under development IEEE 802.15.4ZigBee (IEEE, 2003).Wireless communication the process industry. The technology the production floor can remain in contact with the control centre. Isolated instrumentation, for example pump stations located at remote sites in the mountains, can be integrated into the automation strategy. Wireless technology also offers the advantage of flexibility. Ease of use,visualization, parametrization, and diagnostics through remote links are important considerations.3.1.2. High-layer data specificationsThe communication part of an automation device might order to manage these different types of data, the communication stack defines of the information sources and to the specification of the product data and safety and security data.The information standards for process operation and maintenance are driven by OpenO&M Initiative joint working groups, mainly representing three industrial organizations: MIMOSA (for the asset management related information standards), the OPC Foundation (for data transport standards) and ISA's SP95 (for Enterprise-Control System Integration Standards Committee). One of the most strongly established standards, the OPC, also enables the use of state of the art technologies such as web services, the ability to provide secure data exchange, and the use of encapsulated data with eXtensible Markup Language (XML). On the other Fieldbus) of field devices.3.2. Integration of production and business operationsPlants in the different process industry fields must be seen as production systems: their elements are the process (material transformation), inbound logistics (material transport), the plant (physical shell), automation (automatic operation) and organization (manual operation, supervision, management). Operation is a collaborative process of this production system.Optimization means the best allocation of functions to these components of the production system. This integrated approach is increasingly being expanded to production networks representing complete value-creating production chains. Suppliers and customers are often included in this approach.Virtually seamless of information, communications and automation technology throughout the whole organization is thus needed in order to address the complexity of today's processes. The buzzword in the industry is seamless communications. Manufacturing Execution Systems (MES), which are normally positioned between the Enterprise Resource Planning (ERP) and control system levels, can be used to optimize a business process on the shop floor, improve product quality, increase process reliability and reduce compliance and validation efforts. The well-known production control (MES) systems in the process industriesinclude ABB industrial IT production Planning, Honeywell Experion PKS-Optivision, Metso DNA MES, Tietoenator TIPS and Siemens Simatic IT-Systems. The main modules of the ERP systems are Master Production Schedule, Material Requirements Planning, Logistics and Customer Service Management. The market leader of the ERP systems is the German SAP AG. i2 Technolgies, and ASP AG APO systems are correspondingly the most common APS systems on the market for supply chain management. Plant optimization, accompanied by increased integration of automation systems with the information systems of the production site and the enterprise level, is justifiable also expected to be the main objective of the process automation in these enterprises in the near future.4. Recent accomplishments and future application trends in process automation4.1. Process control and MPCModel predictive control in the continuous process industry, and now covers over 90% of industrial implementations of multivariable control. One reason for its success is its ability to of MPC controlapplication was presented by Richalet, and the developed software was called IDCOM. The dynamic matrix control (DMC) algorithm also represented the first generation of MPC technology and was developed by Shell Oil engineers.A successful industrial controller for the process industries must maintain the system as close as possible to the constraints. The second generation MPC algorithm, like QDMC, provided a systematic way to implement these input and output constraints, but there was no clear way to MPC algorithms distinguished between several levels of constraints ( infeasible solution, addressed the issues resulting from a control structure that changes in real-time, provided a richer set of feedback options, and allowed for a wider range of process dynamics (stable, integrating and unstable) and controller specifications. The increased competition and mergers of several MPC vendors fourth generation MPC products: RMPCT offered by Honeywell, and DMC-plus offered by Aspen Technology with features such as multiple optimization levels to address prioritized control objectives, additional flexibility in thesteady-state target optimization including QP and economic objectives, direct consideration of model uncertainty (robust control design), andimproved identification technology based on prediction error methods and sub-space methods.Thousands of MPC applications reported in a wide variety of application areas. Most of them in refining, but a significant number of applications can also be found in the petrochemical and chemical sectors. Significant growth areas include the pulp and paper and food processing industries. The first multivariable MPC technology to cover the entire papermaking line published . The largest number of nonlinear MPC applications encompass chemicals, polymers and air and gas processing, The size and scope of NMPC applications are typically much smaller than those of linear MPC applications.Major developments in the process control community in general aiming at contributions to systems and control theory are expected, e.g. in nonlinear optimal control, combined state and parameter estimation for nonlinear systems, robustness analysis and robust synthesis methods for nonlinear systems, spatial decomposition, decentralization and of large-scale nonlinear network-like processes and future trends in process control see （Dochain.2006).4.2. Applications of AI methodsMost of the applications of the AI methods in the process industries designed for unit processes in the beginning of the production chain, especially in pulping, mineral and metal processing. A typical feature of these processes is the difficulties involved in constructing detailed mechanistic models. Increasing international competition is forcing the process industry to be more efficient and to emphasize the importance of the be found in the area of quality control of the end products, where a small improvement in control can give a considerable competitive edge to the enterprise compared to its competitors.The importance of artificial intelligence techniques in real-time process control is emphasized in many of the published articles, and the MM processes especially are reported to benefit from the application of AI techniques.4.3. Process monitoring and fault diagnosisMonitoring the quality of the product online and predictingpreventing process disturbances are the key issues in producing chain, and thereby improving the efficiency. Operational safety of processes is ofimportance and therefore should be the first objective of process control. Problems caused by operational faults range from increased operational costs to forced shutdown of processes. The increased complexity and the degree of integration of modern chemical plants means that the potential economic loss is greater and the diagnosis of fault locations more difficult. It is estimated that inadequate management of abnormal process situations causes annual losses of US$ 20 billion in the petrochemical industry in the USA. Consequently, managing disturbances is seen as the next challenge in developing and implementing new control systems.Venkatasubramanian published a review of monitoring methods, especially those applied in the field of chemical processes. They classified the methods according to the form of process knowledge used. One category is based on process models, and includes both qualitative causal models and quantitative methods. The other category is based on process reviewed,e.g. by Komulainen.4.4. The new extended role of operators and operator-support systemsIn recent years the process industry and information technologies in order to remain competitive. This where massive amounts of measurement data are now available. At the same time, the technology the operator's work are the management of critical situations and decision making in a range of problem situations. In critical situations, the decisions must be made quickly and therefore all the relevant information must be readily and easily accessible.A study to analyse the features and use of the operator's support systems at two Finnish paper mills carried out . Automation systems at the plant include a variety of solutions provided by different vendors and which in use for very different periods of time. The production lines management systems: process control, machine control, quality control, web inspection, process analysis, production planning, and condition and runnability monitoring systems. One planning systems. According to the study, only 30–40% of the existing operator-support systems currently installed at production sites were actually used due to the usability problems and operators’ poor knowledge of the systems. The main reasons for infrequent use of process operation support systems are presented in .Most of the information affecting the decision-making process during the critical situations is so called tacit knowledge. Ensuring that this tacit knowledge is retained as large groups of older operators retire, especially in Europe, will be an additional challenge for the process industry. In the future, the efficient management of knowledge supporting the decision making will thus become more and more important. One clear trend in the development of process control systems is to include features for knowledge and information management. The knowledge and performance support systems will be integrated as a part of process control systems, making it an optimal solution to support operations in the whole production line.The study of interactions between and machines is an important aspect in the adoption of control technologies, and involves both technical issues and social implications. Human machine studies consider all the conditions where , modeling and evaluation of machine systems (HMS), which include decision-making and cognitive processes, modeling of performance, real and virtual environments, design methodology, task allocation-sharing and job design, intelligent interfaces, operator support, work organization, and selection and。

毕业设计(论文)英文翻译题目专业班级姓名学号指导教师职称200年月日The Restructuring of OrganizationsThroughout the 1990s, mergers and acquisitions a major source of corporate restructuring, affecting millions of workers and their families. This form of restructuring often is accompanied by downsizing. Downsizing is the process of reducing the size of a firm by laying off or retiring workers early. The primary objectives of downsizing are similar in U.S. companies and those in other countries:●cutting cost,●spurring decentralization and speeding up decision making,●cutting bureaucracy and eliminating layers of especially they did five years ago. One consequence of this trend is that today’s managers supervise larger numbers of subordinates who report directly to them. In 1990, only about 20 percent of managers supervise twelve or more people and 54 percent supervised six or fewer.Because of downsizing, first-line managers quality control, resources, and industrial engineering provide guidance and support. First-line managers participate in the production processes and other line activities and coordinate the efforts of the specialists as part of their jobs. At the same time, the workers that first-line managers supervise are less willing to put up with authoritarian management. Employees want their jobs to be more creative, challenging, fun, and satisfying and want to participate in decisions affecting their work. Thus self-managed work teams that bring workers and first-line managers together to make joint decisions to improve the way they do their jobs offer a solution to both supervision and employee expectation problems. When you ’t always the case. Sometimes entire divisions of a firm are simply spun off from the main company to operate on their own as new, autonomous companies. The firm that spun them off may then become one of their most important customers or suppliers. That AT&T “downsized” the old Bell Labs unit, which is now known as Lucent Technologies. Now, rather than - return is free to enter into contracts with companies other than AT&T. this method of downsizing is usually called outsourcing.Outsourcing means letting other organizations perform a needed service andor manufacture needed parts or products. Nike outsources the production of its shoes to low-cost plants in South Korea and China and imports the shoes for distribution in North America. These same plants also ship shoes to Europe and other parts of Asia for distribution. Thus today’s managers face a new challenge: t o plan, organize, lead, and control a company that may as a modular corporation. The modularcorporation is most is most common in three industries: apparel, auto manufacturing, and electronics. The most commonly out-sourced function is production. By out sourcing production, a company can switch supplier best suited to a customer’s needs.Decisions about what to outsource and what to keep in- to contract production to another company is a sound business decision to contract production to another company is a sound business decision, at least for U.S. manufacturers. It appears to the unit cost of production by relieving the company of some overhead, and it frees the company to allocate scarce resources to activities for which the company examples of modular companies are Dell Computer, Nike, Liz Claiborne fashions, and ship designer Cyrix.As organizations downsize and outsource functions, they become flatter and smaller. Unlike the behemoths of the past, the new, smaller firms are less like autonomous fortresses and more like nodes in a net work of complex relationships. This approach, called the network form of organization, involves establishing strategic alliances among several entities.In Japan, cross-ownership and alliances among firms－called keiretsu－both foreign and U.S. auto parts producers. It also owns 49 percent of Hertz, the car rental company that is also a major customer. Other alliances include involvement in several research consortia. In the airline industry, a common type of alliance is between an airline and an airframe manufacture. For example, Delta recently agreed to buy all its aircraft from Boeing. Boeing Airlines. Through these agreements, Boeing guarantees that it will be able to sell specified models of its aircraft and begin to adapt their operations to the models they will be flying in the future. Thus both sides expect to reap benefits from these arrangements for many years.Networks forms of organizations are prevalent in access to the universities and in small, creative organizations. For example, the U.S. biotechnology industry is characterized by network of relationships between new biotechnology firms dedicated to research and new products development and established firms in industries that can use these new products, such as pharmaceuticals. In return for sharing technical information with the larger firms, the smaller firms gain access to their partners’ resources for product testing, marketing, and distribution. Big pharmaceutical firms such as Merk or Eli Lily gain from such partnerships because the smaller firms typically development cycle in the larger firms.Being competitive increasingly requires establishing and managing strategic alliances with other firms. In a strategic alliance, two or more firms agree to cooperate in a venture that is expected to benefit both firms.企业重组整个20世纪90年代中，合并和收购一直是企业重组的主要起源，影响着千百万的工人和他们的家庭。

（本科毕业设计外文文献翻译学校代码： 10128学 号：题 目：Shear wall structural design of high-level framework 学生姓名： 学 院：土木工程学院 系 别：建筑工程系 专 业：土木工程专业（建筑工程方向） 班 级：土木08-（5）班 指导教师： (副教授)Shear wall structural design of high-level frameworkWu JichengAbstract: In this paper the basic concepts of manpower from the frame shear wall structure, analysis of the structural design of the content of the frame shear wall, including the seismic wall shear span ratio design, and a concrete structure in the most commonly used frame shear wall structure the design of points to note.Keywords: concrete; frame shear wall structure; high-rise buildings The wall is a modern high-rise buildings is an important building content, the size of the frame shear wall must comply with building regulations. The principle is that the larger size but the thickness must be smaller geometric features should be presented to the plate, the force is close to cylindrical. The wall shear wall structure is a flat component. Its exposure to the force along the plane level of the role of shear and moment, must also take into account the vertical pressure. Operate under the combined action of bending moments and axial force and shear force by the cantilever deep beam under the action of the force level to look into the bottom mounted on the basis of. Shear wall is divided into a whole wall and the associated shear wall in the actual project, a whole wall for example, such as general housing construction in the gable or fish bone structure film walls and small openings wall. Coupled Shear walls are connected by the coupling beam shear wall. But because thegeneral coupling beam stiffness is less than the wall stiffness of the limbs, so. Wall limb alone is obvious. The central beam of the inflection point to pay attention to the wall pressure than the limits of the limb axis. Will form a short wide beams, wide column wall limb shear wall openings too large component at both ends with just the domain of variable cross-section rod in the internal forces under the action of many Wall limb inflection point Therefore, the calculations and construction shouldAccording to approximate the frame structure to consider. The design of shear walls should be based on the characteristics of a variety of wall itself, and different mechanical characteristics and requirements, wall of the internal force distribution and failure modes of specific and comprehensive consideration of the design reinforcement and structural measures. Frame shear wall structure design is to consider the structure of the overall analysis for both directions of the horizontal and vertical effects. Obtain the internal force is required in accordance with the bias or partial pull normal section force calculation. The wall structure of the frame shear wall structural design of the content frame high-rise buildings, in the actual project in the use of the most seismic walls have sufficient quantities to meet the limits of the layer displacement, the location is relatively flexible. Seismic wall for continuous layout, full-length through. Should be designed to avoid the wall mutations in limb length and alignment is not up and down the hole. The same time. The inside of thehole margins column should not be less than 300mm in order to guarantee the length of the column as the edge of the component and constraint edge components. The bi-directional lateral force resisting structural form of vertical and horizontal wall connected. Each other as the affinity of the shear wall. For one, two seismic frame shear walls, even beam high ratio should not greater than 5 and a height of not less than 400mm. Midline column and beams, wall midline should not be greater than the column width of 1/4, in order to reduce the torsional effect of the seismic action on the column. Otherwise can be taken to strengthen the stirrup ratio in the column to make up. If the shear wall shear span than the big two. Even the beam cross-height ratio greater than 2.5, then the design pressure of the cut should not make a big 0.2. However, if the shear wall shear span ratio of less than two coupling beams span of less than 2.5, then the shear compression ratio is not greater than 0.15. The other hand, the bottom of the frame shear wall structure to enhance the design should not be less than 200mm and not less than storey 1/16, other parts should not be less than 160mm and not less than storey 1/20. Around the wall of the frame shear wall structure should be set to the beam or dark beam and the side column to form a border. Horizontal distribution of shear walls can from the shear effect, this design when building higher longer or frame structure reinforcement should be appropriately increased, especially in the sensitive parts of the beam position or temperature,stiffness change is best appropriately increased, then consideration should be given to the wall vertical reinforcement, because it is mainly from the bending effect, and take in some multi-storey shear wall structure reinforced reinforcement rate - like less constrained edge of the component or components reinforcement of the edge component. References: [1 sad Hayashi, He Yaming. On the short shear wall high-rise building design [J].Keyuan, 2008, (O2).高层框架剪力墙结构设计吴继成摘要: 本文从框架剪力墙结构设计的基本概念人手，分析了框架剪力墙的构造设计内容，包括抗震墙、剪跨比等的设计，并出混凝土结构中最常用的框架剪力墙结构设计的注意要点。

Computer networking summarizeNetworking can be defined as the linking of people, resources and ideas. Networking occurs via casual encounters, meetings, telephone conversation, and the printed words. Now the computer networking provide beings with new networking capabilities. Computer network are important for services because service tasks are information intensive. During the is transmitted between clients, coworkers, management, funding sources, and policy makers. Tools with rapidly speed up communication will dramatically affect services.Computer network growing explosively. Two decades ago, few people essential part of our infrastructure. Networking is used in every aspect of business, including advertising, production, shipping, planning, bulling, and accounting. Consequently, most corporations in on-line libraries around the world. Federal, state, and local government offices use networks, as do military organizations. In short, computer networks are everywhere.The growth in networking economic impact as well. An entire industry jobs for people with more networking expertise. Companies need workers to plan, acquire, install, operate, and manage the addition computer programming is no longer restricted to individual computers; programmers are expected to design and implement application software that can communicate with software on other computers.Computer networks link computers by communication lines and software protocols, allowing data to be exchanged rapidly and reliably. Traditionally, they split between wide area networks (WANs) and local area networks (LANs). A WAN is a network connected over long-distance telephone lines, and a LAN is a localized network usually in one building or a group of buildings close together. The distinction, computers. Today networks carry e-mail, provide access to public databases, and are beginning to be used for distributed systems. Networks also allow users in one locality to share expensive resources, such as printers and disk-systems.Distributed computer systems are built using networked computers that cooperate to perform tasks. In this environment, each part of the networked system does what it is best at. The of a personal computer or workstation provides a good user interface. The mainframe, on the other the results to the users. In a distributed environment, a user might use in a special language (e. g. Structured Query Language-SQL), to the mainframe, which then parrrses the query, returning the user only the data requested. The user might then use the data. By passing back the user’s PC only the specific information requested, network traffic is reduced. If the whole file were transmitted, the PC would then of one network to access the resources on a different type of network. For example, a gateway could be used to connect a local area network of personal computers to a mainframe computer network. For example, if a company this example, using a bridge makes more sense than joining all thepersonal computers together in one large network because the individual departments only occasionally need to access information on the other network.Computer networking technology can be divided into four major aspects.The first is the data transmission. It explains that at the lowest level electrical signals traveling across wires are used to carry information, and shows be encoded using electrical signals.The second focuses on packet transmission. It explains why computer network use packets, and shows . LANs and WANs discussed above are two basic network.The third covers internetworking—the important idea that allows system, and TCPIP, the protocol technology used in global internet.The fourth explains networking applications. It focuses on , and programs provide services such as electronic mail and Web browsing.Continued growth of the global Internet is one of most interesting and exciting phenomena in networking. A decade ago, the Internet was a research project that involved a few dozen sites. Today, the Internet into a production communication system that reaches millions of people in almost all countries on all continents around the world. In the United States, the Internet connects most corporations, colleges and universities, as well as federal, state, and local government offices. It will soon reach most elementary,junior, and senior addition, many private residences can reach the Internet through a dialup telephone connection. Evidence of the Internet’s impact on society can be seen in advertisements, in magazines and on television, which often contain a reference to an Internet Web site that provide additional information about the advertiser’s products and services.A large organization with diverse networking requirements needs multiple physical networks. More important, if the organization chooses the type network that is best for each task, the organization will network can only communicate with other computers attached to same network. The problem became evident in the 1970s as large organizations began to acquire multiple networks. Each network in the organizations formed an island. In many early installations, each computer attached to a single network and employees employees was given access to multiple svreens and keyboards, and the employee was forced to move form one computer to another to send a massage across the appropriate network. Users are neither satisfied nor productive when they must use a separate computer. Consequently, most modern computer communication syetem allow communication between any two computers analogous to the way a telephone system provides communication between any two telephones. Known as universal service, the concept is a fundamental part of networking. With universal service, a user on any computer in any part of an organization can send messages or data to any other users. Furthermore, a user does not need to change computer systems whenchanging tasks—all information is available to all computers. As a result, users are more productive.The basic component used to commect organization to choose network technologies appropriate for each need, and to use routers to connect all networks into a single internet.The goal of internetworking is universal service across an internet, routers must agree to forward information from a source on one network to a specified destination on another. The task is complex because frame formats and addressing schemes used by underlying networks can differ. As s resulrt, protocol software is needed on computers and routers make universal service possible. Internet protocols overcome differences in frame formats and physical addresses to make communication pissible among networks that use different technologies.In general, internet software provides the appeatrance of a single, seamless communication system to which many computers attach. The syetem offers universal service :each computer is assigned an address, and any computer can send a packet to any other computer. Furthermore, internet protocol software —neither users nor application programs are a ware of the underlying physical networks or the routers that connect them.We say that an internet is a virtual network system because the communication system is an abstraction. That is, although a combination of of a uniform network syetem, no such network exists.Research on internetworking modern networking. In fact,internet techmology . Most large organizations already use internetworking as primary computer communication mechanism. Smaller organizations and individuals are beginning to do so as well. More inportant, the TCPIP technology computers in schools, commercial organications, government, military sites and individuals in almost all countries around the world.电脑网络简述网络可被定义为人、资源和思想的联接。