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1、教学目标 教学内容,Unit 4 Network Technique,教学目标,了解计算机网络的发展史 理解网络安全的相关理论 了解虚拟化技术 掌握电子商务的相关技术 了解目前已经广泛使用的局域网技术,教学内容,Text 1 Evolution of computer networks Text 2 Network Security Text 3 Virtualization Technology Text 4 Electronic Commerce Text 5 LAN-Cruising,Text 1 Evolution of computer networks,Main Contents
2、Words and Expressions Exercises,The term network can mean many different things. It can imply an interconnection of railway tracks for the rail network; highways and streets for transportation networks; telephone lines and switching centers for the phone network; coaxial lines for the cable televisi
3、on network; fiber lines for cable communications networks; or the interconnection of service centers, businesses, and so on to form a network. All of these configurations refer to the means to tie together various resources so that they may operate as a group, realizing the benefits of numbers, shar
4、ing, and communications in such a group.,Text 1 Evolution of computer networks,Text 1 Evolution of computer networks,In computer systems terminology of a network is a combination of interconnected computing equipment and programs used for moving information (and computations) between points (nodes)
5、in the network where it may be generated, processed, stored, or used in whatever manner is deemed appropriate. The interconnection may take on many forms, such as dedicated links, shared links, telephone lines, microwave links, and satellite links. Networks in this sense form a loose coalition of de
6、vices that share information. This was one of the first uses of a network, although it was not the last. Users found that the network could offer more than just information sharing; it could offer other services for remote job execution and ultimately distributed computing.,Text 1 Evolution of compu
7、ter networks,The earliest concept of a network was of a loose binding together of devices or resources for sharing. An early computer network that exhibited these traits was the ARPANET. ARPANET was first brought on-line in 1969 as a research tool to investigate long-haul network issues and to provi
8、de a tool for research and development solutions. It has evolved into the Internet, connecting millions of computers over local area networks, metropolitan area networks, and other wide area networks. ARPANET provided the vehicle for early research into communications protocols dealing with congesti
9、on, control, routing, addressing, remote invocation, distributed computing, distributed operating systems and services, and many other areas.,The reasons for using networks such as ARPANET were to provide greater availability and access to a wider range of devices. Early applications of computers de
10、alt with performing engineering tasks and major data processing functions. As the technology of computers changed, and as researchers and users alike added more and more applications, information access and manipulation took on greater emphasis. Earlier networks provided the necessary information ex
11、change services but were limited to basically just this service. The information availability stimulated more imaginative uses of this information. As this occurred and the technology of networks improved, new applications arose. These new applications not only used information exchange but also rem
12、ote job execution. It began simply as sending a batch job down the link to a less busy host, having the job completed there, and then shipping the results back to the originator.,Text 1 Evolution of computer networks,Text 1 Evolution of computer networks,This sufficed for a while, but it still did n
13、ot provide the real-time or interactive environments that users were beginning to become accustomed to, including more advanced protocols and network operating systems to provide further services for remote job invocation and synchronization. The era of the local area network was coming. The wide ar
14、ea networks biggest shortfall was in throughput or turnaround time for jobs and interprocessor communications. Because of the wide distances, delays of seconds were commonplace and caused added overhead in performing otherwise simple tasks. Network designers saw the need to provide another link in t
15、he network: the local area network.,Local area networks began showing up on the networking landscape in the early to mid 1970s as mostly research activities in universities and government laboratories. It was not until Ethernet was released in the mid 1970s that LANs became more widely available. Si
16、nce that time, numerous LAN designs have been produced to fit an extremely wide spectrum of user requirements-for example, the fiber ring. Additionally, standards have evolved, providing basic LAN topologies and their services to a greater number of users.,Text 1 Evolution of computer networks,Text 1 Evolution of computer networks,Local area networks are finding their way into all aspects of modern society. We find them in our homes through cable modems and phone modems, automobiles via wireles
