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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Unit Five,Technology,Computer Networks,1/13,In general a computer network,as we know tod,a,y,may be said to have,gotten its start with,the,ARPANET,development in the late 1960s and early 1970s.,The initial ARPANET design had a definite structure of,network architecture,and introdu,ced,another key concept:,protocol layering,.,始于,ARPANET,：,Advanced Research Project Agency Network阿帕网络,网络体系结构，网络构架,prutkl,协议,leiri,分层,TCP/IP protocol：Transmission Control Protocol/Internet Protocol,传输控制/网络通讯协议,2/13,Much of our present knowledge about network is a direct result of the ARPANET project.,The,ISO,in the late 1970s,formulated a,refer,ence,model to provide a common basis for the coordination of standards developments and to allow existing and evolving standards activities to be placed into,perspective,with one another.,ISO,国际标准化组织（International Standardization Organization）,参考,pspektiv,透视；透视,3/13,The ultimate aim was to allow an application process in any computer that supported the applicable standards to freely communicate with an application process in any other computer supporting the same standard,irrespective of,its origin of manufacture.,This model,was termed,the,ISO Reference Model for Open System Interconnection,.,不考虑，不顾,ISO开放系统互联参考模型,4/13,It should be stressed,however,that this model,is,not,concerned with,specific applications of computer communication networks.,Rather,it is concerned with the structuring of the communication,software,that is needed to provide a reliable,data,transparent,communication service,(which is independent of any specific manufactures equipment or conventions)to support a wide range of,applications.,和.相关，包括,透明,通信业务,5/13,A network is a series of points interconnected by communication lines,located at the points are computer,switching devices,and/or,user terminals,.,A typical network includes the following components:,host computer,s,node,s,terminal controllers,and terminals.,切换设备,用户终端,节点，网点,6/13,The two basic types of networks are,local-area(LAN),and,wide-area network(WAN),.,A local-area network is two or more computers directly linked within a small area such as a,ro,om,building,or group of closely placed buildings.,A wide-area network is two or more computers that are,geographically,dispersed and linked by communication facilities such as the telephone,system or,microwave relays,.,微波接力,局域网,广域网,7/13,The benefit of network is that it can transmit information rapidly and easily among widely separated people;people can share hardware and software resources on the network;a computer network can also provide high reliability by having alternative source of supply.,8/13,There are four basic building blocks to the Internet,Host,s,Router,s,Client,s and Connections.,In most cases,your computer falls under the“Client”category.,Data is sent from your computer in the form of a“,packet,”.,主机,路由器,客户端,数据包,9/13,You can liken a packet to be similar to an,envelop,it surrounds your data and contains both a return and destination address.,Your computer handles the packets for you,its all done in the,background,without your knowledge.,A Router is a special device.,后台,10/13,Basically routers sit at key points on the Internet and act like,traffic cop,s,at an,intersection,of hundreds of streets.,The Router basically reads the destination address on the packets being sent by your computer and then forwards the packet to the appropriate destination.,交通警察,交叉路口,11/13,In some cases your data will travel through several routers before reaching its ultimate destination.,ConnectionsThis is all term describing how you can connect from one point to another point.,12/13,As an,end user,your only concern is that the connection is good,but for a network engineer,this can mean several different types of technologies,including:Phone Lines,Fiber Optics,ISDN,Frame Relay,Satellite Links.,终端用户,光纤,帧中继,13/13,
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