跪求一遍关于计算机网络的英语作文..字数在1200以上的..

跪求一遍关于计算机网络的英语作文..字数在1200以上的..

Computer networks
Now every almost have computers,and computer good does have its downside - it depends on how you use.If you want to ask me:I on the computer do what,I can tell you,I will do a lot of things in the computer.May first and have out-of-town relatives chat,then can check information,listening to music,watching movies,paint...My favorite on the computer music and watching movies,because it very relaxing my mood.But the most people used compter to surf the internet.Now Let us know about the computer network
Introduction
Computer networks,the wide spread sharing of information among groups of computers and their users,are a central part of the information age.The popular adoption of the personal computer(PC)
and the local area network (LAN) during the 1980s has led to the capacity to access information on a distant database;download an application from overseas;send a message to a friend country;and share files with a colleague-all from a personal computer.
The network that allow all this to be done so easily are sophisticated and complex entities.They rely for their effectiveness on many cooperating computers.The design and deployment of the wordwide computer network can be viewed as one of the great technological wonders of recent decades.Nowadays Intemet is very popular all over the world,especially in some big cities.Do you know when the Intemet was first established?Built in 1960s,the Internet was a crude network of a few computers which shared information.If one of the computers broke down,the whole networks would be unable to work,causing continual problems.At first,just the government had access to the Internet,using it for communications among different branches.However,by 1970s the Internet had been used in universities,banks,and hospitals.At the beginning of 1990s computers became affordable for common people and this affordability increased the use of the Internet by people,It is said that each day tens of millions of people log off,making it the most important part of people's life.
Local Area Network
One of the most dramatic events in computer networking has been the introduction and rapid growth of local area network(LAN) as a way to standardize the system of linking computers used in office systems.As the name suggests,this is a means of connecting a number of computing elements together.At the simplest level,a LAN provides no more more than a shared medium (such as a coaxial cable to which all computers and printers are connected) along with a set of rules that govern the access to that medium.The most widely used LAN,Ethernet,used a mechanism called Carrier Sense Multiple Access-Collosion Detect(CSMA-CD).This means that each connected device can only use the cable when it has established that each connected device is using it.If there is contention,the device looking for a connection backs off and tries again later.The Ethernet transfers data at 10M bits/sec,which is fast enough to make the distance between devices insignificant.They appeat to be connected directly to their destination.
There are many different layouts(such as bus ,star,ring,see Figure 6A-2)and a number of different access protocols for LANs.Despire this variety,all LANs share the feature that they are limited in range (typically they cover one building) and are fast enough to make the connecting network invisible to the devices that use it.
In addition to providing shared access,modern LANs can also give users a wide range of sophisticated facilities.Managenment software packages are available to control the way in which devices are configured on the local area network (LAN),how users are administered,and how network resources are controlled.A widely adopted structure o local network is to have a number of servers that are available to a (usuallu much greater) nember of clients.The former,usually powerful computers,provide service such as print control,file sharing,and mail to the latter,which are usually personal computers.
Routers and brideges
The facilities on most local area network (LAN) are very powerful.Most organizatonns do not wish to have small isolated islands of computing facilities.They usually want to extend facilities over a wider area so that groups can wok wtthout having to be located.Routers and bridges arespecialized devices that allow two or more local area network (LAN) to be connected.The bridges is the more basic device and can only connect local area network (LAN) of the same type.The router is a more intelligent component that can interconnent many different types of computer network.
Many large companies have corporate adta network that are founded on a collection of local area network (LAN) and routers.From the user鈥檚 point of view,this arrangement provides them with a physically diverse network that looks like one coherent resource.
Wide Area Networks
At some point,it becomes impractical to extend a local area network (LAN) any further.Physical limitation sometimes drives this,but more often than not there are more concenient or cheaper ways to extend a computer network.Two major components in most real computer networks are the public telephone and data networks.These provide long-distance links that extend a local area network (LAN) into a wide area network (WAN).Nearly all of the national network operators offer services for the interconnection of computer networks.These services range from simple,low speed data links that work over the public telephone network to sophisticaied high speed data services that are ideally suited to the interconnection of LANs.These high speed data services are usually referred to as broadband connection.It is anticiopated that they will provide the necessary links between LANs that make what is called the information superhighway a reality.