1. Unit Six Network 1.Passage One. Foundation of Network

2. Training target: In this part ， our target is to train your reading comprehension. We have made the flexible sentences strong black and marked the subject ， predicate and object of them. Try to grasp the main idea of these sentences.

3. Text. 1.Definitions （ 1 ） Network: Two or more computers which are linked together and which share resources like data ， programs and peripherals （ like printers ） are network. Network has three essential components: a communication medium （ telephone wire ）， an interface between the computer and the medium ， and software to send and receive information on the interface.Pic6.1shows an example of network.

4. Pic 6.1 network

5.  （ 2 ） Network node: Each computer or shared device （ like a printer ） found on the network is known as a network node.

6.  （ 3 ） Workstation: All of the user computers connected to a network are called workstations. A typical workstation is a computer that is configured with a network interface card ， network software ， and the appropriate cables. Workstations do not necessarily need floppy disk drives because files can be saved on the file server. Almost any computer can serve as a network workstation.

7. （ 4 ） Server: A server is a special computer on a network that provides & controls services （ resources ） for other computers （ clients ） on the network to use. Simply stated ， a server provides service. There are many types of servers available: file server ， print server ， web server and so on. Most servers provide some system of security and management so that only selected users can access （ or modify ） the services/resources that are controlled by those servers.

8. （ 5 ） Protocol: A network protocol is a formal set of rules ， conventions and data structure that governs how computers exchange information over a network. In other words ， protocol is a standard procedure and format that two data communication devices must understand ， accept and use to be able to talk to each other.

9.  （ 6 ） Network architecture: A network architecture can be described in two ways: client-server and peer to peer.

10.  ● Client-server  Client-server （ Pic6.2 ） network is a network comprised of several workstations and one or more servers. Clients （ users ） login to the server and gain access to their files. In client-server network ， an administrator can control the privileges of each user. Files are stored centrally ， simplifying data backup. Security policies are implemented that protect users’ information. Client-server architecture has become the de-facto standard in small ， medium ， and large businesses because of the advantages it offers.

11. Pic 6.2 client-server

12. Peer to Peer Network  This is a type of network where all computers on the network have potential to share resources that they have control over.

13. Macro viruses  This type of set-up is not a client-server structure in the strict sense because the servers are not dedicated machines. All computers on the network can potentially act as both a client and a server. Because of this fact ， there is no central control of the network and therefore this type of network structure is considered to be less secure and harder to manage than the client-server architecture. Pic 6.3 shows an example of peer to peer network.

14. Pic 6.3 peer to peer network

15.  （ 7 ） Network clients: These are general users of the network. Clients have limited access to the resources found on the network. This access is controlled by the network administrator.

16.  （ 8 ） Network administrator: The administrator is the user （ or a group of users ） who has control over how the other users （ network clients ） access and use the network resources. Network administrators manage the use of resources and services used on the network.

17.  2.Types of Network There are three types of network by the area of use.

18.  （ 1 ） Local Area Network （ LAN ） A typical LAN spans a small area like a single building or a small campus and operates between 10 Mbps and 2 Gbps. Because LAN technologies cover short distance ， they provide the highest speed connections among computers.

19. Prevention  （ 2 ） Metropolitan Area Network （ MAN ） MAN is a bigger version of LAN in a city ， it is smaller than a WAN but larger than a LAN.MAN is a public high-speed network ， and runs at a speed of 100 Mbps or even faster ， capable of voice and data transmission over a distance of up to80kilometers （ 50miles ）.

20.  （ 3 ） Wide Area Network （ WAN ） WAN is sometimes called long haul network ， provide communication over large distance. It can span more than one geographical area ， often a country or a continent. Usually WAN operates at slower speed than LAN ， and have much greater delay between connections. Typical speed for a WAN ranges from 56 kbps to155 Mbps.

21. Key words  network 网络，网状物，广播网  interface 接口  workstation 工作站 server 服务器  protocol 协议  LAN 局域网 MAN 城域网 WAN 广域网  peripheral 外围的，外围设备  network node 网络节点  network architecture 网络体系结构  peer to peer network 对等网  network client 网络客户  network administrator 网络管理员  client-server 客户 - 服务器模式

22.  The End