Unit Six

Network

1.Passage One.

Foundation of Network

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.

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.

Pic 6.1 network

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

（ 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.

（ 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.

（ 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.

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

● 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.

Pic 6.2 client-server

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.

Macro viruses This type of set-up is not a client-server stru

cture 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.

Pic 6.3 peer to peer network

（ 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.

（ 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.

2.Types of Network

There are three types of network by the area of use.

（ 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.

Prevention （ 2 ） Metropolitan Area Network （ MA

N ） 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 ） .

（ 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.

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

The End