On LAN

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　 LAN components

　　 Including network hardware and network software . Network hardware mainly includes network server 、 The workstation 、 peripherals ) etc. , If you want to make network interconnection , You also need a bridge 、 Router 、 gateway , And interconnection lines between networks . Network software network interface card 、 Transmission medium , Depending on the transmission medium and Topology , You also need a hub (HUB)、 Concentrator (concentrato Mainly network operating system and network application software that meet specific application requirements .

　　 In order to give a complete picture of LAN The definition of , There must be two ways : One is functional definition , The other is a technical definition . The former will LAN Defined as a group of desktop computers and other devices , Not far from each other in physical address , Systems interconnected in a manner that allows users to communicate with each other and share computing resources such as printers and storage devices . This definition applies to... In an office environment LAN、 Used in factories and research institutions LAN.

　　 Just LAN In terms of the technical definition of , It is defined as a specific type of transmission media ( Such as cable 、 Optical cable and wireless media ) And network adapters ( Also known as network card ) Interconnected computers , A network system monitored by a network operating system .

　　 The difference between functional and technical definitions is obvious , Functional definitions emphasize external behavior and services ; The technical definition emphasizes the composition of LAN The material basis and composition method required .

　　 LAN (LAN) The name itself implies the locality of the geographical scope of the network . Due to the limitations of small geographical scope . Due to the small geographical scope ,LAN Usually better than Wan (WAN) With high transmission rate , for example , at present LAN The transmission rate of is 10Mb/s,FDDI The transmission rate of is 100Mb/s, and WAN At present, the main line speed in China is only 64kbps or 2.048Mbps, The online rate of end users is usually 14.4kbps.

　　 Some protocols in LAN , It will be installed automatically when installing the operating system . If installing Windows 2000 or Windows 95/98 when , The system will install automatically NetBEUI Communication protocol . In the installation NetWare when , The system will install automatically IPX/SPX Communication protocol . Of the three protocols ,NetBEUI and IPX/SPX It can be used directly without setting after installation , but TCP/IP Go through the necessary settings . Therefore, the following mainly focuses on Windows 2000 In the environment TCP/IP Agreement based , Introduce its installation 、 Setup and test methods , Related operations of protocols in other operating systems Windows 2000 Basically the same , Even simpler .

　　 stay Windows 2000 in , If... Is not installed TCP/IP Communication protocol , Can choose “ Start / Set up / Control panel / Network and dial-up connections ”, Right click “ Local connection ” choice “ attribute ” Will appear “ Local connection properties ” Dialog box , Click... In the dialog box “ install ” Button , Choose one of TCP/IP agreement , And then click “ add to ” Button . The system will ask you if you want to “DHCP The server ” Set up ? If you're in a LAN IP The address is fixed ( That's the way it is ), Can choose “ no ”. And then , The system starts copying the required files from the installation disk .

　　 LAN

　　 Select installed TCP/IP agreement , Open it “ attribute ”, Will appear “Internet agreement (TCP/IP) attribute ” The dialog . Enter the assigned... At the specified location “IP Address ” and “ Subnet mask ”, I don't know. You can ask the network administrator . It is recommended that you write down this number before installing the system , After all, it's better to ask others than yourself . If the user wants to access other Widnows 2000 Network resources , You can also do it in “ The default gateway ” Enter the address of the gateway at .

　　 When TCP/IP After the protocol is installed and set , In order to ensure its normal operation , Be sure to test before use . I suggest you use the tools and programs that come with the system ：PING command , This tool can check whether any user is connected with other users in the same network segment , Is the connection with users of other network segments normal , At the same time, you can check your IP Whether the address is the same as that of other users IP Address conflict .

　　 If the server IP The address is 190.201.2.1, If you want to test whether your machine is connected to the server , Just switch to DOS At the prompt , And type the command “PING190.201.2.1” that will do . If something like “Reply from 190.201.2.1……” The response of the , explain TCP/IP The protocol is working ; If the display is similar to “Request timed out” Information about , Explain the of both parties TCP/IP The protocol settings may be wrong , Or other connections to the network ( Such as network card 、HUB Or connection, etc ) There is a problem , Further inspection is needed .

　　 topology

　　 LAN is usually a network system distributed in a limited geographical range , Generally, the geographical range involved is only a few kilometers . LAN is very special , It has a relatively stable and standardized topology . Common LAN topologies are as follows ：

　　 Stars

　　 The network with this structure is connected by workstations in a star mode , Every node device in the network takes the middle prevention node as the center , Connect with the center through the connecting line Node connection , If a workstation needs to transmit data , It must first pass through the central node . Because in the network system with this structure , The central node is the control center , The communication between any two nodes only needs two steps at most , therefore , It can transmit fast , And the network configuration is simple 、 It's easy to build a network 、 Easy to control and manage . But this network system , Low network reliability , Poor network sharing ability , And once the central node fails, the whole network will be paralyzed .

　　 Tree form

　　 Tree structure network is a natural hierarchical structure , Also known as hierarchical centralized network . It is characterized by low network cost , Simple structure . In the network , There is no loop between any two nodes , Each link supports bidirectional transmission , also , The node expansion in the network is convenient 、 flexible , Finding the link path is relatively simple .

　　 But in this structured network system , In addition to leaf nodes and their connected links , The failure of any workstation or link will affect the normal operation of the whole network system .

　　 Bussed

　　 Bus structure network is to connect each node device with a bus . All nodes and workstations in the network transmit information through the bus . The communication connection as a bus can be a coaxial cable 、 Twisted pair , It can also be a flat cable . In the bus structure , As a necessary bus for data communication, the load energy of the bus is limited , This is determined by the physical performance of the communication media itself . therefore , The number of workstation nodes in bus structure network is limited , If the number of workstation nodes exceeds the bus load energy , You need to extend the length of the bus , And add a considerable number of additional switching parts , Make the bus load meet the capacity requirements . Bus structure, simple network 、 flexible , Good expandability . therefore , It is very convenient to insert and disassemble node equipment . in addition , Bus structure and high network reliability 、 The response speed between network nodes is fast 、 Strong ability to share resources 、 Less equipment investment 、 The cost is low 、 Easy to install and use , When a workstation node fails , It has little impact on the whole network system . therefore , Bus structure network is the most widely used network . However, because all workstation communication is through a common bus , therefore , Poor real-time performance .

　　 ring

　　 Ring structure is a closed ring structure network in which each node in the network is connected through a communication link connected end to end . The structure of ring structure network is also relatively simple , Each workstation in the system has equal status . The communication equipment and lines in the system are relatively economical .

　　 In the network, information flows in a fixed direction , There is only one path between two workstation nodes , There is no channel selection problem in the system ; The failure of a node will lead to physical paralysis . Central network , Because the loop is closed , So it's not easy to expand , The system response delay is long , And the information transmission efficiency is relatively low .

　　WAN Compare

　　 Wide area network (WAN), It's what we usually say Internet, It's a network all over the world . LAN (LAN), Compared with wan (WAN) for , It mainly refers to the computer Internet in a small range . This “ Small scale ” It can be a family , A school , A company , Or a government department .BT The public network often mentioned in 、 Extranet , Wide area network (WAN);BT Private networks are often mentioned in 、 Intranet , LAN (LAN).

　　 Every computer on the wan ( Or other network devices ) There are one or more wan IP Address ( Or the public network 、 Extranet IP Address ), Wide area network IP The address usually goes to ISP You can't apply to... Until you pay the fee , Wide area network IP The address cannot be repeated ; LAN (LAN) Every computer on the ( Or its equipment ) All have one or more LANs IP Address ( Or private network 、 Intranet IP Address ), LAN IP The address is assigned within the LAN , Different LAN's IP The address can be repeated , Will not affect each other .

　　 Wide area network (WAN、 Public network 、 Extranet ) And lan (LAN、 The private network 、 Intranet ) Computers exchange data through routers or gateways NAT( Network address translation ) Conduct . As a general rule , LAN (LAN、 The private network 、 Intranet ) External connection request initiated by internal computer , No router or gateway will block it , But the request from Wan for computer connection in LAN , Routers or gateways will intercept in most cases . WLAN WLAN(Wireless Local Area Network) Computer local area network is to connect computer equipment distributed in different physical locations within a few kilometers , A network system that can communicate with each other and share resources with the support of network software . Usually, the transmission medium of computer networking mainly depends on copper cable or optical cable , Form a wired LAN . However, wired networks are limited by wiring in some cases ： wiring 、 Large quantities of rerouting works ; The circuit is easily damaged ; Each node in the network cannot be moved . Especially when connecting nodes far away , It is difficult to lay special communication lines and wiring , cost 、 It takes a lot of time , It's really frightening . All of these problems are to the rapidly expanding demand for networking .

　　WLAN Is to solve the above problems of wired network .WLAN Use electromagnetic waves to send and receive data in the air , Without cable media .WLAN The data transmission rate of has reached the highest 11Mbps, The transmission distance can be as far as 20km above . Wireless networking is a supplement and extension of wired networking , Make computers on the Internet mobile , Network connectivity problem .