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The local area network can realize functions such as file management, application software sharing, scheduling within the printer sharing workgroup, e-mail and fax communication services. The micro-reading editor has sorted out the relevant content of the LAN characteristics for everyone, for your reference and reading!
There are three elements that characterize a LAN:
1 Transmission Medium Also known as transmission medium or transmission medium, it is the physical path between the sender and receiver in the data transmission system. It can be divided into two categories, namely oriented transmission media and non-guided transmission media. In guided transmission media, electromagnetic waves are directed to propagate along solid media (copper wires or optical fibers), while non-guided transmission media refers to free space. The transmission of electromagnetic waves in non-guided transmission media is often called wireless propagation.
2 Topological Structure (Topological Structure) The topological structure of the computer network is to abstract the computer and communication equipment in the network as a point, and the transmission medium as a line. The geometric figure composed of points and lines is the topological structure of the computer network. Network topology: It is divided into logical topology and physical topology. Here we talk about physical topology.
3 Media access control methods (IEEE802.3 LAN protocol, etc.) are commonly called protocols, which are a collection of various protocols and one protocol.
LAN protocol
Some protocols in the LAN will be installed automatically when the operating system is installed. For example, when installing Windows 2000 or Windows 95/98, the system will automatically install the NetBEUI communication protocol. When installing NetWare, the system will automatically install the IPX/SPX communication protocol. Among the three protocols, NetBEUI and IPX/SPX can be used directly without setting after installation, but TCP/IP needs to go through necessary settings. Therefore, the following mainly focuses on the TCP/IP protocol under Windows 2000 environment, and introduces its installation, setting and testing methods. The related operations of the protocols in other operating systems are basically the same as those of Windows 2000, or even simpler.
In Windows 2000, if the TCP/IP communication protocol is not installed, you can select "Start/Settings/Control Panel/Network and Dial-up Connection", right-click "Local Area Connection" and select "Properties", and the "Local Area Connection Properties" dialog box will appear box, click the "Install" button in the dialog box, select the TCP/IP protocol, and then click the "Add" button. The system will ask you whether you want to set "DHCP server"? If the IP address in your LAN is fixed (usually), you can choose "No". The system then starts copying the required files from the installation disk.
In the "Network" dialog box, select the installed TCP/IP protocol, open its "Properties", and the "Internet Protocol (TCP/IP) Properties" dialog box will appear. Enter the assigned "IP address" and "subnet mask" in the designated place, if you don't know, you can ask the network administrator. It is recommended to write down this number before installing the system. After all, it is better to ask for help than to ask for yourself. If the user wants to access resources of other Windows 2000 networks, he can also enter the address of the gateway in the "Default Gateway".
After the TCP/IP protocol is installed and set up, in order to ensure that it can work normally, it must be tested before use. I suggest that you use the tool program that comes with the system: PING command, this tool can check whether any user is connected to other users in the same network segment, whether it is connected to users in other network segments normally, and can also check out its own IP address Whether there is a conflict with another user's IP address.
If the IP address of the server is 190.201.2.1, if you want to test whether your machine is connected to the server, just switch to the DOS prompt and type the command "PING190.201.2.1". If there is a response similar to "Reply from 190.201.2.1...", it means that the TCP/IP protocol is working normally; if a message similar to "Request timed out" is displayed, it means that the settings of the TCP/IP protocol on both sides may be wrong, or There is a problem with other connections of the network (such as network card, HUB or connection, etc.), and further inspection is required.
Topology
A local area network is usually a network system distributed in a limited geographical range, and generally the geographical range involved is only a few kilometers. The local area network is very specific and has a relatively stable and standardized topology. The common LAN topology is as follows:
star shape
The network of this structure is connected by each workstation in a star form. Each node device in the network is centered on the central defense node and connected to the central node through a connecting line. If a workstation needs to transmit data, it must first pass central node. In the network system of this structure, the central node is the control center, and the communication between any two nodes only needs two steps at most, so the transmission speed can be fast, and the network configuration is simple, easy to build, easy to control and manage . However, this network system has low network reliability and poor network sharing capabilities, and once the central node fails, the entire network will be paralyzed.
tree shape
The tree structure network is a natural hierarchical structure, also known as a hierarchical centralized network. It is characterized by low network cost and relatively simple structure. In the network, there is no loop between any two nodes, each link supports two-way transmission, and the expansion of nodes in the network is convenient and flexible, and it is relatively simple to search for link paths.
However, in this structured network system, except for leaf nodes and their connected links, failure of any workstation or link will affect the normal operation of the entire network system.
bus shape
The bus-shaped network is to connect each node device with a bus. All node workstations in the network transmit information through the bus. The communication line used as the bus can be a coaxial cable, a twisted pair, or a flat cable. In the bus structure, the load energy of the bus, which is necessary for data communication, is limited, which is determined by the physical properties of the communication medium itself. Therefore, the number of workstation nodes in the bus structure network is limited. If the number of workstation nodes exceeds the bus load energy, it is necessary to extend the length of the bus and add a considerable number of additional transfer components to make the bus load meet the capacity requirements. . The bus-shaped structure network is simple, flexible, and has good scalability. Therefore, it is very convenient to insert and remove the node device. In addition, the bus structure network has high reliability, fast response speed between network nodes, strong resource sharing capability, less equipment investment, low cost, and convenient installation and use. When a workstation node fails, it will have little impact on the entire network system. Therefore, the bus structure network is the most commonly used network. But because all workstations communicate through a shared bus, the real-time performance is poor.
ring
The 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 the ring structure network is also relatively simple, and the status of each workstation in the system is equal. The communication equipment and lines in the system are relatively economical.
Information in the network has a fixed direction and one-way flow, there is only one path between two workstation nodes, and there is no channel selection problem in the system; the failure of a certain node will cause physical paralysis. In the ring network, because the loop is closed, it is not easy to expand, the system response delay is long, and the information transmission efficiency is relatively low.
WAN comparison
Wide Area Network (WAN), which is what we usually call the Internet, is a network that extends all over the world. Local area network (LAN), as opposed to wide area network (WAN), mainly refers to a computer interconnection network within a small area. This "small scope" can be a family, a school, a company, or a government department. Public network and external network are often mentioned in BT, that is, wide area network (WAN); private network and intranet are often mentioned in BT, that is, local area network (LAN).
Each computer (or other network device) on the WAN has one or more WAN IP addresses (or public network, external network IP addresses), and the WAN IP address can only be applied for after paying the fee at the ISP. The IP address cannot be repeated; each computer (or its device) on the local area network (LAN) has one or more local area network IP addresses (or private network, intranet IP addresses), and the local area network IP addresses are allocated within the local area network. The IP addresses of different LANs can be repeated and will not affect each other.
Wide area network (WAN, public network, external network) and local area network (LAN, private network, intranet) computers exchange data through NAT (network address translation) of routers or gateways. Generally speaking, routers or gateways will not block external connection requests initiated by computers in a local area network (LAN, private network, intranet), but in most cases, routers or gateways will not block requests from WAN to computers in a local area network. The following will be intercepted. Wireless Local Area Network WLAN (Wireless Local Area Network) computer local area network is a network system that connects computer devices in different physical locations within a few kilometers and can communicate with each other and share resources with the support of network software. Usually, the transmission medium of computer networking mainly relies on copper cables or optical cables to form a wired local area network. However, the wired network is limited by the wiring in some occasions: the amount of wiring and rerouting is large; the lines are easily damaged; the nodes in the network cannot be moved. Especially when the nodes far away from each other are to be connected, the construction of laying dedicated communication lines is very difficult, costly, and time-consuming, which is really daunting. These issues all place a rapidly expanding need for networking.
WLAN emerged to solve the above problems of wired network. WLAN uses electromagnetic waves to send and receive data through the air without the need for a cable medium. The data transmission rate of WLAN has been able to reach the highest 11Mbps, and the transmission distance can be as far as more than 20km. The wireless networking method is a supplement and extension to the wired networking method, which makes the computers on the network mobile and solves the problem of network connectivity.