Networks are classified according to different standards. According to network nodes, they can be divided into LAN, man and WAN. According to the switching mode, it can be divided into line switching network, message switching network and packet switching network.
LAN is a computer network implemented in a small range. It is generally unique to the unit in a building, a factory or an institution. The distance of LAN can be within ten kilometers, and the channel transmission rate can reach 1 ~ 20MBps. It has simple structure and easy wiring. The wide area network has a wide range and can be distributed in one province, one country or several countries. The WAN channel transmission rate is low, generally less than 0.1mbps, and the structure is complex. Man is a computer information network established within a city to provide information services for the whole city. At present, many cities in China are building man.
Line switching first appeared in the telephone system. The early computer network used this method to transmit data. The digital signal can be transmitted on the line only after it is transformed into analog signal. Message exchange is a digital network. When communication starts, a message sent by the source machine is stored in the switch. The switch selects an appropriate path to send the message according to the destination address of the message. This method is called store forward method. Packet switching also adopts message transmission, but it does not use the message with variable length as the basic unit of transmission, but divides a long message into many fixed length message packets, and takes the packet as the basic unit of transmission. This not only greatly simplifies the management of computer memory, but also accelerates the propagation speed of information in the network. Because packet switching is superior to line switching and message switching and has many advantages, it has become the mainstream of computer network. （WangLaoKeFenWeiNaSanChongLeiXing）