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## Computer Network It is a computer that connects multiple computers and their external devices with independent functions in different geographical locations through communication lines, and realizes resource sharing and information transmission under the management and coordination of network operating systems, network management software and network communication protocols. System
Main types of networks:
1. Geographical coverage of the network :
A. Local area network:
1. Belong to an organization, owned by a unit or a department .
2. The network generally does not provide public services to the outside world, is easy to manage, and has high security and confidentiality.
3. It is the most common computer network with easy establishment, low investment, quick results, and flexible application.
B. City Area network:
1. Generally a region or a city
C. Wide area network:
1. It can be as small as a region, a city, as large as a country, several countries or even the whole world
2. Provide a wide range of Public Service. The Internet is a typical wide area network.
3. Compared with LAN, WAN has large investment, poor security and confidentiality, and slow transmission rate.
2. According to the circuit structure of the computer network:
A. Bus type
1. This structure uses a public bus as the transmission medium, and each computer accesses the network through the correspondinghardware interface. The signal is broadcasted along the bus
2. It is a typical network that shares the transmission medium. Information sent from the source will be transmitted as far as the length of the medium, and will be seen by all other sites. If more than two nodes send data at the same time, a collision may occur, like two cars colliding on the highway.
Advantages and disadvantages:
Advantages: easy wiring; easy additions and deletions; cable saving;
Disadvantages:
1. Any two sites must pass through the bus to transmit information. The bus is called a transmission bottleneck;When there are many computer sites, it is easy to cause information blocking and transmission Not smooth.
2. If the interface of a computer connected to the bus fails, it will cause the entire network to be paralyzed.
3. When a network failure occurs, fault diagnosis and isolation are difficult.
B, star type
consists of a central node and surrounding slave nodes. The central node and the slave node can communicate directly, while the slave node must be transferred through the central node to communicate.
Advantages and Disadvantages:
Advantages:1. High reliability. The failure of each computer and its interface will not affect other computers, nor will it affect the entire network, nor will it cause network paralysis.
2. Easy fault diagnosis and isolation, and the network is easy to manage and maintain.
3. Good scalability and flexible configuration. Adding, deleting and modifying a site is easy to implement and has nothing to do with other computers
4. High transmission rate. Each node has an exclusive line, eliminating information blocking. The bottlenecks of bus and ring networks are on the lines.
Disadvantages:
1. Large amount of cable usage.
2. The wiring and installation workload is heavy.
3. Network reliability depends on the central node. If the switch or hub is improperly selected, failure
will cause the entire network to be paralyzed.
C, ring type
1. The computer accesses the network through hardware interfaces, and these interfaces are connected end to end to form a link. Information transmissionis also broadcast, one-way and point-by-point in one direction (such as counterclockwise).
Advantages:
Point-to-point and one-way transmission in one direction, very suitable for using optical fiber as the transmission medium.
1. The transmission distance is long and suitable for backbone network.
2. Fault diagnosis is easy to locate.
3. The initial installation is easy and the amount of cables is small. The ring line is also a bus, but the beginning and end are closed.
##3. According to transmission medium:
A. Cable network
1. Coaxial cable: low cost, easy to install, but low transmission rate and anti-interference ability Generally,short transmission distance
2. Twisted pair: commonly used when building a local area network, the advantages and disadvantages are similar to coaxial cables.3. Optical fiber: Mainly used in the backbone part of the network. It is characterized by high cost, high installation technology requirements, long transmission distance, high transmission rate, and anti-interference ability. It is strong and will not be monitored by electronic monitoring equipment. It is an ideal choice for building a high-security network.
B. Wireless network
1. Infrared;
2. Microwave ；
3. Radio；
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