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Wednesday, April 28, 2021

Common sense of network technology

Common sense of network technology

Common sense: (1) common sense related to switch( For example: the function of the switch, whether the switch can identify the virus files, the first program-controlled switch independently developed in China. What are the main manufacturers of the switch at this stage, which of the manufacturers are used in the school, and the switch is handed over to... To be expanded

(1) Common sense related to switches;

(for example: function of switch, whether the switch can identify virus files, the first program-controlled switch independently developed in China, which manufacturers of the switch are mainly produced at this stage, which manufacturer is used in our school, the price of the switch, the identification of the switch, etc.)

The main functions of the switch include physical addressing, network topology, error checking, frame sequence and flow control. At present, the switch has some new functions, such as VLAN (virtual LAN), link convergence, and even firewall.


In 1986, the first program-controlled switch S1240 was successfully offline in bell, Shanghai.

hear nothing of

The price is about 1000-20000 yuan

(2) Common sense related to hubs;

(for example: the function of the hub, the price of the hub, the difference between the hub and the switch (described from the function and identification), etc.)

Function: amplify signal

Transmit signals over the network

No filtering function

No path detection or exchange

Used as a network concentration point

Price: 50-500 yuan

The main function of the relay is to enlarge the received signal by shaping and reproducing, so that the signal being attenuated can be regenerated (restored) to the state of transmission, so as to expand the transmission distance of the network, without the directional transmission capability of the signal.

In Switched Ethernet, the switch provides each user with a dedicated information channel. Unless two source ports attempt to send information to the same destination port at the same time, the source ports and their destination ports can communicate at the same time without conflict.

Switch is only different from hub in operation mode, and other connection modes and speed selection are basically the same as hub.

(3) Common sense related to twisted pair;

(for example: the function of twisted pair, the price, identification, lightning protection of twisted pair, whether the twisted pair is telephone line, etc.).

Function: cheap, easy to install, but easy to interfere, low transmission rate, and shorter transmission distance than coaxial cable.

Price: 1-2 yuan / meter

It's all about lightning protection

Telephone lines can be connected to the Internet, but after the signal is modulated and demodulated, twisted pair can also be used as telephone line. Only four pairs of twisted pair are usually used (super five types: 2 receive 2, and 2 pairs of lines are standby), and only one pair of lines (1 receive and 1 send) are used for telephone.

(4) Common sense related to modulation mediators;

(for example: function and principle of modem, price, identification, etc.).

The device for signal conversion between computer and telephone line consists of modulator and demodulator. Modulator is a device that modulates computer digital signal (such as file, etc.) into sound signal that can be transmitted on the telephone line. At the receiving end, demodulator converts sound signal into digital signal that can be received by computer. Data communication between computers can be realized by modem and telephone line.

Price: about 100 yuan

(5) Common sense related to cables;

(for example: the function of the cable, the price of the cable, the distance of transmission, etc.).

For power, communication and related transmission purposes

Price: 1-20 yuan, meter

(6) Common sense related to optical fiber;

(for example: function and principle of optical fiber, price of optical fiber, transmission distance, difference and connection with cable and twisted pair, etc.).

(7) Common sense related to router;

(for example: router function, router price, differences and contacts with switches and hubs, etc.). Different levels of work

The original switch was working in the data link layer of OSI / RM Open Architecture, that is, the second layer. The router was designed to work in the network layer of OSI model from the beginning. Since the switch works in the second layer of OSI (data link layer), its working principle is relatively simple. While router works in the third layer (network layer) of OSI, it can get more protocol information and router can make more intelligent forwarding decision.

(2) Data forwarding is based on different objects

The switch uses physical address or MAC address to determine the destination address of forwarding data. The router uses the ID number of different networks (i.e. IP address) to determine the address of data forwarding. IP addresses are implemented in software, describing the network where the device is located, sometimes these third-layer addresses are also called protocol addresses or network addresses. MAC address is usually provided by hardware, and is assigned by network card manufacturer, and has been solidified into network card. Generally speaking, it is immutable. IP addresses are usually assigned automatically by network administrators or systems.

(3) Traditional switches can only divide conflict domain and broadcast domain; And routers can divide broadcast domains

The network segment connected by the switch still belongs to the same broadcast domain. The broadcast data packet will spread on all the network segments connected by the switch, which will lead to communication congestion and security vulnerability in some cases. The network segment connected to the router will be assigned to different broadcast domains, and the broadcast data will not pass through the router. Although the switches at or above layer 3 have VLAN function and can also divide broadcast domains, communication and communication between sub broadcast domains cannot be achieved. Routers are still needed for communication between them.

(4) Router provides firewall service

Router only forwards packets with specific address, does not transmit packet transmission that does not support routing protocol and unknown target network packet, thus preventing broadcast storm.

Router price: about 100 ~ 1000 yuan

(8) Common sense related to the server;

(for example, the server's features, etc.).

Web server is also known as the world wide web server, and its main function is to provide online information browsing service.

The server functions include agent Internet access, security verification, e-mail service, etc

It refers to a special computer that provides some services to client in the network environment. The server is equipped with computer with network operating system (such as Windows 2000 server, Linux, UNIX, etc.) and various server application system software (such as web service and e-mail service).

(9) Common sense related to network card;

(for example: network card function, network card type, home used what network card, etc.).

Network card is a network component working in the data link layer, and it is an interface between the computer and transmission medium in the LAN. It can not only realize the physical connection and electrical signal matching with the transmission medium of the LAN, but also involve the transmission and reception of frames, the encapsulation and unpacking of frames, media access control, data coding and decoding, and data cache functions.

The network card can also be divided into 10Mbps network card, 100Mbps network card, 10/100mbps adaptive network card (Figure 1) and Giga network card (Figure 2) according to its transmission rate (i.e. the bandwidth it supports). Among them, 10/100mbps adaptive network card is the most popular network card, its maximum transmission rate is 100Mbps, which can automatically determine whether it works at 10Mbps or 100Mbps according to the speed of the network connection object. The maximum transmission rate of gigabit network card is 1000Mbps.

(10) Common sense related to bridge;

(for example: bridge function, bridge and traditional switch differences and connections, etc.).

The network and communication means are extended to forward data signals in various transmission media, and the distance of the network is extended. At the same time, the signals with addresses are selectively sent from one transmission medium to another, and the irrelevant communication between two media systems can be effectively restricted.

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