【Internet】Network Miscellaneous Talk (3) Do you really understand the Internet?

Knowledge points involved

What is the Internet, Introduction to the Internet, How to access the Internet, Internet in my country, How to access the Internet, Asymmetric Digital Subscriber Loop, Public Switched Telephone Network, Integrated Services Digital Network, Several ways to access the Internet, In-depth understanding of Internet technology , What are PSTN, ISDN, and ADSL.
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foreword

Everyone already knows that the Chinese name of the Internet is the Internet, which is the largest information network in the world today and one of the largest knowledge treasure houses of all mankind. Through the Internet, users can realize global e-mail, WWW information query, e-mail, file transfer, network entertainment, voice and image communication services and other functions. At present, the Internet has become one of the information infrastructures covering the whole world.
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1. Introduction to the Internet

The predecessor of the Internet was the military experimental network of the US Defense Advanced Research Projects Agency (ARPA, Advanced Research Projects Agency) in 1969. Massachusetts Institute of Technology, its design goal is that when a part of the network is destroyed due to war, other hosts can still operate normally. In the early 1980s, ARPA and the Communications Agency of the US Department of Defense successfully developed the TCP/IP protocol for heterogeneous networks and put it into use. In 1986, with the support of the US Defense Science Foundation (NSF, National Science Foundation), some supercomputers distributed in various places were connected through high-speed communication lines. After more than ten years of development, the prototype of the Internet was formed.

1. Popularity of the Internet

The Internet connects computers distributed all over the world, and names each computer according to unified rules, and formulates a unified network protocol TCP/IP to coordinate information exchange between computers. Anyone and any group can access the Internet. Being open to users and service providers is an important reason for the success of the Internet. The TCP/IP protocol is like the Esperanto used in the Internet. As long as the users on the Internet use the TCP/IP protocol, everyone can communicate conveniently. It doesn't matter who you are on the Internet, what matters is what kind of information you provide. Every host who voluntarily connects to the Internet has various types of information resources. Whether it is a server of a multinational company or a computer connected to the Internet, it is only a node among the tens of millions of Internet sites; whether it is a president, a celebrity or a commoner, it is only one of the tens of millions of Internet users. No one can fully own or control the Internet. The Internet is an open network that does not belong to any organization or individual. As long as it is a host that complies with the protocol TCP/IP, it can access the Internet. The Internet represents a group of infinitely growing information resources worldwide, and its rich content is difficult to describe in any language. It is the first practical information network, and network users can be both information consumers and information providers. With the access of one computer after another, the practical value of the Internet is getting higher and higher. Therefore, the early operation nature of the Internet, which was mainly based on scientific research and education, is being broken through, and the application fields are becoming wider and wider. E-government with the help of the Internet is also developing rapidly.

2. Services provided by the Internet

In general, the Internet can provide the following main services.
(1) World Wide Web (WWW) service: You can browse news, download software, buy goods, listen to music, watch TV scenes, chat online, study online, etc. through WWW service.
(2) E-mail (E-mail) service: E-mails can be sent and received through the e-mail server on the Internet for information transmission.
(3) Search engine service: It can help users quickly find the information they need, the website they want to visit, the software they want to download or the goods they need.
(4) File transfer (FTP) service: It provides a real-time file transfer environment, and can connect to remote hosts through FTP service to download and upload files.
(5) Electronic bulletin board (BBS) service: It provides a place to publish various information on the Internet, and it is also an interactive real-time application. In addition to publishing information, BBS also provides functions such as newsgroups, sending and receiving e-mails, and chatting.
(6) Remote login (Telnet) service: You can enter the remote computer system through the remote login program. As long as you have an account on a certain computer on the Internet, no matter where you are, you can use this computer through remote login, just like using a local computer.
(7) Newsgroup (UseNet) service: This is a service developed for users who need to conduct special research and lectures. Through newsgroups, you can express your own opinions and appreciate others' opinions.

2. my country's Internet

1. my country's Internet construction and operation

China is the 71st national network to join the Internet. In May 1994, the "National Computing and Network Facility of China" (NCFC, The National Computing and Network Facility Of China, also known as Zhongguancun network) connected to the Internet. Subsequently, my country successively built four nationwide public computer networks based on TCP/IP technology and interconnected with the Internet. They are: China Public Computer Internet CHINANET, China Jinqiao Information Network CHINAGBN, China Educational Research Computer Network CERNET, And China Science and Technology Network CSTNET, the first two are commercial networks, and the latter two are public welfare networks. In the past two years, China Unicom Internet, China Netcom Public Internet, Broadband China, China International Economic and Trade Internet, China Mobile Internet, etc. have been built successively.
CHINANET was founded in 1995 and is operated by China Telecom. It is the largest of the above-mentioned networks and the most important Internet backbone network in my country. It is connected to the Internet through the international outlet, thus making CHINANET a part of the Internet. CHINANET has flexible access methods and access points all over the country, which can facilitate users to access the Internet and enjoy rich resources and various services on the Internet. CHINANET consists of three parts: core layer, access layer and network management center. The core layer mainly provides domestic high-speed relay channels and connects to the "access layer", and is also responsible for the interconnection with the Internet. The core layer constitutes the CHINANET backbone network. The access layer is mainly responsible for providing user ports and various resource servers.
At the end of 2003, China Network Information Center (CNNIC, China Network Information Center) announced: my country has about 30.89 million computers on the Internet, about 79.5 million Internet users in my country, 340,040 domain names under CN, and 595,550 WWW sites . The operational backbone network includes: China Telecom Corporation, China Unicom Corporation, China Netcom Corporation, China Jitong Corporation, China Mobile Communications Corporation, China Communications Broadcasting Satellite Corporation, China has 4 .com network concept stocks listed on NASDAQ, namely Sina , Sohu, NetEase, CDC.

2. my country's export distribution

The total capacity of China's international export bandwidth is 27 216Mbps, and the connected countries include the United States, Canada, Australia, the United Kingdom, Germany, France, Japan, South Korea, etc. The specific distribution is as follows: China Science and Technology Network (CSTBET): 155 Mbps
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·China Public Computer Internet (CHINANET): 16 500 Mbps.
· China Education and Research Network (CERNET): 447 Mbps.
· China Unicom Internet (UNINET): 1490 Mbps.
· China Netcom Public Internet (Netcom Control Service) (CNCNET): 3592 Mbps.
·Broadband China CHINA169 network (Netcom Group): 4475 Mbps.
· China International Economic and Trade Internet (CIETNET): 2 Mbps.
· China Mobile Internet (CMNET): 555 Mbps.

3. How to access the Internet

If a user wants to use the services provided by the Internet, he must first connect his computer to the Internet, and then he can access various services and information resources provided by the Internet.

1. Access to the Internet through the Public Switched Telephone Network (PSTN, Public Switched Telephone Network)

The so-called access to the Internet through the public switched telephone network means that the user's computer uses a modem to connect to the Internet Service Provider (ISP, Internet Service Provider) through an ordinary telephone, and then accesses the Internet through the ISP. Figure 2-1 shows the structure that can access the Internet through PSTN.
Both the user's computer and the remote access server (RAS, Remote Access Server) of the IS are connected to the telephone network through a modem. When users access the Internet, they establish a connection with the ISP's RAS through dial-up, and access the Internet through the ISP's router. On the client side, either a computer can be directly connected to the telephone network through a modem, or a proxy server can be used to indirectly connect a local area network to the telephone network through a modem. Due to the limited transmission rate supported by telephone lines, the maximum transmission rate of better lines can reach about 50kbps at present, and the transmission rate of general lines can only reach 30~40kbps, while the transmission rate of poorer lines will be even lower. Therefore, this method is only suitable for personal or small business use. In addition to being limited by the rate, another feature of the telephone dial-up line is that it needs to establish a connection through dial-up. Due to technical reasons, the connection is sometimes disconnected during the transmission of a large amount of information.

2. Access to the Internet through the Integrated Services Digital Network (ISDN, Integrated Services Digital Network)

In recent years, ISDN lines have developed very rapidly in China, and it is also a good choice to surf the Internet through it. This refers to the N-ISDN that adopts the basic rate interface (BRI, Basic Rate Interface) 2B+D, which realizes end-to-end transparent transmission based on the rate of 64kbps between user terminals, and the Internet transmission rate can reach up to 128kbps , providing end-to-end digital connections, used to carry various communication services including voice and non-voice, and can simultaneously support Internet access, phone calls,

Fax and other services, commonly known as the line.
For now, the largest market for ISDN is surfing the Internet. The Internet speed of ordinary telephone lines is mostly about 40kbps, and the maximum is only 56kbps, while ISDN is 64kbps, and the maximum can reach 128kbps; analog telephone lines can only transmit analog voice signals, and can only provide a single telephone service. However, ISDN realizes the digitalization of subscriber lines and can support multiple services at the same time. ISDN can access multiple devices at the same time, but the telephone cannot be directly connected to the telephone line like an analog telephone, but needs to be connected to a device called a network terminal (NT, Network Terminal) first (this device is a local end device) , generally provided by the telecommunications bureau), and then connected to telephones, fax machines, and adapter cards for Internet access.
Non-ISDN standard terminals and ordinary telephones can access the ISDN network through terminal adapters (TA, Terminal Adapter) and network terminals. Other standard ISDN user terminal equipment such as standard ISDN terminals, digital telephones or G4 fax machines are connected to the ISDN network through network terminals. The figure is a schematic diagram of various terminals accessing the ISDN network.

3. Access to the Internet through Asymmetric Digital Subscriber Loop (ADSL)

ADSL (Asymmetric Digital Subscriber Line, Asymmetric Digital Subscriber Line) is a member of the xDSL family. DSL (Digital Subscriber Line, Digital Subscriber Loop) is a series of transmission technologies based on ordinary copper telephone lines, including ordinary DSL, HDSL (symmetrical DSL), ADSL (asymmetrical DSL), VDSL (very high bit rate DSL), SDSL (Single Line DSL), CDSL (Consumer DSL), etc.
The main features of ADSL modem technology are: ADSL technology uses the existing telephone copper wire as the basis, and can provide various services for almost all homes and businesses. To conduct interactive communications or obtain other related services. In this kind of interactive communication, the downlink of ADSL can provide higher bandwidth than the uplink, that is, the uplink and downlink bandwidths are not equal, and are generally around 1:10. If the uplink rate of the line is 640kbps, the downlink has a high-speed transmission rate of 6.4Mbps. This is why ADSL is called an asymmetrical digital subscriber loop, and its asymmetrical characteristics make it suitable for developing Internet services. At the same time, ADSL adopts frequency division multiplexing technology, which can transmit telephone voice and data stream together. The user only needs to install an ADSL client device, and connect it in parallel with the telephone through a splitter (voice and data separator), so that it can be used in a common Talking and surfing the Internet at the same time on the telephone line without interfering with each other. Therefore, using the ADSL access mode is equivalent to adding a high-speed Internet dedicated line without changing the original call mode. It can be seen that there is a big difference between ADSL technology and dial-up Internet modulation technology.
Modulation technology is the key to ADSL. In ADSL modulation technology, high-speed digital signal processing technology and better performance transmission pattern are generally used to obtain high speed and long distance in transmission. ADSL can provide a maximum downlink rate of 8Mbps and an uplink rate of 640kbps on the existing copper wire loop, that is, an ordinary telephone line, with a transmission distance of 3-5km. It is one of several major broadband network access methods at present. Its advantage is to fully utilize the existing telephone line network and provide users with high-bandwidth services by installing ADSL equipment at both ends of the line. Since there is no need to rewire, the cost is reduced, thereby reducing the user's Internet access costs.
There are mainly two ADSL access methods:
(1) Dedicated line network access: users have fixed static IP addresses and are online 24 hours a day.
(2) Virtual dial-up network access method: It is not a real telephone dial-up, but the user enters the account number and password, passes identity verification, obtains a dynamic IP address, and can grasp the initiative of surfing the Internet.

The ADSL access model mainly consists of a central switching office module and a remote module, as shown in Figure 2-3: the
central switching office module includes the ADSL Modem in the center and the access multiplexing system (DSLAM, DSL Access Multiplexer), the ADSL Modem in the center is called ATU-C (ADSL Transmission Unit
-Central).
The remote module is composed of user ADSL Modem and filter, and the user ADSL Modem is usually called ATU-R (ADSL Transmission Unit-Remote).
ADSL installation includes two parts: central office line adjustment and user end equipment installation. In terms of the central office, the ISP connects the ADSL central office equipment in series with the user's original telephone line; the ADSL installation at the user end is also very simple and convenient, as long as the telephone line is connected to the filter, and a two-way cable is used between the filter and the ADSL Modem. The core telephone line is connected, and the ADSL Modem and the network card of the computer are connected with a cross network cable to complete the hardware installation, and then the IP, DNS and gateway parameters in the TCP/IP protocol are set, and the installation is completed.

4. Access to the Internet through the LAN

The so-called "access to the Internet through a LAN" means that the user accesses the Internet through a LAN, and the LAN uses a router to connect with an ISP through a data communication network, and then connects to the Internet through the ISP. The figure shows the structure of accessing the Internet through a LAN.

There are many types of data communication networks, such as DDN, ISDN, X.25, frame relay and ATM networks, etc., all of which are operated and managed by the telecommunications department. At present, the operators of the domestic data communication network mainly include China Telecom and China Unicom. When this access method is used, the cost for the user on the leased line is relatively high, and the user end is usually a local area network with a certain scale, such as an enterprise network or a campus network.

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#Summarize
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The above is what I want to talk about today. This article mainly introduces what is the Internet, how to access the Internet, and the practical application of Internet technology. I also look forward to sharing more with you. Let’s give it a thumbs up from handsome guys and beauties. Let’s work together in 2023! ! !