Network, simply put, is to connect isolated workstations or hosts with physical links to form data links, so as to achieve the purpose of resource sharing and communication.
Computer network is a system that connects many computer systems with different geographical locations and independent functions through communication equipment and lines, and realizes network resource sharing with well-functioning network software (network protocol, information exchange mode and network operating system, etc.). ).
The word network has many meanings, which can be interpreted as:
1, the streaming network is also called the network. It is generally used for modeling pipeline system, transportation system and communication system. Sometimes it refers to a computer network, or a system in which the Internet is composed of related individuals, such as interpersonal network, traffic network and political network.
2. A graph composed of nodes and lines. Represents the research object and its relationship. Sometimes lines with arrows indicate that there is a certain order relationship from one node to another. The numerical values marked next to nodes or lines are called point weights or line weights, and sometimes they are not marked with numbers. In mathematical language, the network is a graph, which is generally considered as a weighted graph. In addition to the mathematical definition, the network also has a specific physical meaning, that is, the network is a model abstracted from a certain kind of practical problems, and what kind of network is customarily called, such as switching network, transmission network, communication network, planning network and so on. In a word, the network is a model abstracted from similar problems and expressed and studied by graph theory in mathematics.
Computer network is a system that connects several autonomous computer systems distributed in different places with communication lines and communication equipment, and shares hardware, software and data resources according to the same network protocol.
Four elements to realize the network
1, communication lines and communication equipment
2. Computers with independent functions
3, network software software support
4. Realize data communication and resource sharing.
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The development history of computer network
1946 the world's first electronic computer came out more than ten years ago, because of its high price, the number of computers was very small. The so-called computer network in the early days was mainly produced to solve this contradiction. Its form is to directly connect a computer with several terminals through communication lines. We can also regard this method as the simplest prototype of LAN.
The earliest Internet was established by the Advanced Research Projects Agency (ARPA) of the US Department of Defense. Many concepts and methods of modern computer network, such as packet switching technology, all come from ARPAnet. ARPAnet not only studied the packet switching technology of leased line interconnection, but also studied the packet switching technology of wireless and satellite networks, which led to the emergence of TCP/IP.
In 1977- 1979, ARPAnet introduced the current TCP/IP architecture and protocol. Around 1980, all the computers on ARPAnet started the conversion of TCP/IP protocol, and the initial Internet with ARPAnet as the backbone network was established. 1983, all ARPAnet computers completed the conversion to TCP/IP, and realized TCP/IP on UNIX (BSD 4.1). The biggest contribution of ARPAnet in technology is the development and application of TCP/IP protocol. Two famous science education networks have been established successively: China Science Network and BITNET. 1984, NSF of the National Science Foundation planned to establish 13 National Supercomputing Center and National Education Science and Technology Network. Then it replaced the backbone position of ARPANET. 1988 the internet began to open to the outside world. 199 1 June, 2006, among computers connected to the Internet, commercial users surpassed academic users for the first time, which was a milestone in the development history of the Internet, and the growth rate of the Internet was out of control.
The development stage of computer network
First Generation: Remote Terminal Connection
In the early 1960s.
Terminal-oriented computer network: the host is the center and controller of the network. Terminals (keyboards and monitors) are distributed everywhere and connected to the host computer. Users use remote hosts through local terminals.
Communication between terminals and hosts is only provided, and communication between subnets is impossible.
The second generation: computer network stage (LAN)
The mid-1960s
Multiple hosts are interconnected to realize communication between computers.
Comprise a communication subnet and a user resource subnet.
End users can access the hardware and software resources of local hosts and all hosts on the communication subnet.
Circuit switching and packet switching.
The third generation: computer network interconnection stage (wide area network, Internet)
198 1 year, the International Organization for Standardization (ISO) formulated the basic reference model (OSI/RM) for interconnection between computers produced by different manufacturers.
The birth of TCP/IP protocol
The fourth generation: information superhighway (high-speed, multi-service, large data volume)
Broadband integrated services digital network: information superhighway
ATM technology, ISDN, gigabit Ethernet
Interactive: Internet TV on demand, video conference, videophone, online shopping, online banking, online library and other high-speed, visual.
Development history of China's network
1, the phased development of the Internet
From 65438 to 0987, China Academic Network sent the first e-mail to the world, marking the development of Internet in China. After decades of development, four mainstream network systems have been formed, namely: CSTNET, Science and Technology Network of China Academy of Sciences; CERNET Education and Scientific Research Network of the Ministry of Education; CHINANET of the former Ministry of Posts and Telecommunications and CHINAGBN of Jinqiao Network of the former Ministry of Electronics.
The development of Internet in China can be roughly divided into three stages:
The first stage is1987-1993, which is also the stage of research and experiment. During this period, some scientific research departments and universities in China began to internetize Internet technology, and carried out scientific research projects and scientific cooperation, but the network application at this stage was limited to a small range of e-mail services.
The second stage is 1994 to 1996, which is also the initial stage. 1In April, 1994, Zhongguancun Education and Scientific Research Demonstration Network Project entered the Internet, and China was officially recognized as a country with Internet. After that, many Internet networking projects such as Chinanet, CERnet, CSTnet and Chinagbnet were launched nationwide, and the Internet began to enter public life and developed rapidly in China. By the end of 1996, the number of Internet users in China had reached 200,000, and the services and applications developed by the Internet were gradually increasing.
The third stage, from 1997 to now, is the fastest and fastest stage of Internet in China. After 1997, the number of netizens in China basically doubled every six months. Today, the number of netizens has exceeded100000. According to the statistical report released by China Internet Network Information Center (CNNIC), as of June 30, 2003, the total number of Internet users in China was 68 million. This figure increased by 8.9 million compared with the beginning of the year and 22.2 million compared with the same period in 2002.
At present, there are five commercial Internet backbone units with independent international import and export routes in China, as well as non-profit Internet backbone units for education, science and technology, economy and trade. At present, there are more than 600 Internet access service providers (ISPs), of which 140 operates across provinces.
With the improvement of network foundation, the adoption of new technologies for user access, the diversification of access methods and the improvement of service capabilities of operators, the bottleneck problem caused by slow access network speed will be further improved, and the internet access speed will be faster, thus promoting more applications to be realized online.
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Network classification
By coverage:
Local area network LAN (the range of action is usually several meters to dozens of kilometers)
Man (between Wan He Lan)
Wide area network WAN (the scope of action is generally tens to thousands of kilometers)
Classification by topological structure
Bus type
toroidal
star
reticulation
According to the way of information exchange:
circuit switching
Message exchange
packet switching technology
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Network security
Network security is an important issue related to national security and sovereignty, social stability and the inheritance and development of national culture. With the acceleration of global informatization, its importance is becoming more and more important. "Home is the country", and the security issue is urgent.
Network security is a comprehensive subject involving computer science, network technology, communication technology, cryptography technology, information security technology, applied mathematics, number theory, information theory and other disciplines.
Network security means that the hardware, software and data in the network system are protected from accidental or malicious reasons, and the system runs continuously and reliably without interrupting network services.
Network security is essentially information security on the network. Broadly speaking, all technologies and theories related to the confidentiality, integrity, availability, authenticity and controllability of information on the network are the research fields of network security.
The specific meaning of network security will change with the change of "angle". For example, from the perspective of users (individuals, enterprises, etc.). ), they hope that information related to personal privacy or business interests will be protected by confidentiality, integrity and authenticity when transmitted on the network, so as to prevent others or opponents from using eavesdropping, impersonation, tampering, denial and other means to infringe on users' interests and privacy and access and destroy them.
From the perspective of network operators and managers, they hope to protect and control the access, reading and writing of local network information, so as to avoid threats such as "trap door", virus, illegal access, denial of service and illegal occupation of control network resources, and to prevent and defend the attacks of network hackers.
For the security department, they hope to filter and stop illegal, harmful or state secrets, so as to avoid the disclosure of confidential information, avoid harm to society and cause great losses to the country.
From the perspective of social education and ideology, unhealthy content on the Internet will hinder social stability and human development and must be controlled.
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The purpose of the network
online communication
Shi Lan, executive deputy director of China Modern Media Committee, believes that network communication has three basic characteristics: global, interactive and hypertext link. Therefore, its definition of network communication is: with the global mass information as the background and a large number of participants as the object, the participants are also the recipients and publishers of information and can feedback information at any time. Its text formation and reading are completed in hypertext, and there are random links between various texts and different education levels (International Press, No.6, 2000, p. 49).
Others believe that "network communication" is a new term widely used in communication science in recent years. It is relative to newspapers, radio and television. Network communication refers to the Internet with multimedia, network and digital technology as its core, also known as network communication, which is the product of modern information revolution (International Press, No.6, 2000, p. 49).
We believe that the so-called network communication actually refers to the dissemination of human information (including news, knowledge and other information) through computer networks. The information spread in the network is stored in digital form on optical, magnetic and other storage media, spread at high speed through the computer network, and read and used by computers or similar devices. Network communication is based on computer communication network to transmit, exchange and utilize information, so as to achieve the purpose of social and cultural communication. There are a large number of readers on the network, which can spread at high speed through the network.
The related disciplines of network communication mainly include: communication, politics, sociology, psychology, journalism, economics, computer science and so on.
network phone
Internet phone, also called IP phone, transmits voice through Internet Protocol (IP). The traditional international call is analog transmission, which first converts the voice into a signal and transmits the voice to the other party through copper cable. VoIP converts voice into data signals through the gateway, then compresses them into data packets, and then sends them out from the Internet. When the receiver receives the data packet, the gateway will decompress it and turn it into voice again for the other party to listen to. At present, there are generally three ways to connect VoIP: PC-to-PC, PC-to-phone, and phone-to-phone. VoIP uses TCP/IP protocol, and through special software (often compressed, which is also the technical key point of VoIP software), the voice of the calling party is converted into digital signals, and then packaged into small data packets. Small data packets are free to find network free space and transmit voice data to each other. After receiving the data packet, the special equipment or software of the other party will make the reverse process of converting the voice into the data packet. If the receiver of the other party is inconsistent, technical treatment is needed. During the whole call, we don't need to rent a dedicated line, just use the network at will, which greatly saves the call cost. Generally, the cost is a few cents at home and a few cents internationally, so the cost is very low.
VoIP is a revolutionary product, which can make real-time transmission and two-way calls through the Internet. You can call other telephone users around the world at a very low cost through your local Internet service provider (ISP) or telephone company, and VoIP calls are free internally. From office workers to home users, students, surfers, gamers and grandparents, VoIP provides a new, simple and economical way to talk to friends and colleagues all over the world.
network television
IPTV, namely interactive network TV, is a brand-new technology that uses the infrastructure of broadband network and takes computer (PC) or "TV+IPS TB" as the main terminal equipment to provide users with various interactive digital media services such as video on demand, Internet access, e-mail and games.
online education
Network education refers to a kind of network teaching and learning service provided to educators and learners by giving full play to various educational functions and rich advantages of network education resources under the guidance of modern educational ideas and learning concepts. This service is embodied in the transmission of content by digital technology and the development of learner-centered non-face-to-face education activities.
Network finance
The so-called online finance, also known as e-finance, refers to the financial activities realized on the Internet, including online financial institutions, online financial transactions, online financial markets and online financial supervision. It is different from traditional financial activities in physical form, and it is a financial activity in electronic space. Its existence form is virtualized and its operation mode is networked. It is the product of the rapid development of information technology, especially internet technology, and it is a financial operation mode that meets the needs of e-commerce development in the network era.
Network insurance
Network insurance is a new insurance marketing model based on computer network, which is different from the traditional insurance agent marketing model.
The emergence and development of network insurance is a historical trend and represents the development direction of international insurance industry.
At present, domestic insurance websites can be roughly divided into two categories: the first category is the self-built websites of insurance companies, which mainly promote their own types of insurance, such as "PA 18" of Ping An Insurance and "Taikang Online" of Taikang Life Insurance; The second category is independent third-party insurance websites, which are funded by professional Internet service providers (ISP). It does not belong to any insurance company, but also provides insurance services, such as electronic insurance and online insurance. Obviously, these two types of websites represent the development level of online insurance in China. A rational and objective study and analysis of their implementation strategies and market operation modes can help us grasp the development of online insurance in China.
Network insurance is a huge social system project, involving banking, telecommunications and other industries, and it takes a long time to perfect this project. The attack of network hackers makes the current computer network system lack security, and there are hidden dangers in network insurance; However, online insurance is prone to fraud due to human factors and the profound and complicated background and interest relationship between insurance parties. Therefore, it is difficult to support online insurance only by online operation. How to prohibit and punish insurance fraud by using online insurance? How to realize online underwriting and online claim payment? Network insurance has a long way to go in China.
Network insurance technology is a set of "security reinforcement system" researched by national scientific and technological researchers to maintain the security of servers and resist the invasion of hackers, viruses and worms. As of February 7, 2007, 65438, a new generation of "security reinforcement system" was broadcast by the Central News Network.
Internet marketing
The full name of On-lineMarketing or Cybermarketing is online direct selling, which belongs to a form of direct selling. It is the product of the combination of enterprise marketing practice, modern information communication technology and computer network technology. Refers to various marketing activities (including network research, network promotion, network new product development, network promotion, network distribution, network services, etc.). Based on electronic information technology, the enterprise takes computer network as the medium and means.
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internet language
Network language is a new language form which is different from traditional print media with the development of network. As soon as it was born, it was favored by the majority of netizens and developed rapidly. Network languages include pinyin or English abbreviations. The numbers of network animations and pictures with certain meanings and vivid images are mainly used by internet addicts at first to improve the efficiency of online chat or some needs, and over time they have formed a specific language. The emergence of network neologisms mainly depends on its own vitality. If those vibrant online languages can stand the test of time, they can be accepted after the convention is established.
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The origin of online games
Business model: The rapid expansion of the online game market stimulated the development of the online service industry, and online games began to enter the charging era. Many consumers are willing to pay high fees to play online games. From the hourly 12 of "Cashmere Island" to the hourly $6 of "Elf", the mainstream charging method of the second-generation online games is hourly charging. Although there has been a special case of monthly fee, it has not formed a climate.
1978, in the University of Essex, England, Roy Trubshaw wrote the world's first MUD game-Mud1with DEC- 10. This is a multi-person world with pure words, with 20 interconnected rooms and 10 instructions. After logging in, users can interact through the database.
After leaving the University of Essex, Trubshaw handed over the maintenance of MUD 1 to Richard Bater. Bater continues to improve the game by using-"muddl-a special language developed by Trubshaw. He increased the number of rooms to 400, further improved the database and chat system, added more tasks, and made a scoring program for each player.
After 1980 connected to ARPAnet, the number of players from abroad increased greatly, which swallowed up a lot of system resources. The university had to limit the login time of users to reduce the load of DEC- 10. In the early 1980s, Bater made a clean break of the source code of MUD 1 for the reference of colleagues and researchers in other universities, and this source code was circulated. By the end of 1983, hundreds of illegal copies had appeared on ARPAnet, and MUD 1 quickly spread all over the world, and many new versions appeared. Today, this oldest MUD system has been authorized to CompuServe, one of the largest online information service organizations in the United States, and it has been renamed as "British Legend", and it is still running today, becoming the longest running MUD system.
MUD 1 is the first real-time multiplayer interactive online game, which can ensure the sustainable development of the whole virtual world. Although this system will be restarted several times every day, the scenes, monsters and puzzles in the game will remain unchanged after the restart, which makes the role played by players can continue to develop. Another important feature of MUD 1 is that it can run on any PDP- 10 computer in the world, not limited to the internal system of the University of Essex.
1982, john tyler and kelton Flynn formed Casmai Company, which left many memorable works in the development history of online games. Kesmai's first contract was signed with CompuServe. At that time, john tyler saw an advertisement called "MegaWars" played by CompuServe-"If you can write such a game, you can get a monthly tax of $30,000", so he sent a handbook of "The Island of Kesmai" developed with kelton Flynn. Camay Island runs on UNIX system, while CompuServe uses DEC-20 computer, so Camay Company redevelops a DEC-20 version for CompuServe. This game has been in operation for about 13 years, and it was officially charged in 1984. The charging standard is $0/2 per hour/kloc. In the same year, MUD 1 also launched its first commercial version on Compunet in the UK.
1984, Mark Jacobs founded AUSI Company (the predecessor of Mythic Entertainment Company, the developer of King Arthur's Dark Age) and launched the game Aradath. Jacobs built a server platform at home and installed eight telephone lines to run this role-playing game. The charging standard of the game is 40 dollars per month, which is the first online game in the history of online games to adopt a monthly subscription system. Monthly subscription system is conducive to accelerating the popularization of online games and will play an important role in the popularization of online games. Unfortunately, the monthly subscription system did not have the conditions for growth at that time. In 1990, AUSI set the price of Longmen at $20 per hour. Although this ratio is surprising, some people are still willing to spend more than 2000 dollars a month to play this game. Therefore, the monthly subscription system did not attract people's attention in the late 1980s and early 1990s.
1985, Bill Lohden persuaded the Information Service Department of General Electric Company (GE) to invest and establish a commercial network service platform based on ASCII text similar to CompuServe, which was called Genie (GE Network for Information Exchange). GEnie was officially listed on June 5438+ 10, and its low charging standard caused great repercussions among users, which also made CompuServe, who has always had a strong sense of superiority, feel the pressure of competition. GEnie system actually uses the server of GE Information Service Department to provide services to users in the free time at night, so the charge is very low, and the price at night is about 6 dollars per hour, almost half that of CompuServe.
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Network-Four Backbone Networks in China
China public computer internet (CHINANET)
Also known as Internet of Ministry of Posts and Telecommunications and China Public Internet, it is an electronic information network based on Internet network technology managed by Ministry of Posts and Telecommunications. 1995 started networking and provided services to the society in May. CHINANET consists of backbone network and access network. Backbone network is its main information channel, which is composed of network nodes of municipalities and provincial capitals. Access network is a network formed by network connection established in various provinces (regions). CHINANET's flexible access mode and access points all over the country can easily access the Internet, enjoy the rich information resources and various services on the Internet, and provide a convenient network environment for the interconnection of domestic computers and the enjoyment of domestic information resources.
China Education and Research Network (CERNET)
1994 started, and 1995 completed the first phase of the project, including Beijing (network center), Shanghai, Nanjing, Guangzhou, Wuhan, Xi 'an, Chengdu and Shenyang. There is an international special line connecting the United States. The national backbone network (*** 1 1 64Kbps DDN dedicated line) was opened in June 1995. After the completion of the second phase of the project, the national backbone network and international networking have been gradually upgraded, with the backbone network reaching more than 2Kbps and international networking reaching more than 8Kbps.
China science and technology network
Sponsored by China Academy of Sciences, jointly built by Tsinghua and Peking University. In April, 1994 opened a special line connection with the Internet. 65438+1May 2, 19941day, the setting of the main server of the highest domain name CN in China was completed, and the TCP/IP connection with the Internet was realized. By the end of 1995, the project of "networking 100 institutes" was basically completed. By the end of 1997, more than 100 Ethernet, more than 3,000 computers and more than 1000 users have been connected, making it a national scientific research and education network with large area, large consumption, good performance, large communication volume and complete service facilities.
China Jinqiao Information Network
That is, the national public economic information communication network managed by the former Ministry of Electronic Industry provides data communication and information services for the government, enterprises and institutions and the public. Jinqiao network was connected to the Internet at the end of the year, and 24 cities have been opened. More than 0/000 local and remote simulation terminals have been developed to provide comprehensive Internet services.