Internet originated from ARPAnet established by ARPA, the predecessor of DARPA, in 1969. The original ARPANET was mainly used for military research purposes. 1972, ARPANET first met the public and became the symbol of the birth of modern computer network. Another important contribution of ARPAnet in technology is the development and use of TCP/IP protocol family. ARPAnet has laid a foundation for the existence and development of Internet, and solved a series of theoretical and technical problems of interconnection between heterogeneous computer networks.
At the same time, the emergence and development of local area network and other wide area networks have played an important role in the further development of the Internet. Among them, the National Science Foundation (NSF) has the greatest influence, which established the National Science Foundation Network (NSFnet). It completely replaced ARPAnet as the backbone of the Internet in June 1990, but NSFnet's greatest contribution to the Internet is to open the Internet to the whole society. With the rapid growth of online traffic, in September, 1990, an advanced network and science company, ANS (Advanced Network &; Science Company). Its purpose is to build a T3 backbone network nationwide, which can transmit data at a rate of 45Mb/s, equivalent to transmitting 14 00 pages of text information per second. As of 199 1, all backbone networks of NSFnet have been connected with T3 backbone networks provided by ANS.
In recent ten years, with the development of society, science and technology, culture and economy, especially the development of computer network technology and communication technology, people pay more and more attention to the development and utilization of information resources, which effectively stimulates the development of the Internet. On the Internet, there are more than 65,438+000 businesses classified according to demand, including advertising companies, airlines, agricultural production companies, arts, navigation equipment, bookstores, chemical industry, communications, computers, consulting, entertainment, finance and trade, various shops and hotels, etc. It covers all aspects of social life and is the epitome of the information society.
The main functions of the Internet: rich information resources (WWW); Convenient communication service (email); Aauto Quicker E-commerce (8488, the earliest business platform in China).
Internet backbone network: ANSNET.
From the network designer's point of view, the Internet is a computer interconnection network.
From the user's point of view, the Internet is an information resource network.
There are two main types of communication lines in the Internet: wired lines and wireless lines.
Internet is mainly composed of communication lines, routers, servers, clients and information resources.
All computers connected to the Internet are collectively referred to as hosts.
The server is the provider of Internet services and information resources, and the client is the user of Internet services and information resources.
TCP/IP protocol is the link that links them together. TCP/IP is a set of protocols, which specifies the addressing mode, naming mechanism, information transmission rules and various service functions of hosts in the Internet.
IP (Communication Rules) is mainly responsible for addressing datagrams transmitted between computers and managing the fragmentation process of these datagrams.
The network layer running IP protocol can provide the following three services for its high-level users:
1.2. Reliable data transmission service. Service.
4. Connectionless transport services.
6. Do your best to provide services.
The IP address consists of two parts, 1. Network number and 2. Host number. As long as two hosts have the same network number, they belong to the same logical network, regardless of their physical location.
Class A IP addresses are used for large networks, Class B IP addresses are used for medium-sized networks, and Class C addresses are used for small networks. Only 256 devices can be connected at most. Class d IP is used for multi-destination address transmission, and class e is reserved for future use.
The network number and host number of the IP address are subdivided by the subnet mask.
The format of IP datagram can be divided into two parts: header area and data area, in which the data area includes the data that needs to be transmitted by the high layer, and the header area is the control information added to correctly transmit the high layer data.
In the Internet, devices that need routing generally adopt table-driven routing algorithm.
There are two basic forms of routing tables: 1. Static routing table. 2. Dynamic routing table. Dynamic routing table is dynamically established by routers in the network automatically sending routing information to each other.
TCP provides reliable data transmission service for the application layer. TCP is an end-to-end transport protocol because it can provide a direct connection from one application of the host to another application of the remote host. (Virtual connection)
TCP and UDP design ports to identify multiple targets on the host.
Internet domain name is defined by the domain name system in TCP/IP protocol set.
This naming structure in the Internet only represents a logical organization, and does not represent the actual physical connection. With the help of a group of independent and cooperative domain name servers, there are a large number of domain name servers in the Internet, and each domain name server keeps a comparison table of host names and IP addresses in the domain. This group of name servers is the core of the analysis system.
There are two ways to resolve domain names: 1. Recursive parsing. 2. Repeatedly distinguish.
The basic services provided by the Internet mainly include:
1. email.
2. Remote login Telnet
3. File transfer FTP.
4.WWW service 5. Service.
E-mail service adopts client/server working mode.
Users need to send and receive emails with the help of email applications installed on the client.
An e-mail application should have the following two basic functions:
1. Create and send email.
2. Receive, read and manage e-mail.
When sending mail to the mail server, the e-mail application uses the simple mail transfer protocol SMTP. When reading from the mail server, you can use POP3 protocol or IMAP protocol.
When accessing an IMAP server with an e-mail application, the user can decide whether to copy the mail to the client and whether to keep a copy of the mail in the IMAP server. Users can read and manage mail directly on the server.
E-mail consists of two parts: the title and the body (actual content).
Remote terminal protocol, Telnet protocol, is a part of TCP/IP protocol, which accurately defines the interaction process between local client and remote server.
The remote login service provided by the Internet can realize:
1. Local users interact with programs running on remote computers.
2. When a user logs in to a remote computer, he can execute any application program on the remote computer, and can shield the differences between different computers.
Users can use personal computers to accomplish many tasks that only mainframes can accomplish.
Network virtual terminal: provides a standard keyboard definition to shield the differences of keyboard input in different computer systems.
Internet users usually use three types of FTP client applications, namely traditional FTP command line, browser and FTP download tool.
This connection with other texts in the text forms the biggest feature of hypertext: disorder.
The process of selecting hot words is actually the process of selecting some information link clues.
Hypertext Transfer Protocol HTTP is an application layer transfer protocol between WWW client and WWW server.
The HTTP session process includes the following four steps:
1. connection. 2. request. 3. answer. 4. close.
URL consists of three parts: protocol type, host name and path, and file name.
The pages stored in the WWW server are structured documents written in HTML.
The main feature of HTML is that it can contain links to other documents, that is, URLs of other pages.
Another feature is that multimedia information, such as sound, image and video, can be collected together.
For organizations, the home page is usually the default page of the WWW server, that is, users only need to give the host name of the WWW server when inputting the URL, without specifying the specific path and file name, and the WWW server will automatically return its default page to users.
A search engine is a World Wide Web server on the Internet. Its main task is to actively search information from other WWW servers on the Internet and automatically index it, and store the indexed contents in a large database that can be queried.
Internet newsgroup is an international forum that uses the Internet to discuss special topics, and USENET is still the largest online newsgroup.
On the one hand, ISP provides users with Internet access services, on the other hand, it provides users with various types of information services.
Users' computers can be connected to ISP through various communication lines, but they can be divided into two categories: telephone lines and data communication lines.
At one end of communication, the modem is responsible for converting the digital information output by the computer into signals that can be transmitted through ordinary telephone lines, and at the other end, converting the signals received from telephone lines into digital signals that can be processed by the computer.
The cost of accessing the Internet through telephone lines usually consists of three parts: account opening fee, Internet access fee (connection fee and disk space occupation fee) and telephone fee.