According to the switching function of the network, it can be divided into: (1): circuit switching, message switching, packet switching and hybrid switching;
(2) According to the topological structure of the network, it is divided into bus structure, star structure, ring structure and cellular structure (which is produced with the emergence of wireless communication technology);
(3) Classification by scope of action: local area network (LAN), wide area network (WAN) and metropolitan area network.
Internet, also known as Internet, is the most influential international computer network in the world. Its accurate description is that the Internet is a network of networks. It uses TCP/IP network protocol to connect various physical networks of different types, scales and geographical locations into a whole. It is also an international communication network collection, which combines modern communication technology with modern computer technology and integrates various information resources in various departments and fields, thus forming an information resource network enjoyed by online users. Its appearance is the inevitable and symbol of the world from industrialization to informationization.
E-mail, referred to as e-mail, translated from English (e-mail) refers to letters written, sent and received through electronic communication systems. The most widely used communication system today is the Internet, and email is also one of the most popular and commonly used functions on the Internet.
Format of mail address
On the Internet, the e-mail address is just like your own identity. Generally speaking, the format of an email address is as follows: someone @ domain _ name+ suffix.
Domain_name here is the identifier of the domain name, that is, the domain name of the mail destination to which the mail must be delivered. Someone is an email address on the domain name. Suffixes generally represent the nature of domain names and area codes. For example: com, edu.cn, gov, org and so on.
Domain names are technically mail exchanges, not machine names.
Common e-mail protocols are as follows: SMTP (Simple Mail Transfer Protocol), POP3 (post office protocol) and IMAP (Internet Mail Access Protocol). These protocols are defined by the TCP/IP protocol family.
SMTP (Simple Mail Transfer Protocol): SMTP is mainly responsible for how the underlying mail system transmits mail from one machine to another.
POP (post office protocol): The current version is POP3, which is a protocol for transmitting mail from an e-mail box to a local computer.
IMAP (Internet Mail Access Protocol): The current version is IMAP4, which is an alternative protocol to POP3. It provides new mail retrieval and mail processing functions, so that users can see the title summary of the mail without downloading the mail body, and can operate the mail and folder directories on the server from the mail client software. IMAP protocol enhances the flexibility of e-mail, reduces the direct harm of spam to the local system, and relatively saves the time for users to check e-mail. In addition, IMAP protocol can remember users' offline mail operations (such as moving mail, deleting mail, etc.). ) will be automatically executed the next time you open the network connection.
At present, two mail acceptance protocols and one mail sending protocol support secure server connection. Support for SSL connections is integrated in most popular e-mail client programs.
4. In the TCP/IP network, clients can download or load files on the file server through the file transfer protocol, thus realizing resource sharing. FTP server has become an important resource on the Internet.
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5.ISP (Internet Server Provider) is a company and institution that provides users with Internet access and/or Internet information services. The former is also called IAP (Internet Access Provider) and the latter is also called ICP (Internet Content Provider). Because connecting to the Internet requires renting international channels, the cost is beyond the reach of ordinary users. Internet access providers, as intermediaries providing access services, need to invest a lot of money to establish transfer stations, rent international channels and a large number of local telephone lines, purchase a series of computer equipment, and provide access services to local users through centralized use and decentralized pressure. In a sense, IAP is the only way for hundreds of millions of users around the world to access the Internet. Internet content providers publish comprehensive or specialized information on the Internet and earn profits by charging advertising fees and user registration fees.
6. Remote login is one of the most basic information services provided by the Internet. Remote login is the process of making the local computer temporarily become the analog terminal of the remote computer with the support of the network communication protocol Telnet. To log on to a remote computer, you must become a legal user of the computer system in advance and have the corresponding account and password. Give the domain name or IP address of the remote computer when logging in, and enter the user name and password according to the system prompt. After logging in successfully, users can use the open functions and resources of the system in real time, such as * * * enjoying its software and hardware resources and databases, and using the Internet information services provided by it, such as E-mail, FTP, Archie, Gopher, WWW, WAIS, etc.
Telnet is a powerful resource sharing tool. Many university libraries provide online retrieval services through Telnet, and some government departments and research institutions also open their databases to the public so that users can query through Telnet.