Computer Network Technology and Application

Chapter 20 Services Provided by the Internet (2)
2. File Transfer Protocol
FTP is one of the most widely used protocols on the Internet and it provides a generic type user interface.

(1) FTP uses the client/server model. The user uses the local FTP client process to request a file transfer; another FTP server process running on the remote host responds to the user request and transfers the specified file to the corresponding on the host.

(2) FTP provides anonymous and authorized access.Anonymous services allow users not to register on the FTP server in advance, and generally use the "anonymous" user name, and use the user's email address for the password; non-anonymous services must apply to the server management for a user name and password in advance, that is, must obtain authorization.

6.4.2 Working principle of FTP
(1) The service process of the FTP client first establishes a TCP connection to port 21 of the FTP server.

(2) The FTP client sends the user's ID, password, etc. through the connection, and changes the current directory of the remote system through the connection command.

(3) When transferring files, the FTP server establishes a data connection with the client on port 20.

(4) When the transmission ends, immediately disconnect the data connection.

(5) The control connection is always open, and the data connection is turned on or off according to the situation.

6.4.3 Example of using IIS to establish FTP service

IIS is the abbreviation of Internet Information Service (InternetInfomation Service), which is a component of Microsoft Windows operating system. The main functions of IIS include providing WWW server, FTP server, etc.It makes it not only possible but also easy to publish information on the Internet.

1. Install IIS steps
(1) Start the operating system and "Add/Remove Programs" in the Control Panel.

(2) Click "Add/Remove Windows Components", and the "Windows Components Wizard" dialog box appears, select "Internet Information Services" from the list.

(3) Click "Next" and follow the steps shown in the wizard.

2. Run IIS
Open IIS Manager, select "Start Menu" → "Programs" → "Administrative Tools" → "Internet Information Services".

3. Create an FTP site
(1) Right-click a domain, create an FTP, and set permissions, such as read and write, and the settings represent whether uploading or downloading is possible.

(2) Open the FTP properties, and make connection settings: limited/unlimited connections and processing methods for timed-out connections.

(3) Set security account attributes: If it is FTP with a lot of public information, you can choose "Allow anonymous login".

(4) Set main directory properties: including local path, directory listing style, etc.

(5) Set directory security: You can choose to deny access to a certain host.

(6) Create a virtual directory: avoid system directory exposure and improve security.

Tip: The FTP software more commonly used than IIS is SERVER-U, and a trial version can be downloaded from the Internet.

6.5 Web Services
6.5.1 Understanding WWW
The World Wide Web (WWW) provides the most popular and popular information retrieval service on the Internet. The WWW provides a simple way for computer network users to use a WWW browser (such as IE or others) to access various media.It has changed the way people observe and create information, and has strongly promoted the widespread application of the Internet.

In 1945, Vannevar Bush (the father of Hypertext) proposed memex, which was the first prototype of hypertext (including not only text, but also voice and graphics). After that, many people studied different hypertext systems.

In 1989, Tim Berners Lee, a scientist at CERN, first proposed the concept of WWW, and used it as a tool for scientists in the field of high-energy physics to transmit new methods and new results.

In late 1990, the first WWW software appeared on computers.

In 1992, CERN officially published WWW, and Marc Andrecsen and others wrote the NCSAMOSAIC program, which made the development of WWW browsers mature day by day.

In 1994, the amount of WWW data transmitted on the Internet exceeded that of FTP for the first time, and became the most popular means of accessing Internet resources.

6.5.2 WWW Terminology
1. Browser

A web browser is software that displays files on a web server or file system and allows users to interact with those files.It is used to display text, images and other information on the World Wide Web or local area network.These texts or images can be hyperlinks to other websites, and users can quickly and easily browse various information.Web pages are generally in HTML format.Some web pages require specific browsers to display correctly.

We use a browser to access a certain server in the working mode of client/server. The client is a browser that requests WWW documents on a site on the Internet, and the WWW server is a computer that saves WWW information. Requests are made on the machine to transmit hypertext information between the server and the browser.

The role of the browser is to display the hypertext information returned from the server to the user.At present, commonly used browsers on the market include IE, NETSCAPE, FireFox, MyIE, etc. The following only introduces IE and FireFox two browsers.

(1) IE
Windows Internet Explorer, formerly known as Microsoft Internet Explorer, referred to as MSIE (commonly referred to as Internet Explorer, referred to as IE), is a web browser launched by Microsoft Corporation. Internet Explorer provides rich web browsing and building features, such as Microsoft Update is designed in the browser and so on.

(2) FireFox
FireFox (Firefox browser) is a product developed by Mozilla, an open source foundation organization. It is a completely open source free software. Anyone can get its source code and modify it.

The high security of Firefox browser is an important indicator. It has the function of blocking pop-up windows, which can effectively prevent unauthorized pop-up windows.Do not load harmful ActiveX controls, and run fast, occupying less system resources.

The size of FireFox 2.0 is only 5.7M, which is 1/9 of that of IE. It loads fewer controls during operation and runs fast. When browsing web pages, it adopts paging mode, which can speed up page loading.

2. Hypertext Transfer Protocol (HTTP)

The role of HTTP (Hypertext Transfer Protocol) is to explain and display the hypertext (Hypertext, written in HTML or other languages) found on the WWW. The HTML language itself contains various methods for formatting hypertext, so it allows browsers to It formats each text type to obtain the WWW page (WebPage or HomePage) screen display effect that the designer originally intended.

The HTTP protocol defines the transmission method of hypertext on the Internet, and the documents retrieved by this protocol contain links that users can further retrieve.When a browser connects to a remote server, it only retrieves the original information and quickly drops the connection.

This connection is non-persistent, and it is only reopened when more detailed information needs to be transmitted to the client, thus reducing the resource occupation of the Internet to a minimum.

The first document that the computer gets from the remote server is the home page (Home Page), which will contain many pointer URLs to other servers.By analogy, the entire Internet is an interconnected organic whole (WebSpace).

3. URL (Uniform Resource Locator)

A Uniform Resource Locator (UniformResource Locator, URL), also called a web page address, is a standard resource address on the Internet.It is an identification method used to completely describe the addresses of web pages and other resources on the Internet.

Every web page on the Internet has a unique name identifier, usually called a URL address. This address can be a local disk, or a certain computer on the LAN, and more often it is a site on the Internet.Simply put, a URL is a web address, or "web address."

For target files on Internet servers or World Wide Web servers, you can use "Uniform Resource Locator (URL)" addresses starting with "http://", and Web servers use "Hypertext Transfer Protocol (HTTP)".

The general format of a URL is as follows:
protocol://hostname[:port]/path/[;parameters][? query]# fragment description:

(1) protocol (protocol)
Specifies the transport protocol to use, valid scheme names for the protocol attribute are listed below.The most commonly used is the HTTP protocol, which is also the most widely used protocol in the WWW.

The file resource is a file on the local computer.The format is file://
ftp Access resources via FTP.The format is FTP://
gopher accesses this resource through the Gopher protocol.The format is gopher://
http Access the resource via HTTP.The format is http://
https Access the resource over secure HTTPS.The format is HTTPS://
The mailto resource is an email address, accessed through SMTP.The format is mailto:

MMS plays the resource by supporting the MMS (streaming media) protocol (representing software: WindowsMediaPlayer).The format is mms://
ed2k accesses this resource through P2P software that supports the ed2k (dedicated download link) protocol (representative software: eMule).

The format is ed2k://
Flashget accesses this resource through P2P software that supports the Flashget: (dedicated download link) protocol (representing software: Express).The format is Flashget://
thunder accesses this resource through P2P software that supports the thunder (dedicated download link) protocol (representing software:

Thunder).The format is thunder://
news accesses this resource through NNTP.The format is news:

Tencent communicates with users (representative software: QQ, TM) by supporting the Tencent (dedicated chat connection) protocol.The format is tencent://message/? uin=Number&Site=&Menu=yes
Msnim supports msnim (dedicated chat connection) protocol and user dialogue (representative software: MSN, WLM).

The format is msnim:chat? contact=Email address
(2) hostname (hostname)

Refers to the domain name system (DNS) host name or IP address of the server where the resource is stored.

(3) port (port number)

Optional parameter, when omitted, the default port of the scheme will be used. Various transport protocols have default port numbers, such as the default port number of http is 80.

(4) path (path)
A string separated by zero or more "/" symbols is generally used to indicate a directory or file address on the host.

(5) parameters (parameters)
Optional for specifying special parameters.

(6) query (query)
Optional, used to pass parameters to dynamic webpages (such as webpages made with technologies such as CGI, ISAPI, PHP/JSP/ASP/ASP.NET), there can be multiple parameters separated by "&;" symbols, each The parameter name and value are separated by the "=" symbol.

(7) fragments
Information fragment, which is a character string, used to specify the fragment in the network resource.For example, there are multiple noun explanations in a web page, and fragments can be used to directly locate a noun explanation.

Tip: The Windows operating system is not case-sensitive to the URL, but it is case-sensitive in the Unix/Linux system.

For example: http://www.uibe.edu.cn/yxxl/index.html, tell the WWW browser to use the http protocol, and find the file index.html from the yxxl subdirectory on the WWW server of the University of International Business and Economics.

Tips: URL forwarding is to guide the users visiting the current domain name to another specified network address through the special settings of the server.

For example, URL forwarding allows users to automatically turn to a designated website "http://www.QQ.com" when they visit http://www.123.com. The URL forwarding function is a domain name registration provided by the World Wide Web. subsequent value-added services.

(End of this chapter)