Some basic knowledge of the network _ Application skills

What is WWW?


WWW is the Internet Multimedia Information Inquiry Tool, is the Internet in recent years, the development of services, but also the fastest growing and currently used the most extensive services. Because of the WWW tools, the Internet has developed rapidly in recent years, and the number of users has grown rapidly.

www introduction

WWW is the World Wide Web (Global information Network) abbreviation, also can be referred to as the web, the Chinese name is "www". It originated in March 1989 by the European Quantum Physics Laboratory CERN (the European Laboratory for Particle physics) developed by the master-slave structure of the distributed Hypermedia system. Through the World Wide Web, people can quickly and easily get rich information by using simple methods.

As users access information resources through a Web browser, there is no need to care about technical details, and the interface is very friendly, so the web on the Internet on the launch of a warm welcome, popular around the world, and rapid development of explosive.

The development and characteristics of www

For a long time, people have only received information through traditional media such as television, newspapers, magazines and radio. However, with the development of computer network, people want to obtain information, no longer satisfied with the traditional media that the way of unilateral transmission and acquisition, and hope to have a subjective selectivity. Now, the network provides various kinds of database system, such as literature periodical, industry information, meteorological information, paper retrieval and so on. 　　Because of the development of computer network, information acquisition becomes very timely, rapid and convenient. By the year 1993, WWW technology has made a breakthrough, which solves the problem of text display, data connection and image transmission in the remote Information service, making www become the most popular way of information dissemination on the Internet.

The Web server is now the largest computer group on the Internet, with many Web documents and a wide network of linked networks, which is unimaginable. It can be said that the WEB has taken a pioneering step towards the popularization of the Internet, the most exciting achievement on the Internet in recent years.

WWW is a client/server architecture that is used to organize and store various WWW resources and to respond to requests from client software to transfer the resources required by the client to platforms such as Windows 95 (or WINDOWS98), Windows NT, UNIX, or Linux.


What is Java?


Java is a programming language introduced by Sun. It is a language that is executed by way of interpretation, and syntax rules are similar to C + +. At the same time, Java is a cross-platform programming language. Programs written in the Java language are called "applets" (small applications), using the compiler to compile it into a class file, it will exist in the WWW page, and the corresponding markup on the HTML file, the user side as long as the client software installed Java can directly run the "Applet" online. Java is ideal for corporate networks and the Internet environment and is now one of the most popular and influential programming languages on the Internet. Java has many commendable advantages, such as simple, object-oriented, distributed, interpretive, reliable, secure, structural neutrality, portability, high-performance, multithreading, dynamic and so on. Java has abandoned C + + in a variety of advantages and disadvantages of more than the benefits of the function and a lot of rarely used features. Jave can be run with any microprocessor, programs developed in Java can be transmitted over the network and run on any client.


What is HTML?


HTML (Hypertextmark-uplanguage), the Hypertext Markup Language, is the description language of www. The purpose of designing an HTML language is to be able to easily link text or graphics stored in one computer to text or graphics on another computer, to form an organic whole, without having to consider whether the specific information is on the current computer or on other computers on the network. We simply use the mouse to click an icon in a document, and the Internet immediately goes to the content associated with this icon, which may be stored on another computer on the network. HTML text is a descriptive text consisting of HTML commands that can describe text, graphics, animations, sounds, tables, links, and so on. The structure of HTML consists of a head, a body, two parts of the head, which describes the information required by the browser, and the body contains the specific content to be described.


What is online chat?


Online chat (chat) is the use of the WWW server-specific CGI program, two people (or more people) through the browser real-time conversation through the keyboard. It should be noted that only the exclusive server and hosting server can open chat rooms.

What is a browser?


The Global Network (WEB,WWW) is an attempt to organize all the information on the Internet, including local information that you would like to add, into a hypertext file format. Although the dream may be a bit unrealistic, the global network does give you access to all the resources on the internet, just "read" the appropriate files in the browser.

A browser is a translation of text documents (and other types of files) found on the Internet into Web pages. Web pages can contain graphics, audio and video, as well as text; As a result, the web has sparked interest in the formerly text-based Internet.

A browser is an application on your hard disk, just like a word processor (such as WordPerfect or Microsoft Word).

HTML is the formatted language on which the network is based.

The HTML document looks very different from the Web page displayed on the browser. The Web page you see on the screen is the browser's translation of HTML documents.

The images you see are called by HTML documents, but they are not part of it-they are separate documents.

The browser reads the location of the images from the HTML code and places them on the Web page.

Similarly, audio or video files are called by HTML files and then assembled by the browser.

The cache of browsers is another important factor:

Because documents on the Web take time to download, browsers can temporarily store images on your hard disk to avoid downloading the same files repeatedly. The cache can and should be emptied at least once every four or five hours.

What is ISDN?


"First-line", the professional name is "Narrowband Integrated Services Digital Network" (N-ISDN), it is based on the telephone line for the development of a common telephone line to provide voice, data, images and other integrated services for the community to provide economic, high-speed, multi-functional, covering a wide range of access to simple means of communication. Its greatest advantage is to be able to carry out a variety of telecommunications services, such as telephone, fax, videophone, conference TV, such as integrated in a network to achieve.　　All users who join this network can realize that only a pair of telephone lines are connected to different terminals for different types of high speed and high quality business communication. "First-line" business provides users with both basic rate (2b+d,144kbps) and one-time group rate (30b+d,2mbps) interface. The basic rate interface consists of two independent working B channels (64Kkbps) and a D channel (16Kkbps), where B channels are typically used to transmit voice, data, and images, and D channels are used to transmit signaling or packet information.


What is ADSL?


ADSL technology is an asymmetric digital subscriber line to achieve broadband access interconnection network technology, ADSL as a transport layer of technology, make full use of existing copper resources, on a pair of twisted pair to provide uplink 640kbps downlink 8Mbps bandwidth, thus overcoming the traditional users in the "last kilometer" of the "bottleneck", To achieve a true sense of broadband access.

The principle of ADSL:

The traditional telephone system uses the low-frequency portion of the copper wire (band 4kHz below). and ADSL using DMT (discrete multi-audio) technology, the original telephone line 0Hz to 1.1MHz frequency band divided into 256 frequency-wide 4.3kHz of the sub-band. Among them, the band below 4kHz is still used to transmit pots (traditional telephone service), 20kHz to 138kHz frequency band to transmit uplink signal, 138kHz to 1.1MHz frequency band is used to transmit downlink signal. The DMT technology adjusts the number of bits that are modulated on each channel according to the condition of the circuit, so that the line can be used more fully. Generally speaking, the greater the signal-to-noise ratio of the sub channel, the more bits are modulated on the channel. If the signal-to-noise ratio of a sub channel is poor, discard it. At present, ADSL can reach the uplink 640kbps, downlink 8Mbps data transmission rate.

It can be seen from the above, for the original telephone signal, still use the original band, and based on ADSL business, using the frequency band outside the voice. Therefore, the original telephone business is not affected by any effect.


The basic condition of ADSL:

With the rapid and healthy development of international interconnection network, the application of E-commerce, the Internet is fast, efficient and convenient, has gone into thousands of households, become an essential part of people's lives, the application of the Internet has also been rapid development. Users can access the Internet in a variety of ways, digital, broadband, fiber to the user (FTTH) is the inevitable direction of future access, due to the high cost of fiber to households, in the next few years, most users will continue to use the existing transitional broadband access technology, including N-ISDN, Cable Modem, ADSL, etc., which ADSL (asymmetric digital subscriber loop) is the most promising and competitive one, will be in the next more than 10 years or even dozens of years dominate.


Advantages of ADSL:

DSL (digital subscriber lines, Digital subscriber line) is a copper telephone line for transmission medium transmission technology combination, it includes HDSL, SDSL, VDSL, ADSL and RADSL, etc., generally referred to as xDSL. Their main difference is reflected in the signal transmission speed and distance, as well as the uplink and downlink rate of the different symmetry of the two aspects.
HDSL and SDSL support symmetric t1/e1 (1.544mbps/2.048mbps) transmissions. The effective transmission distance of HDSL is 3-4 km, and it needs two to four pairs of copper twisted telephone lines; SDSL maximum effective transmission distance of 3 km, just a pair of copper wire. In comparison, symmetric DSL is more suitable for enterprise point-to-point connection applications, such as file transfer, video conferencing and other data to send and receive roughly the corresponding work. Compared to asymmetric DSL, the market for symmetric DSL is much lower.
VDSL, ADSL and RADSL belong to asymmetric transmission. VDSL technology is the fastest of xDSL technology, on a pair of copper twisted telephone line, uplink data rate is 13 to 52Mbps, downlink data rate of 1.5 to 2.3 Mbps, but the VDSL transmission distance of only hundreds of meters, VDSL can be a cost-effective alternative to the fiber to the home, the current Shenzhen VOD (video on Demand) is implemented by this access technology; ADSL supports up to 640Kbps to 1Mbps on a pair of copper wire, downlink rate 1Mbps to 8Mbps, Effective transmission distance within 3-5 km range; RADSL can provide the same speed range as ADSL, but it can dynamically adjust the user's access speed according to the quality of twisted-pair copper wire and the distance of transmission. It is the RADSL of these features that make RADSL the ideal technology for high-speed surfing on the web, video-on-demand (IAV), remote local area network (LAN) access, where users often download much more information than the uploaded information (send instructions).

What is a URL?


The URL (uniform resoure Locator: Uniform Resource Locator) is the address of the WWW page, which is composed of the following sections from left to right:

· Internet resource type (Scheme): Indicates the tools that the WWW client uses to manipulate. such as "http://" means the WWW server, "ftp://" represents the FTP server, "gopher://" represents the gopher server, and "NEW:" represents the newgroup newsgroup.

• Server address (host): Indicates the name of the server on which the WWW page resides.

• Ports (port): sometimes (not always), for access to some resources, you need to give the appropriate server to provide the port number.

• Path (PATH): Indicates the location of a resource on the server (the format is the same as the format in the DOS system, usually with a directory/subdirectory/filename structure). As with ports, paths are not always required.

The URL address format is arranged as: Scheme://host:port/path, for example, Http://www.sohu.com/domain/HXWZ is a typical URL address.

What is URL forwarding?

The so-called URL forwarding, is through the server's special settings, will access your current domain name of the user to boot to another network address you specify.

What is an IP address?


In the network, we often encounter the concept of IP address, which is an important concept in the network. An IP address is a unique 32bit address assigned to each host connected to the Internet on a worldwide scale. The structure of the IP address allows us to easily address on the Internet. IP addresses are usually expressed in more intuitive, 4 decimal digits with dot dividers, each corresponding to 8 binary bit strings, such as the IP address of a host: 128.20.4.1

The Internet IP address is unified by the Inter NIC (Internet Network Information Center) for global address planning, management, and the Inter NIC, APNIC, ripe three network information centers specifically responsible for the United States and other areas of IP address allocation. Usually each country needs to set up an organization to apply the IP address to the relevant international organizations and then assign it to the client.


What is FTP (file transfer)?


Files Transfer Protocol FTP (file Transfer Protocol) is one of the traditional services of the Internet. FTP enables users to transfer files between two networked computers, which is the primary way to deliver files on the Internet. With Anonymous (Anonymous) FTP, users have free access to Internet-rich resources. In addition, FTP also provides login, directory query, file operation and other session control functions.

What is BBS (bulletin board service)?


BBS (Bulletin Board Service, bulletin board services) is an electronic information service system on the Internet. It provides a public electronic whiteboard, which each user can write on, can publish information or make comments. Most of the BBS by educational institutions, the management of research institutions or commercial institutions. Like Blackboard in everyday life, electronic bulletin boards are divided into numerous bulletin boards according to different themes and topics, and the bulletin boards are based on the requirements and preferences of most BBS users, who can read the latest ideas about a topic ( Just a few seconds ago, you can put your ideas in the bulletin board without reservation. In the same way, people respond quickly to your point of view (sometimes you can see what others think of your point of view after a few seconds). If you need to communicate alone, you can send the words you want to say directly to someone's e-mail. If you want to chat with someone you're using, you can start the chat program, which is a gossip person, and even though you don't know each other, you can talk to each other intimately. In BBS, the communication between people broke the limit of space and time. When interacting with others, it is not necessary to consider their age, education, knowledge, social status, wealth, appearance, health status, and these conditions are often in other forms of communication unavoidable. Similarly, there is no way to know the true social identity of the person who is talking. In this way, the people who participate in BBS can be in an equal position with other people to carry out any problem discussion. This is not possible for all other forms of communication that are available. BBS is convenient to people, you can log on through the Internet, you can also dial in through the telephone network. BBS station is often made by some interested in this way to see the establishment, for all the free open. Moreover, because BBS's participation is multitudinous, therefore each aspect topic has the enthusiastic person. It can be said that on the service S can find any topic you are interested in.

What is an FTP server?

Simply put, the FTP-enabled server is the FTP server, and here's what the FTP protocol (File Transfer Protocol) is about.
Generally speaking, the primary purpose of user networking is to realize information sharing, and file transfer is one of the most important contents of information sharing. Early implementation of the Internet to transfer files, is not an easy thing, we know that the Internet is a very complex computer environment, there are PCs, workstations, there are Macs, there are large machines, according to statistics connected to the Internet on the computer has tens of millions of units, And these computers may run different operating systems, there are running UNIX servers, there are running DOS, Windows PC and running MacOS Apple, and so on, and a variety of operating systems file communication problem, need to establish a unified file transfer protocol, which is called FTP. There are different FTP applications based on different operating systems, and all of these applications adhere to the same protocol so that users can transfer their files to others or get files from other user environments.
Like most Internet services, FTP is also a client/server system. The user connects to the FTP server program on the remote host through a client program that supports the FTP protocol. The user sends a command to the server program through a client program that executes the commands issued by the user and returns the results of the execution to the client. For example, a user sends a command asking the server to send a copy of a file to the user, and the server responds to the command and sends the specified file to the user's machine. The client program receives the file on behalf of the user and stores it in the user directory.
In the use of FTP, users often encounter two concepts: "Download" (Download) and "Upload" (Upload). The download file is the copy of the file from the remote host to your computer, and the upload file is the copy of the file from your computer to the remote host. In Internet language, a user can upload (download) files to (from) a remote host through a client program.
When you use FTP, you must first log in, and you can upload or download files after you have the appropriate permissions on the remote host. That is, you must have the appropriate authorization for which computer you want to transfer files to. In other words, the file cannot be routed unless there is a user ID and password. This is contrary to the openness of the Internet, the FTP host on the internet is more than tens of millions, it is impossible to require each user on each host account. Anonymous FTP is created to solve this problem.
Anonymous FTP is a mechanism by which a user can connect to and download files from a remote host without becoming a registered user. The system administrator has established a special user ID, named Anonymous, where anyone on the internet can use the user ID.
The FTP program connects anonymous FTP hosts in the same way as connecting to a normal FTP host, except that you must enter a anonymous when you require a user ID ID, and the password for that userid can be any string. It is customary to use your own e-mail address as a password to enable system maintenance programs to record who is accessing these files.
It is noteworthy that anonymous FTP does not apply to all Internet hosts, but only to those hosts that provide this service.
When a remote host provides an anonymous FTP service, certain directories are specified to be open to the public, allowing anonymous access. The rest of the directories in the system are in the hidden state. As a security measure, most anonymous FTP hosts allow users to download files from them, rather than allowing them to upload files to them, that is, users can copy all files on an anonymous FTP host to their machines, but they cannot copy any of the files on their machines to an anonymous FTP host. Even though some anonymous FTP hosts do allow users to upload files, users can only upload files to a specified upload directory. The system administrator then checks the files and moves them to another public download directory for other users to download, in which case the remote host's users are protected from uploading problematic files, such as files with viruses.
As an Internet user, you can copy files between any two Internet hosts via FTP. However, most people have only one Internet account, and FTP is primarily used to download public files, such as shareware, company technical support files, and so on.
There are thousands of anonymous FTP hosts on the Internet that contain countless files for free copies. In fact, almost all types of information, all types of computer programs can be found on the Internet. This is one of the important reasons the Internet attracts us.
Anonymous FTP users have the opportunity to access the world's largest information base, the information base is cumulative, and is still growing, never closed, involving almost all topics. And all of this is free.
Anonymous FTP is a common method of publishing software on the Internet. The reason the Internet continues to this day is because people use programs that provide standard services through standard protocols. A lot of programs like this are published via anonymous FTP, and anyone can access them.
There is a huge number of anonymous FTP hosts and more files on the Internet, so how exactly do you know which directory on which anonymous FTP host a particular file is located? This is exactly what the Archie server is doing. Archie will automatically search the FTP host, construct a database containing all the file directory information, so you can find the location information of the desired file directly.