Lecture 15

INTRODUCTION TO COMPUTER

LECTURE NO 15

INTERNET The process of connecting separate networks is called internetworking. A collection of networked networks is described as being Internet worked. Internet is a worldwide network of networks. HOW THE INTERNET WORKS The single most important thing to understand about the Internet is that it potentially can link your computer to any other computer. Anyone with access to the Internet can exchange text, data files and programs with any other user. TCP/IPTHE UNIVERSAL LANGUAGE OF THE INTER NET The set of commands and timing specifications is used by the inter net is called Transmission Control Protocol /Internet Protocol, universally abbreviated as TCP/IP. The TCP/IP protocol includes the specifications that identify individual computers and exchange data between computers. They also include rules for several categories of application programs, so programs that run on different kinds of computers can talk to one another. TCP/IP software looks different on different kinds of computers but it always presents the same appearance to the network. Therefore it does not matter if the system at another end of a connection is a supercomputer that fills a room, a pocket size personal communication device, or anything in between, as long as it recognizes TCP/IP protocols, it can send and receive data through the internet. A Network of Networks – Backbone and Gateways Most computers are not connected directly to the internet, they are connected to smaller networks that connect through gateway to the Internet backbone. That is why the Internet is sometimes described as “ a network of networks”. Addressing Schemes IP and DNS addresses Internet activity can be defined as computers communicating with other computers using TCP/IP. The computer that originates as transaction must identify its intended destination with a unique address. Every computer on the internet has a four parts is a number between 0 and 255, so an IP address looks like this: 192.168.0.1 Most computers on the internet also have an address called a Domain Name System(DNS) an address that uses words rather than numbers. DNS addresses have two parts: an individual name, followed by a domain (a name for a computer connected to the Internet) that generally identifies the type of institution that uses the address, such as .com for commercial businesses or edu for schools, colleges, and universities. The University of Washington’s DNS address is Washington .edu; Microsoft’s is Microsoft.com. Within the United States, the last three letters of the domain usually tell what type of institution owns the computer.

MAJOR FEATURES OF THE INTERNET E-MAIL The single most common use of the Internet is for the exchange of electronic mail, or e-mail. Anyone with an e-mail account can send messages to other users 1

INTRODUCTION TO COMPUTER

LECTURE NO 15

of the Internet and to many networks connected to the Internet through gateways. Most e-mail programs also permit users to attach data files and program files to messages. NEWS In addition to the messages distributed to mailing lists by e-mail, the Internet also supports a form of public bulletin board called News. There are approximately 15,000 news groups, each devoted to discussion of a particular topic. A newsreader program----the client software ---obtains articles form a news server, which exchanges them with other servers through the Internet. To participate in News, you must run a newsreader program to log onto a server.

Common Usenet Domains DOMAIN COMP SCI SOC News Rec Misc

DESCRIPTION Computer-related topics Science and technology (except computers) Social issues and politics Topics related to Usenet Hobbies, arts, and recreational activities Topics that do not fit one of the other domains

Telnet-Remote Access to Distant Computers Telnet is the Internet tool for using one computer to control a second computer. Using Telnet, you can send commands that run programs and open text or data files. The Telnet program is a transparent window between your own computer and a distant host system, a computer that you are logging onto. A Telnet connection sends input form your keyboard to the ghost and displays text from the host on your screen. Connecting to a Telnet host is easy; enter the address, and the Telnet program sets up a connection. When you see a logon message from the host, you can send an account name and password to start an operating session. Access to some telnet hosts is limited to users with permission from the owner of the host, but many other hosts offer access to members of the general Internet public. FTP File Transfer Protocol, on FTP, is the Internet tool used to copy files form one computer to another. When a user has accounts on more than one computer, FTP can be used to transfer data of programs between them. There are also public FT P archives that will permit anyone to make copies of their files. These archives contain thousands of individual programs and files on almost every imaginable subject. Anyone with an FTP client program can download and use these files. Gopher All kinds of information are available through the Internet, but much of it can be difficult to fine without a guide. Gopher organizes directories of documents, images, programs, public Telnet hosts, and other resources into logical menus. The first Gopher was created at the University of Minnesota (home of the Golden Gophers) to provide easy access to information on computers all over the 2

INTRODUCTION TO COMPUTER

LECTURE NO 15

University’s campus. When a user selected an item form a Gopher menu, the Gopher server would automatically download that item to the user’s computer. A Gopher menu can include links to anything on the Internet, including files of all kinds, host computers, and other Gopher menus. Some menus and submenus are organized by subject, and others list resources in a particular geographical region. Most menus also include pointers to the local server’s top-level menu or to the “Mother Gopher” in Minnesota that lists all the Gopher servers in the world. Internet Relay Chat (IRC) Internet Relay Chat (IRC), or just chat is a popular way for Internet users to communicate in real-time with other users. Real-time communication means communication with other users right now. Unlike e-mail, chat does not require a waiting period between the time you send a message and the other person or group of people receives the message. IRC is Internet because it enables a few or many people join in a discussion. IRC is a multi user system where people join are discussion groups where chat users convene to discuss a topic. Chat messages are typed on a user’s computer and sent to the IRN channel, whereupon all users who have joined that channel receive the message. Users can then read, reply to, or ignore that message, or create their own message. The World Wide Web The World Wide Web (the Web or WWW) was created on 1989 at the European Particle Physics Laboratory in Geneva, Switzerland, as a method for incorporating footnotes, Figures, and cross-references into online hypertext document s in which a reader can click on a word or phrase in a document and immediately jump to another location within the same document, or to another file. The second file ma be located on the same computer as the original document or anywhere else on the Internet. Because the user does not have to learn separate commands and addresses to jump to a new location, the World Wide Web organized widely scattered resources into a seamless whole. The latest generation of Web browsers, including Mosaic. Netscape Navigator, and Microsoft’s Internet Explorer, can open file viewers and other application programs automatically when they receive graphic images, audio, video, a other files. The internal structure of the World Wide Web is built on a set of rules called Hypertext Transfer Protocol (HTTP) and a page-description language called Hypertext Markup Language (HTML). HTTP uses Internet addresses in a special format called a Uniform Resource Locator, or URL, URLs look like this: type://address/path http//www.uiuc.edu

3