Internet and the World Wide Web

1. Internet and the World Wide Web

2. The Internet is made up of more than 100,000 interconnected networks in over 100 countries, comprised of commercial, academic and government networks. • From the user’s point of view, the Internet is a way of connecting to essentially any other machine on the network.

3. Main Uses of the Internet • electronic mail (email) • World Wide Web • newsgroups and bulletin boards • chat rooms and instant messaging • telnet • ftp

4. Email • Uses mail composing and reading programs (e.g., MS Outlook) • Email can be sent directly from many Microsoft applications like Word and Excel, with the corresponding documents or spreadsheets included as attachments.

5. World Wide Web • Provides a standardized way for information residing on one computer (the web server) to be downloaded and read by another computer (the client). • The file(s) to be downloaded from the server use HTML (hypertext markup language), and the downloading takes place using HTTP (hypertext transfer protocol).

6. On the client computer, a web browser isused to display the information contained in the downloaded files. • The most commonly used web browsers are Netscape and Internet Explorer. • Web pages can provide access to a wide variety of information, all of which can potentially be downloaded to any computer.

7. Usenet (User Network) newsgroups, which allow anyone to post messages and read everyone else’s postings, have been around since long before the Web was created.

8. These newsgroups are organized around specific subjects of interest to particular subscribers. • Newsgroups can be selected and read directly from your Web browser.

9. Chat rooms provide another popular Internet service. • Internet Relay Chat (IRC) offers multiuser text conferencing on diverse topics. • Dozens of IRC servers provide hundreds of channels that anyone can log onto and participate in via the keyboard.

10. Internet Access • Today, all the major online services provide full Internet access. • In addition, thousands of Internet service providers (ISPs) have risen out of the woodwork to offer individuals and organizations access.

11. TCP/IP • All data is transmitted along the Internet using what is called TCP/IP. • TCP stands for Transmission Control Protocol and IP stands for Internet Protocol.

12. These protocols were developed by DARPA (Defense Advanced Research Projects Agency) to enable communication between different types of computers and computer networks, back when when what is now the Internet was just a small collection of widely distributed experimental networks known as the ARPAnet.

13. The Internet Protocol is a connectionless protocol which provides packet routing. • A packet is a unit of data formatted for transmission on a network.

14. Data is broken up into packets for sending over a packet switching network. • All the data packets making up a single message may not take the same route to get to their destination; they are reassembled once they have arrived.

15. Internet Services • Although most new users interact with the Internet via their Web browsers, for years, command-line UNIX utilities have been used.

16. For example, an FTP (File Transfer Protocol) program allows files to be transferred between machines.

17. Telnet is a terminal emulation program that lets you log onto a computer in the Internet and run a program, assuming you have an account that lets you access that computer. • Note: In the CCS labs, use F-Secure SSH, which is a more secure version of telnet.

18. World Wide Web • The World Wide Web is an Internet facility that links documents locally and remotely. • The Web document is called a Web page, and links in the page let users jump from page to page (hypertext) whether the pages are stored on the same server or on servers around the world.

19. The fundamental Web format is a text document embedded with HTML (Hypertext Markup Language) tags that provide the formatting of the page as well as the hypertext links (URLs--Uniform Resource Locators) to other pages.

20. HTML codes are common alphanumeric characters that can be typed with any text editor or word processor.

21. Numerous Web publishing programs, such as Frontpage, provide a graphical interface for Web page creation and automatically generate the codes.

22. Many word processors, such as Word, and publishing programs also export their existing documents to the HTML format, allowing Web pages to be created by users without learning any coding system.

23. Web pages are maintained at Web sites, which are computers that support the Web's HTTP (Hypertext Transfer Protocol) protocol.

24. When you access a Web site, you generally first link to its home page, which is an HTML document that serves as an index to the site's contents. • Large organizations create and manage their own Web sites. Smaller ones have their sites hosted on servers run by their Internet service providers (ISPs).

25. Many individuals have developed personal Web home pages since many ISPs include this service with their monthly access charge. • Individuals can post their resumes, hobbies and whatever else they want as a way of introducing themselves to the world at large.

26. How to transfer a file over the Internet • There are two ways to transfer files over the Internet. • One is to send a file along with an e-mail message, and • the other is to use an FTP program.

27. Via E-mail • E-mail programs have the ability to "attach a file" to a message, which means that any type of file (program, graphics, spreadsheet, etc.) can be transmitted along with the text message.

28. This is the simplest way to send a file via the Internet. • However, although widely used, it can be problematic. • Old e-mail programs, light versions of e-mail programs and some mail gateways can cause problems.

29. The standard Internet mail protocol supports only text. • And if the computer receiving the message does not have the Word program, for example, an attached Word document will be unreadable by the recipient.

30. Sending files via FTP and the Web • The protocol on the Internet that was designed to handle file transfers is FTP (file transfer protocol). .

31. With a Web browser, you can download from an FTP site. • You would use the ftp:// prefix and address (URL), which includes the domain name and directories.

32. Internet addresses • There are two kinds of addresses that are widely used on the Internet. • One is a person's e-mail address, and the other is the address of a Web site, which is known as its URL.

33. The format for addressing an email message to an Internet user is USER NAME @ DOMAIN NAME.

34. For example, your address might be ldecaprio@lynx.neu.edu. • There are no spaces between any of the words. • ldecaprio is the user name and lynx.neu.edu is the domain name. • The .edu stands for the academic top level domain category.

35. How to Find Someone Else's Address • There are Web sites that maintain directories, or white pages, of e-mail addresses. • New sites are coming online all the time. You may have to try several sites to find someone, and there's no guarantee. In the meantime, check out:

36. www.bigfoot.com • www.four11.com • www.whowhere.com • www.switchboard.com • www.infospace.com

37. IP address • An Internet Protocol address is the physical address of a computer attached to a TCP/IP network. • Every client and server station must have a unique IP address.

38. Client workstations have either a permanent address or one that is dynamically assigned to them each dial-up session. IP addresses are written as four sets of numbers separated by periods; for example, 204.171.64.2.

39. URL • Uniform Resource Locator is the address that defines the route to a file on the Web or any other Internet facility. • URLs are typed into the browser to access Web pages, and URLs are embedded within the pages themselves to provide the hypertext links to other pages.

40. For example, http://www.ccs.neu.edu retrieves the home page of the College of Computer Science Web site. The http:// is the Web protocol, and www.ccs.neu.edu is the domain name.

41. If the page is stored in another directory, or if a page other than the home page is required, slashes are used to separate the names. • For example, http://www.ccs.neu.edu/index.html points to the index page.

42. If a required page is stored in a subdirectory, its name is separated by a slash. • Like path names in DOS and Windows, subdirectories can be several levels deep. • For example, the components of the following hypothetical URL are described below:

43. http://www.abc.com/clothes/shirts/formal.html means the following: • http:// protocol • www.abc.com/ domain name • clothes/ subdirectory name • shirts/ subdirectory name • formal.html document or file name

44. Internet domain names • An Internet domain name is an organization's unique name combined with a top level domain name (TLD). • For example, ccs.neu.edu is the domain name of the College of Computer Science.

45. The following are the top level domains (the .edu, .mil and .gov domains are traditionally U.S. domains). • .com commercial • .net gateway or host • .org non-profit organization • .edu educational and research • .gov government • .mil military agency • .int international intergovernmental

46. The .int domain name is not widely used. • Outside of the U.S., the top level domains are typically the country code; for example, uk for United Kingdom.

47. Country code • A country code is a two-character component of an e-mail or Web address that identifies a country. • Web servers read addresses from right to left. • So, on encountering sven@univ.oslo.net.se, the message would first be sent to Sweden, since se is the country code for Sweden.

48. Swedish routers would then send the message to univ.oslo.net where it will be waiting for Sven the next time he logs on.

49. Search Engines and Sites • There are various Web sites that maintain databases about the contents of other Web sites. • Most sites are free and are paid for by advertising banners, while others charge for the service.

50. Some of the best known search sites are: • Yahoo! • Lycos • Infoseek • Altavista • There are many others. Here is a more complete list of such sites: