Internet and Web Concepts

1. Internet and Web Concepts • What is a URL? • The Internet and the World Wide Web (subset) • What is a browser? • HTTP is? • cs.uiuc.edu means… • What is “hypertext?” • What do we mean by client-server? Course Guide p. 59 CS 105 Fall 2005

2. Server Client HTTP Home Page Browser LAN Modem ISP KEY CONCEPTS CS 105 Fall 2005

3. Sweden New York • LAN = Local Area Network • LAN—physical or wireless connection in a home, office, classroom CS 105 Fall 2005

4. Connecting to the Internet ISP (Internet Service Provider)—connects to the Internet, and the user pays the hook-up fee and use charges. Examples: AOL, MSN, UIUC • Modem—Uses a phone line to reach a server • Cable — needs a cable modem (not really a modem!) Only if you have a T1 line do you have a direct connection to the Internet Course Guide p. 59 CS 105 Fall 2005

5. Other means of connecting • DSL (Digital Subscriber Line) — uses a DSL transceiver. You use your regular phone line, too. • ISDN connections use a special digital phone line that must be installed to your home by your local telephone company. They need a “Terminal Adapter”– also often called a “modem” (but it isn’t one) • Wireless Involves no wiring, just an antenna! CS 105 Fall 2005

6. Converting a voice to digits • Digital phones convert your voice into binary information (1s and 0s) and then compress the data • The person you talk to hears your voice after the 1s and 0s are changed back to sound CS 105 Fall 2005

7. VOIP -- Internet Telephony • Make your phone calls over the Internet! Voice over Internet Protocol; using packet based networks instead of the standard telephones to send voice data CS 105 Fall 2005

8. Terminology TCP/IP Transmission Control Protocol/ Internet Protocol TCP/IP is an agreed format that computers on the Internet use to communicate. Any computer that understands TCP/IP can connect to the Internet. Involves packets. Course Guide p. 60

9. Programs communicate, not computers A program on one computer uses protocol software to contact a program on another computer– a protocol is an agreed format that computers on the Internet use to communicate. • E-mail protocols: • SMTP - Simple Mail Transfer Protocol • POP - Post Office Protocol • File transfer protocol: FTP CS 105 Fall 2005

10. Terminology • HTTP -- HyperText Transfer Protocol The protocol used for a web document (HTML). Example: http://www.uiuc.edu • HTTPS: • A HTTP protocol that provides for more secure web communications by including encryption methods.

11. Hyperlinks • Provide text, graphics, sound or video links • Blue underlined fonts are unexplored • Magenta links have been previously accessed www.microsoft.com www.microsoft.com CS 105 Fall 2005

12. Client/________ Relationship What is a server? • Some computers on the network offer services that others can access. • ftp server -- email • Yahoo, Google -- • Library catalogues Your query goes to the server Server sends back information Course Guide p. 61 CS 105 Fall 2005

13. Electronic messages are sent to your account and stored on a ___________________. You send a message to someone. First it goes to a server CS 105 Fall 2005

14. Email software is later used to download messages from the __________ that is storing the message. You receive email from the server, where it has been stored for you CS 105 Fall 2005

15. Sample Email Address Jin45@uiuc.edu username@hostname.com “at” Name of your ISP’s host computer Your userID CS 105 Fall 2005

16. Using ph to find a person’s email address • http://www.uiuc.edu/cgi-bin/ph CS 105 Fall 2005

17. Peer-to-Peer • Systems like KaZaa • Files held on individual machines rather than centralized server CS 105 Fall 2005

18. Internet Addressing -IP Addresses • Computer ports, called servers, connected to the Internet have unique addresses. 222.230.112.5 IP number is a 32-bit address in four parts, of 8 bits each, and therefore, in 8 bits you can only represent the numbers 0 to 255 (256 possible numbers). Thus this address is not possible: 299.230.112.5 222.230.112.6 222.230.112.7 Course Guide p. 63 CS 105 Fall 2005

19. Internet Addressing -Domain names • These 4-part numbers are converted into easy-to-remember domain names. uiuc.edu, google.com, eBay.com google amazon CS 105 Fall 2005

20. Spam, Phishing – Where does this link take you? CS 105 Fall 2005

21. Domain Naming System • provides mnemonic help in identifying sites • organizes the names of computers, subnetworks, and larger networks • reading left-to-right, information becomes more general cs.uiuc.edu educational site University of Illinois @ Urbana-Champaign Computer Science Department CS 105 Fall 2005

22. http://www.cs.uiuc.edu/~roberta/ http:// ....... specifies Hypertext Transfer Protocol, / www.cs.uiuc.edu ......... Identifies location of web server ~ means bypass intermediate directories and go straight to the directory named roberta (~ is called a tilde) index.html ........ is the name of the home page and will appear whether or not you type index.html! The URL CS 105 Fall 2005

23. Internet Addressing -URL Example Secure Protocol https://netfiles.uiuc.edu/moor12/www/cluster/news.html Folder HTML Document Top Level Domain Student or Employee CS 105 Fall 2005

24. Internet Addressing -Top level domains • You can find out who owns a domain name. • www.networksolutions.com/cgi-bin/whois/whois uiuc.edu google.com whitehouse.gov CS 105 Fall 2005

25. Top Level Domains .com Commercial businesses .org Non-profit organizations .net Network services .gov Government agencies .edu Educational institutions .mil Military .int International .nom For individual users .web Web-based businesses .AERO, .BIZ, .COOP, .INFO, .MUSEUM, .NAME, and .PRO CS 105 Fall 2005

26. Common Country Domains • .au Australia • .fi Finland • .cn China • .uk United Kingdom • .us United States • .il Israel • .ch Switzerland • .mx Mexico CS 105 Fall 2005

27. Country IDs Course Guide p. 65 CS 105 Fall 2005

28. Terminology • HyperText Markup Language (HTML) A convention of codes used to display content such as words, pictures, etc. Without HTML code, a document would be unreadable by a Web browser. Right now, HTML is the Language of the World Wide Web, but the web is moving toXHTML Extensible Markup Language (XML) is the universal format for structured documents and data on the Web—it is compatible with XHTML but not with HTML. XML is built into the Windows XP operating system.