Understanding Networks and the Internet

1. Get the Net! The Internet and World Wide Web Some of this material can be found in Chapters 7 and 8 in Computing Essentials 2000-2001 (O’Leary and O’Leary)

2. Networks • A network is a collection of computers connected together so that they can share information • A network is called a local area network(or LAN) if the constituent computers are all located in the same vicinity

3. Other networks • Metropolitan area networks (MANs) are spread throughout a city or county. For example, a cellular phone network • Wide area networks (WANs) are spread over an even wider area, a telephone company, for instance

4. Client/Server • In the client/server arrangement, a more powerful computer (the server) manages the resources shared by the rest of network (the clients) • The client requests to use the server’s resources • A client crashes (bad news); the server crashes (disaster)

5. i vs. I Internet • When two or more networks are connected, they form an internet(small i) • The Internet(capital I) is the global collection of connected networks • “The biggest WAN of them all”

6. A Little History • An early ancestor of the Internet was called ARPANET (Advanced Research Project Agency Network) • It was built in the late 60’s by a collaboration of universities and the military • One desired feature was a network that would still function if part of it was “knocked out”

7. Connections • The whole point of being “connected” is that information can be passed back and forth • information (signals) can be sent through the air (as in radio or non-cable television), but computers are typically “wired”

8. Wire • twisted pair wire looks like the wire to your telephone • coaxial cable looks like the wire to your cable tv • fiber optic cable sends light beams • each successive wire has more bandwidth; bandwidth is related to the rateof information that can be send • (bandwidth  wire thickness)

9. Bandwidths • Voiceband • Refers to the transmission rate of the phone lines • Modems are one way to connect computers to the internet; the connection is via the phone line • Their speed measured in bits per second (bps) • Medium band (faster) • Broadband (even faster) • Broadband has high enough information rate to carry several “channels” at once

10. Packets • The information is broken into pieces, called packets, which are sent individually over the wire • The packets must also contain the information that allows the computer to reassemble them • more like sending letters than talking on the phone

11. Routers • packets are to letters as routers are to sorters in the post office • A router is the intelligent part of the connection that directs the information to the right place • The analog of one’s address is and zip code is the Internet protocol(IP) address • DEMO (of sorts)

12. Inter Vs. Intra • inter: between or among • intra: within or inside of • intranet: a set-up like the Internet (having browsers, email, etc.) but not connected to the outside world (often used by companies wanting to maintain some privacy)

13. Firewalls • A firewall restricts the flow of information both in and out • an attempt to have the best of both worlds: connectivity and access to information on one hand, privacy and security on the other • In the mail analogy, it is as though your mail is being censored

14. The Web  The Net • The World Wide Web is only part of the Internet • The Internet also includes • e-mail(electronic mail): to send messages to and receive messages from on the same or other networks • ftp(file transfer protocol): to put or get files from other computers (we’ll use this to post our web pages later in the semester)

15. The Net > The Web • The Internet also incudes: • telnet: to log onto a computer that one is not physically in front of (we’ll use this to post our web pages later in the semester) • gopher: to find files on the internet; gopher is a precursor to a “search engine” • usenet: to promote discussions on various topics among discussion or news groups

16. The World Wide Web • The Web is a hyperlinked multimedia database • HUH? • It is a vast collection of information stored in files (hence a database) • Above we are using the term database is a loose sense; some only use “database” to mean a highly-structured collection of information • It appears as documents with text, as well as graphics, audio, animation, and video (hence multimedia)

17. The Web • Finally, the documents (web pages) are connected to one another via hyperlinks, a reference to another web page which if clicked takes one to that page • Moving about in this fashion is generally referred to as “surfing”

18. Web Vs. Tree • Gopher is older than the Web and also allows one to access files • It has a “hierarchical” or tree structure • The branches are analogous to folders and files • One could not jump from branch to another; one had to climb back down the tree • The Web, if less structured, is more highly connected

19. Tree (like Windows Explorer) Web

20. Getting Around (URL’s) • the fancy term for a web site address is a uniform resource location(URL) • A URL consists of several parts, e.g. • http://www.lasalle.edu/lsu-site/it/notes.htm#attach • protocol: a set of standards allowing computers to exchange information • http - “hypertext transfer protocol” (others: ftp, gopher, telnet, news)

21. URL’s (cont.) • http://www.lasalle.edu/lsu-site/it/notes.htm#attach • domain: denotes the computer that holds the web page (stands in for the IP address) • often starts with www (World Wide Web) • ends with the type of organization operating the site or the country • edu (education), gov (government), mil (military), org (organization), net (networks), uk (United Kingdom), ch (Switzerland)

22. URL’s (cont.) • http://www.lasalle.edu/lsu-site/it/notes.htm#attach • the folder (or directory) containing the file, also known as the path • http://www.lasalle.edu/lsu-site/it/notes.htm#attach • the file or document (often an html file) • http://www.lasalle.edu/lsu-site/it/notes.htm#attach • anchor or fragment, indicates a specific part of a document

23. Hyperlinks • target: takes you from one part of a web page to another • relative: takes your from one web page to another, but the web pages are on the same web site • absolute: takes you to another web page on another web site

24. Web File Types • “We’d like you to know a little bit about our four files.” • Hypertext markup language(HTML) text with hyperlinks • Extensible Markup language (XML) is trying to overcome some limitations of HTML • Graphics Interchange Format(GIF) graphics, especially computer drawn pictures • Joint Photographic Experts Group(JPEG), graphics, esp. photos • Portable document format(PDF), mix of text and graphics • Higher quality but requires reader (special software)

25. Browsers and Search Engines • browser: software used to navigate (move around) the web • e.g. Netscape Navigator or Microsoft Internet Explorer • search engine: software used to locate information on the Web • e.g. Yahoo, Alta Vista, InfoSeek, Lycos, HotBot