Get the Net! The Internet and World Wide Web

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

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

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

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

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

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

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

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

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

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

The Web  The Net n The World Wide Web is only part of the Internet n The Internet also includes – (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

The Net > The Web n The Internet also incudes: – telnet: to log onto a computer that one is not physically in front of –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

The World Wide Web n The Web is a hyperlinked multimedia database n HUH? n It is a vast collection of information stored in files (hence a database) n It appears as documents with text, as well as graphics, audio, animation, and video (hence multimedia)

The Web n 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 n Moving about in this fashion is generally referred to as “surfing”

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

Tree (like Windows Explorer) Web

Getting Around (URL’s) n the fancy term for a web site address is a uniform resource location (URL) n A URL consists of several parts, e.g. n –protocol: a set of standards allowing computers to exchange information –http - “hypertext transfer protocol” (others: ftp, gopher, telnet, news)

URL’s (cont.) n –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)

URL’s (cont.) n –the folder (or directory) containing the file, also known as the path n –the file or document (often an html file) n –anchor or fragment, indicates a specific part of a document

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

Web File Types n “We’d like you to know a little bit about our four files.” n Hypertext markup language (HTML) text with hyperlinks n Graphics Interchange Format (GIF) graphics, especially computer drawn pictures n Joint Photographic Experts Group (JPEG), graphics, esp. photos n Portable document format (PDF), mix of text and graphics

Browsers and Search Engines n browser: software used to navigate the web n e.g. Netscape Navigator or Microsoft Internet Explorer n search engine: software used to locate information on the Web n e.g. Yahoo, Alta Vista, InfoSeek