Get the Net!

The Internet and World Wide Web

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

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

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”

A Little History

An early ancestor of the Internet was called ARPANET (Advanced Research Project Agency)

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”

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”

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 rate of information that can be send

(bandwidth wire thickness)

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

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)

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)

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

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

The Net > The Web

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

The Web is a hyperlinked multimedia database

HUH? It is a vast collection of information

stored in files (hence a database) It appears as documents with text, as

well as graphics, audio, animation, and video (hence multimedia)

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”

Web Vs. Tree

Gopher is older than the Web and also allows one to access files

It has a “hierarchical” or tree structure 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

Tree (like WindowsExplorer)

Web

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)

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)

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

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

Web File Types

“We’d like you to know a little bit about our four files.”

Hypertext markup language (HTML) text with hyperlinks

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

Browsers and Search Engines

browser: software used to navigate 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