Local Area Network (LAN) with 2 or more computers
sharing information
To transfer information from one computer to another required transporting cards, tape, disk, diskette, ....
Better way to share information is to create connection
Local Area Network (LAN) with 2 or more computers
sharing information
Unexpected result -- electronic mail (email)
Connect networks to make network of networks ....
A network can withstand failures of some connections and still continue to operate
Research and development projects in 1980s sponsored by National Science Foundation (NSF) and Department of Defense (DOD)
"Internet" is short for "Interconnected Network of Networks"
A "protocol" is a standardized method -- in this case for communication
Internet transfers messages (information) as packets of characters (bytes)
Computer that is directly connected to Internet is called "Internet node"
Each Internet node has software that transfers information using the Internet Protocol (IP)
Most (but not all) Internet nodes
have IP Host Name --
ocean.cs.purdue.edu
indynet.indy.net
inet.d48.lilly.com
alw.nih.gov
blackbird.afit.af.mil
philadelphia.libertynet.org
Each Internet node MUST have IP Host Number --
128.10.2.28
199.3.65.1
40.33.1.1
128.231.128.7
129.92.1.2
128.91.1.141
At end of IP name...
Commercial (.com)
Education (.edu)
Government (.gov)
Military (.mil)
Internet (.net)
Non-profit organizations (.org)
Outside the US, different naming schemes. Typically last two characters of IP name identify country (toronto.cbc.ca, mitsubishi.co.jp, club.eng.cam.ac.uk)
The .edu domain is for "colleges and universities".
The .us domain is used for "technical schools and pre-college schools" (among other state-related domains).
The .us domain is predominantly used by state government agencies, K-12 schools, community colleges, technical/vocational schools, and private schools
For example, the Lafayette Indiana School Corporation's Website is at http://www.lsc.k12.in.us
Transmission Control Protocol (TCP) and Internet Protocol (IP) software provide communications -- TCP/IP
Internet refers to the
physical side of the global network plus TCP/IP software
Web refers to a body of information -
- abstract space of knowledge
CERN -- collective of European high-energy physics researchers
CERN (Conseil European pour la Recherche Nucleaire) members located in number of different countries
In 1989 Tim Berners-Lee (from England) proposed global
hypertext (Web) project
Documents can have links (connections) to other documents and other things
Hypertext links (hyperlinks) can create a complex virtual web of
connections
http://www.wunderground.com/index.html
Possible to represent nearly any file or service on the Internet with a URL
First part of URL (before two slashes) specifies method of access
Second part -- typically address of computer where data or service is located
Further parts may specify name of file, port to connect to, or text to search for in document
http://www.wunderground.com works because index.html is the default file
Client-server paradigm
Server program sends copies of documents on request
Requires computer on Internet and server software always running
Client program sends message to server to request copy of document
Clients and servers communicate via TCP/IP
Client and server may establish "persistent connection" so that all pages after first arrive more quickly
Computers (nodes) on the Internet use several different operating systems: Microsoft Windows (95, 98, 2000, Millennium, NT, XP), Unix, Linux, Macintosh
Operating system provides user interface, a way for the user to interact with the operating system
Graphical User Interface (GUI)
Command line interface
Web browsers are available for each kind of operating system
Internet was built using UNIX machines
Notepad, Wordpad, and similar editors create text files -- useful as Web files
Often useful for building Web pages on one computer and FTP'ing them to computer that has Web server
Telnet protocol developed in 1980 provides for remote access
With telnet can type in Unix commands to one computer from window opened on another computer
Secure Shell (SSH), 1995, designed to take the place of Telnet
SSH implements Telnet in a secure manner; operates over TCP and provides strong authentication and secure communications
user-id@IP-Host-Name
fkjohnson@prozac.lilly.com
Mail tools (Elm, Pine, Pegasus, Eudora, Netscape, Microsoft Outlook) major features:
Create message
Send message to one or more people
Send "courtesy copies" (cc) to one or more people
Send "blind courtesy copies" (bcc) to one or more people (usually yourself)
Read message
Save message (usually in "folders")
Forward message to someone else
Reply to message
Aliases for often-used email addresses --
johnson: fkjohnson@prozac.lilly.com
Aliases for groups of email addresses --
officers: dlwilson@prozac.lilly.com, brsmith@acctg.lilly.com,
fkjohnson@prozac.lilly.com, dunsmore@purdue.edu
Delete message
Post Office Protocol (POP) -- download incoming email messages to local machine
Server erases any messages that have been downloaded to client machine
Best to use if you always read email from same machine
Internet Message Access Protocol (IMAP) -- keep messages on IMAP server
Best to use if you read email from various machines
Avoid "Hi" or "Hello"
Decide on subject after writing email message by choosing most relevant phrase
If you reply to a message, most mail tools will automatically create a Subject line for you
Be sure to change that Subject line when the conversation drifts away from the original subject
Check your spelling
Use good grammar
Use (but don't overuse) *asterisks* or CAPITAL LETTERS for emphasis
Include relevant lines from the other person prefaced by > in your reply...
> Do you think we should have the
> meeting at 2:00 today or would it be
> better to have it tomorrow?
I would prefer tomorrow.
No Flaming -- Don't say anything via email that you would not say
face-to-face in front of your mother
"Sign" your email message at least with your name followed by a line of dashes, underscores, or equal signs...
Betty Williamson
==================
Make sure to "sign" the email message with your real name ... especially if your email address is NOT your real name
An unsigned email message from bigstinky@hotmail.com is like a phone call from someone who refuses to identify himself
(The "signing" rule above may be relaxed if you are certain the recipient knows who you are....)
Keep signatures to 6 lines or less...
==============================
Dr. H. E. Dunsmore
Department of Computer Science
Purdue University
West Lafayette, Indiana 47907
==============================
Images, sounds, animations, word processing files, etc.
Modern email clients use: MIME (Multipurpose Internet Mail Extensions) (also known as Base64)
File is encoded to characters for mail transport
File extension identifies what it is...
.txt = text
.gif, .jpg, .jpeg, .bmp = image
.exe = executable program
.doc = Word file
.htm, .html = HTML file
Causes some unexpected and usually undesirable event
Virus often designed to spread automatically to other computer users
Effects range from just sending virus to others, sending files to someone else, deleting some files, to completely disabling computing system
Viruses can be transmitted as email attachments, downloaded programs from Web, or on diskette or CD
User that virus came from may be oblivious that he or she has it
Some viruses work immediately
Others are "time bombs" until date or situation causes virus to go to work
Some protection by only opening attachments and programs from trusted individuals and organizations
More protection from anti-virus software that screens email attachments and checks files periodically and removes any viruses found
No completely fool-proof way to avoid viruses
Be careful about .exe, .doc, and .vbs attachments or any such files given to you by any means
Typically warning arrives via email with well-meaning people forwarding it to others ad nauseam
Recent hoax warned people to look for file named Sulfnbk.exe and to delete it (bad virus!) immediately. Sulfnbk.exe is actually standard Windows system file. If deleted, Windows will not work.
If you get message about virus, check it out by going to one of the leading virus Web sites
Hoaxes are not limited to viruses. Internet and Web are full of mis-information.
Problem -- anyone can publish anything via email and Websites. Appearing on computer screen gives it air of authenticity.
No response is often best way to be removed from junk mail or undesireable mailing lists
Now greater than 50% of all email
Spammers gather email addresses by purchasing mailing lists and scanning web pages and newsgroups
Spammers rarely remove an email address from their database upon request
Request confirms that email address actually exists and is being used
Some spam filtering may be done by ISP
Further filtering can be done by user
SpamAssassin examines each message to detect if it is a junk email message
Netscape email tool places messages in Junk folder; learning software
NCSA's Software Design Group -- produced versatile, multi-platform interface to World-Wide Web -- called it Mosaic
Mosaic was created during a four-month period in late 1992 and early
1993 by Marc Andreessen and some other students
Due to easy, point-and-click hypermedia interface, Mosaic set standard for Web interfaces
Marc Andreessen left University of Illinois to become Vice President for Technology of Netscape Communications
First version of Netscape browser available October, 1994
Big improvement -- Continuous document streaming, enabling users to view documents while they were still being downloaded rather than waiting for the entire document to load
Netscape has been responsible for advances in HTML
Microsoft's Internet Explorer also based on Mosaic browser
Developed specifically for use with Windows 95 operating system
"Cookie" is little morsel of information sent from Web
server to Web browser (usually during first visit)
After browser receives cookie, whenever requests Web page from that server, sends back that cookie
Shopping applications can store information about past (or currently) selected items
Fee services can send back registration information -- freeing client from typing IDs and passwords
Sites can store user preferences on client
Cookie might be...
.gap.com,shirts,pants
Why keep cookie at browser instead of server? Faster!
Cookies can be modified, removed, expired
Cookie limit -- cookies used least recently removed
Robots, Crawlers, Worms, and Spiders
"Crawl around and find what we can"
Continuously running program (robot, crawler, worm, spider) pursuing hyperlinks throughout Web
Start with set of documents. Identify new places to explore by looking at outbound links. Visit those links. Index most useful terms.
Problems with Search Engines --
Effective descriptive phrases
Search Engines show Web as it was, not as it is
Links that don't work or have been moved
File had to be downloaded to browser in its entirety before playing began
Such files could be very large. Delay could be lengthy.
Streaming audio/video begins playing almost immediately and can continue indefinitely
Can be used for "live" events
Streaming audio/video player required. Can be launched by browser or embedded in browser window.
RealAudio, LiquidAudio, Streamworks, Shockwave Audio, RealVideo
Java applets
Background sounds
Macromedia Flash images and video
Adobe Portable Document Format (PDF) -- requires Adobe Acrobat software
Document can be converted to PDF format while still maintaining original fonts, images, and layout
PDF very popular for email transmission of documents as well
Links to subpages
Be consistent among pages at Website
General rule -- don't make long pages
Each page has link (buttons or images are nice) back to homepage
Each page has "last changed" date
Judicious use of background images and text colors
Judicious use of images
Design for multiple browsers
Can link to any Website, but do not steal material
Reference things taken in part from other sites and give URL
Avoid items in poor taste -- that you would not show to your mother