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An Introduction to Internet
- Shailesh
Greetings Newbie
Newbie is Internet
slang for a new
Internet user. Because
the Internet is vast and
complex you can
remain a newbie in
some sense for a long
time. It's not that it is
difficult to learn. It's
just diverse.
The Internet
The Internet is a "network of networks" that links computers
around the world. These computers range from PCs and Macs to
supercomputers, but they all use a set of rules called TCP/IP to
exchange information. Driven by the popularity of services like
electronic mail, file transfer, news groups, and the World-Wide
Web, the Internet's growth rate has been astonishing:
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1983: 500 hosts
1987: 20,000 hosts
1992: 1,000,000 hosts
1994: 4,000,000 hosts
1996: 12,900,000 hosts
1997: 19,540,000 hosts
TCP/IP
• The most accurate name for the set of protocols
we are describing is the "Internet protocol suite".
TCP and IP are two of the protocols in this suite.
Because TCP and IP are the best known of the
protocols, it has become common to use the term
TCP/IP or IP/TCP to refer to the whole family.
• The file transfer protocol (FTP)
• Remote login. The network terminal protocol
(TELNET)
• computer mail.
What You Can Do With It
• Log in to most of the world's libraries.
• Send email to your global colleagues.
• Join automated, special interest mailing lists
and newsgroups and learn the latest.
• Search worldwide databases and obtain
documents.
• Get tons of useful software, free!
• Be part of live, discussion groups or on-line
classes .
Remote Login
Over the Internet you can log in to any computer on
which you have an account or which allows public
logins. This includes many database services and
almost all library catalogs. The means of doing this is
called Telnet. Telnet is the remote login facility of
Internet, and once a connection is made, works
transparently. It's a heady experience to log into your
account, Telnet to Yale to check on a book, then to U
of Michigan for a weather report, then to Stanford for
a bibliographic search--all from the comfort and
convenience of home.
Magic
Telnet makes your computer seem to be connected
to a remote computer. What you enter from your
keyboard is redirected to the remote computer.
What the remote computer outputs is redirected to
your monitor. It doesn't matter how far away the
other computer is.
How To Do It
To Telnet to another computer you simply type telnet
followed by the address of the computer to which you
are connecting.
For example: telnet newton.dep.anl.gov
You can also use the remote computer's IP address:
telnet 146.139.100.50
This sometimes works when a domain name will not.
Caught In The Web
The World Wide Web, or WWW, or W3, or simply
"the web," is an ambitious attempt to organize all
the information available on the Internet as a set of
interrelated hypertext documents. Hypertext is text
that contains embedded links to other text, which
contains links to yet other text, and so on, forming
an interrelated web of active cross references.
Each link is actually a pointer to another document
or Internet resource. When you select a link you
jump to that location. In this way the world of
Internet information is tied together.
Hyper Text
• HTML HyperText Markup Language
the language used to create Web pages.
• HTTP HyperText Transfer Protocol the
client/server protocol for moving
hypertext files on the Internet.
Hypertext Text containing links that,
when chosen by a user, will "jump" to
another block of text, either in the
same document or in another.
A Very, Very Brief History Of
The Web
Even though the European
Laboratory for Particle Physics, CERN, can be
credited for laying the foundation of the Web,
the National Center for Supercomputing
Applications, NCSA, developed many of the
tools that made the Web usable to mere
mortals.
What Is A Search Engine?
Search engines are Web sites that can look-up and
retrieve Internet resources based on a term you
input. Let's say you want to look for Web sites that
contain information about sky diving. You type the
words sky diving in the search engine's dialog box
and it will return a list of sites that feature sky
diving in their content. There are many search
engines on the Web you can use for free. The most
popular is Yahoo! Lycos and HotBot are very good
too. For detailed searches it's best to use more than
one.
URL
• Tim Berners-Lee at CERN developed the
World Wide Web using HTTP and one other
incredibly useful concept: the Universal
Resource Locator (URL). The URL is an
addressing scheme that lets browsers know
where to go, how to get there, and what to
do after they reach the destination.
URL Breakup
Web Power
The web is so powerful because the links within
documents may point to any type of Internet
resource: a Telnet session, a Usenet newsgroup,
an ftp site etc. To use the web you need a
browser--one as simple as the line oriented
browser, Lynx, which is default with the shell
account in VSNL, or as rich and complex as
Netscape which runs as a Windows program
capable of displaying images, playing sounds,
and leaping to links with mouse click ease.
What's A Browser?
A browser is a computer software program that
allows a user to view Web pages while
connected to the Internet. There are two browser
programs currently in vogue -- Netscape
Navigator from Netscape Communications and
Internet Explorer from Microsoft Corporation.
Both are equal to the task but Navigator is the
most common program with roughly 70 percent
of Web users using it. IE is quickly gaining a
larger share of the action, though.
In a simplified overview, six things normally happen
when you fire up your Web browser and visit a site
on the World Wide Web:
1.Your browser decodes the first part of the URL and
contacts the server.
2.Your browser supplies the remainder of the URL to
the server.
3.The server translates the URL into a path and file
name.
4.The server sends the document file to the browser.
5.The server breaks the connection.
6.Your browser displays the document.
Electronic Mail
Electronic mail, or e-mail, is a fast, easy, and
inexpensive way to communicate with other
Internet users around the world. Each day
millions of mail messages traverse the Internet.
They are carried by a standard system called
SMTP (Simple Mail Transport Protocol), part of
TCP/IP. An important restriction imposed by
SMTP is that it can only handle TEXT data.
That is, character data, like the characters you
can type on your keyboard. To mail binary type
data it must first be encoded as text data.
Uuencoded Files
Most standard mail work only with text
files, so if you want to mail a binary file,
you must first convert it to a text file. This
is what the program uuencode does.
Uuencoded files are often given the file
extension ".uue" To decode the file on the
other end use the unix program uudecode.
Uudecode does not remove the original
encoded file from your directory after
decoding.
Mailing Lists
There are thousands of ongoing discussion groups carried
out over the Internet via email. They work by subscription
that is, if you have a special interest, you send your
subscription request to the person (or computer) that
maintains the mailing list and you are added to the
number who automatically receive the group's common
email each day. You may then post your invaluable
insights to the group and read the less valuable insights of
others by simply using your email program. Some groups
are moderated, meaning that someone controls what gets
posted, but most are not. Joining a list is called
"subscribing," but there is no charge.
Controlling Your Mailing Lists
The best advice anyone can get who is new
to automated mailing lists is: if you have an
urge to subscribe, lie down until it passes!
The vast riches of the lists invariably tempt
the new user to oversubscribe. If you belong
to more than 6 groups, you are receiving far
more mail than you can handle, because even
a moderately active list can generate dozens
of messages each day.
The second best advice is:
keep the acknowledgment letter you receive
from the list immediately after subscribing.
It contains valuable information on how to
get off the list, to hold your mail when you
are on vacation, etc., etc.
FTP
FTP is an acronym for File Transfer Protocol,
a very important part of the TCP/IP suite of
protocols. It allows you to transfer any sort
of file from any of thousands of remote
computer systems to your own. You can
transfer executable computer programs,
graphics, sound, video or any other sort of
files from remote archives to your own
Internet host computer.
And it's all free.
Which Way Is Up?
When you transfer a file from a remote
computer to your own, you say "I
downloaded a file." When you transfer
from your own computer to another one,
you say "I uploaded a file.” Down = to you;
Up = away from you. These terms can be
confusing.
I Wish To Remain Anonymous
The restriction to using remote computers is that
you must have authorization to use them (an
account, a user ID and a password). FTP gets
around this problem by allowing a service called
"anonymous ftp." That is, when you connect to a
remote computer that allows anonymous ftp you
enter your user ID as "anonymous." When asked
for a password enter your full email address, eg:
[email protected]. Some systems verify your email
address, some do not, but in any event it is proper
netiquette to provide it to the remote host.
Ye Be Properly Warned Says I
Many ftp archives do not check their
offerings for viruses. Before running any
ftped file scan it with a good, current virus
checker. All systems at SRA have McAfee
Anti virus installed.
UseNet
Usenet (short for user's network) is a giant collection of
discussion groups, each centered upon a special topic of
interest--boxing, bee keeping, photography, whatever.
There are more than 5000 such groups within Usenet,
the majority of which are devoted to topics of non-local
interest. No one is in charge of Usenet. The procedures
for transporting data (NNTP = network news transport
protocol), posting articles, and forming new groups
have been established through tradition (Usenet began
in 1979 at U of North Carolina). There is no control
over content and there is no censorship. Whoever you
are, you are sure to find lots of disagreeable things on
Usenet--so ignore them.
The News?
Though the discussion groups are called - newsgroups
they have little to do with news in the traditional sense.
They are more likely to be very specialized discussions
of research trends, recipes, fan clubs... You name it.
You can find most areas of human interest discussed
somewhere on Usenet. It is a great place to go when
you have specific questions and need expert answers.
You simply post your question to the group and soon
you will see an answer posted. It all depends on the
group, of course. If your question is inappropriate, you
can also expect to see some very deflating comments
posted.
HTML
HyperText Markup Language the language used to create Web
pages. Web documents are ordinary text files that can be created
with any word processing program. They include tags that control
their appearance. For example, the boldface above is achieved
with these tags:
<B>tags</B>
Tags can also define a word or phrase as a link. Selecting a link
lets the user go to another document (or to another section of the
same document). HTML documents (often called "pages") can
also include color graphics and clips of digitized audio or video.
Users need a web browser program (for example, Netscape
Navigator) to view web pages.
Frames
Frames give you a way to organize and structure
the content of your HTML documents by letting
you create compound documents that the user can
view within the main window of the browser. The
main window is divided into rectangular frames.
Then, for each frame, a HTML document is
specified which contains the content (text and
images) to fill the frame.
Forms
Forms provide a way to
prompt the user for
information and to carry
out actions based on that
input. A form consists of
one or more input controls
that the user uses to enter
text and to select choices.
the form collects the data
and sends it to a
destination specified in the
form element.
CGI
The Common Gateway Interface (CGI)
specification lets Web servers execute other
programs and incorporate their output into
the text, graphics, and audio sent to a Web
browser. The server and the CGI program
work together to enhance and customize the
World Wide Web's capabilities.
ISAPI
Process Software has proposed a standard called
ISAPI (Internet Server Application Programming
Interface), which promises some real advantages
over today's CGI practices.
In a nutshell, the proposal says that it doesn't make
sense to spawn external CGI tasks the traditional
way. The overhead is too high, the response time
too slow, and coordinating the tasks burdens the
Web server. Instead of using interpreted scripts or
compiled executables, Process proposes using
DLLs (dynamic link libraries).
Java
Java, a new programming
language developed by
Sun Microsystems, allows
you to create selfcontained programs and
components (applets),
that aren't tied to any
specific hardware
platform or operating
system.
Scripting Languages
Scripting languages are an intermediate stage
between HTML and programming languages such as
Java, C++, and Visual Basic. HTML is generally used
for formatting and linking text. Programming
languages are generally used for giving a series of
complex instructions to computers. Scripting
languages fall somewhere in between. The primary
difference between scripting languages and
programming languages is that the syntax and rules of
scripting languages are less rigid and intricate than
those of programming languages.
Component Model
A component model is an architecture and
set of APIs that allow developers to define
software components that can be
dynamically combined together to create an
application. A component model consists of
two major elements: components and
containers.
Components
• Microsoft® ActiveX™ controls are software
components that provide dynamic features on your
pages. For example, a stock ticker control could be
used to add a live stock ticker to a page, or an
animation control could be used to add animation
features.
• Java Applets are software components that can be
placed on Web pages; however, they cannot interact
with the page or with other Java applets on the page.
• Java Beans are the Sun Microsystems equivalent of
ActiveX. Java Beans enhance the Java platform by
allowing richer, more dynamic interaction.
Client: In-Process Component
• Runs inside a container
– Explorer, Navigator
– Client-side scripts can provide illusion of
interaction
• Leading technologies include Active-X and
Java Beans
Server: In-Process Component
• Runs inside a container
• Leading technology is a transaction server
such as CICS or Microsoft’s Transaction
Server (under DCOM)
Client/Server Tradeoffs
• Thick client
– Business logic runs on the client
– Offloads processing from server
– Can take full advantage of client OS
• Thick server
– Business logic runs on the server
– Centralizes processing on the server
– Returns to mainframe model
Client Tradeoffs
• Simple clients can use VBScript or
JavaScript
• Serious clients need components (applets or
Active X components), which changes the
deployment model
Server Tradeoffs
• Simple servers can use common gateway
interface (CGI)
• Serious servers need components (e.g.
Microsoft’s Active Server Pages)
Tools Available
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HTML 3.2
CGI
ISAPI/ASP
NSAPI
Java
Open Technology
Open Technology
Microsoft (Interdev)
Netscape (Livewire)
Open Technology
(JDK/VJ++/Symantec
Cafe)
Conclusion
This course was intended only as an
Introduction to the vast and forever growing
field of Internet. But now that you are WebSmart, you should be able to find out more
about the web and Internet.
Where do you want to go tomorrow?
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Check out http://www.amazon.com and order books online
search for some information at http:// www.yahoo.com
Register at http:// www.alumini.net and get a web presence
Go to http:// www.rediff.com for Desi stuff
Or check out the Beeb at http:// www.bbc.co.uk
Indian bureaucracy at http:// www.doe.gov.in
For some tips on programming jump to http://
www.programmersheaven.com
• Get tips on photography from New York Institute of
Photography http:// www.nyip.com
• Surf to http:// www.cry.inindia.com
• At Case Western University you'll find some interesting
tutorials on HTML - http:// www.cwru.edu/help