Transcript Slides of module 3:Global Applications

Global Applications
CS 105
Introduction
• The growth in computer speed, power, and
pervasiveness took even the experts by
surprise.
– I think there is a world market for maybe five
computers — Thomas Watson, chairman of IBM 1943
– Where a calculator like the ENIAC is equipped with
18,000 vacuum tubes and weighs 30 tons, computers
in the future may have only 1,000 vacuum tubes and
perhaps weigh 1.5 tons – Popular Mechanics, ca.
1947
– There is no reason anyone would want a computer in
their home – ken Olson, president, chairman and
founder of Digital Equipment Corp., 1977
History and Technology
• In the cold war days of 1960s, the U.S.
Department of Defense decided the
country needed a national network
connecting the scores of government and
research computers.
• The network had to be decentralized.
• If one computer went down, the rest of the
system would adapt by passing messages
around the inactive site.
• The Addressing System that we are using
today in Internet was invented at that time.
Internet
• What later become known as Internet was
born as ARPANET in 1969 connecting
four host Computers at UCLA, UCSB,
Univ. of Utah and Stanford.
• Internet: Network of networks.
How does it work?
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IP Address
Message
Packets. Why?
Format of Packets.
TCP (Transmission Control Protocol)
DNS (Domain Name Server)
Responsibilities of TCP vs. IP
E-Mail
• Originally, email was thought to be nothing
more than a minor feature, but email grew to
be a large source of traffic on the Net.
• SMTP (Simple Mail Transfer Protocol)
• Alice sends an E-mail to her friend Bob.
E-Mail
• Email is faster than the postal mail, but slower than
talking over the phone or conversing in person.
• Any new technology brings with it a set of social
consequences that are determined by the nature of the
technology itself.
• We have no way of verifying the person who sends the
email.
• Internet robots can collect email addresses.
• Social consequences eventually bring about laws
governing acceptable and unacceptable behavior.
E-Mail
• Different mail client program:
– Unix: pine
– Web-based email systems
– Store messages in the remote server or download
messages into local drive.
• Email messages can be plain ASCII text or
HTML format.
– HTML can include text, pictures, and links to web
pages.
– HTML email can carry a Web bug: an invisible piece
of code that silently notifies the sender about the
user’s information.
Mailing List
• Mailing lists enable you to participate in
email discussion groups on specialinterest topics.
• Lists can be small and local, or large and
global.
• They can be administered by a human
being or automatically administered by
programs.
E-Mail
• Don’t write something in E-mail which you don’t
want to be appeared some where else.
• Don’t broadcast email you receive unless you
first have the sender’s permission.
World Wide Web
• www consists of a vast number of
computers connected to internet. These
computers all have software, known as
browsers, that allows them to send and
receive documents according to a protocol
known as the Hypertext Transfer Protocol
(HTTP).
• Hypertext ?
Factors in Web Growth
• Easy to use
• Easy to Search
• Easy to make a webpage
HTML
• A webpage is described as an ordinary
text document containing a number of html
tags. The document is called HTML
document.
• Tags are sequence of characters which
are interpreted in special ways specifying
format of the text, links, images, sound
and so on.
• HTML (Hypertext Markup Language)
HTML
• A browser can read HTML document and
present it as specified by the html tags.
• A html document is not a WYSIWYG.
• Example
• We have more on this in next module.
Other Applications
• Blog
– Is information that is instantly published to a
Web site. Blog scripting allows someone to
automatically post information to a Web site.
Many people will read it and they may post
responses.
Other Applications
• Instant Messaging: real time
communication
• It is synchronous communication.
• Email and newsgroups are asynchronous:
sender and receiver do not have to log on
at the same time.
Other Applications
• Voice over IP (also called VoIP, IP
Telephony, Internet telephony, and
Digital Phone) is the routing of voice
conversations over the Internet or any
other IP-based network.