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?

• 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 special-interest 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.