THE INTERNET

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Introduction to Computing CS101

LESSON 28

INTRODUCTION TO THE INTERNET

During the Last Lecture

(Computer Networks)

We looked at the role of networks in computing

We looked at several different types of networks

We familiarized ourselves with networking topologies and protocols

Computer Network

Multiple computers that are connected together to share information and other resources

Types of Computer Networks according to the network access policy

Private

Public

Types of Computer Networks

according to the distance between nodes

LAN: Local Area Network

WAN: Wide Area Network

Network Topologies

The pattern in which computers are connected to form a network

Popular patterns:

Point-to-point

Star

Bus

Ring

Networks are also formed by combining 2 or more of these 4 basic patterns

Networking Protocols

Networks use protocols, or rules, to exchange information through shared channels. These protocols

prevent collisions of data caused by simultaneous transmission between two or more computers. Several

protocols are available for various types of networks. Here we discuss two that are popular for LANs:

Ethernet; Token Ring

Types of Communication Channels

Wire

Wireless

Wireless (Radio) LANs Are Becoming Popular

Key benefits:

Key challenges:

Set-up time

Security & privacy

Set-up cost

Quality of service

Today's Gal:Maintenance cost

Cost

C t se

Introduction to oht Internet

To become able to appreciate the role of the Internet in today's computing

To become familiar with the history and evolution of the Internet

an accident!

�This car was involved in that accident

It belongs to ...

Mr. Tom Peters of Palo Alto, California

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After the accident, Mr. Peters ...

filled out a form, giving info about:

Himself

The circumstances of the accident

Estimated repair expenses

& then ...

1/ 7

� Mr. Peters's fax machine

2/ 7 ACME Insurance Group's server in New York

3/ 7

Bhola eServices (Pvt) Ltd's server at Davis Rd, Lahore

4/ 7

Claims processing in Lahore

5/ 7

Bhola eServices (Pvt) Ltd's server at Davis Rd, Lahore

6/ 7

ACME Insurance Group's server in New York

7/ 7

Mr. Peters's home PC

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Key Question!

Why process the insurance claim in Pakistan?

Answer: Everybody Wins!

Tom Peters

ACME Insurance

Bhola eServices

Answer: Everybody Wins!

Tom Peters

Lower premium

ACME Insurance

Bhola eServices

Quicker turnaround

Answer: Everybody Wins!

Tom Peters

ACME Insurance

Better margins due to 50% saving

Bhola eServices

on claim processing costs

Answer: Everybody Wins!

Tom Peters

ACME Insurance

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Introduction to Computing CS101

Bhola eServices

Internal rate of return (IRR)

of 60-80%

The Key Point ...

Bhola eServices (Pvt) Ltd is ...

... supplying a service

... using local, attractively-priced workers

... to a remote, overseas client

... over the Internet ... & making good money in the process!

Internet

Enables users located at far-way locations to easily share information with others located all over the

world

Enables users to easily and inexpensively communicate with others located all over the world

Enables the users to operate and run programs on computers located all over the world

The Internet is unlike any previous human invention. It is a world-wide resource, accessible to all of the

humankind.

Internet Users Worldwide

673M in 2002

1B+ in 2005

(48% wireless)

1.2M Internet users in Pakistan in 5/2000

(1% of population)

In early 2002,

54% of Australian population

51% of Singaporean population

39% of Japanese population

3% of Chinese population

Key Characteristics

Geographic Distribution

Global - reaches around the world

Robust Architecture

Adapts to damage and error

Speed

Data can travels at near `c' on copper, fiber, airwaves

Key Characteristics

Universal Access

Same functionality to everyone

Growth Rate

The fastest growing technology ever

Freedom of Speech

Promotes freedom of speech

The Digital Advantage

Is digital: can correct errors

28.1 Internet: Network of Networks

A large number of networks, interconnected physically

Capable of communicating and sharing data with each other

From the user's point view, Internet a collection of interconnected networks looks like a single,

unified network

28.2 Internet Networking Protocols

Communications on the Internet is controlled by a set of two protocols: TCP and IP

TCP/IP Transmission Control Protocol/Internet Protocol

Networking protocol used by all computers and networks on the Internet

Originally developed by the US DoD for Unix, but now available for most other OSes

TCP breaks down the message to be sent over the Internet into packets

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Introduction to Computing CS101

IP routes these packets through the Internet to get them to their destination

When the packets reach the destination computer, TCP reassembles them into the original message

Tools & Services Available on the Internet

Electronic mail (POP, IMAP, SMTP)

Instant messaging (ICQ, MSN)

Remote login (telnet)

File transfer (ftp)

Network news (nntp)

WWW (http)

1960's

1969 - DoD-ARPA creates an experimental network ARPANET as a test-bed for emerging

networking technologies

ARPANET originally connected 4 universities & enabled scientists to share info & resources across

long distances

ARPANET continued to expand throughout the 70's and 80's

1970's

Networking tools developed in the 70's include:

1972 - The National Center for Supercomputing Apps. (NCSA) develops the telnet application for

remote login, making it easier to connect to a remote computer

1973 - FTP (File Transfer Protocol) is introduced, standardizing the transfer of files between networked

computers

1980's

1983 - The TCP/IP protocols becomes the only set of protocols used on the ARPANET

This sets a standard for all networks, and generates the use of the term Internet as the net of nets

ARPANET splits into two nets to keep military & non-military network sites separate: ARPANET and

MILNET

1980's

In 1982 and 1983, the first desktop computers begin to appear

Many are equipped with an OS called Berkeley Unix, which includes networking SW, allowing easy

connection to the Internet using telnet

The PC revolution continues through the 80's, making access to computer resources & net-worked info

increasingly available to public

1985-86: NSF connects the US's six supercomputing centers together, calling it the the NSFNET, or

NSFNET backbone

To expand access to the Internet, NSF developed regional nets, which were then connected to the

NSFNET backbone

Plus, NSF supported institutions (universities, etc.) in their efforts to connect to the regional nets

1987 - NSF awards a grant to Merit Network, Inc. to operate & manage future development of the

NSFNET

Merit collaborates with IBM & MCI on R&D for fast networking technologies

1989 - The backbone network is upgraded to T1, making it able to transmit data at speeds of 1.5 Mb/s

(approx. 60 pages of text/second)

1990's1990 - The ARPANET is dissolved

1991 - Gopher is developed at the U of MN

It provides a hierarchical, menu-based method for providing & locating info on the Internet

1993 - CERN releases WWW, developed by Tim Berners-Lee

It uses HTTP and hypertext, revolutionizing the way info is presented & accessed on Internet

1993 - The NSFNET is upgraded to T3 (45 Mb/s or about 1800 pages/s)

1993-1994 - Web browsers Mosaic & Netscape Navigator are introduced

Their GUI makes WWW & Internet more appealing to the general public

1995 - NSFNET is replaced by a new architecture, called vBNS which utilizes regional networks and

Network Access Points

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Introduction to Computing CS101

Who runs the Internet?

Who owns it?

Today's Goal:

Introduction to the Internet

We looked at the role Internet plays in today's computing

We reviewed some of the history and evolution of the Internet

Next Lecture:

Internet Services

We will try to familiarize ourselves with with some of the Internet services:

http (surfing, shopping, searching)

ftp

News groups, message boards, forums

Instant messaging

Multimedia delivery

Keyword

Pair of parenthesis

Function `arguments' separated by

Function

commas

identifier

Function definition

function writeList( heading, words ) {

enclosed in a pair

document.write( heading + "<BR>" ) ;

of curly braces

for ( k = 0 ; k < words.length ; k = k + 1 ) {

document.write( words[ k ] + "<BR>" ) ;

}

}29.3 Function Identifiers

The naming rules for function identifiers are the same as were discussed for variable and array identifiers

29.4 Arguments of a Function

A comma-separated list of data

Arguments define the interface between the function and the rest of the Web page

Arguments values are passed to the function by value (some popular languages pass arguments `by

reference' as well)

To ensure that a function is defined before it is called up, define all functions in the HEAD portion of Web

pages

function popUp( message ) {

A function call appearing

window.alert( message ) ;

as a complete statement

}

popUp( "Warning!" ) ;

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Introduction to Computing CS101

function add( a, b ) {

c=a+b;

return c ;

}

sum = add( 2, 4 ) ;

document.write( sum ) ;

function popUp( message ) {

window.alert( message ) ;

}

popUp( "Warning!" ) ;

function add( a, b ) {

c=a+b;

return c ;

}

sum = add( 2, 4 ) ;

function popUp( message ) {

document.write( sum ) ;

window.alert( message ) ;

}

a = popUp( "Warning!" ) ;

document.write( a ) ;

What will get written by

this statement?

undefined

What would this

function add( a, b ) {

modifica-tion do?

c=a+b;

return c ;

}

document.write( add( 2, 4 ) ) ;

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Introduction to Computing CS101

What Would this Statement Do?

factorial( factorial ( 3 ) ) ;

This is termed as the

recursive

use of a function

Methods

Methods are functions

They are unusual in the sense that they are stored as properties of objects

Object: A named collection of properties (data, state) & methods (instructions, behavior)

All objects have the "name"

A collection of

property: it holds the name of

properties & methods

the object (collection)

nam

method 2

prop

method 3

method 1

prop

29.5 Event Handlers

Special-purpose functions that come predefined with JavaScript

They are unusual in the sense that they are many times called in the HTML part of a Web page and not the

<SCRIPT> ... </SCRIPT> part

More on event handlers in a future lecture

Predefined, Top-Level or Built-In Functions

Event handlers are not the only functions that come predefined with JavaScript. There are many others.

Practically, there is no difference between predefined functions and those that are defined by the

programmer (termed as user-defined or custom functions)

There are many of them, but here we discuss only two: parseInt( ), parseFloat( )

The dictionary meaning of `Parse': To

breakdown into simpler components and

analyze

parseInt( )

Syntax: parseInt ( string )

string1 = "3.14159" ;

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