Lec 18 Internet & www

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CS1010 Introduction to Computing

Lecture 18

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Today’s Goals

(Introduction to the 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

To look at several services provided by the

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It belongs to …

Mr. Tom Peters of

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After the accident, Mr. Peters …

filled out a form, giving info about:

Himself

The circumstances of the accidentEstimated repair expenses

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1/

7

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2/

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3/

7

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Claims processing in Lahore

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5/

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6/

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7/

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Key Question!

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Answer: Everybody Wins!

Tom Peters

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Answer: Everybody Wins!

Tom Peters

ACME Insurance

Bhola eServices

Lower premium &

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Answer: Everybody Wins!

Tom Peters

ACME InsuranceBhola eServices

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Answer: Everybody Wins!

Tom Peters

ACME Insurance

Bhola eServices

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The Key Point …

Bhola eServices (Pvt) Ltd is … … supplying a service

… using local, attractively-priced workers … to a remote, overseas client

over the Internet

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Internet

:

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What else does

the Internet

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What Else?

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

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The Internet is unlike

any previous human

invention. It is a

world-wide resource,

accessible to all of

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Internet Users Worldwide

2.4B in 2012

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10.8M

Internet users in Pakistan in

5/2012

(

10%

of population)

In early 2012,

82

% of

Australian

population

75

% of

Singaporean

population

80

% of

Japanese

population

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Key Characteristics (1)

Geographic Distribution

Global - reaches around the world

Robust Architecture

Adapts to damage and error

Speed

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Key Characteristics (2)

Universal Access

Same functionality to everyone

Growth Rate

The fastest growing technology ever

Freedom of Speech

Promotes freedom of speech

The Digital Advantage

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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

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Intranet

An intranet is a network based on TCP/IP protocol (an internet) belonging to an

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Internet Networking Protocols

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

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TCP/IP (1)

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

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TCP/IP (2)

Transmission Control Protocol/Internet Protocol

TCP breaks down the message to be sent over the

Internet into packets

IP routes these packets through the Internet to get

them to their destination

When the packets reach the destination computer,

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Tools & Services Available on the Internet

Electronic mail (POP, IMAP, SMTP)

Instant messaging (ICQ, MSN, Skype)

Remote login (telnet)File transfer (ftp)

Voice over internet protocol (voip)

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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

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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,

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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

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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

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1980's

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

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1980's

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

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1990's

1990 - The ARPANET is dissolved

1991 - Gopher is developed.

It provides a hierarchical, menu-based method for

providing & locating info on the Internet

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

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1990's

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

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Who runs the Internet

?

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Internet Addressing

Regular post cannot be delivered unless we write a

destination address on the envelope

Same is true for the Internet

Regular post can be delivered at the intended

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180.150.151.104

www.uol.edu.pk

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IP Address (1)

A unique identifier for a computer on a TCP/IP

network

Format: four 8-bit numbers separated by periods.

Each 8-bit number can be 0 to 255

Example:

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IP Address (2)

Networks using TCP/IP route messages based on

the IP address of the destination

Any IP addresses (as long as they are unique) can

be assigned within a Private Network

However, connecting a Private Network to the

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?

server

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Client/Server Structure of the

Web

Web site is a collection of files that reside on computers,

called Web servers, that are located all over the world and are connected to each other through the Internet.

When you use your Internet connection to become part of the Web, your computer becomes a Web client in a worldwide client/server network.

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Domain Names

IP addresses are fine for computers, but difficult to

recognize and remember for humans

A domain name is a meaningful, easy-to-remember

‘label’ for an IP address

Examples:

180.150.151.104 www.uol.edu.pk

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A fully qualified domain name can be made up of a

top level domain (TLD), second level domain (SLD).

Seven popular Top Level Domains are:

.com, .edu, .org, .gov, .net, .countryname, .int

SLDs represent the name of a company/institution/

entity

Subdomains represents the functional unit of a

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cs . uol . edu . pk

Sub

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DNS: Domain Name System (1)

DNS is the way that Internet domain names are

located & translated into IP addresses

Maintaining a single, central table of domain

name/IP address relationships is impractical

Billions of DNS-IP translations take place every day

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Internet Services

There are many, but we will look at only the following:

FTP

Telnet Web eMail

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FTP: File Transfer Protocol

Used to transfer files between computers on a TCP/

IP network (e.g Internet)

Simple commands allow the user to:

List, change, create folders on a remote computer

Upload and download files

Typical use: Transferring Web content from the

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Telnet Protocol

Using Telnet, a user can remotely log on to a

computer (connected to the user’s through a TCP/IP

network, e.g. Internet) & have control over it like a local user, including control over running various programs

In contrast, FTP allows file operations only

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The Web

The greatest, shared resource of information

created by humankind

A user may access any item on the Web through a

URL, e.g.

http://www.uol.edu.pk/cs/index.html

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http://www.uol.edu.pk/cs/index.html

Protocol Identifier

Server Address

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What is the World Wide Web?

A huge resource of information

Logically unified, but physically distributed

Logically unified: Any one from any where can

access the information using a very simple scheme

consisting of links & URLs

Physically distributed: The information is stored on

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What is a Web site?

A collection of related documents available on the

Web

The first portion of the URLs in the Web pages of a

Web site is the same e.g.

http://www.uol.edu.pk/ – http://www.uol.edu.pk/cs

http://www.uol.edu.pk/cs1010

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What is a URL?

Uniform Resource Locator

The unique address assigned to each unique

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Examples

http://dawn.com

http://www.uol.edu.pk/cs

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User’s

Computer

User launches the browser on his/her computer

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User’s

Computer

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User’s

Computer

The browser breaks down the URL

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User’s

Computer

DNS Server

Browser sends server’s name to the DNS server

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User’s

Computer

Web

In ter net

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User’s

Computer

Web Server

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User’s

Computer

Web

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User’s

Computer

Browser displays index.html

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eMail

Computer-to-computer messaging

Inexpensive, and quite quick, but not instant!

The most popular service on the Internet, even

more than surfing, but soon to be overtaken by instant messaging

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But first, the components:

eMail client

SMTP server

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eMail Clients

Programs used for writing, sending, receiving, and

displaying eMail messages

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SMTP: Simple Mail Transfer Protocol

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POP3: Post Office Protocol

A protocol used for receiving eMail messages

A POP3 server maintains text files (one file per user

account) containing all messages received by a user

eMail client interacts with the POP3 server for

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To use pop3 server, you must have an account

on it, it prepares a text file (1 text file per user, all messages that arrived are stored in same text file)

Email client talk with pop3 server, search for

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Sender’s Computer

The message is prepared using the eMail client

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Sender’s Computer

SMTP Server

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Sender’s Computer

SMTP Server

POP3 Server

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Sender’s Computer

POP3 Server

The receiver picks it at his/her convenience

Receiver's Computer SMTP

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Sender’s Computer SMTP Server SMTP Server In ter net

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Sender’s Computer

SMTP Server

POP3 SMTP

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Sender’s Computer SMTP Server POP3 Server SMTP Server

The receiver picks it at his/her convenience

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The Trouble with eMail

Slow response times

No way of knowing if the person we are sending

eMail to is there to read it

The process of having a conversation through eMail

by exchanging several short messages is too

cumbersome

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Instant Messaging

The IM services available on the Internet (e.g. ICQ,

AIM, MSN Messenger, Yahoo! Messenger) allow us

to maintain a list of people (contacts) that we interact with regularly

We can send an instant messages to any of the

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Using Instant Messaging (1)

Whenever a contact in our list comes online, the IM

client informs us through an alert message and by playing a sound

To send an instant message to a contact, just click

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Using Instant Messaging (2)

The selected contact will receive that message

almost immediately after you press ‘Enter’

When the contact’s IM client receives the message,

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Using Instant Messaging (3)

That contact then can type a response to the

received message, and send it instantly

Several such conversations can be carried out

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VoIP: Voice over IP

Voice delivered from one device to another using

the Internet Protocol

Voice is first converted into a digital form, is broken

down into packets, and then transmitted over a TCP/IP network (e.g. Internet)

Four modes:C2C

C2TT2C

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Pro

Much cheaper than traditional phone service

Con

Noticeably poor quality of voice as compared with land-line phone service, but not much

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What is a Web Search Engine?

Search engines continuously scan the Web and compile a

list of all the Web pages that they find

The search engine with the largest such list (or index) is

Google – with a list of over 2 billion Web pages and over

330 million images

We use the search engine by typing a “search key word” or

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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

Figure

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