1 CS1010 Introduction to Computing
Lecture 18
(INTERNET & WWW)
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
Internet
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an accident !
This car was involved in that accident
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It belongs to …
Mr. Tom Peters of
Palo Alto, California
After the accident, Mr. Peters …
filled out a form, giving info about:
– Himself
– The circumstances of the accident – Estimated repair expenses
& then …
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1/ 7
Mr. Peters’s fax machine
2/ 7
ACME Insurance Group’s server
in New York
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3/ 7
Bhola eServices (Pvt) Ltd’s
server at Davis Rd, Lahore
4/ 7
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5/ 7
Bhola eServices (Pvt) Ltd’s
server at Davis Rd, Lahore
6/ 7
ACME Insurance Group’s server
in New York
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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
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Answer: Everybody Wins!
• Tom Peters
• ACME Insurance
• Bhola eServices
Lower premium
&
Quicker turnaround
Answer: Everybody Wins!
• Tom Peters
• ACME Insurance
• Bhola eServices
Better margins due to
50% saving on claim
processing costs
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Answer: Everybody Wins!
• Tom Peters
• ACME Insurance
• 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!
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Internet :
the enabler !
What else does the Internet
enable ?
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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
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.
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Internet Users Worldwide
2.4B in 2012
4B+ in 2020
(48% wireless)
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
42% of Chinese population
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Key Characteristics (1)
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 (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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inter.net
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
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Internet ---- Web ?
Internet ---- Intranet ?
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Intranet
An intranet is a network based on TCP/IP
protocol (an internet) belonging to an
organization, usually a corporation,
accessible only by the organization's
members, employees, or others with
authorization . An intranet's Web sites
look and act just like any other Web sites,
but the firewall surrounding an intranet
fends off unauthorized access.
Internet Networking Protocols
Communications on the Internet is controlled by a set of two protocols:
TCP and IP
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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
now available for most other OSes
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,
TCP reassembles them into the original message
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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)
Chronology of events that led to
today’s Internet
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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
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
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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
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-
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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
Plus, NSF supported institutions (universities, etc.)
in their efforts to connect to the regional nets
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
1989 - The backbone network is upgraded to T1,
making it able to transmit data at speeds of 1.5
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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
It uses HTTP and hypertext, revolutionizing the
way info is presented & accessed on Internet
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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A lot has happened since 1995
Who runs the Internet ?
Who owns it ?
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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
address even if the given address is not precise.
That is not the case for Internet addressing
180.150.151.104
www.uol.edu.pk
IP address
DNS address
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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:
– 125.209.78.67 (IP address of the UOL Web server)
? client server52
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.
• A Web browser is the software that you run on your computer to make it work as a web client.
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
Internet requires using unique, registered IP
addresses
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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
74.125.225.49 www.google.com
• 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
company/institution.
cs . uol . edu . pk
Sub
Domain SLD TLD
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
– The DNS-IP tables get updated continuously
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Internet Services
There are many, but we will look at only the following:
• FTP
• Telnet
• Web
• Instant messaging
• VoIP
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
developer’s PC to the Web server
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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
• Typical use: Configuring and testing of a remote
Web server
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
• Before, going any further, let us dissect this URL
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http://www.uol.edu.pk/cs/index.html
Protocol Identifier
Server Address
Directory &
File Name
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
Internet-connected computers that are spread all
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
Are the URLs of three distinct Web pages on a single Web site
What is a URL?
• Uniform Resource Locator
• The unique address assigned to each unique
page on the Web
Examples
http://dawn.com
http://www.uol.edu.pk/cs
http://www.smeda.org.pk
How does the Web work?
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User’s
Computer
User launches the browser on his/her computer
Browser
User’s
Computer
User types in the URL into the browser
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User’s
Computer
The browser breaks down the URL
http://www.uol.edu.pk/cs/index.html
http
Protocol Identifier
www.uol.edu.pk Server’s Name
cs/index.html Directory &
File Name
User’s
Computer
DNS Server
Browser sends server’s name to the DNS server
Domain Name IP Address
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User’s
Computer
Web Server
In ter net
Browser establishes a connection with the server
User’s
Computer
Web
Browser sends a ‘GET’ request for cs/index.html
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User’s
Computer
Web Server
Server sends the requested file to the browser
User’s
Computer
Browser displays index.html
X
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• 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
• Billions are sent every day
How does an eMail system work?
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But first, the components:
• eMail client
• SMTP server
• POP3 server
eMail Clients
• Programs used for writing, sending, receiving, and displaying eMail messages
• Examples: Outlook, Communicator, Hotmail,
YahooMail, Gmail.
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SMTP: Simple Mail Transfer Protocol
A protocol used to send and receive eMail
messages over a TCP/IP network
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
discovering and downloading new eMail messages
• 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 new message, in case yes, extract it and
display on user’s computer.
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Sender’s Computer
The message is prepared using the eMail client
eMail Client
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Sender’s Computer
SMTP Server
The eMail client sends it to the SMTP server
Sender’s Computer
SMTP Server
POP3 Server
If the receiver is local, it goes to the POP3 server
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Sender’s Computer
POP3 Server
The receiver picks it at his/her convenience
Receiver's Computer SMTP
Server
Sender’s Computer
SMTP Server
SMTP In
ter net
Otherwise, it is sent to receiver's SMTP server
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Sender’s Computer
SMTP Server
POP3 Server
SMTP Server
Which forwards it to the local POP3 server
Sender’s Computer
SMTP Server
POP3 SMTP
The receiver picks it at his/her convenience
Receiver's
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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
Instant messaging (IM) solves these problems
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
contacts in our list as long as that contact is online
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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
on the contact in the IM client, and start typing the
message
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,
it alerts the contact with a blinking message and by
playing a sound
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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
simultaneously, each occupying a separate IM
windows
How instant messaging works?
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User launches the IM client
My Computer IM Client
Int ern
e
t
IM client finds the IM server & logs in
My Computer IM Server
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It sends communication info (IP address, etc) to the IM server
My Computer IM Server
Temporary File
IM server finds user’s contacts & sends him/her the communication info for the ones online
My Computer IM Server
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IM server also tells the contacts that the user is online; sends his/her communication info to them
My Computer IM Server
Contact’s Computer
My Computer IM Server Contact’s
Computer
Now the user’s & the contact’s IM clients are ready to communicate directly (P2P)
The IM server doesn’t
play any part in this
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My Computer IM Server
Contact
A’s Computer
As new contact’s come online, IM server informs them about the user being online & vice versa
Contact
B’s Computer
My Computer IM Server Contact
A’s Computer
Multiple, simultaneous conversations are possible
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My Computer IM Server
Contact
A’s Computer
When the user logs-off, his/her IM client informs the IM server
Contact
B’s Computer
My Computer IM Server Contact
A’s Computer
IM server erases the temporary file and informs the
user’s contact’s about his/her ‘offline’ status
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Key Point
• Once the IM server provides the communication info to the user and his/her contact’s IM client, the two are able to communicate with each other
without the IM server’s assistance
• This server-less connection is termed as a P2P
connection
Question
• Why do we require the server in the first place?
• Why doesn’t my IM client look for the user’s
contact’s IM client without the IM server’s help?
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Answer
• Many users (including almost all home users) do not have permanent IP addresses. They are assigned
temporary IP addresses by their ISP each time they connect to the Internet
• The server-based IM scheme removes the need of having permanent IP numbers
• It also gives IM users true mobility, allowing them the use of IM from any Internet-connected
computer
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
– C2T
– T2C
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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
worse than cell phone service
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
“query” on its Web page. It looks for those keyword in its
index, and displays a list of Web pages that contain that
keyword
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