The document provides an overview of the internet, describing it as a vast network of interconnected networks that allows data exchange across the globe using protocols like TCP/IP. It details the structure and functionality of internet protocols, addressing schemes (IP addresses and domain names), and various methods of connecting to the internet such as dial-up, DSL, and satellite connections. Additionally, it explains the World Wide Web, highlighting how web browsers function with HTML documents and the process of searching for information online.

1. UNIT-1 WT
Introduction to Networks and www

2. Internet
• It is the largest network in the world that
connects hundreds of thousands of individual
networks all over the world.
• The popular term for the Internet is the
“information highway”.
• Rather than moving through geographical space,
it moves your ideas and information through
cyberspace – the space of electronic movement
of ideas and information.

3. Internet
• No one owns it
• It has no formal management organization.
• As it was originally developed by the Department
of defense, this lack of centralization made it less
vulnerable to wartime or terrorist attacks.
• To access the Internet, an existing network need
to pay a small registration fee and agree to certain
standards based on the TCP/IP (Transmission
Control Protocol/Internet Protocol) .

4. • The Internet was created by the Advanced Research Projects Agency (ARPA)
and the U.S. Department of Defense for scientific and military
communications.
• The Internet is a network of interconnected networks. Even if part of its
infrastructure was destroyed, data could flow through the remaining
networks.
• The Internet uses high-speed data lines, called backbones, to carry data.
Smaller networks connect to the backbone, enabling any user on any
network to exchange data with any other user.
• ARPANET, NSFnet, Internet
• Internetworking: the process of connecting separate networks
The Internet: Then and Now

5. The uses of the Internet
• Send e-mail messages.
• Send (upload) or receive (down load) files
between computers.
• Participate in discussion groups, such as
mailing lists and newsgroups.
• Surfing the web.

6. • TCP/IP
• Routing Traffic Across the Internet
• Addressing Schemes
• Domains and Subdomains
How the Internet Works

7. • Every computer and network on the Internet uses the same protocols
(rules and procedures) to control timing and data format.
• The protocol used by the Internet is the Transmission Control
Protocol/Internet Protocol, or TCP/IP.
• No matter what type of computer system you connect to the Internet, if
it uses TCP/IP, it can exchange data with any other type of computer.
How the Internet Works - TCP/IP

8. • Most computers don't connect directly to the Internet. Instead, they
connect to a smaller network that is connected to the Internet backbone.
• The Internet includes thousands of host computers (servers), which
provide data and services as requested by client systems.
• When you use the Internet, your PC (a client) requests data from a host
system. The request and data are broken into packets and travel across
multiple networks before being reassembled at their destination.
How the Internet Works -
Routing Traffic Across the Internet

9. The Operation of the Internet
• Packets of information flow between machines governed by common rules
(protocols):
– Internet protocol (IP)
– Transport control protocol (TCP)
• Internet is a packet-switching network
– Messages are decomposed into packets, containing part of the
message, plus information on the sending and receiving machines
and how the packet relates to the other packets
– Packets travel independently and possibly on different routes
through the Internet
– Packets are reassembled into the message at the receiving
machine.

11. • In order to communicate across the Internet, a computer must have a
unique address.
• Every computer on the Internet has a unique numeric identifier, called
an Internet Protocol (IP) address.
• Each IP address has four parts – each part a number between 0 and 255.
An IP address might look like this: 205.46.117.104.
How the Internet Works -
Addressing Schemes

12. Where to Begin? Internet Addresses
• Because the Internet is a global network of computers each
computer connected to the Internet must have a unique
address. Internet addresses are in the
form nnn.nnn.nnn.nnn where nnn must be a number from 0 -
255. This address is known as an IP address. (IP stands for
Internet Protocol; more on this later.)
• The picture below illustrates two computers connected to the
Internet; your computer with IP address 1.2.3.4 and another
computer with IP address 5.6.7.8. The Internet is represented
as an abstract object in-between.

13. • If you connect to the Internet through an Internet Service
Provider (ISP), you are usually assigned a temporary IP
address for the duration of your dial-in session. If you
connect to the Internet from a local area network (LAN)
your computer might have a permanent IP address or it
might obtain a temporary one from a DHCP (Dynamic
Host Configuration Protocol) server. In any case, if you are
connected to the Internet, your computer has a unique IP
address.

14. Check It Out - The Ping Program
IF you're using Microsoft Windows or a flavor of Unix and have a
connection to the Internet, there is a handy program to see if a
computer on the Internet is alive. It's called ping, probably after
the sound made by older submarine sonar systems.If you are using
Windows, start a command prompt window. If you're using a
flavor of Unix, get to a command prompt. Type ping
www.yahoo.com. The ping program will send a 'ping' (actually an
ICMP (Internet Control Message Protocol) echo request message)
to the named computer. The pinged computer will respond with a
reply. The ping program will count the time expired until the reply
comes back (if it does). Also, if you enter a domain name (i.e.
www.yahoo.com) instead of an IP address, ping will resolve the
domain name and display the computer's IP address. More on
domain names and address resolution later.

15. Protocol Stacks and Packets
So your computer is connected to the Internet and has a unique address.
How does it 'talk' to other computers connected to the Internet? An
example should serve here: Let's say your IP address is 1.2.3.4 and
you want to send a message to the computer 5.6.7.8. The message you
want to send is "Hello computer 5.6.7.8!". Obviously, the message
must be transmitted over whatever kind of wire connects your
computer to the Internet. Let's say you've dialed into your ISP from
home and the message must be transmitted over the phone line.
Therefore the message must be translated from alphabetic text into
electronic signals, transmitted over the Internet, then translated back
into alphabetic text. How is this accomplished? Through the use of
a protocol stack. Every computer needs one to communicate on the
Internet and it is usually built into the computer's operating system
(i.e. Windows, Unix, etc.). The protocol stack used on the Internet is
referred to as the TCP/IP protocol stack because of the two major
communication protocols used. The TCP/IP stack looks like this:

16. Protocol LayerComments
Application Protocols LayerProtocols specific to applications such as WWW, e-mail,
FTP, etc.
Transmission Control
Protocol Layer
TCP directs packets to a specific application on a computer
using a port number.
Internet Protocol Layer IP directs packets to a specific computer using an IP address.
Hardware Layer Converts binary packet data to network signals and back.
(E.g. ethernet network card, modem for phone lines, etc.)

17. • In addition to an IP address, most Internet hosts or servers have a Domain
Name System (DNS) address, which uses words.
• A domain name identifies the type of institution that owns the computer.
An Internet server owned by IBM might have the domain name ibm.com.
• Some enterprises have multiple servers, and identify them with
subdomains, such as products.ibm.com.
How the Internet Works -
Domains and Subdomains

19. • The World Wide Web
• E-Mail
• News
• Telnet
• File Transfer Protocol (FTP)
• Internet Relay Chat (IRC)
Major Features of the Internet

20. What is Web?
• The Web (World Wide Web) consists of information
organized into Web pages containing text and graphic
images.
• It contains hypertext links, or highlighted keywords
and images that lead to related information.
• A collection of linked Web pages that has a common
theme or focus is called a Web site.
• The main page that all of the pages on a particular
Web site are organized around and link back to is
called the site’s home page.

21. How to access the Internet?
• Many schools and businesses have direct
access to the Internet using special high-
speed communication lines and equipment.
• Students and employees can access
through the organization’s local area
networks (LAN) or through their own
personal computers.
• Another way to access the Internet is
through Internet Service Provider (ISP).

22. How to access the Internet?
• To access the Internet, an existing network need
to pay a small registration fee and agree to certain
standards based on the TCP/IP (Transmission
Control Protocol/Internet Protocol) reference
model.
• Each organization pays for its own networks and
its own telephone bills, but those costs usually
exist independent of the internet.
• The regional Internet companies route and
forward all traffic, and the cost is still only that of a
local telephone call.

23. Internet Service Provider (ISP)
• A commercial organization with permanent
connection to the Internet that sells
temporary connections to subscribers.
• Examples:
• Prodigy, America Online, Microsoft
network, AT&T Networks.

24. How to access the Web?
• Once you have your Internet connection, then
you need special software called a browser to
access the Web.
• Web browsers are used to connect you to
remote computers, open and transfer files,
display text and images.
• Web browsers are specialized programs.
• Examples of Web browser: Netscape
Navigator (Navigator) and Internet Explorer.

25. Client/Server Structure of the Web
• Web 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.

26. Hypertext Markup Language (HTML)
• The public files on the web servers are ordinary
text files, much like the files used by word-
processing software.
• To allow Web browser software to read them,
the text must be formatted according to a
generally accepted standard.
• The standard used on the web is Hypertext
markup language (HTML).

27. Hypertext Markup Language (HTML)
• HTML uses codes, or tags, to tell the Web browser
software how to display the text contained in the
document.
• For example, a Web browser reading the following line of
text:
<B> A Review of the Book<I>Wind Instruments of
the 18th Century</I></B>
• recognizes the <B> and </B> tags as instructions to display
the entire line of text in bold and the <I> and </I> tags as
instructions to display the text enclosed by those tags in
italics.

28. Addresses on the Web:IP Addressing
• Each computer on the internet does have a
unique identification number, called an IP
(Internet Protocol) address.
• The IP addressing system currently in use on
the Internet uses a four-part number.
• Each part of the address is a number ranging
from 0 to 255, and each part is separated from
the previous part by period,
• For example, 106.29.242.17

29. IP Addressing
• The combination of the four IP address parts
provides 4.2 billion possible addresses (256 x
256 x 256 x 256).
• This number seemed adequate until 1998.
• Members of various Internet task forces are
working to develop an alternate addressing
system that will accommodate the projected
growth.
• However, all of their working solutions require
extensive hardware and software changes
throughout the Internet.

30. Domain Name Addressing
• Most web browsers do not use the IP address t locate
Web sites and individual pages.
• They use domain name addressing.
• A domain name is a unique name associated with a
specific IP address by a program that runs on an
Internet host computer.
• This program, which coordinates the IP addresses and
domain names for all computers attached to it, is
called DNS (Domain Name System ) software.
• The host computer that runs this software is called a
domain name server.

31. Domain Name Addressing
• Domain names can include any number of parts separated by
periods, however most domain names currently in use have
only three or four parts.
• Domain names follow hierarchical model that you can follow
from top to bottom if you read the name from the right to the
left.
• For example, the domain name gsb.uchicago.edu is the
computer connected to the Internet at the Graduate School of
Business (gsb), which is an academic unit of the University of
Chicago (uchicago), which is an educational institution (edu).
• No other computer on the Internet has the same domain name.

32. Uniform Resource Locators
• The IP address and the domain name each identify a particular
computer on the Internet.
• However, they do not indicate where a Web page’s HTML
document resides on that computer.
• To identify a Web pages exact location, Web browsers rely on
Uniform Resource Locator (URL).
• URL is a four-part addressing scheme that tells the Web
browser:
 What transfer protocol to use for transporting the file
 The domain name of the computer on which the file resides
 The pathname of the folder or directory on the computer on
which the file resides
 The name of the file

33. Structure of a Uniform Resource Locators
http://www.chicagosymphony.org/civicconcerts/index.htm
protocol
Domain name
pathname
filename
http => Hypertext Transfer Protocol

34. HTTP
• The transfer protocol is the set of rules that the
computers use to move files from one computer to
another on the Internet.
• The most common transfer protocol used on the
Internet is the Hypertext Transfer Protocol (HTTP).
• Two other protocols that you can use on the Internet
are the File Transfer Protocol (FTP) and the Telnet
Protocol

35. How to find information on the Web?
• A number of search tools have been developed and
available to you on certain Web sites that provide
search services to help you find information.
• Examples:
 Yahoo  www.yahoo.com
 Excite  www.excite.com
 Lycos  www.lycos.com
 AltaVista  www/alta-vista.com
 MSN WebSearch  www.search.msn.com

36. How to find information on the Web?
• You can find information by two basic means.
• Search by Topic and Search by keywords.
• Some search services offer both methods, others only
one.
• Yahoo offers both.
 Search by Topic
You can navigate through topic lists
 Search by keywords
You can navigate by entering a keyword or phase into
a search text box.

37. Modes of connecting to internet
• There exist several ways to connect to the
internet. Following are these connection types
available:
• Dial-up Connection
• ISDN
• DSL
• Cable TV Internet connections
• Satellite Internet connections
• Wireless Internet Connections

38. Modes of connecting to internet
1. Dial-up Connection
• Dial-up connection uses telephone line to connect PC
to the internet. It requires a modem to setup dial-up
connection. This modem works as an interface
between PC and the telephone line.
• There is also a communication program that instructs
the modem to make a call to specific number provided
by an ISP.
• Dial-up connection uses either of the following
protocols:
• Serial Line Internet Protocol (SLIP)
• Point to Point Protocol (PPP)

39. Modes of
connecting to
internet
The following diagram shows the accessing
internet using modem:

40. Modes of connecting to internet
2. ISDN
• ISDN is acronym of Integrated Services Digital Network. It
establishes the connection using the phone lines which carry digital
signals instead of analog signals.
• There are two techniques to deliver ISDN services:
• Basic Rate Interface (BRI)
• Primary Rate Interface (PRI)
• Key points:
• The BRI ISDN consists of three distinct channels on a single ISDN
line: t1o 64kbps B (Bearer) channel and one 16kbps D (Delta or
Data) channels.
• The PRI ISDN consists of 23 B channels and one D channels with
both have operating capacity of 64kbps individually making a total
transmission rate of 1.54Mbps.

41. Modes of connecting to internet
The following diagram shows accessing internet
using ISDN connection:

42. Modes of connecting to internet
• 3. DSL
• DSL is acronym of Digital Subscriber Line. It is a form of broadband
connection as it provides connection over ordinary telephone lines.
• Following are the several versions of DSL technique available today:
• Asymmetric DSL (ADSL)
• Symmetric DSL (SDSL)
• High bit-rate DSL (HDSL)
• Rate adaptive DSL (RDSL)
• Very high bit-rate DSL (VDSL)
• ISDN DSL (IDSL)
• All of the above mentioned technologies differ in their upload and
download speed, bit transfer rate and level of service.

43. Modes of connecting to internet
The following diagram shows that how we can
connect to internet using DSL technology:

44. Modes of connecting to internet
4. Satellite Internet Connection
• Satellite Internet connection offers high speed
connection to the internet. There are two types
of satellite internet connection: one way
connection or two way connection.
• In one way connection, we can only download
data but if we want to upload, we need a dialup
access through ISP over telephone line.
• In two way connection, we can download and
upload the data by the satellite. It does not
require any dialup connection.

45. • The following diagram shows how internet is
accessed using satellite internet connection:

46. Modes of connecting to internet
5. Cable TV Internet Connection
• Cable TV Internet connection is provided through Cable TV
lines. It uses coaxial cable which is capable of transferring
data at much higher speed than common telephone line.
• Key Points:
• A cable modem is used to access this service, provided by
the cable operator.
• The Cable modem comprises of two connections: one for
internet service and other for Cable TV signals.
• Since Cable TV internet connections share a set amount of
bandwidth with a group of customers, therefore, data
transfer rate also depends on number of customers using
the internet at the same time.

47. Modes of connecting to internet
5. Cable TV Internet Connection
• Cable TV Internet connection is provided through Cable TV
lines. It uses coaxial cable which is capable of transferring
data at much higher speed than common telephone line.
• Key Points:
• A cable modem is used to access this service, provided by
the cable operator.
• The Cable modem comprises of two connections: one for
internet service and other for Cable TV signals.
• Since Cable TV internet connections share a set amount of
bandwidth with a group of customers, therefore, data
transfer rate also depends on number of customers using
the internet at the same time.

48. Modes of connecting to internet
6. Wireless Internet Connection
• Wireless Internet Connection makes use of radio
frequency bands to connect to the internet and offers a
very high speed. The wireless internet connection can
be obtained by either WiFi or Bluetooth.
• Key Points:
• Wi Fi wireless technology is based on IEEE 802.11
standards which allow the electronic device to connect
to the internet.
• Bluetooth wireless technology makes use of short-
wavelength radio waves and helps to create personal
area network (PAN).

49. Classful
and
Classless
Addressing

50. Classful addressing

51. Problems with Classful Addressing:
• The problem with this classful addressing method is that millions
of class A address are wasted, many of the class B address are
wasted, whereas, number of addresses available in class C is so
small that it cannot cater to the needs of organizations.
• Class D addresses are used for multicast routing and are therefore
available as a single block only.
• Class E addresses are reserved.
•
• Since there are these problems, Classful networking was replaced
by Classless Inter-Domain Routing (CIDR) in 1993.

52. Classless addressing
• Classless Addressing is an improved
IP Addressing system. It makes the allocation
of IP Addresses more efficient. It replaces the
older classful addressing system based on
classes. It is also known as Classless Inter
Domain Routing (CIDR).

53. Subnetting and Supernetting
• Subnetting is the procedure to divide the
network into sub-networks or small networks.
• Supernetting: Supernetting is the procedure
of combine the small networks into larger
space. Subnetting is implemented via
Variable-length subnet masking,
While supernetting is implemented via
Classless interdomain routing.

54. W3C
Consortium
• The World Wide Web
Consortium (W3C) is an
international community
where Member organizations,
a full-time staff, and the
public work together to
develop Web standards. Led
by Web inventor and Director
Tim Berners-Lee and CEO
Jeffrey Jaffe, W3C's mission is
to lead the Web to its full
potential.

55. 13.2 Basic Terminologies
• Computer connected to a network is called a host
• The connection is made using a device called a
Network Interface Card or NIC
• What exactly is the
"network" shown in the
diagram?
• As we shall see it may be
one network or a
composite of multiple
networks

56. 13.2 Basic Terminologies
• What is the Internet? Consider the postal system…

57. 13.2 Basic Terminologies
• Now consider an email

58. 13.2 Basic Terminologies
• Each cloud represented computers of an
Internet Service Provider (ISP)
• The ISP clouds are not directly connected
• Instead they are connected by routers, which
are special purpose computer for this purpose
• How do these routers know where to send
information? A universal system of addresses
called Internet Protocol (or IP) Addresses is
part of the answer

59. 13.3 Networking Software
• Need to address issues such as
– Arbitrary message size and physical limitations of
network packets
– Out of order delivery of packets
– Packet loss in the network
– Bit errors in transmission
• Software is logically in a protocol stack
configuration

60. 13.3 Networking Software
• A protocol is the set of rules used to describe all
of the hardware and (mostly) software
operations used to send messages from
Processor A to Processor B
• A protocol describes the syntax, semantics and
timing of communication between two devices
• Common practice is to attach headers/trailers to
the actual payload forming a packet or frame.

61. 13.3.1 Need for a Layered
Protocol Stack
• Good abstraction
• Simpler to understand than OGP
• Easier to design, analyze, implement and test
• Design concept is suites or families
• What do we mean by layers? Or a layered
protocol? Consider the army…

62. 13.3.1 Need for a Layered
Protocol Stack
General
Colonel
Captain
Sergeant
Private
General
Colonel
Captain
Sergeant
Private

63. 13.3.2 Internet Protocol Stack
Physical
Link
Network
Transport
Application
Layer 1
Layer 2
Layer 3
Layer 4
Layer 5

64. 13.3.2 Internet Protocol Stack
• Application: HTTP, SMTP, FTP, etc. Shield applications
using network from network details
• Transport: Breaks message into packets, handles things
like out of order packets, may deal with reliability
• Network: Responsible for routing, does best effort
delivery
• Link: Moves the packet using a protocol such as
Ethernet, Token Ring, and ATM
• Physical: Responsible for physically (electrically,
optically, etc.) moving the bits of the packet from one
node to the next.

65. 13.3.2 Internet Protocol Stack
• Application: HTTP, SMTP, FTP, etc. Shield applications
using network from network details
• Transport: Breaks message into packets, handles things
like out of order packets, may deal with reliability
• Network: Responsible for routing, does best effort
delivery
• Link: Moves the packet using a protocol such as
Ethernet, Token Ring, and ATM
• Physical: Responsible for physically (electrically,
optically, etc.) moving the bits of the packet from one
node to the next.

66. 13.3.2 Internet Protocol Stack
Manufacturers group their protocol software together into a
family and give it a nice name…
• Novell Corporation
• Banyan Systems
• Apple Computer
• Digital Equipment
• IBM
• “The Internet Biggie”
• Netware
• VINES
• AppleTalk
• DECNET
• SNA
• TCP/IP

67. 13.3.2 Internet Protocol Stack
• Layer 5: Application-Sends application specific
messages
• Layer 4: Transport-Sends segments
• Layer 3: Network-Sends packets
• Layer 2: Datalink-Sends frames
• Layer 1: Physical-Sends bits

68. 13.3.2 Internet Protocol Stack

69. 13.4 Transport Layer
• Assume
– send (destination-address, message)
– receive (source-address, message)
• Functionality of transport layer
– Support arbitrary message size at the application
level
– Support in-order delivery of messages
– Shield the application from loss of messages
– Shield the application from bit errors in
transmission.