Computer network

1. Introduction to Computer
Networks
A computer network is a collection of
interconnected computers and other
devices which are able to communicate
with each other and share hardware
and software resources.

2. Are there any advantages of
networked computers over stand
alone computers? Yes, there are
many. A few of these advantages
are:
Resource Sharing
Cost saving
Collaborative user interaction
Time saving
Increased storage

3. Types of Networks
• • • •
A computer network may span any
amount of geographical area. It can be
on a table, in a room, in a building, in a
city, in a country, across continents or
around the world. On the basis of area
covered computer networks are
classified as:
PAN - Personal Area Network
LAN - Local Area Network
MAN - Metropolitan Area Network

4. PAN:-A PAN is a network of
Communicating devices
(Computer,Phone, MP3/MP4 Player,
Camera etc.) in the proximity of an
individual. It can cover an area of a few
meters radius.
When you have to transfer songs from
one cell phone to another, you set up a
PAN of two phones. When files are
transferred from a PC to an MP3 player,
a PAN is set up between the two. There
can also be multiple devices in PAN. A

5. span a group of nearby buildings.
LAN :-
A LAN is a network of computing/Communicating
devices in a room, building, or campus.
It can cover an area of a few meters to a few
kilometers radius. A networked office building,
school, or home usually contains a single LAN,
though sometimes one building can contain a few
small LANs (Like some schools have independent
LANs in each computer lab.). Occasionally a LAN
can span a group of nearby buildings

6. MAN:-
A MAN is a network of
computing/communicating
devices within a city. It can cover an
area of a few kilometers to a few
hundred kilometers radius. A
network of schools, or banks, or
Government offices etc., within a
city, are examples of MANs.

7. WAN :
A WAN is a network of
computing/communicating devices
crossing the limits of a city, country,
or continent. It can cover an area of
over hundreds of kilometer radius. A
network of ATMs, BANKs, National
Government Offices, International
Organizations' Offices etc., spread
over a country, continent, or covering
many

8. Network Devices
Modem:-A modem (modulator–
demodulator) is a network hardware
device that modulates one or more
carrier wave signals to encode digital
information for transmission and
demodulates signals to decode the
transmitted information.
Hub:-A Hub is an electronic device that
connects several nodes to form a network

9. Switch:-A Switch is an intelligent device
that connects several nodes to form a
network
and redirects the received information
only to the intended node(s)
Repeater:-A Repeater is a device that is
used to regenerate a signal which is on
its way
through a communication channel. A
repeater regenerates the received signal
and re-transmits it to its destination.

10. Gateway:- A Gateway is a device, which
is used to connect different types of
networks and perform the necessary
translation so that the connected
networks can
Router:-The main purpose of a router is to
connect multiple networks and forward
packets destined either for its own networks
or other networks. A router is considered a
layer-3 device because its primary
forwarding decision is based on the
information in the layer-3 IP packet,
specifically the destination IP address.

11. Network Topologies:
Physical arrangement of computers in a
network is called network topology.
Bus Topology:-In bus topology all the
nodes are connected to a main cable
called
backbone. If any node has to send
some information to any other node, it
sends the signal to the backbone. The
signal travels through the entire length
of the backbone and is received by the

12. Characteristics of Bus topology:
Advantages-
It is easy to install.
It requires less cable length and
hence it is cost effective.
Failure of a node does not affect the
network.
Disadvantages-
In case of cable (backbone) or
terminator fault, the entire network
breaks down.
Fault diagnosis is difficult.

13. Star Topology:
In star topology each node is directly
connected to a hub/switch. If any
node has to send some information
to any other node, it sends the signal
to the
hub/switch. This signal is then
broadcast (in case of a hub) to all the
nodes but is
accepted by the intended node(s). In

14. Characteristics of Star topology:
Advantages-
It is more efficient topology as
compared to bus topology.
It is easy to install
It is easy to diagnose the fault in
Star topology.
It is easy to expand depending on the
specifications of central hub/switch
Disadvantages-
Failure of hub/switch leads to failure of

15. Tree Topology:
Tree topology is a combination of bus
and star topologies. It is used to
combine multiple star topology
networks. All the stars are connected
together like a bus.This bus-star
hybrid approach supports future
expandability of the network .
Characteristics of Tree topology:
It offers easy way of network
expansion
Even if one network (star) fails, the
other networks remain connected

16. Mesh Topology:
In mesh topology each device is connected
to every other device on the network
through a dedicated point-to-point link.
When we say dedicated it means that the
link only carries data for the two connected
devices only.
Advantages of Mesh topology-
1. No data traffic issues as there is a dedicated
link between two devices which means the link is
only available for those two devices.
2. Mesh topology is reliable and robust as failure
of one link doesn’t affect other links and the
communication between other devices on the
network.

17. Disadvantages of Mesh topology-
1. Amount of wires required to
connected each system is tedious and
headache.
2. Since each device needs to be
connected with other devices, number of
I/O ports required must be huge.

18. Introduction to Internet:-
Internet is a global communication
system that links together thousands
of individual networks. It allows
exchange of information between two
or more computers on a network. Thus
internet helps in transfer of messages
through mail, chat, video & audio
conference, etc. It has become
mandatory for day-to-day activities:
bills payment, online shopping and

19. URL (Uniform Resource Locator)
A URL (Uniform Resource Locator) is a
unique identifier used to locate a
resource on the internet. It is also
referred to as a web address. URLs
consist of multiple parts -- including a
protocol and domain name -- that tell
a web browser how and where to
retrieve a resource. Domain names
are used in URLs to identify particular
Web servers. For example, in the URL
http://www.cbse.nic.in/welcome.htm,

20. *WWW-World Wide Web .The World Wide
Web (WWW) is a network of online content
that is formatted in HTML and accessed via
HTTP.
*Web- a set of related web pages located
under a single domain name.
*email-messages distributed by electronic
means from one computer user to one or
more recipients via a network.
* Chat-exchange messages online in real
time with one or more simultaneous users
of a computer network.

21. Website: Related webpages from a
single web domain is termed as a
website. A website has multiple
webpages providing information
about a particular entity.
Web page: Web page is an electronic
document designed using HTML. It
displays information in textual or
graphical form. It may also contain
downloadable data files, audio files or
video files. Traversal from one
webpage to another web page is
possible through hyperlinks. A web

22. Static web page: A
web page which
displays same
kind of information
whenever a user visits
it is known as a static
web page. A static web
page
generally has .htm
or .html as extension
Dynamic web page: An
interactive web page is a
dynamic webpage. A
dynamic web page uses
scripting languages to
display changing content
on the web
page. Such a page
generally has .php, .asp
or .jsp as
extension

23. Web Server: A Web server is a
computer or a group of computers that
stores web pages on the internet. It
works on client/server model. It
delivers the requested web page to
web browser. Web servers use special
programs such as Apache or IIS to
deliver web pages over the http
protocol. Each server has a unique IP
address and domain name. In order to
access a webpage, the user writes the
URL of the site on the address bar of

24. Web hosting: Web hosting is the
process of uploading/saving the web
content on a web server to make it
available on WWW. In case an
individual or a company wants to make
its website available on the internet, it
should be hosted on a web server.

25. Web browser: Web browser is
software program to navigate the
web pages on the internet. A bowser
interprets the coding language of the
web page and displays it in graphic
form. Internet works on client –server
model. A web browser is a client which
requests the information from the web
server. The web server sends the
information back to the client. Some of
the web browsers are: Netscape
Navigator, Internet Explorer,

26. What is add ones in browser?
Add-ons are tools which integrate into
your browser. They're similar to regular
apps or programs, but only run when
the browser runs. Add-ons can allow
the viewing of certain types of Web
content, such as Microsoft's Silver light
or Adobe Flash Player, necessary for
Netflix movies and YouTube videos,
respectively.

27. How do browser plugins work?
A plugin is a piece of software that
acts as an add-on to a web browser
and gives the browser additional
functionality. Plugins can allow a
web browser to display additional
content it was not originally
designed to display.

28. Cookies: When the user browses a website,
the web server sends a small text file to
the web browser known as a cookie.
Generally a cookie contains the name of the
website from which it has come from and a
unique ID tag. Some cookies are stored on
your hard drive until you delete them or
they reach their expiry date. These may be
used to remember your preferences
when you use the website. While, some
cookies last only until the browser is closed
are not stored on your hard drive. They are
usually used to track the pages that you