Computer Networks | Computer Science for Grade 12 PDF Download

 Page 1


In this Chapter
 » Introduction to Computer 
Networks
 » Evolution of Networking
 » Types of Networks 
 » Network Devices
 » Networking Topologies
 » Identifying Nodes 
in a Networked 
Communication
 » Internet, Web and the 
Internet of Things
 » Domain Name System
Chapter
“Hoaxes use weaknesses in human 
behavior to ensure they are replicated and 
distributed.  In other words, hoaxes prey on 
the Human Operating System.” 
                                — Stewart Kirkpatrick
10.1 INTRODUCTION TO COMPUTER NETWORKS
We are living in a connected world. Information 
is being produced, exchanged, and traced across 
the globe in real time. It's possible as almost 
everyone and everything in the digital world is 
interconnected through one way or the other.
Figure 10.1: Interconnection forming a social network
Computer Networks
10 
Chpater-10.indd   181 11-09-2020   16:41:16
Page 2


In this Chapter
 » Introduction to Computer 
Networks
 » Evolution of Networking
 » Types of Networks 
 » Network Devices
 » Networking Topologies
 » Identifying Nodes 
in a Networked 
Communication
 » Internet, Web and the 
Internet of Things
 » Domain Name System
Chapter
“Hoaxes use weaknesses in human 
behavior to ensure they are replicated and 
distributed.  In other words, hoaxes prey on 
the Human Operating System.” 
                                — Stewart Kirkpatrick
10.1 INTRODUCTION TO COMPUTER NETWORKS
We are living in a connected world. Information 
is being produced, exchanged, and traced across 
the globe in real time. It's possible as almost 
everyone and everything in the digital world is 
interconnected through one way or the other.
Figure 10.1: Interconnection forming a social network
Computer Networks
10 
Chpater-10.indd   181 11-09-2020   16:41:16
COMPUTER NETWORKS
A group of two or more similar things or people 
interconnected with each other is called network (Figure 
10.1). Some of the examples of network in our everyday 
life includes:
•	 Social network
•	 Mobile network
•	 Network of computers
•	 Airlines, railway, banks, hospitals networks
A computer network (Figure 10.2) is an interconnection 
among two or more computers or computing devices. 
Such interconnection allows computers to share data 
and resources among each other. A basic network may 
connect a few computers placed in a room.
The network size may vary from small to large 
depending on the number of computers it connects. 
A computer network can include different types of 
hosts (also called nodes) like server, desktop, laptop,  
cellular phones.
Networking 
Device
Figure 10.2: A computer network
Apart from computers, networks include networking 
devices like switch, router, modem, etc. Networking 
devices are used to connect multiple computers in 
different settings. For communication, data in a network 
is divided into smaller chunks called packets. These 
packets are then carried over a network.  Devices in a 
network can be connected either through wired media 
like cables or wireless media like air.
In a communication network, each device that is a 
part of a network and that can receive, create, store 
or send data to different network routes is called a 
node. In the context of data communication, a node 
can be a device such as a modem, hub, bridge, switch, 
router, digital telephone handset, a printer, a computer  
or a server.
Activity 10.1
Identify some other 
networks in the 
real world. 
Chpater-10.indd   182 11-09-2020   16:41:17
Page 3


In this Chapter
 » Introduction to Computer 
Networks
 » Evolution of Networking
 » Types of Networks 
 » Network Devices
 » Networking Topologies
 » Identifying Nodes 
in a Networked 
Communication
 » Internet, Web and the 
Internet of Things
 » Domain Name System
Chapter
“Hoaxes use weaknesses in human 
behavior to ensure they are replicated and 
distributed.  In other words, hoaxes prey on 
the Human Operating System.” 
                                — Stewart Kirkpatrick
10.1 INTRODUCTION TO COMPUTER NETWORKS
We are living in a connected world. Information 
is being produced, exchanged, and traced across 
the globe in real time. It's possible as almost 
everyone and everything in the digital world is 
interconnected through one way or the other.
Figure 10.1: Interconnection forming a social network
Computer Networks
10 
Chpater-10.indd   181 11-09-2020   16:41:16
COMPUTER NETWORKS
A group of two or more similar things or people 
interconnected with each other is called network (Figure 
10.1). Some of the examples of network in our everyday 
life includes:
•	 Social network
•	 Mobile network
•	 Network of computers
•	 Airlines, railway, banks, hospitals networks
A computer network (Figure 10.2) is an interconnection 
among two or more computers or computing devices. 
Such interconnection allows computers to share data 
and resources among each other. A basic network may 
connect a few computers placed in a room.
The network size may vary from small to large 
depending on the number of computers it connects. 
A computer network can include different types of 
hosts (also called nodes) like server, desktop, laptop,  
cellular phones.
Networking 
Device
Figure 10.2: A computer network
Apart from computers, networks include networking 
devices like switch, router, modem, etc. Networking 
devices are used to connect multiple computers in 
different settings. For communication, data in a network 
is divided into smaller chunks called packets. These 
packets are then carried over a network.  Devices in a 
network can be connected either through wired media 
like cables or wireless media like air.
In a communication network, each device that is a 
part of a network and that can receive, create, store 
or send data to different network routes is called a 
node. In the context of data communication, a node 
can be a device such as a modem, hub, bridge, switch, 
router, digital telephone handset, a printer, a computer  
or a server.
Activity 10.1
Identify some other 
networks in the 
real world. 
Chpater-10.indd   182 11-09-2020   16:41:17
COMPUTER SCIENCE - CLASS XII
Interconnectivity of computing devices in a network 
allows us to exchange information simultaneously with 
many parties through email, websites, audio/video 
calls, etc. Network allows sharing of resources. For 
example, a printer can be made available to multiple 
computers through a network; a networked storage 
can be accessed by multiple computers. People often 
connect their devices through hotspot, thus forming a 
small personal network.
10.2 EVOLUTION OF NETWORKING
In the 1960s a research project was commissioned by 
Advanced Research Projects Agency Network (ARPANET) 
in the U.S. Department of Defence to connect the 
academic and research institutions located at different 
places	 for	 scientific	 collaborations.	 The	 first	 message	 was	
communicated between the University of California, Los 
Angeles (UCLA) and Stanford Research Institute (SRI). 
Slowly but gradually, more and more organisations 
joined the ARPANET, and many independent smaller 
networks were formed. Few of the milestones in the 
magnificent	 journey	 of	 evolution	 of	 computer	 networks	
is depicted in the timeline shown in Figure 10.3.
Activity 10.2
Create a hotspot using 
a smartphone and 
connect other 
devices to it. 
ARPANET became 
functional by 
connecting UCLA and 
SRI
Domain Name System 
introduced
The term Internet was 
coined, 
First commercial use of 
ARPANET, was started 
in the name of Telenet
The idea of Advanced 
Research Project Agency 
Network (ARPANET) is 
conceptualized
TCP/IP introduced as 
standard protocol on 
ARPANET
Roy Tomlinson develops 
network messaging or 
E-mail. Symbol @ 
comes to mean "at"
National Science 
Foundation brings 
connectivity to more 
people with its NSFNET 
program
1986
First version of Wi-fi 
(802.11) standard was 
introduced
1997
The Berners-Lee at 
CERN developed HTML 
and URL, thus giving 
birth to World Wide Web 
(www)
1990
1983 1969
1982
1961
1971
1974
Figure 10.3: Timeline showing evolution of networking
Chpater-10.indd   183 11-09-2020   16:41:17
Page 4


In this Chapter
 » Introduction to Computer 
Networks
 » Evolution of Networking
 » Types of Networks 
 » Network Devices
 » Networking Topologies
 » Identifying Nodes 
in a Networked 
Communication
 » Internet, Web and the 
Internet of Things
 » Domain Name System
Chapter
“Hoaxes use weaknesses in human 
behavior to ensure they are replicated and 
distributed.  In other words, hoaxes prey on 
the Human Operating System.” 
                                — Stewart Kirkpatrick
10.1 INTRODUCTION TO COMPUTER NETWORKS
We are living in a connected world. Information 
is being produced, exchanged, and traced across 
the globe in real time. It's possible as almost 
everyone and everything in the digital world is 
interconnected through one way or the other.
Figure 10.1: Interconnection forming a social network
Computer Networks
10 
Chpater-10.indd   181 11-09-2020   16:41:16
COMPUTER NETWORKS
A group of two or more similar things or people 
interconnected with each other is called network (Figure 
10.1). Some of the examples of network in our everyday 
life includes:
•	 Social network
•	 Mobile network
•	 Network of computers
•	 Airlines, railway, banks, hospitals networks
A computer network (Figure 10.2) is an interconnection 
among two or more computers or computing devices. 
Such interconnection allows computers to share data 
and resources among each other. A basic network may 
connect a few computers placed in a room.
The network size may vary from small to large 
depending on the number of computers it connects. 
A computer network can include different types of 
hosts (also called nodes) like server, desktop, laptop,  
cellular phones.
Networking 
Device
Figure 10.2: A computer network
Apart from computers, networks include networking 
devices like switch, router, modem, etc. Networking 
devices are used to connect multiple computers in 
different settings. For communication, data in a network 
is divided into smaller chunks called packets. These 
packets are then carried over a network.  Devices in a 
network can be connected either through wired media 
like cables or wireless media like air.
In a communication network, each device that is a 
part of a network and that can receive, create, store 
or send data to different network routes is called a 
node. In the context of data communication, a node 
can be a device such as a modem, hub, bridge, switch, 
router, digital telephone handset, a printer, a computer  
or a server.
Activity 10.1
Identify some other 
networks in the 
real world. 
Chpater-10.indd   182 11-09-2020   16:41:17
COMPUTER SCIENCE - CLASS XII
Interconnectivity of computing devices in a network 
allows us to exchange information simultaneously with 
many parties through email, websites, audio/video 
calls, etc. Network allows sharing of resources. For 
example, a printer can be made available to multiple 
computers through a network; a networked storage 
can be accessed by multiple computers. People often 
connect their devices through hotspot, thus forming a 
small personal network.
10.2 EVOLUTION OF NETWORKING
In the 1960s a research project was commissioned by 
Advanced Research Projects Agency Network (ARPANET) 
in the U.S. Department of Defence to connect the 
academic and research institutions located at different 
places	 for	 scientific	 collaborations.	 The	 first	 message	 was	
communicated between the University of California, Los 
Angeles (UCLA) and Stanford Research Institute (SRI). 
Slowly but gradually, more and more organisations 
joined the ARPANET, and many independent smaller 
networks were formed. Few of the milestones in the 
magnificent	 journey	 of	 evolution	 of	 computer	 networks	
is depicted in the timeline shown in Figure 10.3.
Activity 10.2
Create a hotspot using 
a smartphone and 
connect other 
devices to it. 
ARPANET became 
functional by 
connecting UCLA and 
SRI
Domain Name System 
introduced
The term Internet was 
coined, 
First commercial use of 
ARPANET, was started 
in the name of Telenet
The idea of Advanced 
Research Project Agency 
Network (ARPANET) is 
conceptualized
TCP/IP introduced as 
standard protocol on 
ARPANET
Roy Tomlinson develops 
network messaging or 
E-mail. Symbol @ 
comes to mean "at"
National Science 
Foundation brings 
connectivity to more 
people with its NSFNET 
program
1986
First version of Wi-fi 
(802.11) standard was 
introduced
1997
The Berners-Lee at 
CERN developed HTML 
and URL, thus giving 
birth to World Wide Web 
(www)
1990
1983 1969
1982
1961
1971
1974
Figure 10.3: Timeline showing evolution of networking
Chpater-10.indd   183 11-09-2020   16:41:17
COMPUTER NETWORKS
10.3 TYPES OF NETWORKS
There are various types of computer networks ranging 
from network of handheld devices (like mobile phones 
or tablets) connected through Wi-Fi or Bluetooth within 
a single room to the millions of computers spread across 
the globe. Some are connected wireless while others are 
connected through wires.
Based on the geographical area covered and data 
transfer rate, computer networks are broadly categorised 
as:
•	 PAN ( Personal Area Network)
•	 LAN (Local Area Network)
•	 MAN (Metropolitan Area Network)
•	 WAN (Wide Area Network)  
10.3.1 Personal Area Network (PAN)
It is a network formed by connecting a few personal 
devices like computers, laptops, mobile phones, smart 
phones, printers etc., as shown in Figure 10.4. All these 
devices lie within an approximate range of 10 metres. 
A personal area network may be wired or wireless. 
For example, a mobile phone connected to the laptop 
through USB forms a wired PAN while two smartphones 
communicating with each other through Bluetooth 
technology form a wireless PAN or WPAN. 
Figure 10.4:  A Personal Area Network
NOTES
Chpater-10.indd   184 11-09-2020   16:41:17
Page 5


In this Chapter
 » Introduction to Computer 
Networks
 » Evolution of Networking
 » Types of Networks 
 » Network Devices
 » Networking Topologies
 » Identifying Nodes 
in a Networked 
Communication
 » Internet, Web and the 
Internet of Things
 » Domain Name System
Chapter
“Hoaxes use weaknesses in human 
behavior to ensure they are replicated and 
distributed.  In other words, hoaxes prey on 
the Human Operating System.” 
                                — Stewart Kirkpatrick
10.1 INTRODUCTION TO COMPUTER NETWORKS
We are living in a connected world. Information 
is being produced, exchanged, and traced across 
the globe in real time. It's possible as almost 
everyone and everything in the digital world is 
interconnected through one way or the other.
Figure 10.1: Interconnection forming a social network
Computer Networks
10 
Chpater-10.indd   181 11-09-2020   16:41:16
COMPUTER NETWORKS
A group of two or more similar things or people 
interconnected with each other is called network (Figure 
10.1). Some of the examples of network in our everyday 
life includes:
•	 Social network
•	 Mobile network
•	 Network of computers
•	 Airlines, railway, banks, hospitals networks
A computer network (Figure 10.2) is an interconnection 
among two or more computers or computing devices. 
Such interconnection allows computers to share data 
and resources among each other. A basic network may 
connect a few computers placed in a room.
The network size may vary from small to large 
depending on the number of computers it connects. 
A computer network can include different types of 
hosts (also called nodes) like server, desktop, laptop,  
cellular phones.
Networking 
Device
Figure 10.2: A computer network
Apart from computers, networks include networking 
devices like switch, router, modem, etc. Networking 
devices are used to connect multiple computers in 
different settings. For communication, data in a network 
is divided into smaller chunks called packets. These 
packets are then carried over a network.  Devices in a 
network can be connected either through wired media 
like cables or wireless media like air.
In a communication network, each device that is a 
part of a network and that can receive, create, store 
or send data to different network routes is called a 
node. In the context of data communication, a node 
can be a device such as a modem, hub, bridge, switch, 
router, digital telephone handset, a printer, a computer  
or a server.
Activity 10.1
Identify some other 
networks in the 
real world. 
Chpater-10.indd   182 11-09-2020   16:41:17
COMPUTER SCIENCE - CLASS XII
Interconnectivity of computing devices in a network 
allows us to exchange information simultaneously with 
many parties through email, websites, audio/video 
calls, etc. Network allows sharing of resources. For 
example, a printer can be made available to multiple 
computers through a network; a networked storage 
can be accessed by multiple computers. People often 
connect their devices through hotspot, thus forming a 
small personal network.
10.2 EVOLUTION OF NETWORKING
In the 1960s a research project was commissioned by 
Advanced Research Projects Agency Network (ARPANET) 
in the U.S. Department of Defence to connect the 
academic and research institutions located at different 
places	 for	 scientific	 collaborations.	 The	 first	 message	 was	
communicated between the University of California, Los 
Angeles (UCLA) and Stanford Research Institute (SRI). 
Slowly but gradually, more and more organisations 
joined the ARPANET, and many independent smaller 
networks were formed. Few of the milestones in the 
magnificent	 journey	 of	 evolution	 of	 computer	 networks	
is depicted in the timeline shown in Figure 10.3.
Activity 10.2
Create a hotspot using 
a smartphone and 
connect other 
devices to it. 
ARPANET became 
functional by 
connecting UCLA and 
SRI
Domain Name System 
introduced
The term Internet was 
coined, 
First commercial use of 
ARPANET, was started 
in the name of Telenet
The idea of Advanced 
Research Project Agency 
Network (ARPANET) is 
conceptualized
TCP/IP introduced as 
standard protocol on 
ARPANET
Roy Tomlinson develops 
network messaging or 
E-mail. Symbol @ 
comes to mean "at"
National Science 
Foundation brings 
connectivity to more 
people with its NSFNET 
program
1986
First version of Wi-fi 
(802.11) standard was 
introduced
1997
The Berners-Lee at 
CERN developed HTML 
and URL, thus giving 
birth to World Wide Web 
(www)
1990
1983 1969
1982
1961
1971
1974
Figure 10.3: Timeline showing evolution of networking
Chpater-10.indd   183 11-09-2020   16:41:17
COMPUTER NETWORKS
10.3 TYPES OF NETWORKS
There are various types of computer networks ranging 
from network of handheld devices (like mobile phones 
or tablets) connected through Wi-Fi or Bluetooth within 
a single room to the millions of computers spread across 
the globe. Some are connected wireless while others are 
connected through wires.
Based on the geographical area covered and data 
transfer rate, computer networks are broadly categorised 
as:
•	 PAN ( Personal Area Network)
•	 LAN (Local Area Network)
•	 MAN (Metropolitan Area Network)
•	 WAN (Wide Area Network)  
10.3.1 Personal Area Network (PAN)
It is a network formed by connecting a few personal 
devices like computers, laptops, mobile phones, smart 
phones, printers etc., as shown in Figure 10.4. All these 
devices lie within an approximate range of 10 metres. 
A personal area network may be wired or wireless. 
For example, a mobile phone connected to the laptop 
through USB forms a wired PAN while two smartphones 
communicating with each other through Bluetooth 
technology form a wireless PAN or WPAN. 
Figure 10.4:  A Personal Area Network
NOTES
Chpater-10.indd   184 11-09-2020   16:41:17
COMPUTER SCIENCE - CLASS XII
10.3.2 Local Area Network (LAN)
It is a network that connects computers, mobile phones, 
tablet, mouse, printer, etc., placed at a limited distance. 
The geographical area covered by a LAN can range from 
a	 single	 room,	 a	 floor,	 an	 office	 having	 one	 or	 more	
buildings in the same premise, laboratory, a school, 
college, or university campus. The connectivity is done 
by 	 means 	 of 	 wires, 	 Ethernet 	 cables, 	 fibre 	 optics, 	 or 	 Wi-Fi. 	
A Local Area Network (LAN) is shown in Figure 10.5.
Explore	and	find	out	
the minimum internet 
speed required to 
make a video call.
 
Figure 10.5:  A Local Area Network
LAN is comparatively secure as only authentic 
users in the network can access other computers or 
shared resources. Users can print documents using 
a connected printer, upload/download documents 
and software to and from the local server. Such LANs 
provide the short range communication with the high 
speed data transfer rates. These types of networks can 
be extended up to 1 km. Data transfer in LAN is quite 
high, and usually varies from 10 Mbps (called Ethernet) 
to 1000 Mbps (called Gigabit Ethernet), where Mbps 
stands for Megabits per second. Ethernet is a set of rules 
that decides how computers and other devices connect 
with each other through cables in a local area network  
or LAN.
10.3.3 Metropolitan Area Network (MAN)
Metropolitan Area Network (MAN) is an extended form of 
LAN which covers a larger geographical area like a city or 
a town. Data transfer rate in MAN also ranges in Mbps, 
Chpater-10.indd   185 11-09-2020   16:41:18