Textbook: Inside Internet | Computer Science for Class 8 PDF Download

 Page 1


T ejas:	 W e	 w ould	 like	 to	 understand	 the	 connections	 and	 hardw are	 used	 to	 create	
the network in the lab, office and library.
Moz: How are the computers and devices connected in your lab?                                    
Jy oti:	 Computers	 are	 connected	 using	 netw ork	 cables	 (see	 Fig.1).	 One	 side	 of	
the cable is connected to a network port on the computer and the other side to 
a box with several ports (see Fig. 2).        Motherboard
Moz:  The  box is called a network switch or hub. A switch is used to interconnect 
computers in a small area and create a network (see Fig.3). Such a network is 
called LAN (local area network).
  LAN
1
2
3
Aim: In this lesson, you will learn:
-	Netw ork	components	and	connectivity .
- Internet connectivity mechanism.
- Basic concept of Client – Server – Applications. 
- Netw ork,	Data	and	Internet	security .
2 Inside Internet
A computer network is two or more computers, or other electronic devices, connected together so that they can exchange data. •	
A 	computer	netw ork	allows	computers	to	share	files,	and	applications.	Users	can	communicate	with	each	other	and	share	devices. •	
Any	computer	that	needs	to	be	connected	to	the	netw ork	has	a	NIC	(netw ork	interface	card)	which	is	usually	built	into	the	motherboard. •	
Recall
A Local Area Network interconnects computers in a limited area such as a home, school, •	
computer	laboratory,	or	office	building.	
Cables	(wires)	or	low-power	radio	(wireless)	are	used	for	the	connections	in	a	LAN.	 •	
Concept
LAN (Local Area Network)
Fig.1 Network cable
Fig.2 Network Ports
Internet
T ejas:	 W e	 had	 only	 one	 computer	 lab	 in	 our	 school	 till	 now .	 This	 y ear	 w e	 will	 hav e	 2	 more	
such labs. All of them will be interconnected. We can also access internet from any of the  
computers, in any lab.
Jy oti:	 The	 computers	 in	 our	 school	 office	 and	 library	 will	 be	 also	 on	 this	 netw ork.	 W e	 can	 share	
printers. If one printer has a problem we can print using the printer in another lab.       Computer	 Netw ork	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 
         Advantages of a computer network.
Page 2


T ejas:	 W e	 w ould	 like	 to	 understand	 the	 connections	 and	 hardw are	 used	 to	 create	
the network in the lab, office and library.
Moz: How are the computers and devices connected in your lab?                                    
Jy oti:	 Computers	 are	 connected	 using	 netw ork	 cables	 (see	 Fig.1).	 One	 side	 of	
the cable is connected to a network port on the computer and the other side to 
a box with several ports (see Fig. 2).        Motherboard
Moz:  The  box is called a network switch or hub. A switch is used to interconnect 
computers in a small area and create a network (see Fig.3). Such a network is 
called LAN (local area network).
  LAN
1
2
3
Aim: In this lesson, you will learn:
-	Netw ork	components	and	connectivity .
- Internet connectivity mechanism.
- Basic concept of Client – Server – Applications. 
- Netw ork,	Data	and	Internet	security .
2 Inside Internet
A computer network is two or more computers, or other electronic devices, connected together so that they can exchange data. •	
A 	computer	netw ork	allows	computers	to	share	files,	and	applications.	Users	can	communicate	with	each	other	and	share	devices. •	
Any	computer	that	needs	to	be	connected	to	the	netw ork	has	a	NIC	(netw ork	interface	card)	which	is	usually	built	into	the	motherboard. •	
Recall
A Local Area Network interconnects computers in a limited area such as a home, school, •	
computer	laboratory,	or	office	building.	
Cables	(wires)	or	low-power	radio	(wireless)	are	used	for	the	connections	in	a	LAN.	 •	
Concept
LAN (Local Area Network)
Fig.1 Network cable
Fig.2 Network Ports
Internet
T ejas:	 W e	 had	 only	 one	 computer	 lab	 in	 our	 school	 till	 now .	 This	 y ear	 w e	 will	 hav e	 2	 more	
such labs. All of them will be interconnected. We can also access internet from any of the  
computers, in any lab.
Jy oti:	 The	 computers	 in	 our	 school	 office	 and	 library	 will	 be	 also	 on	 this	 netw ork.	 W e	 can	 share	
printers. If one printer has a problem we can print using the printer in another lab.       Computer	 Netw ork	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 
         Advantages of a computer network.
Moz: Yes. Suppose some data has to be sent from your computer (A) 
to	 Jy oti’ s	 computer	 (B).	 Sender	 (A)	 usually	 splits	 the	 data	 into	 small	
chunks, called packets. Each packet also has some extra information, 
called a header. The addresses of sender (A) and receiver (B) are put 
in the header. Then A sends the packets to the switch. The switch has  
in-built software that reads the header of each packet, determines the 
port at which the receiver is connected and forwards the packet on 
the corresponding cable (see Fig.4). Such a type of communication in 
which small units of data (or packets) are routed through a network, 
based on the destination address contained within each packet, is  
called packet-switching.
Jy oti:	 The	 packet	 is	 similar	 to	 a	 letter	 enclosed	 in	 an	 env elope.	 The	 env elope	
has the sender and receiver’s addresses.
T ejas:	 Why	 is	 the	 message	 divided	 into	 so	 many	 chunks	 of	 packets?	 
Why is it not sent as a single packet?
Moz: Breaking the message down into packets allows the same cables 
(physical path) to be shared among many users in the network. As 
a result, the capacity of the network to accommodate simultaneous  
users is increased.
Jy oti:	 Do	 the	 packets	 hav e	 some	 numbering?	 At	 the	 destination	 computer ,	
after all the packets are received, they have to get compiled into the  
full message.
Moz:	 Y es.	 The	 packets	 are	 numbered.	 These	 are	 called	 Sequence	 Numbers.
The packet also has information of total length of the message. 
Computer
Printer
Switch / Hub
Server
T ejas:	 Suppose,	 I	 w ant	 to	 access	 a	 file	 on	 Jy oti’ s	 computer .	 What	 happens	 when	 I	 perform	 the	 action?	
Does	the	switch	relay	the	data	betw een	our	computers	through	the	LAN?
Fig.3 LAN
Fig.4 Packet Switching in a Data Network
Many paths may be used for
 
a single communication as 
individual packets are routed
 
to a destination
Prior to tramsmission, each ?
communication is broken in
to packets which are 
addressed and numbered. 
During peak periods,
 communication may be 
delayed, but not denied.
At the destination, packets 
may be reassembled into
 order according to their 
sequence number.
Packet contains
Souce 
address
Destination 
address
Sequence 
number
Data Header
Router
No fixed path is established.
 
?
Packets are routed according 
to the best path available at 
the time.
Server
Router Router
Router
Computer
Router
Page 3


T ejas:	 W e	 w ould	 like	 to	 understand	 the	 connections	 and	 hardw are	 used	 to	 create	
the network in the lab, office and library.
Moz: How are the computers and devices connected in your lab?                                    
Jy oti:	 Computers	 are	 connected	 using	 netw ork	 cables	 (see	 Fig.1).	 One	 side	 of	
the cable is connected to a network port on the computer and the other side to 
a box with several ports (see Fig. 2).        Motherboard
Moz:  The  box is called a network switch or hub. A switch is used to interconnect 
computers in a small area and create a network (see Fig.3). Such a network is 
called LAN (local area network).
  LAN
1
2
3
Aim: In this lesson, you will learn:
-	Netw ork	components	and	connectivity .
- Internet connectivity mechanism.
- Basic concept of Client – Server – Applications. 
- Netw ork,	Data	and	Internet	security .
2 Inside Internet
A computer network is two or more computers, or other electronic devices, connected together so that they can exchange data. •	
A 	computer	netw ork	allows	computers	to	share	files,	and	applications.	Users	can	communicate	with	each	other	and	share	devices. •	
Any	computer	that	needs	to	be	connected	to	the	netw ork	has	a	NIC	(netw ork	interface	card)	which	is	usually	built	into	the	motherboard. •	
Recall
A Local Area Network interconnects computers in a limited area such as a home, school, •	
computer	laboratory,	or	office	building.	
Cables	(wires)	or	low-power	radio	(wireless)	are	used	for	the	connections	in	a	LAN.	 •	
Concept
LAN (Local Area Network)
Fig.1 Network cable
Fig.2 Network Ports
Internet
T ejas:	 W e	 had	 only	 one	 computer	 lab	 in	 our	 school	 till	 now .	 This	 y ear	 w e	 will	 hav e	 2	 more	
such labs. All of them will be interconnected. We can also access internet from any of the  
computers, in any lab.
Jy oti:	 The	 computers	 in	 our	 school	 office	 and	 library	 will	 be	 also	 on	 this	 netw ork.	 W e	 can	 share	
printers. If one printer has a problem we can print using the printer in another lab.       Computer	 Netw ork	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 
         Advantages of a computer network.
Moz: Yes. Suppose some data has to be sent from your computer (A) 
to	 Jy oti’ s	 computer	 (B).	 Sender	 (A)	 usually	 splits	 the	 data	 into	 small	
chunks, called packets. Each packet also has some extra information, 
called a header. The addresses of sender (A) and receiver (B) are put 
in the header. Then A sends the packets to the switch. The switch has  
in-built software that reads the header of each packet, determines the 
port at which the receiver is connected and forwards the packet on 
the corresponding cable (see Fig.4). Such a type of communication in 
which small units of data (or packets) are routed through a network, 
based on the destination address contained within each packet, is  
called packet-switching.
Jy oti:	 The	 packet	 is	 similar	 to	 a	 letter	 enclosed	 in	 an	 env elope.	 The	 env elope	
has the sender and receiver’s addresses.
T ejas:	 Why	 is	 the	 message	 divided	 into	 so	 many	 chunks	 of	 packets?	 
Why is it not sent as a single packet?
Moz: Breaking the message down into packets allows the same cables 
(physical path) to be shared among many users in the network. As 
a result, the capacity of the network to accommodate simultaneous  
users is increased.
Jy oti:	 Do	 the	 packets	 hav e	 some	 numbering?	 At	 the	 destination	 computer ,	
after all the packets are received, they have to get compiled into the  
full message.
Moz:	 Y es.	 The	 packets	 are	 numbered.	 These	 are	 called	 Sequence	 Numbers.
The packet also has information of total length of the message. 
Computer
Printer
Switch / Hub
Server
T ejas:	 Suppose,	 I	 w ant	 to	 access	 a	 file	 on	 Jy oti’ s	 computer .	 What	 happens	 when	 I	 perform	 the	 action?	
Does	the	switch	relay	the	data	betw een	our	computers	through	the	LAN?
Fig.3 LAN
Fig.4 Packet Switching in a Data Network
Many paths may be used for
 
a single communication as 
individual packets are routed
 
to a destination
Prior to tramsmission, each ?
communication is broken in
to packets which are 
addressed and numbered. 
During peak periods,
 communication may be 
delayed, but not denied.
At the destination, packets 
may be reassembled into
 order according to their 
sequence number.
Packet contains
Souce 
address
Destination 
address
Sequence 
number
Data Header
Router
No fixed path is established.
 
?
Packets are routed according 
to the best path available at 
the time.
Server
Router Router
Router
Computer
Router
Jy oti:	I	hav e	seen	laptops	connecting	to	the	netw ork	without	a	cable.
T ejas:	 In	 some	 places	 like	 airports	 and	 some	 offices,	 cables	 are	 not	 required	 at	 all.	 Any one	 with	 a	
laptop or a tablet can access Internet. 
Moz: These are called wireless connections. Radio signals are used to connect a computer to the 
network. A wireless antenna to send and receive data is built into the laptops. Similarly, the switch 
also	 has	 an	 antenna	 for	 transmitting	 and	 receiving	 data	 wirelessly	 such	 a	 LAN	 is	 called	 WLAN	 
(W ireless	Local	 Area	Netw ork).	(See	Fig.5)
T ejas:	 W e	 know	 that	 w e	 can	 access	 applications	 like	 Gmail,	 Amazon	 online	 book	 store	 from	 any	
country. How does a computer in one country connect to a computer in another country? 
Moz: Computers across long distances are usually connected with optical fibre cables, satellite radio 
links,	 or	 microw av e	 radio	 links.	 Such	 a	 netw ork	 is	 called	 W AN	 (wide	 area	 netw ork).	 Internet	 is	 an	
example	of	W AN.	T w o	or	more	LANs	can	also	be	a	part	of	a	W AN.	(See	Fig.6)	
A	 LAN	 that	 uses	 radio	 signals	 to	 connect	 computers	 is	 called	 	 •	 WLAN (wireless local area 
network).	One	commonly	used	type	of	radio	signals	is	called	WiFi.
A •	 wireless switch 	 with	 one	 or	 two	 antennas	 usually	 sticking	 out	 the	 back	 of	 the	 switch,	 is	
used for sending and receiving data 	to	and	from	the	computers	in	WLAN.
The	range	of	wireless	connection	is	around	50	meters. •	
Computers	 and	 other	 devices	 capable	 of	 sending	 and	 receiving	 data	 wirelessly	 can	 •	
become	part	of	a	WLAN,	when	they	are	within	range.
Concept
WLAN	(Wireless	LAN)
  WLAN (Wireless LAN)
Computer
Printer
Server
Packet: 	 A	 packet	 is	 a	 formatted	 unit	 of	 data.	 A	 packet	 consists	 of	 two	 kinds	 of	 data:	 control	
information	 (header)	 and	 user	 data	 (also	 known	 as	 payload).	 The	 header	 provides	 the	
information	 the	 network	 needs	 to	 deliver	 the	 user	 data.	 For	 example:	 source	 and	 destination	
addresses,	 error	 detection	 codes	 like	 checksums,	 and	 sequencing	 information.	 Typically,	
control	information	is	found	in	packet	headers	and	trailers,	with	payload	data	in	between.
Packet switching: A	 message	 from	 one	 computer	 on	 the	 Internet	 to	 another	 gets	 divided	
into	 packets	 before	 being	 sent.	 Each	 packet	 is	 then	 transmitted	 individually	 and	 can	 even	
follow	 different	 routes	 to	 the	 destination.	 Once	 all	 the	 packets	 forming	 a	 message	 arrive	 at	 the	
destination,	 they	 are	 recompiled	 into	 the	 original	 message.	 Such	 a	 type	 of	 communication	 in	
which	 small	 units	 of	 data	 (or	 packets)	 are	 routed	 through	 a	 network,	 based	 on	 the	 destination	
address	contained	within	each	packet,	is	called	packet-switching.
Concept
Packet
Fig.5 WLAN
Wireless Tower
Switch / Hub
Page 4


T ejas:	 W e	 w ould	 like	 to	 understand	 the	 connections	 and	 hardw are	 used	 to	 create	
the network in the lab, office and library.
Moz: How are the computers and devices connected in your lab?                                    
Jy oti:	 Computers	 are	 connected	 using	 netw ork	 cables	 (see	 Fig.1).	 One	 side	 of	
the cable is connected to a network port on the computer and the other side to 
a box with several ports (see Fig. 2).        Motherboard
Moz:  The  box is called a network switch or hub. A switch is used to interconnect 
computers in a small area and create a network (see Fig.3). Such a network is 
called LAN (local area network).
  LAN
1
2
3
Aim: In this lesson, you will learn:
-	Netw ork	components	and	connectivity .
- Internet connectivity mechanism.
- Basic concept of Client – Server – Applications. 
- Netw ork,	Data	and	Internet	security .
2 Inside Internet
A computer network is two or more computers, or other electronic devices, connected together so that they can exchange data. •	
A 	computer	netw ork	allows	computers	to	share	files,	and	applications.	Users	can	communicate	with	each	other	and	share	devices. •	
Any	computer	that	needs	to	be	connected	to	the	netw ork	has	a	NIC	(netw ork	interface	card)	which	is	usually	built	into	the	motherboard. •	
Recall
A Local Area Network interconnects computers in a limited area such as a home, school, •	
computer	laboratory,	or	office	building.	
Cables	(wires)	or	low-power	radio	(wireless)	are	used	for	the	connections	in	a	LAN.	 •	
Concept
LAN (Local Area Network)
Fig.1 Network cable
Fig.2 Network Ports
Internet
T ejas:	 W e	 had	 only	 one	 computer	 lab	 in	 our	 school	 till	 now .	 This	 y ear	 w e	 will	 hav e	 2	 more	
such labs. All of them will be interconnected. We can also access internet from any of the  
computers, in any lab.
Jy oti:	 The	 computers	 in	 our	 school	 office	 and	 library	 will	 be	 also	 on	 this	 netw ork.	 W e	 can	 share	
printers. If one printer has a problem we can print using the printer in another lab.       Computer	 Netw ork	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 
         Advantages of a computer network.
Moz: Yes. Suppose some data has to be sent from your computer (A) 
to	 Jy oti’ s	 computer	 (B).	 Sender	 (A)	 usually	 splits	 the	 data	 into	 small	
chunks, called packets. Each packet also has some extra information, 
called a header. The addresses of sender (A) and receiver (B) are put 
in the header. Then A sends the packets to the switch. The switch has  
in-built software that reads the header of each packet, determines the 
port at which the receiver is connected and forwards the packet on 
the corresponding cable (see Fig.4). Such a type of communication in 
which small units of data (or packets) are routed through a network, 
based on the destination address contained within each packet, is  
called packet-switching.
Jy oti:	 The	 packet	 is	 similar	 to	 a	 letter	 enclosed	 in	 an	 env elope.	 The	 env elope	
has the sender and receiver’s addresses.
T ejas:	 Why	 is	 the	 message	 divided	 into	 so	 many	 chunks	 of	 packets?	 
Why is it not sent as a single packet?
Moz: Breaking the message down into packets allows the same cables 
(physical path) to be shared among many users in the network. As 
a result, the capacity of the network to accommodate simultaneous  
users is increased.
Jy oti:	 Do	 the	 packets	 hav e	 some	 numbering?	 At	 the	 destination	 computer ,	
after all the packets are received, they have to get compiled into the  
full message.
Moz:	 Y es.	 The	 packets	 are	 numbered.	 These	 are	 called	 Sequence	 Numbers.
The packet also has information of total length of the message. 
Computer
Printer
Switch / Hub
Server
T ejas:	 Suppose,	 I	 w ant	 to	 access	 a	 file	 on	 Jy oti’ s	 computer .	 What	 happens	 when	 I	 perform	 the	 action?	
Does	the	switch	relay	the	data	betw een	our	computers	through	the	LAN?
Fig.3 LAN
Fig.4 Packet Switching in a Data Network
Many paths may be used for
 
a single communication as 
individual packets are routed
 
to a destination
Prior to tramsmission, each ?
communication is broken in
to packets which are 
addressed and numbered. 
During peak periods,
 communication may be 
delayed, but not denied.
At the destination, packets 
may be reassembled into
 order according to their 
sequence number.
Packet contains
Souce 
address
Destination 
address
Sequence 
number
Data Header
Router
No fixed path is established.
 
?
Packets are routed according 
to the best path available at 
the time.
Server
Router Router
Router
Computer
Router
Jy oti:	I	hav e	seen	laptops	connecting	to	the	netw ork	without	a	cable.
T ejas:	 In	 some	 places	 like	 airports	 and	 some	 offices,	 cables	 are	 not	 required	 at	 all.	 Any one	 with	 a	
laptop or a tablet can access Internet. 
Moz: These are called wireless connections. Radio signals are used to connect a computer to the 
network. A wireless antenna to send and receive data is built into the laptops. Similarly, the switch 
also	 has	 an	 antenna	 for	 transmitting	 and	 receiving	 data	 wirelessly	 such	 a	 LAN	 is	 called	 WLAN	 
(W ireless	Local	 Area	Netw ork).	(See	Fig.5)
T ejas:	 W e	 know	 that	 w e	 can	 access	 applications	 like	 Gmail,	 Amazon	 online	 book	 store	 from	 any	
country. How does a computer in one country connect to a computer in another country? 
Moz: Computers across long distances are usually connected with optical fibre cables, satellite radio 
links,	 or	 microw av e	 radio	 links.	 Such	 a	 netw ork	 is	 called	 W AN	 (wide	 area	 netw ork).	 Internet	 is	 an	
example	of	W AN.	T w o	or	more	LANs	can	also	be	a	part	of	a	W AN.	(See	Fig.6)	
A	 LAN	 that	 uses	 radio	 signals	 to	 connect	 computers	 is	 called	 	 •	 WLAN (wireless local area 
network).	One	commonly	used	type	of	radio	signals	is	called	WiFi.
A •	 wireless switch 	 with	 one	 or	 two	 antennas	 usually	 sticking	 out	 the	 back	 of	 the	 switch,	 is	
used for sending and receiving data 	to	and	from	the	computers	in	WLAN.
The	range	of	wireless	connection	is	around	50	meters. •	
Computers	 and	 other	 devices	 capable	 of	 sending	 and	 receiving	 data	 wirelessly	 can	 •	
become	part	of	a	WLAN,	when	they	are	within	range.
Concept
WLAN	(Wireless	LAN)
  WLAN (Wireless LAN)
Computer
Printer
Server
Packet: 	 A	 packet	 is	 a	 formatted	 unit	 of	 data.	 A	 packet	 consists	 of	 two	 kinds	 of	 data:	 control	
information	 (header)	 and	 user	 data	 (also	 known	 as	 payload).	 The	 header	 provides	 the	
information	 the	 network	 needs	 to	 deliver	 the	 user	 data.	 For	 example:	 source	 and	 destination	
addresses,	 error	 detection	 codes	 like	 checksums,	 and	 sequencing	 information.	 Typically,	
control	information	is	found	in	packet	headers	and	trailers,	with	payload	data	in	between.
Packet switching: A	 message	 from	 one	 computer	 on	 the	 Internet	 to	 another	 gets	 divided	
into	 packets	 before	 being	 sent.	 Each	 packet	 is	 then	 transmitted	 individually	 and	 can	 even	
follow	 different	 routes	 to	 the	 destination.	 Once	 all	 the	 packets	 forming	 a	 message	 arrive	 at	 the	
destination,	 they	 are	 recompiled	 into	 the	 original	 message.	 Such	 a	 type	 of	 communication	 in	
which	 small	 units	 of	 data	 (or	 packets)	 are	 routed	 through	 a	 network,	 based	 on	 the	 destination	
address	contained	within	each	packet,	is	called	packet-switching.
Concept
Packet
Fig.5 WLAN
Wireless Tower
Switch / Hub
Moz: What are the different methods of connecting to the Internet? You must have used at least  
one method.
Jy oti:	 At	 home	 w e	 hav e	 to	 connect	 a	 dongle	 (with	 USB	 connector)	 to	 the	 computer	 to	
connect to the internet (see Fig.7)
Moz: From where do you get this dongle?
Jy oti:	W e	hav e	to	buy	it	from	the	internet	service	provider .							ISP
Processor (CPU)
1
A	router	is	a	network	device	that	connects	together	two	or	more	networks. •	
A common use of a router is to join a home or business network (LAN) to the  •	
Internet	(WAN).	
The	 router	 will	 typically	 have	 the	 Internet	 cable	 plugge d	 into	 it,	 as	 well	 as	 a	 cable,	 or	 cables	 •	
to	computers	or	switch	on	the	LAN.	
Some	routers	are	also	wireless	capable.	 •	
Info
Router
An Internet service provider (ISP) is an organization that provides access to the Internet. •	
Jy oti:	 Is	 there	 a	 switch	 betw een	 the	 LANs	 or	 computers	 communicating	 across	 long	 
distances? (See Fig.4)
Moz:	 Y es.	 It	 is	 a	 special	 type	 of	 switch	 that	 has	 more	 functions	 than	 a	 LAN	 switch.	 It	 is	 called	 a	router. 
It	 has	 softw are	 to	 send	 and	 receiv e	 packets	 correctly	 across	 W ANs.	 Routers	 communicate	 with	 each	
other	to	ensure	that	y our	packets	are	deliv ered	to	the	correct	destinations	across	the	W AN/	Internet.
Recall
A	 Network	 which	 is	 geographically	 spread	 over	 large	 areas	 with	 links	 between	 computers	 •	
is	called	a	WAN	(wide	area	network).	
The	 long	 distance	 connections	 are	 done	 using	 technologies	 such	 as	 optical	 fibre	 cables,	 •	
satellite	radio	links	or	microwave	radio	links.
Concept
WAN	(Wide	Area	Network)
 WAN
Broadcasting Broadcasting
Satellite
LAN WLAN
Mumbai Office
Delhi office
Client
Client
Client
Wireless Switch
Client
Client
Client
Switch / Hub
1
Fig.6 WAN
Fig.7 Pendrive
Page 5


T ejas:	 W e	 w ould	 like	 to	 understand	 the	 connections	 and	 hardw are	 used	 to	 create	
the network in the lab, office and library.
Moz: How are the computers and devices connected in your lab?                                    
Jy oti:	 Computers	 are	 connected	 using	 netw ork	 cables	 (see	 Fig.1).	 One	 side	 of	
the cable is connected to a network port on the computer and the other side to 
a box with several ports (see Fig. 2).        Motherboard
Moz:  The  box is called a network switch or hub. A switch is used to interconnect 
computers in a small area and create a network (see Fig.3). Such a network is 
called LAN (local area network).
  LAN
1
2
3
Aim: In this lesson, you will learn:
-	Netw ork	components	and	connectivity .
- Internet connectivity mechanism.
- Basic concept of Client – Server – Applications. 
- Netw ork,	Data	and	Internet	security .
2 Inside Internet
A computer network is two or more computers, or other electronic devices, connected together so that they can exchange data. •	
A 	computer	netw ork	allows	computers	to	share	files,	and	applications.	Users	can	communicate	with	each	other	and	share	devices. •	
Any	computer	that	needs	to	be	connected	to	the	netw ork	has	a	NIC	(netw ork	interface	card)	which	is	usually	built	into	the	motherboard. •	
Recall
A Local Area Network interconnects computers in a limited area such as a home, school, •	
computer	laboratory,	or	office	building.	
Cables	(wires)	or	low-power	radio	(wireless)	are	used	for	the	connections	in	a	LAN.	 •	
Concept
LAN (Local Area Network)
Fig.1 Network cable
Fig.2 Network Ports
Internet
T ejas:	 W e	 had	 only	 one	 computer	 lab	 in	 our	 school	 till	 now .	 This	 y ear	 w e	 will	 hav e	 2	 more	
such labs. All of them will be interconnected. We can also access internet from any of the  
computers, in any lab.
Jy oti:	 The	 computers	 in	 our	 school	 office	 and	 library	 will	 be	 also	 on	 this	 netw ork.	 W e	 can	 share	
printers. If one printer has a problem we can print using the printer in another lab.       Computer	 Netw ork	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 
         Advantages of a computer network.
Moz: Yes. Suppose some data has to be sent from your computer (A) 
to	 Jy oti’ s	 computer	 (B).	 Sender	 (A)	 usually	 splits	 the	 data	 into	 small	
chunks, called packets. Each packet also has some extra information, 
called a header. The addresses of sender (A) and receiver (B) are put 
in the header. Then A sends the packets to the switch. The switch has  
in-built software that reads the header of each packet, determines the 
port at which the receiver is connected and forwards the packet on 
the corresponding cable (see Fig.4). Such a type of communication in 
which small units of data (or packets) are routed through a network, 
based on the destination address contained within each packet, is  
called packet-switching.
Jy oti:	 The	 packet	 is	 similar	 to	 a	 letter	 enclosed	 in	 an	 env elope.	 The	 env elope	
has the sender and receiver’s addresses.
T ejas:	 Why	 is	 the	 message	 divided	 into	 so	 many	 chunks	 of	 packets?	 
Why is it not sent as a single packet?
Moz: Breaking the message down into packets allows the same cables 
(physical path) to be shared among many users in the network. As 
a result, the capacity of the network to accommodate simultaneous  
users is increased.
Jy oti:	 Do	 the	 packets	 hav e	 some	 numbering?	 At	 the	 destination	 computer ,	
after all the packets are received, they have to get compiled into the  
full message.
Moz:	 Y es.	 The	 packets	 are	 numbered.	 These	 are	 called	 Sequence	 Numbers.
The packet also has information of total length of the message. 
Computer
Printer
Switch / Hub
Server
T ejas:	 Suppose,	 I	 w ant	 to	 access	 a	 file	 on	 Jy oti’ s	 computer .	 What	 happens	 when	 I	 perform	 the	 action?	
Does	the	switch	relay	the	data	betw een	our	computers	through	the	LAN?
Fig.3 LAN
Fig.4 Packet Switching in a Data Network
Many paths may be used for
 
a single communication as 
individual packets are routed
 
to a destination
Prior to tramsmission, each ?
communication is broken in
to packets which are 
addressed and numbered. 
During peak periods,
 communication may be 
delayed, but not denied.
At the destination, packets 
may be reassembled into
 order according to their 
sequence number.
Packet contains
Souce 
address
Destination 
address
Sequence 
number
Data Header
Router
No fixed path is established.
 
?
Packets are routed according 
to the best path available at 
the time.
Server
Router Router
Router
Computer
Router
Jy oti:	I	hav e	seen	laptops	connecting	to	the	netw ork	without	a	cable.
T ejas:	 In	 some	 places	 like	 airports	 and	 some	 offices,	 cables	 are	 not	 required	 at	 all.	 Any one	 with	 a	
laptop or a tablet can access Internet. 
Moz: These are called wireless connections. Radio signals are used to connect a computer to the 
network. A wireless antenna to send and receive data is built into the laptops. Similarly, the switch 
also	 has	 an	 antenna	 for	 transmitting	 and	 receiving	 data	 wirelessly	 such	 a	 LAN	 is	 called	 WLAN	 
(W ireless	Local	 Area	Netw ork).	(See	Fig.5)
T ejas:	 W e	 know	 that	 w e	 can	 access	 applications	 like	 Gmail,	 Amazon	 online	 book	 store	 from	 any	
country. How does a computer in one country connect to a computer in another country? 
Moz: Computers across long distances are usually connected with optical fibre cables, satellite radio 
links,	 or	 microw av e	 radio	 links.	 Such	 a	 netw ork	 is	 called	 W AN	 (wide	 area	 netw ork).	 Internet	 is	 an	
example	of	W AN.	T w o	or	more	LANs	can	also	be	a	part	of	a	W AN.	(See	Fig.6)	
A	 LAN	 that	 uses	 radio	 signals	 to	 connect	 computers	 is	 called	 	 •	 WLAN (wireless local area 
network).	One	commonly	used	type	of	radio	signals	is	called	WiFi.
A •	 wireless switch 	 with	 one	 or	 two	 antennas	 usually	 sticking	 out	 the	 back	 of	 the	 switch,	 is	
used for sending and receiving data 	to	and	from	the	computers	in	WLAN.
The	range	of	wireless	connection	is	around	50	meters. •	
Computers	 and	 other	 devices	 capable	 of	 sending	 and	 receiving	 data	 wirelessly	 can	 •	
become	part	of	a	WLAN,	when	they	are	within	range.
Concept
WLAN	(Wireless	LAN)
  WLAN (Wireless LAN)
Computer
Printer
Server
Packet: 	 A	 packet	 is	 a	 formatted	 unit	 of	 data.	 A	 packet	 consists	 of	 two	 kinds	 of	 data:	 control	
information	 (header)	 and	 user	 data	 (also	 known	 as	 payload).	 The	 header	 provides	 the	
information	 the	 network	 needs	 to	 deliver	 the	 user	 data.	 For	 example:	 source	 and	 destination	
addresses,	 error	 detection	 codes	 like	 checksums,	 and	 sequencing	 information.	 Typically,	
control	information	is	found	in	packet	headers	and	trailers,	with	payload	data	in	between.
Packet switching: A	 message	 from	 one	 computer	 on	 the	 Internet	 to	 another	 gets	 divided	
into	 packets	 before	 being	 sent.	 Each	 packet	 is	 then	 transmitted	 individually	 and	 can	 even	
follow	 different	 routes	 to	 the	 destination.	 Once	 all	 the	 packets	 forming	 a	 message	 arrive	 at	 the	
destination,	 they	 are	 recompiled	 into	 the	 original	 message.	 Such	 a	 type	 of	 communication	 in	
which	 small	 units	 of	 data	 (or	 packets)	 are	 routed	 through	 a	 network,	 based	 on	 the	 destination	
address	contained	within	each	packet,	is	called	packet-switching.
Concept
Packet
Fig.5 WLAN
Wireless Tower
Switch / Hub
Moz: What are the different methods of connecting to the Internet? You must have used at least  
one method.
Jy oti:	 At	 home	 w e	 hav e	 to	 connect	 a	 dongle	 (with	 USB	 connector)	 to	 the	 computer	 to	
connect to the internet (see Fig.7)
Moz: From where do you get this dongle?
Jy oti:	W e	hav e	to	buy	it	from	the	internet	service	provider .							ISP
Processor (CPU)
1
A	router	is	a	network	device	that	connects	together	two	or	more	networks. •	
A common use of a router is to join a home or business network (LAN) to the  •	
Internet	(WAN).	
The	 router	 will	 typically	 have	 the	 Internet	 cable	 plugge d	 into	 it,	 as	 well	 as	 a	 cable,	 or	 cables	 •	
to	computers	or	switch	on	the	LAN.	
Some	routers	are	also	wireless	capable.	 •	
Info
Router
An Internet service provider (ISP) is an organization that provides access to the Internet. •	
Jy oti:	 Is	 there	 a	 switch	 betw een	 the	 LANs	 or	 computers	 communicating	 across	 long	 
distances? (See Fig.4)
Moz:	 Y es.	 It	 is	 a	 special	 type	 of	 switch	 that	 has	 more	 functions	 than	 a	 LAN	 switch.	 It	 is	 called	 a	router. 
It	 has	 softw are	 to	 send	 and	 receiv e	 packets	 correctly	 across	 W ANs.	 Routers	 communicate	 with	 each	
other	to	ensure	that	y our	packets	are	deliv ered	to	the	correct	destinations	across	the	W AN/	Internet.
Recall
A	 Network	 which	 is	 geographically	 spread	 over	 large	 areas	 with	 links	 between	 computers	 •	
is	called	a	WAN	(wide	area	network).	
The	 long	 distance	 connections	 are	 done	 using	 technologies	 such	 as	 optical	 fibre	 cables,	 •	
satellite	radio	links	or	microwave	radio	links.
Concept
WAN	(Wide	Area	Network)
 WAN
Broadcasting Broadcasting
Satellite
LAN WLAN
Mumbai Office
Delhi office
Client
Client
Client
Wireless Switch
Client
Client
Client
Switch / Hub
1
Fig.6 WAN
Fig.7 Pendrive
A 	P e r i p h e r al 	d e v i c e 	i s 	an 	e x t e r n al 	o b j e c t 	t h at 	p r o v i d e s 	i n p u t 	an d 	o u t p u t 	f o r 	t h e 	c o m p u t e r .	E x am p l e :	k e y b o ar d ,	m o n i t o r . •	
Recall
Moz: Right. The dongle is a USB device that can be plugged into a computer for internet access. It has 
an inbuilt wireless that connects to the ISP , similar to mobile phones.
T ejas:	On	a	mobile	phone,	w e	can	access	the	internet	by	enabling	some	settings.		
Jy oti:	 I	 hav e	 seen	 some	 connections	 that	 use	 telephone	 lines.	 A 	 device	 called	 modem	 is	 connected	 to	
the computer in such connections.
Moz: Right. Similar to the peripheral devices, a modem converts the data and 
instructions entered using the device into a pattern of electrical signals. These signals 
correspond to binary code that can be processed by a digital computer. (see Fig. 8)              
      Peripheral devices 
Multi user internet connections
Single	user	internet	connection
DSL (digital subscriber line) Modem: •	 is a device used to connect a 
computer	or	router	to	the	internet	through	a	telephone	circuit.	
Broadband Modem: •	 	 Uses	 DSL	 or	 a	 cable	 Internet	 service	 to	 connect	
to	 the	 internet.	 Here,	 the	 DSL	 line	 connects	 to	 your	 phone	 jack	 and	 the	
USB	line	or	Ethernet	to	your	computer.
Mobile broadband: •	 	 Uses	 a	 wireless	 internet	 card,	 such	 as	 a	 USB	
dongle,	 to	 connect	 to	 the	 internet.	 This	 dongle	 can	 be	 used	 (wherever	
the	 ISP	 provides	 coverage)	 by	 plugging	 it	 into	 the	 USB	 port	 on	 a	 net	
book,	PC	or	laptop.
Portable Internet Devices •	 like smart phones use a variety of wireless 
technologies	 such	 as	 3G,	 WiFi	 and	 WiMAX	 technology	 to	 connect	 to	
the	Internet.	
WiFi router at home: •	 	 Extension	 of	 single	 user	 by	 connecting	 WiFi	
access	switch	to	Broadband	Modem.
Fiber-to-the-building Broadband (FTTH) •	 	 uses	 fiber	 optic	 cables	 to	
connect	 to	 the	 Internet.	 Such	 optics-based	 systems	 can	 deliver	 digital	
information	very	efficiently.	
Wireless mesh networks: •	 	 In	 these,	 the	 network	 connection	 is	 spread	
out	 among	 dozens	 or	 even	 hundreds	 of	 wireless	 mesh	 nodes	 that	
“talk”	 to	 each	 other	 to	 provide	 the	 network	 connection	 across	 a	 large	
geographical	area.
Satellite Connections: •	 	 Internet	 connection	 through	 a	 satellite	 dish	 to	
upload and download data communications is often used for areas that 
are	geographically	difficult,	such	as	mountains.
Info
Internet	access	–	Single	user	and	multiuser
1
Fig.8 Modem