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40. Expand the following terms:
(a) XML (b) GSM
(c) SMS (d) MAN
Ans. (a) XML– Extensible Markup Language
(b) GSM– Global System for Mobile communication
(c) SMS– Short Messaging Service
(d) MAN– Metropolitan Area Network
41. How many switching techniques are there? Explain any one.
Ans. There are three switching techniques:
(a) Circuit Switching
(b) Packet Switching
(c) Message Switching
Circuit Switching: In this technique, first the complete physical connection between two computers is
established and then data is transmitted from the source computer to the destination computer. The
entire dedicated line is used by the caller and the receiver and no other user can use it even if the line
becomes idle. When the data transmission is over, the line is disconnected and is available for the next
communication.
42. How are Trojan horses different from Worms? Mention any one difference. [Sample Paper]
Ans. A Trojan horse is a term used to describe malware that appears to the user to perform a desirable function
but which, in fact, facilitates unauthorized access to the user’s computer system.
A computer Worm is a self-replicating program. It uses a network to send copies of itself to other nodes
and that too without human intervention.
43. What is a communication channel? Name the basic types of communication channels available.
Ans. A communication channel is also known as communication media or transmission media. Communication
media can be wireless or wired. Wireless media is also known as unguided media while wired media is
also known as guided media.
Following are three basic types of communication channels available:
(a) Twisted Pair Cables
(b) Coaxial Cables
(c) Fibre-optic Cables
44. Define baud, bps and Bps. How are these interlinked?
Ans. Baud is a unit of measurement for the information-carrying capacity of a communication channel.
bps (bits per second) refers to a thousand bits transmitted per second.
Bps (Bytes per second) refers to a thousand bytes transmitted per second.
All these terms are measurement units used to refer to the amount of information travelling through a
single channel at any one point of time.
45. Differentiate between star topology and bus topology.
Ans. The main points of difference between star and bus topology are: Bus topology

Star topology
Computer Science with Python–XII 8.74 with each other. all computers with each other.
A central hub is required to connect all computers A long cable known as backbone is used to connect

The data is transmitted from the sender to the The data is transmitted through a long cable from
the sender to the receiver.
receiver by passing through the hub.
No collision takes place through transmission of Collision can take place as the data can be
data.
transmitted from both ends at the same time.
If the central hub fails, the entire network shuts If there is a break in a cable, no transmission takes
place.
down.