Computer Science (New) - For Class IX - UNIT. UNIT. 4. Data Communication And Computer Network - Text Book Exercise And Activity

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Chapter No.4. Data Communication And Computer Network
Text Book Exercise And Activity

Text Book Exercise

B. Respond the following:

1. List the properties of a good communication system. Explain any one.?
Ans: Properties of a Good Communication System:
The effectiveness of a data communications system depends on the fundamental characteristics which include:

1. Delivery
2. Accuracy and
3. Timeliness

S.No.	Characteristic	Description
1.	Delivery	Making sure that the data is delivered is the first fundamental characteristic of any communication network. The system must be able to deliver data in correct order to the correct destination.
2.	Accuracy	The system must deliver the data accurately. Data that has been altered during transmission and left uncorrected is not useful.
3.	Timeliness	The data must be delivered in a timely manner. Late delivered data is useless.

(Note: Describe anyone (Delivery or Accuracy or Timeliness, as mention in question)

2. Explain different components of a communication system using single example?
Ans: COMPONENTS OF A COMMUNICATION SYSTEM:
A Communication system has following five components:

(i) Message:
It is the information or data to be communicated.
Example: Common forms of information include text, numbers, pictures, audio and video.

(ii) Sender:
It is the device that generates and sends a message.
Example: It can be a computer, telephone handset, etc.

(iii) Receiver:
Any particular digital electronic device which has capability to receive data in form of message. The location of receiving computer is generally different from the sending computer.
Example: Like sender, it can also be a computer, telephone handset, etc.

(iv) Medium:
It is the channel or path through which the message is carried from sender to the receiver.
Example: Some examples include twisted-pair cable, coaxial cable, radio waves, etc.

(v) Protocol:
Protocols are the rules and procedures on which computers exchange data on network.
Sender and receiver follow same protocols to communicate with each other.
In other words, a protocol is an agreement between two parties or venders, using communication devices.
Example: FTP, TCP/IP, HTTP etc.

EXAMPLE OF COMMUNICATION SYSTEM:
When a person talk with another person directly, then the speaker is the sender who conveying the message as information in the form of sound waves through a communication channel, the intervening air and listener are the receiver.
If the distance between the speaker and the listener is large sound waves cannot reach from the speaker to the listener directly and communication is not possible. To make communication possible, different communication channel or method is used like microphone and speakers via telephone or internet services etc.

3. Write the function of following network devices.
Amplifiers, Routers, Switch, Hub
Ans: AMPLIFIERS:
Amplifiers are used to overcome attenuation and make signal stronger again. It is measured in decibels.

ROUTERS:

• A Router is a device that connects two or more networks.
• Routers are a combination of hardware and software.
• The main function of a router is to determine the optimal data path and transfer the information through that path, also known as network traffic controller.

SWITCH:

• A switch or network switch is a networking device that connects computers and other devices like printers, scanners and cameras on a network.
• Data cables from all computers and other devices of network are plugged into the switch to enable communication between them.

HUB:

• In a star topology, all the computers are connected to a central device called hub or switch.
• To communicate with any computer, the sender must send information to the hub. Then the hub transmits that information to the destination.

Q.No.4: List the causes of signal impairments. Explain any one.
Ans: TRANSMISSION IMPAIRMENTS OR FLAWS AND FAULTS IN TRANSMISSION SIGNALS:
Sometimes, signals traveling through transmission media lose their quality. This means that received signal is not same as the signal that was sent. This phenomenon is called transmission impairments. Transmission impairments are those defects that occur when data is transmitted.

CAUSES OF SIGNAL IMPAIRMENTS OR TYPES OF FLAWS AND FAULTS IN TRANSMISSION SIGNALS:
There are three causes of impairment i.e.:

1. Attenuation
2. Distortion and
3. Noise

(i) Attenuation:
Attenuation means loss of energy. A signal loses its energy due to the resistance of medium while it is transmitted. Its strength decreases with increase in distance. Amplifiers are used to overcome attenuation and make signal stronger again. It is measured in decibels.

(ii) Distortion:
Distortion means change in the shape of the signal. A composite signal has several frequencies. When it travels through a medium different component of signal may reach at different time at destination because each component has different speed in that medium. This is called distortion. They have different phases at sender and receiver ends.

(iii) Noise:
Unwanted signal that mixes up with the original signal during the transmission of data is called noise. It can be induced noise, crosstalk noise, thermal noise and impulse noise which may damage the signal.

(Note: Explain any one cause as mention in question)

5. What is the difference between radio wave and microwave?
Ans: Difference Between Radio Wave And Microwave:

S.NO.	Basis	Radio Wave	Micro wave
1.	Direction	These are omni directional in nature.	These are unidirectional in nature.
2.	Penetration	At low frequency, they can penetrate through solid objects and walls but at high frequency they bounce off the obstacle.	At low frequency, they can penetrate through solid objects and walls but at high they cannot penetrate.
3.	Frequency range	3 KHz to 1 GHz	1 GHz to 300 GHz
4.	Security	These offer poor security.	These offer medium security.
5.	Attenuation	High	Variable
6.	Government License	Some frequencies in the radio waves require government license to use these.	Some frequencies in the microwaves require government license to use these.
7.	Usage cost	Setup and usage cost is moderate.	Setup and usage cost is high.
8.	Communication	These are used in long distance communication.	These are used in long distance communication.

6. Why OSI model is broken up in layers?
Ans: The OSI model is conceptual. It is broken up into layers so a person can visualize network communication from the application to the medium. It works going up the stack at the destination as well. Rather than just "all the magic happens", it is broken down so we can visualize the steps a computer takes when it encapsulates data.
Breaking things down into layers also allows for better troubleshooting. If there is no data being received on our NIC, then we can assume it is a layer 1 or 2 problem.
If we are getting routing errors, then we most likely have a layer 3 problem. It allows an administrator to better pinpoint an issue.

7. Explain the purpose of Standard Organization.
Ans: PURPOSE OF STANDARD ORGANIZATIONS:

• Standard Organization develops, coordinates, revises, amends and reissues technical standards.
• These standards are intended to address the requirements of a group of concerned devices.
• There are several organizations working on standardization of computing equipment to enable the interoperability among different devices manufactured by different companies in different regions.
• Example: ISO, IEEE, IETF, ITU and ANSI are the examples of standard organizations.

8. List one merit and one demerit of each topology.
Ans: (i) BUS TOPOLOGY:
Advantage Or Merit of Bus Topology:

• Simplicity
• Cable required is least compared to other network topology.
• Used in small networks.
• It is cost effective i.e. low cost.
• It is easy to understand.
• Easy expansion of the network i.e. easy to expand joining two cables together.

Disadvantage Or Demerit of Bus Topology:

• A breakdown in the bus cable brings the entire network down.
• If network traffic is heavy or nodes are more the performance of the network decreases.
• Cable has a limited length.
• It is slower than the ring topology.

(ii) RING TOPOLOGY:
Advantage Or Merit of Ring Topology:

• Transmitting network is not affected by high traffic or by adding more nodes, as only the nodes having tokens can transmit data.
• Cheap to install and expand.

Disadvantage Or Demerit of Ring Topology:

• The failure of a link or a computer can make the entire network nonfunctional.
• Troubleshooting is difficult in ring topology.
• Adding or deleting the computers disturbs the network activity.

(iii) STAR TOPOLOGY:
Advantage Or Merit of Star Topology:

• The advantages of star topology are easy to set up and easy expansion of the network.
• Another feature of Star Topology is that if one link to the hub breaks, only the station using that link is affected not the whole network.
• Fast performance with few nodes and low network traffic.
• Hub can be upgraded easily.
• Easy to troubleshoot.

Disadvantages Or Demerits of Star Topology:

• Cost of installation is high.
• Expensive to use.
• If the hub fails then the whole network is stopped because all the nodes depend on the hub.
• Performance is based on the hub that is it depends on its capacity.

(Note: Write down only one merit and one demerit for each topology as asked in question)

9. Give one example of LAN, WAN and MAN.
Ans: Example Of Local Area Network (LAN):

• Networking between two computers.
• Networking in the home, school, library, laboratory, college / university campus or office.
• Wi-Fi which is also known as wireless LAN.

Example Of Metropolitan Area Network (MAN): 

• Cable TV network
• Telephone networks providing high speed DSL lines.
• IEEE 802. 16 or WiMAX, that provides high-speed broadband access with Internet connectivity to customer premises.

Example Of Wide Area Network (WAN):

• Internet is the example of WAN.

(Note: Give any one example of each as mention in question.)

10. How can we measure bit rate and baud rate? Give an example of each.
Ans: Both bit rate and baud rate are generally used in data communication.
Bit rate is the transmission of number of bits per unit of time (second). Bit rate can be ranging from bps (bits per second) for smaller values to kbps (kilo bits per second) and mbps (megabits per second).
For Example:
DSL connection may be able to download data at 10 kbps, means 10,000 bits are transferred within one second.

Baud rate is defined as the number of signal units transmitted per unit of time (second).
For Example:
If a signal changes 1200 times in one second, it would be measured at 1200 baud.

Formula:
We can measure bit rate and baud rate by the following formula, which relate both:

Bit rate = baud rate x the number of bits per signal unit

OR

Baud rate = bit rate / the number of bits per signal unit

Example:

• When Bit rate and Baud rate are Same:
  Assume 9600 bits are transferred per second and 1 bit used to represent signal level i.e either logic 0 or logic 1 then bit rate is 9600 because number of bits transferred per second are 9600 and baud rate is 9600 because number of changes happening per seconds are also the same.
  
  
• When Bit rate and Baud rate are not same:
  If 9600 bits are transferred per second and 2 bits used to represent the signal level then bit rate is 9600 because the number of bits transferred per second are 9600 but baud rate is 4800 because two bits representing signal level.
  
  

C. Match the columns:

S.NO.	A	S.NO.	B	C
(i)	Parts of an IPV4 address	(a)	WAN	(i)-(b)
(ii)	Physical address	(b)	Network and Host	(ii)-(e)
(iii)	Change in shape of signals	(c)	Transport layer	(iii)-(f)
(iv)	A networking connecting two continents	(d)	Data link layer	(iv)-(a)
(v)	TCP and UDP are used at	(e)	Cannot be changed	(v)-(c)
(vi)	In OSI model the layer responsible to decide the format of data	(f)	Distortion	(vi)-(d)

Activity

More Short Questions Answers

1. List out the names of standards organizations?
Ans: ISO, IEEE, IETF, ITU, ANSI are the examples of standard organizations.

Computer Science (New) - For Class IX - UNIT. 4. Data Communication And Computer Network - Short and Descriptive Questions Answers

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Chapter No.4. Data Communication And Computer Network
Descriptive Questions Answers

Q.1: Define communication and data communication?
Ans: COMMUNICATION:
Communication is the process of sharing a message.
Example:
A conversation between two people is an example of communication.

DATA COMMUNICATION:
Data communications refers to the sharing of a virtual message. Data communication is the exchange of digital messages between two devices. It involves a sender and a receiver which communicate via some form of transmission medium such as a cable.
Example:
Electronic communications, like emails and instant messages and phone calls are examples of data communications.

Q.2: Define the following terminologies of data communication?

• Data
• Data Communication
• Data Transmission
• Analog Signals
• Digital Signals
• Data Rate / Bit Rate
• Baud Rate
• Signal to Noise Ratio

Ans: BASICS TERMINOLOGIES OF DATA COMMUNICATION

(i) Data:

• Collection of raw facts and figures is called data. The word data is derived from Latin language and it is plural of Datum.
• The text, numbers, symbols, images, voice and video which are processed by computers and digital devices are called data. Data can be considered as unprocessed information.

(ii) Data Communication:
Data Communication is the process of transferring data electrically from one place to another. It is the process of exchange of data and information between two partiesExample:  Such as human and electronic or computing device.

(iii) Data Transmission:
The data transmission means emission of data in any direction via wireless or wired medium. Transmission may occur between source and destination.

(iv) Analog Signals:
Analog signals are a continuously varying signals or waves that change with time period and used to represent data. An analog signal can be used to measure changes in some physical quantities
Example: Such as light, sound, pressure or temperature.

(v) Digital Signals:
A digital signal is an electrical signal that is converted into a pattern of bits to represent a sequence of discrete values, at any given time. It can only be one of the finite numbers represented as 0 or 1.

(vi) Data Rate / Bit Rate:

• Data rate is the rate at which data is transferred. It is normally measured in bits per second. Bit is the actual binary digit which is the basic unit of data transmission. Bit can hold either 0 or 1.
• Bit Rate:
  Data rate can be ranging from bps (bits per second) for smaller values to kbps (kilo bits per second) and mbps (megabits per second). It is also called bit rate.
• Data rate becomes faster when more bits are transferred in one second.
• Formula Of Bit Rate:
  
  Bit rate = baud rate x the number of bits per signal units.

(vii) Baud Rate:

• The baud rate is the number of signals transmitted per second and one signal can represent one or more bits. It is used to describe the maximum change in an electronic signal.
• For example, if a signal changes 1200 times in one second, it would be measured at 1200 baud.
• Formula of Baud Rate:
  
  Baud rate = bite rate / the number of bits per signal units.

(viii) Signal to Noise Ratio:

• Signal-to-noise ratio (abbreviated SNR or S/N) is a measure. It is dened as the ratio of signal power to the noise power, often expressed in decibels.
• Uses: It is used in engineering that compares the level of a desired signal and the level of background noise.

Q.3: Differentiate between:
(a) analog and digital signals
(b) Data rate or Bite rate and baud rate?

 Ans: Difference Between Analog Signals and Digital signals

S.No.	Analog Signals	Digital signals
1.	An analog signal is a continuous wave that changes by time period.	A digital signal is a discrete wave that carries information in binary form.
2.	Analog signal has no fixed range.	Digital signal has a finite number i.e. 0 and 1.
3.	An analog signal can easily be disturbed by other signals or waves.	A digital signal is less prone to other signals disturbance.
4.	The human voice is example of an analog signal.	Signals used by computer are the digital signal.
5.	An analog signal is represented by a sine wave.	A digital signal is represented by square waves.
6.	Analog signals are long term waves need to be boosting.	Digital signals are short term signals remain within digital devices / electronic.

Difference between Data Rate/Bit Rate and Baud Rate:

S.NO.	Data Rate/Bit Rate	Baud Rate
1.	Bit rate tells the number of bits transmitted per unit of time (Second).	Baud rate is used when we want to know the number of signal units transmitted per unit of time (Second).
2.	Bit rate is the number bits (0's and 1's) transmitted per second.	Baud rate is the number of times a signal is traveling comprised of bits. One signal can represent more than one bit.
3.	Formula:  Bit rate = baud rate x the number of bits per signal unit	Formula:  Baud rate = bit rate / the number of bits per signal unit

Q.No.4: Explain different components of a communication system using examples? Also write down single example?
Ans: COMPONENTS OF A COMMUNICATION SYSTEM:
A Communication system has following ve components:

(i) Message:
It is the information or data to be communicated.
Example: Common forms of information include text, numbers, pictures, audio and video.

(ii) Sender:
It is the device that generates and sends a message.
Example: It can be a computer, telephone handset, etc.

(iii) Receiver:
Any particular digital electronic device which has capability to recieve data in form of message. The location of receiving computer is generally different from the sending computer.
Example: Like sender, it can also be a computer, telephone handset, etc.

(iv) Medium:
It is the channel or path through which the message is carried from sender to the receiver.
Example: Some examples include twisted-pair cable, coaxial cable, radio waves, etc.

(v) Protocol:
Protocols are the rules and procedures on which computers exchange data on network.
Sender and receiver follow same protocols to communicate with each other.
In other words, a protocol is an agreement between two parties or venders, using communication devices.
Example: FTP, TCP/IP, HTTP etc.

EXAMPLE OF COMMUNICATION SYSTEM:
When a person talk with another person directly, then the speaker is the sender who conveying the message as information in the form of sound waves through a communication channel, the intervening air and listener are the receiver.
If the distance between the speaker and the listener is large sound waves cannot reach from the speaker to the listener directly and communication is not possible. To make communication possible, different communication channel or method is used like microphone and speakers via telephone or internet services etc.

Q.5: What are the properties of a Good Communication System?
Ans: Properties of a Good Communication System:
The effectiveness of a data communications system depends on the fundamental characteristics which include delivery, accuracy and timeliness.

S.No.	Characteristic	Description
1.	Delivery	Making sure that the data is delivered is the first fundamental characteristic of any communication network. The system must be able to deliver data in correct order to the correct destination.
2.	Accuracy	The system must deliver the data accurately. Data that has been altered during transmission and left uncorrected is not useful.
3.	Timeliness	The data must be delivered in a timely manner. Late delivered data is useless.

Q.No.6: Define the transmission medium or communication channel. Name its group?
Ans: TRANSMISSION MEDIUM:
Transmission Medium or Communication Channel is a wireless or physical path between the sender and receiver through which data is sent and received from one place to another. Data is transmitted normally by electromagnetic or electrical signals through different types of wires, atmosphere or vacuum.
Transmission media is broadly classified into two groups:

1. Guided: It has three common types, which are:
   i. Coaxial
   ii. Fiber Optics
   iii. Twisted (a) Unshielded (b) Sheilded
   
   
2. Unguided: It has three major types
   i. Radiowaves
   ii. Microwaves
   iii. Infrared

Q No.7: Define guided media and describe different types of guided media?
Ans: GUIDED MEDIA:
In guided media signals are transmitted in a narrow pathway by using physical links. It is also called Wired or Bounded transmission media. The physical links are the cables that are tangible or have physical existence.

TYPES OF GUIDED MEDIA:
There are three common types of guided media used for the networks. Each of them has its own characteristics like transmission speed, effect of noise, physical appearance, cost, etc.

1. Twisted Pair Cable
2. Coaxial Cable
3. Fiber-Optic Cable

(i) Twisted Pair Cable:
This cable is made by two separate wires twisted together. A twisted pair cable is made up of insulated copper wires. The insulation and twisting of wires prevent external interference. Each pair of wires has unique color code.
Use: This type of cable is widely used in different kinds of data and voice infrastructures.

Types Of Twisted Pair Cable:
There are two types of twisted pair cables:

• (a) Unshielded Twisted Pair (UTP)
• (b) Shielded Twisted Pair (STP)

(a) Unshielded Twisted Pair (UTP):
This type of cable can block interference but it is vulnerable to external interference. It is less expensive and easy to install.
Use: It is mostly used for telephonic applications.

(b) Shielded Twisted Pair (STP):
This type of cable consists of a special coating to block external interference.
Use: It is used in fast-data-rate Ethernet and also in voice and data channels of telephone lines.

(ii) Coaxial Cable:
Coaxial cable is also known as coax. It has an outer plastic covering containing two parallel conductors each having a separate insulated protection cover.
Use: Cable TVs and analog television networks widely use coaxial cables.

(iii) Fiber-Optic Cable:
In optical fiber or fiber-optic cable data is transferred in the form of light. It uses the concept of reflection of light through a core made up of glass or plastic. The core is surrounded by a less dense glass or plastic covering called the cladding.
Use: It is used for transmission of large volumes of data at very high speed.

Q No.8: Define unguided media and describe different types of unguided media?
Ans: UNGUIDED MEDIA:
Unguided media is also termed as wireless or unbounded transmission media. It does not require physical medium such as wire for the transmission of electromagnetic signals.

TYPES OF UNGUIDED MEDIA:
There are three major types of Unguided Media.

1. Radio Waves
2. Microwaves
3. Infrared

(i) Radio Waves:
Radio waves are also called electromagnetic waves. These are easy to generate and can penetrate through buildings. Radio waves are omnidirectional and propagated in all directions. It means that sending and receiving antennas do not need to be aligned.
Use: FM, AM radios, television and cordless phones use radio waves for transmission.

(ii) Microwaves:
Microwave transmission is a line of sight transmission i.e. the sending and receiving antennas need to be properly aligned with each other. The distance covered by the signal is directly proportional to the height of the antenna.
Use: These are mostly used for mobile phone communications tower and television broadcast.

Types Of Microwaves:
There are two types of microwave transmissions:
(a) Terrestrial and
(b) Satellite

• (a) Terrestrial: Terrestrial microwaves have both stations having antennas on earth.
• (b) Satellite: In satellite system, some antenna are on satellite in orbit and others are on stations on earth. They work at remote places.
  Use: It can be used in mobile devices.

(iii) Infrared:
It uses infrared light to transmit signals. LED is used to transmit signals and light-receivers (photodiodes) to receive signals. They use terahertz frequency. It cannot penetrate walls or other objects. Infrared light is transmitted generally line of sight (point to point).
Use: Wireless infrared communications can be used to establish short range wireless links or wireless Local Area Network.

Q.No.9: Differentiate between:

• Guided and unguided media
• Radio wave, microwave and infrared wave

Ans: DIFFERENCE BETWEEN GUIDED AND UNGUIDED MEDIA:

S.NO.	GUIDED MEDIA	UNGUIDD MEDIA
1.	In guided media signals are transmitted in a narrow pathway by using physical links.	It does not require physical medium such as wire for the transmission of electromagnetic signals.
2.	It is also called Wired or Bounded transmission media.	Unguided media is also termed as wireless or unbounded transmission media.
3.	Wired transmission	Wireless transmission
4.	It provides direction to signal for travelling.	It does not provide any direction. Unguided media is generally suited for radio broadcasting in all directions.
5.	Transmission speed is generally faster.	Transmission speed is generally slow.
6.	Types: Twisted pair cable, coaxial cable and fibre optic cable.	Types: Radio wave, microwave and infrared.

Difference Between Radio Wave, Microwave And Infrared Wave

S.NO.	Basis	Radio waves	Microwaves	Infrared waves
1.	Direction	These are omni directional in nature.	These are unidirectional in nature.	These are unidirectional in nature.
2.	Penetration	At low frequency, they can penetrate through solid objects and walls but at high frequency they bounce off the obstacle.	At low frequency, they can penetrate through solid objects and walls but at high they cannot penetrate.	They can not penetrate through any solid objects and walls
3.	Frequency range	3 KHz to 1 GHz	1 GHz to 300 GHz	300 GHz to 400 GHz
4.	Security	These offer poor security.	These offer medium security.	These offer high security.
5.	Attenuation	High	Variable	Low
6.	Government License	Some frequencies in the radio waves require government license to use these.	Some frequencies in the microwaves require government license to use these.	There is no need of government license to use these waves.
7.	Usage cost	Setup and usage cost is moderate.	Setup and usage cost is high.	Usage cost is very less.
8.	Communication	These are used in long distance communication.	These are used in long distance communication.	These are not used in long distance communication.

Q.No.10: Describe the different types of flaws and faults (impairment) in transmission signals?
Ans: TRANSMISSION IMPAIRMENTS OR FLAWS AND FAULTS IN TRANSMISSION SIGNALS:
Sometimes, signals traveling through transmission media lose their quality. This means that received signal is not same as the signal that was sent. This phenomenon is called transmission impairments. Transmission impairments are those defects that occur when data is transmitted.

CAUSES OF IMPAIRMENTS OR TYPES OF FLAWS AND FAULTS IN TRANSMISSION SIGNALS:
There are three causes of impairment i.e.:

1. Attenuation
2. Distortion and
3. Noise

(i) Attenuation:
Attenuation means loss of energy. A signal loses its energy due to the resistance of medium while it is transmitted. Its strength decreases with increase in distance. Amplifiers are used to overcome attenuation and make signal stronger again. It is measured in decibels.

(ii) Distortion:
Distortion means change in the shape of the signal. A composite signal has several frequencies. When it travels through a medium different component of signal may reach at different time at destination because each component has different speed in that medium. This is called distortion. They have different phases at sender and receiver ends.

(iii) Noise:
Unwanted signal that mixes up with the original signal during the transmission of data is called noise. It can be induced noise, crosstalk noise, thermal noise and impulse noise which may damage the signal.

Q.No.11: Describe the communication device and their functions?
Ans: COMMUNICATION DEVICES:
Ans: A communication device is any type of hardware capable of transmitting and receiving data, instructions and information.

(i) Switch:
A switch or network switch is a networking device.
Function:

• It connects computers and other devices like printers, scanners and cameras on a network.
• Data cables from all computers and other devices of network are plugged into the switch to enable communication between them.

(ii) Router:
Routers are a combination of hardware and software.
Function:

• A Router is a device that connects two or more networks.
• The main function of a router is to determine the optimal data path and transfer the information through that path, also known as network traffic controller.

(iii) Modem:
Modem is short for Modulator and Demodulator. Modulation is the process of converting digital signals into analog signals. Demodulation is quite opposite; it converts analog signals into digital signals.
Function:

• Modem has the ability of sending and receiving signals that allows computers to share information with each other.
•  This sharing of information is possible over phone lines, cables or satellite connections.

Types Of Modem:

• Dial-up Modem:
  A dialup modem can be internal or external.
  Function:
  Dialup modems use standard telephone lines to transmit and receive information.
  It is important to remember that telephone lines carry only analog signals, whereas data packets sent by the computer are in digital form. In order to send these packets across a telephone line, modem converts digital signals into analog.
  
  
  
  
• DSL Modem:
  DSL stands for Digital Subscriber Line.
  Function:
  Like dial-up modem DSL modem also uses telephone lines to transfer digital signals.
  DSL modem has a built-in network switch which enables use of twisted pair wires to deliver data and voice at high speed as compare to dial-up modem.
  Some DSL modems also have wireless communication functionality.
  
  
  
  
• ISDN Modem:
  Integrated Services Digital Network is a digital phone connection. It is faster and expensive technology.
  Function:
  It can transmit data, voice and video over a normal telephone line at the same time which was not done before.
  Since ISDN work on digital transmission it converts analog voice to digital signals before transmission.
• 
  
  

(iv) Network Interface Card (NIC):
Network cards also known as Network Interface Cards (NICs) are hardware devices. They are installed on the mother board. Modern motherboards have built-in NICs.
Function:

• It connect a computer with the network.
• They are responsible for establishing a physical connection between the network and the computer.
• Computer data is translated into electrical signals and sent to the network via Network Interface Cards.

Q.No.12: Define the term computer network? Or Define and explain the term computer network?
Ans: COMPUTER NETWORKS:
Computer networks are just like a highway on which data can travel. A computer network connects parts of distributed system including hardware and software. It shares common functions and features like data and devices which is very important nowadays.
A computer network is a group of computers and related equipment connected by a communication links to share data and other resources.
The Related Equipment may be printer, scanners, fax machines, server, etc.
The Resources may include a file server, internet connection, etc.

Q.No.13: Define the term computer networking or networking?
Ans: Networking:
Networking is the act of joining computers and its accessories so that exchange of information and sharing of resources take place.
In today's world, networking plays a vital role in computers and telecommunication fields. Modern organizations create a networking environment and device connectivity for fast, inexpensive and reliable communication.

Q.No.14: Classify the network types on the basis of their characteristics? Or Describe the types of computer networks?
Ans: Types of Computer Networks:
Computer networks can be categorized by their size as well as their purpose.
The size of a network can be expressed by the geographical area they occupy and the number of computers that are part of the network. Networks can cover anything from a handful of devices within a single room to millions of devices spread across the entire globe.
There are three types of computer networks:

1. Local Area Network (LAN)
2. Metropolitan Area Network (MAN)
3. Wide Area Network (WAN)

(i) Local Area Network (LAN):
LAN is a group of computer and peripheral devices which are connected in a limited area such as school, laboratory, home and office building.
Purpose:

• Useful resources like internet access, storage space and printers can be shared through LAN.
• It can be built with inexpensive hardware such as hubs, switches, network adapters and network cables.
• Data and software are also shared through LAN.

Example:
Some examples of LAN are:

• Networking between two computers.
• Networking in the home, school, library, laboratory, college / university campus or office.
• Wi-Fi which is also known as wireless LAN. 

(ii) Metropolitan Area Network (MAN):
In MAN, computer network can spread across an entire city, college campus, or a small region. It can cover the area of several miles and may include multiple small networks or LANs.
Purpose:

• MANs offer very fast communication but they are expensive to establish. Therefore, only large business organization or universities set up MAN.
• It also requires security measures to prevent unauthorized access.

Example:
Some examples of MAN are:

• Cable TV network
• Telephone networks providing high speed DSL lines.
• IEEE 802. 16 or WiMAX, that provides high-speed broadband access with Internet connectivity to customer premises.

(iii) Wide Area Network (WAN):
A Wide Area Network is used for long distance transmission of data. WAN helps to cover a larger geographical area and connect cities, provinces or even countries.
Purpose:

• Using WAN technology, computers may be linked together in different countries using satellites, microwaves or telecommunication links. Therefore, large business, research and educational organizations situated at longer distances use WAN.
• A WAN may include multiple MANs and LANS. WANs are set up with expensive devices and need some dedicated connections.

Example:

• Internet is the example of WAN.

Q.No.15: Define Topology. Explain its type?
Ans: Definition Of Topology:
The physical layout in which computers are connected is called topology. The topology of network describes the way computers are connected. Topology is a major design consideration for computer networking.

Types Of Topology:
(i) BUS TOPOLOGY:

• In Bus Topology computers and other devices are connected with a single cable.
• The central cable is the backbone of the network and every device communicates with the other device through this bus.
• It transmits data only in one direction.

Advantage Or Merit of Bus Topology:
The advantages of Bus Topology are:

• Simplicity
• Cable required is least compared to other network topology.
• Used in small networks.
• It is cost effective i.e. low cost
• It is easy to understand.
• Easy expansion of the network i.e. easy to expand joining two cables together

Disadvantage Or Demerit of Bus Topology:
The disadvantage of the Bus Topology is that:

• A breakdown in the bus cable brings the entire network down.
• If network traffic is heavy or nodes are more the performance of the network decreases.
• Cable has a limited length.
• It is slower than the ring topology.

(ii) RING TOPOLOGY:
In Ring Topology, computers are connected in a ring or circle shape. The signal travels around the loop in one direction and passes through each computer.
The recipient of the message receives the message while another computer acts like a repeater to send it to the next computer.

Advantage Or Merit of Ring Topology:

• Transmitting network is not affected by high traffic or by adding more nodes, as only the nodes having tokens can transmit data.
• Cheap to install and expand.

Disadvantage Or Demerit of Ring Topology:

• The failure of a link or a computer can make the entire network nonfunctional.
• Troubleshooting is difficult in ring topology.
• Adding or deleting the computers disturbs the network activity.

(iii) STAR TOPOLOGY:
In a star topology, all the computers are connected to a central device called hub or switch. To communicate with any computer, the sender must send information to the hub. Then the hub transmits that information to the destination.
Advantage Or Merit of Star Topology:

• The advantages of star topology are easy to set up and easy expansion of the network.
• Another feature of Star Topology is that if one link to the hub breaks, only the station using that link is affected not the whole network.
• Fast performance with few nodes and low network traffic.
• Hub can be upgraded easily.
• Easy to troubleshoot.

Disadvantages Or Demerits of Star Topology:

• Cost of installation is high.
• Expensive to use.
• If the hub fails then the whole network is stopped because all the nodes depend on the hub.
• Performance is based on the hub that is it depends on its capacity

Q.No.16: Define standards and network standards. Explain the purpose of standard organisation?
Ans: STANDARDS:
Standards are rules that define the appearance, functionality, or protocols of some equipment.

NETWORK STANDARD:
Network standards define rules of communications among computing devices. This ensures that companies (i.e. Cisco and IBM) that manufacture computing and networking products follow these uniform standards. By following standards, all hardware become compatible in the network, allowing efficient networking to take place. They are essential for network communication.

STANDARD ORGANIZATIONS (PURPOSE):

• Standard Organization develops, coordinates, revises, amends and reissues technical standards.
• These standards are intended to address the requirements of a group of concerned devices.
• There are several organizations working on standardization of computing equipment to enable the interoperability among different devices manufactured by different companies in different regions.
• Example: ISO, IEEE, IETF, ITU and ANSI are the examples of standard organizations.

Q.No.17: Write few lines about different standard organisations?
Ans: (i) International Organization for Standardization (ISO):

• It covers a wide range of fields.
• The ISO has members from the standards committees of various governments across the world.
• It is even responsible for developing models which provides high level of system compatibility, quality enhancement, improved productivity and reduction in costs.
• The ISO is also responsible for endorsing and coordinating the functions of the other standards organizations.

(ii) Institute of Electrical and Electronic Engineering (IEEE):

• It is an international professional non-prot organization.
• Electronics, computer and communication engineers, researchers, scientists and students are the members of IEEE.
• This organization develops communication and information processing standards for all elds related to electrical and computer engineering.

(iii) International Engineering Task Force (IETF):

• It is a large international community of network designers, operators, vendors and researchers concerned with the development of internet architecture and smooth operation of the internet.

(iv) International Telecommunication Union (ITU):

• This organization is a specialized agency that is responsible for resolving the issues that concern with information and communication technologies.

(v) American National Standards Institute (ANSI):

• It is the official standards agency for the United States.
• ANSI is a completely private, non-prot organization comprised of equipment manufacturers and users of data processing equipment and services.
• It supervises standards for products, services, processes, systems and personnel in the United States.
• ANSI membership is comprised of people from professional societies, industry associations, governmental and regulatory bodies, and consumer goods.

Q.No.18: Define network architecture?
Ans: NETWORK ARCHITECTURE:
It is the design of a computer network. It is a framework for the specification of a network's physical components, their functional organization and configuration, operational procedures and communication protocols used.
Example: Like OSI / TCP layered architecture.

Q.No.19: Define ISO's OSI model. Name the all layers of OSI's ISO model and describe their functions?
Ans: ISO's OSI Model:
The Open Systems Interconnection (OSI) model is a conceptual model developed by ISO. It characterizes and standardizes the communication functions of a telecommunication and computing network.
Purpose: Its goal is the interoperability of different communication systems with standard 86 communication protocols.

LAYERS OF ISO's OSI MODEL WITH THEIR FUNCTIONS:
This model divides a communication system into seven abstraction layers.

S.NO.	Layers	Functions
1.	Application	This layer enables users to access the network with applications such as email, file transfer, etc. These applications produce the data, which is transferred over the network.
2.	Presentation	It receives information from the application layer and converts it to uniform network format (ASCII or Unicode) which is acceptable by rest of OSI model and destination. Encryption and decryption are also the responsibility of this layer. This layer also reduces number of transfer bits by compression.
3.	Session	This layer establishes, maintains and ends a session or logical connection between applications on two computers. It manages who can transmit data at a certain time and for how long. This layer adds checkpoints. If session fails only data after the most recent checkpoint need to be transmitted.
4.	Transport	It ensures the reliable transmission of data. Transport layer manages error control, flow control and quality of the service. If the data is not properly transmitted it requests to resend.
5.	Network	The function of this layer is the selection of the shortest and suitable path from source to destination, from the number of routes available. It is also responsible to convert logical address (IP address) to physical address (MAC address).
6.	Data link	This layer is responsible to transmit data using physical addresses. Data Link Layer ensures error free transmission of packets. Packet in this layer is referred as Frame.
7.	Physical	It is responsible for converting electrical signals into bits. It also defines the cable types to be used as transmission media, cards, topology and other physical aspects.

Q.No.19: Define TCP/IP model. Name all the layers of TCP/IP model and describe their functions?
Ans: TCP/IP Model:
TCP/ IP is a suite of communication protocols used to interconnect network devices on the internet. These are set of rules and procedures. TCP/IP specifies how data is exchanged over the internet by providing end-to-end communications. It also identifies how data should be broken into packets, addressed, transmitted, routed and received at the destination.

TCP/IP LAYERS WITH THEIR FUNCTIONS:
With reference to OSI layers, we can understand the functions of TCP/IP layers.

OSI Layers	TCP/IP Layers	Function
Application	Application Layer	Using protocols like HTTP and FTP, this layer allows interaction with applications.  Application layer is also responsible to encode and decode data and establish communication between two devices.
Presentation
Session
Transport	Transport Layer	Using protocols like UDP and TCP, this layer establishes a logical connection between two devices and makes sure the reliable delivery of data.
Network	Internet Layer	It is responsible for packet forwarding by accessing physical path.
Data link	Network Access Layer	Using the logical addressing this layer decides how data will be sent across different networks paths.
Physical

Q.No.20: What is a network address? OR Define network address?
Ans: NETWORK ADDRESSING:
Network addresses are like our house addresses. They must be unique and distinctive. This avoids confusion for the postman. A network address is any Logical or Physical Address that uniquely identifies it from others. This address is needed to distinguish a network node or device on a computer network. It is a numeric or symbolic number or address that is assigned to any device that seeks access to network or is the part of a network. Physical and Logical Address are different.

Q.No.21: Write down differences between Physical address and Logical address?
Ans: Differences Between Physical Address And Logical address

S.No.	Physical Address	Logical address
1.	Physical address is attached with ROM of the NIC card.	Logical address is assigned to a device.
2.	Physical Addressing means MAC (Media Access Control) provided by manufacture and attached address of the NIC. The card which is used to connect your machine to the internet.	Logical addressing means IP addressing that is provided by your Internet Service Provider (ISP) or set by network administrator.
3.	Physical addressing cannot be can be changed. They are also called hardware address.	Logical Address can be changed.
4.	Physical address is a 48 bit mac address.	Logical address is a 32 bit IP Address.
5.	It is globally Unique and permanent.	It is unique in one network and temporary.

Q.No.22: Define and explain IPV4 address.
Ans: IPV4 ADDRESS:

• IPV4 stands for Internet Protocol version 4. IP address is a unique number or address used to identify a device on a network. The device could be a computer, printer, smart phone, tablet, etc.
• Every device connected to the internet must have an IP address to communicate with other devices.
• IP address acts as a telephone number or a car registration number.
• It shows ownership and location.
• IP address allows a device to communicate and be located by other devices on the internet.
• IP version 4 (IPV4) addresses are comprised of four number segments separated by dots.

Example: of an IP address is:

Parts Of IPV4:
An IPV4 address is made up of 32 binary bits, which is divided into two parts:
Network: The network portion of the address mentions the computer network.
Host: The host portion identifies the computer or any other computing device.

Computer Science (New) - For Class IX - UNIT. 5. Computer Security and Ethics - Text Book Exercise And Activity

GO TO INDEX

Chapter No.5: Computer Security and Ethics
Short Questions Answers And Text Book Exercise

Text Book Exercise

B. Respond the following:
1. Why is computer security important? Write any three reasons.
Ans: COMPUTER SECURITY:
"Computer security is the protection against theft or damage to our computer hardware, software and information present on them from threat of viruses or unauthorized use."
Explanation:
The computer has become an important part of our life. We store important data on our computers in the shape of documents, pictures, programs, etc. Therefore, we expect that all our information must remain safe and our computer runs properly without any problem.
Few threats can cause problems for our computers. These threats may be different types of viruses or unauthorized use of a computer. To prevent our computer from such threats, we need to abide by computer security.

Reason Of Importance of Computer Security:

1. Prevent from viruses and malware:
   ► Computer security is important for our computer's overall health.
   ► It keeps our information protected and helps prevent viruses and malware, which allows programs to run quicker and smoother.
   
   
2. Secure Private Information:  
   ► It safeguards confidential and sensitive information.
   ► The advancement in science and technology has changed day to day activities. We rely on computers and mobile phones, where we access a lot of information which we do not want to share with others. This information may include our passwords, banking details, contacts, pictures, etc. To protect this information we need to make our devices secured that no one can damage or access this information without our consent.
   
   
3. Provide Safe Environment:
   ► Computer Security is important as it enables people to perform their work in safe environments.
   ►It helps in the execution of essential business processes.

2. Explain Cyber Bullying with an example.
Ans: Cyber Bullying or Harassment:
Cyber bullying or harassment is a type of cyber-crime in which electronic means like a computer, mobile phone or internet are used for online bullying or harassment.
Example:
Harmful bullying behavior can include:

• Posting rumors
• Threats
• Passing inappropriate remarks
• Leaking personal information
• Blackmailing and
• Committing hate speech

Effect Of Cyber Bullying or Harassment On Victim:

• The perpetrator does it with the intent to cause harm to the victim.
• Victims may experience lower self-esteem, intent to commit suicide and a variety of negative emotional responses, including being scared, frustrated, angry and depressed.

3. Why is information accuracy important?
Ans: INFORMATION ACCURACY:
The information accuracy is the type of measurement that assures the information is correct and true.
Importance Of Information Accuracy:

• Information accuracy is important because inaccurate information is harmful in different fields like medical history, Business records, Government data, etc.
• It is necessary that the information should not be generated from the malicious data.
• For information accuracy, the data must be from reputable sources.
• In the era of information explosion, we need to be more careful while using or disseminating information. The use of unreliable sources results in inaccurate information.
• Especially, the accuracy of information shared on social media is often questionable.

4. What is Ethical Hacking?
Ans: Ethical Hacking:
Ethical Hacking sometimes called as Penetration Testing is an act of intruding / penetrating into system or networks to find out threats, vulnerabilities in those systems which a malicious attacker may find and exploit causing loss of data, financial loss or other major damages. The purpose of ethical hacking is to improve the security of the network or systems by fixing the vulnerabilities found during testing. Ethical hackers may use the same methods and tools used, by the malicious hackers but with the permission of the authorized person for the purpose of improving the security and defending the systems from attacks by malicious users.
Ethical hackers are expected to report all the vulnerabilities and weakness found during the process to the management.

5. Your friend has become a victim of cyber harassment. What two advices will you give him or her?
Ans: Pakistan is in the list of the fastest-growing countries that are using the internet. This opens the doors for the fact that cyber bullying is increasing as well but yet there is no legislation for cyber-crimes in Pakistan.
If my friend becomes the victim of cyber harassment, I will give him advice that:
(i) Report To Trusted People:
First thing is to report such incidents to the trusted people that are highly likely parents and teachers.
(ii) Complaint To Government Authorities:
Write down an application (in English or in Urdu), describe complete problem, provide as much evidences, details as he/she can and send it to FIA National Response Center for Cyber Crimes. OR send an online complaint through the form available on the website or by calling helpline 1991 which is available 24/7.

6. Write any two measures to avoid email account hacking.
Ans: Email attachments have been a popular medium to spread viruses and hack email accounts.
To avoid email account hacking, we should take following measures:

Do not open email attachments or click on hyperlinks from unknown senders:

• The infected emails may come from an unknown or fake email address.
• Users must check the origin of the email before opening the attached files or clicking any link that is given in the email.
• People in our contact list may also send us infected files as they may not be aware of it themselves.

Spam or junk mails must be checked carefully before clicking on its attachment:

• Use spam blocking or filtering tools to block unsolicited emails, instant messages and pop-ups.
• Do not click on internet links which have unusual labels, images or captions in spasm emails.
• Only download attachments from trusted sources.

7. How is software piracy harmful for software developers?
Ans: Software Piracy:
Software piracy is referred to the illegal use, copying or distribution of copyrighted software.

Impact Of Software Piracy On Software Industry and developers:
Software piracy is a huge threat to the software industry and developers..

• It causes a significant loss of revenue for developers and vendors.
• Because of piracy, vendors have fewer resources to devote to research and development of new products.
• Since they earn less profit, they are forced to pass these costs on to their customers.
• Software companies have tried various techniques to stop software piracy but most of them have remained unsuccessful.
• They applied for copy- protection which demands the user to enter certain keys or credentials. Today, most software require registration which is mainly online. However, these measures could not stop software piracy.

8. Give two examples of phishing.
Ans: Example Of Phishing:
1. False Emails: In Phishing, perpetrators contact the target person through email, telephone or text message and pose as a legitimate and trusted individual. He or she asks the target to provide sensitive data such as personally identifiable information, banking and credit card details and passwords for different reasons.

2. Fake Websites:
In Phishing, perpetrators send phishing emails that include links to fake websites, such as the mobile account login page or for a known mail provider, asking the victim to enter their credentials or other information into the fake site’s interface.
In both cases, the information is then used to access different accounts and can result in identity theft and financial loss.

9. What is an Intellectual Property Right?
Ans: Intellectual Property:
When any person develops software, writes a book or research paper or invents any method or the machine, it becomes the intellectual property of that person. Thus Intellectual property is intangible creations of the human intellect.

Intellectual Property Right:
Just like other property the intellectual property can be stolen. To prevent theft or illegal use or spread of intellectual property, Intellectual Property Right is exercised.

• Through these rights, intellectual property is protected with the help of copyrights, patents, and trademarks.
• They allow creators or owners of patents, trademarks or copyrighted works to benefit from their work or investment. 
• Under these rights, no other person or organization can copy or reproduce any other's intellectual property.
• Intellectual property rights are acclaimed worldwide.
• In Pakistan, Intellectual Property Organization ( IPO ) regulates the matters regarding intellectual property rights.

10. Differentiate the following on the given criteria. OR Define and differentiate various types of viruses: Malware , Virus, Worm, Adware and Spyware.

Criteria	Virus	Worm	Adware	Spyware
Level of danger	Viruses are harmful.  They can range from displaying irritating messages to make all the documents inaccessible or even delete them.	Harmful as It can do several malicious tasks to cause damage	Normally, these are not as dangerous as other malware.	Poses high-risk threats.  can completely shut down computer, or  permanently erase or damage files.
How is it initiated?	Viruses generally latch on a host file and when they execute they infect other files or programs.	A worm can replicate itself without any human interaction. It does not need to attach itself to a file or program to cause damage.	Adware is advertising-supported software or programs include games, desktop toolbars or utilities.  Commonly, adware is web-based and collects web browser data to target advertisements, especially pop-ups.	Spyware can come through cookies or even when we install software without reading its terms and conditions.
Damage that can be done to data and hardware	It can also modify other computer programs, insert its own code and change computer settings.	It can do several malicious tasks, such as dropping other malware, copying itself onto devices physically attached to the affected system, deleting files, and consuming internal storage and memory resources.	They present endless ads and pop-up windows that could potentially consume memory and processing resources. Adware can also change the different settings of internet browsers like homepage and default search engine.	Spyware takes control over a mobile phone or computer without the user's knowledge.  They capture information like web browsing history, e-mail messages, usernames and passwords and online payment information.
Effect on computer speed	Slower operating speed	Slow down computer performance	Adware annoys the user and slows down the processing.	Slowing down computer performance, even shut down system
Means to spread	A computer virus is a computer program that can spread across computers and networks by making copies of itself, usually without the user's knowledge. Boot Sector, Resident, Macro Viruses and File Infector are some examples of viruses.	A computer worm spreads copies of itself from computer to computer.	Adware is advertising-supported software.  The advertisements produced by adware are sometimes in the form of a pop-up or sometimes in little windows that may not be closed.	Spyware can come through cookies or even when we install software without reading its terms and conditions.  System monitors, cookies trackers, rootkits and key-loggers are few examples of Spyware.

C. Match the columns:

S.NO.	A	S.NO.	B	C
(i)	Presenting someone's ideas as your own without acknowledging the author.	(a)	Adware	(i) (e)
(ii)	An advertising software that presents ads and pop-up windows to spread virus.	(b)	Cracker	(ii) (a)
(iii)	Crime that is committed through a computer system.	(c)	PIN	(iii) (f)
(iv)	A secretive security code that verifies user's identity.	(d)	Antivirus	(iv) (c)
(v)	A person that gains unauthorized access to other computers by bypassing passwords.	(e)	Plagiarism	(v) (b)
(vi)	A utility software that prevents threats and data loss from a computer.	(f)	Cybercrime	(vi) (d)

Short Answers

Q.1: Explain how to seek help against Cyber-Crime
Ans: Seek Help In Case of Becoming a Victim

1. Report To Trusted People:
   First thing is to report such incidents to the trusted people that are highly likely parents and teachers.
2. Complaint To Government Authorities:
   The government has also taken measures to curb cyber crimes especially cyber bullying and harassment.
   In Pakistan, the National Response Center for Cyber Crimes has been set up to help the victims of cyber crimes. An online complaint can be launched through the form available on the website or help may be sought by calling helpline 1991 which is available 24/7.

Q.2: Identify that a virus, worm, adware, spyware and Malware can spread through different ways?
Ans: Virus:
A computer virus is a computer program that can spread across computers and networks by making copies of itself, usually without the user's knowledge.

Worm:
A computer worm spreads copies of itself from computer to computer.

Spyware:
Spyware can come through cookies or even when we install software without reading its terms and conditions.

Adware:
Adware is advertising-supported software. The advertisements produced by adware are sometimes in the form of a pop-up or sometimes in little windows that may not be closed.

Activity

Activity 1:
Organize a poster exhibition in which students suggest measures to the audience how to use the computer and the internet safely. Some focused topics may be:

• Prevent your computers from Viruses and Malware.
• Say no to cyber bullying and harassment.
• Say no to piracy and plagiarism.
• How to cope with cyber crimes?

Activity 2:
During classroom discussion put the following situations before students and discuss what will they do in such a situation? And why?

• You receive a phone call. The caller claims that you have won a huge prize and for delivering the prize they need an advance payment.
• You receive a file from an unknown email address which asks your bank account details or user Email ID and Password.
• While surfing an unknown website, the website demands to access content by providing your Facebook or Gmail account's credentials.

Activity 3:
Make a list of the services that free antivirus software does not offer.

Activity 4:
Search newspapers or internet to nd any news about a cyber crime. Specially in which the criminal was caught and punished.

Activity 5:
Thesis and research articles are generally checked through Turnitin which is an Internet-based paid plagiarism detection service.
There are other free online services where students can check the plagiarism in their document. Some are:
www.duplichecker.com
www.quetext.com
www.plagscan.com
Write an essay on any topic, and copy and paste some text from internet websites in your essay. Then check plagiarism of your document.