FBISE Notes Computer for class 9th

Chapter 4: Data Communication

Write short answers to the following questions.

i. Differentiate between analog and digital signals.

Ans: Analog signals:

Analog signal is in continuous form. It varies continuously within a range. For example, the sound is an analogue signal. Analogue transmission uses signals that are exactly the same as sound waves.

Digital signals:

Digital signals are not continuous. They switch between two discrete, low and high voltage levels. In digital computers, the low voltage level represents binary 0 and the high voltage level represents binary 1.

ii. Why digital signals are used in computer systems?

Ans: Information represented in digital form can be easily transmitted by pulses of electricity. Digital data can be compressed relatively easily, thereby increasing the efficiency of transmission. That is why digital signals are used in computer systems.

iii. Name the properties of a good communication system.

Ans: Properties of a Good Communication System:

The following are the properties of a good communication system.

• Delivery
• Accuracy
• Timeliness

iv. Give any three reasons why a guided communication medium is more reliable than an unguided medium.

Ans: The purpose of Guided media is to reduce cross-talk and electromagnetic interference and make the transmission more reliable.

• It provides high-quality transmission at an extremely fast speed. It can transmit trillions of bits per second.
• Guided media is not affected by electromagnetic fields and can transmit both analog and digital signals.
• Guided media is used for data transmission over long distances.

That is why a guided communication medium is more reliable than an unguided medium.

v. What is meant by transmission impairment?

Ans: Transmission Impairments:

The errors that occur during data communication from one point to another are called transmission impairments.

Impairments occur due to imperfect characteristics of communication medium. As a consequence, the received and the transmitted signals are not always the same.

vi. Differentiate between attenuation and distortion.

Ans: Attenuation:

Attenuation is the fall of signal Strength with the distance as the signal travels through the communication media. If the attenuation is too much, the receiver may not be able to detect the signal at all.

Distortion:

Distortion refers to a change in the Shape or frequency of a digital signal when it is transmitted over a communication line. 

The communication line delays the signal frequency by different amounts because different frequency components travel at different speeds.

vii. What is cross talk?

Ans: Cross Talk:

Cross-talk occurs in guided media. As a signal is transmitted through a wire, undesired signals enter the path of the transmitted signal due to electromagnetic radiation. It is caused because of putting several wires together in a single cable.

viii. What is a dial-up modem? Why is it used?

Ans: Dial-up Modem:

A Dialup modem provides an internet connection through a telephone line. The maximum speed of a Dial-up modem is 56 Kilobits per second which is very slow. It is being replaced by a faster DSL connection for the internet.

Use of Dial-up Modem:

A telephone line is used for voice transmission which is an analog signal.

ix. Define data rate and baud rate.

Ans: Data Rate:

Data rate is the speed with which data can be transmitted from one device to another. It is generally measured in Kilobits per second (kbps) or Megabits per second (mbps)

Baud Rate:

Baud is the rate of change of electrical signals per second during data communications. An electrical signal can have two or more than two states to represent binary digits 0 and 1.

x. Define bandwidth.

Ans: Bandwidth:

Bandwidth describes the overall data transmission capacity of a medium or channel. It represents the amount of data that passes through a network connection per unit of time. Bandwidth is also measured in bits per second like data rate.

Write long answers to the following questions.

i. Describe the components of communication with the help of a diagram.

Ans: Components of a Communication System:

A communication system consists of the following five basic components:

• Sender
• Receiver
• Message
• Transmission Medium
• Protocol

Sender

It is the device which sends the message. In other words, it is the source of messages that can be a computer, telephone handset, etc.

Receiver:

It is the device which receives the message. In other words, it is the destination of a message that can be a computer, radio, telephone handset, etc.

Message:

It is the data to be transmitted. It can be text, graphics, images, sound or video.

Transmission Medium:

It is the physical pathway (also known as a channel) over which the message is sent from sender to receiver. Some examples of transmission media are coaxial cable, Fibre optic cable, microwaves, etc.

Protocol:

It is the set of rules between the two communicating devices that govern the process of data communication. Without a protocol, two devices may be connected but they cannot communicate with each other.

ii. Explain asynchronous and synchronous transmission modes with examples.

Ans: Asynchronous and Synchronous Transmission modes:

Asynchronous and synchronous transmissions are the methods by which characters are transferred between components within the computer or between the computer and an external network.

Asynchronous Transmission:

The transmission mode in which the time interval between each character is not the same is known as asynchronous transmission.

• In asynchronous transmission, each character is transmitted with additional control information. Control information consists of additional start and stop bits.
• The start bit is generally 0 and the stop bit is 1.
• Between the start and stop bits, the bits representing a character are transmitted at uniform time intervals.
• Asynchronous transmission is slow because of the additional bits transmitted with each character. It is Suitable for low-speed connection between the system unit and the keyboard or mouse.

Synchronous Transmission:

The transmission mode, in which the time interval between the characters is always the same, is known as synchronous transmission.

• In synchronous transmission, there is no control information added to the characters.
• Data consisting of 0s and 1s is transmitted as one long stream of bits. The receiver counts the bits as they arrive and recognizes the characters.
• Synchronous transmission is faster than asynchronous transmission because it does not require extra start and stop bits. Therefore, it is used for fast data communication between computers in computer networks.

iii. Describe the following guided media.

a) Twisted pair cable

b) Coaxial cable

c) Fiber optic cable

Ans:  

a) Twisted pair cable:

A twisted pair cable is the most commonly used cable for data communication. It consists of pairs of wires twisted around one another. The purpose of twisting the cables is to reduce crosstalk electromagnetic interference and make the transmission more reliable. The telephone cable consists of two twisted insulated wires.

b) Coaxial cable:

Coaxial cable is used for local area networks and cable television systems. It consists of copper wire surrounded by an insulating layer. The insulating layer itself is surrounded by a conductive layer. Insulation reduces interference and distortion.

c) Fiber optic cable:

Fiber optic cable consists of smooth hair-thin Strands of transparent material. In Fibre optic communication, the transmitter has a Converter that converts electrical signals into light waves. These light waves are transmitted over the Fibre optic cable.

iv. Describe any three types of unguided media.

Ans:  The Following are three types of unguided media:

Microwave:

Microwave signals travel through open space like radio waves. Microwaves provide a much faster transmission rate than telephone lines or coaxial cables. Microwave antennas are installed on high buildings or high towers. The transmitting and the receiving sites must be within sight of One another. Microwaves are used for satellite communication and other long-distance wireless communications.

Infra-red:

Infrared waves are light energy that we cannot see. It travels through space at the speed of light. It is used for short-distance communication. Infra-red, waves are usually used in remote controls for television, DVD payers, and other similar devices. Infra-red wireless Signals are disrupted by persons or objects in between the transmitter and receiver but it does not get interference from other radio signals.

It is also used in industrial, Scientific, and medical appliances and night-Vision devices.

Bluetooth:

Bluetooth is a wireless communication technology that uses radio waves to connect portable electronic devices over a short distance. It eliminates the need for cable connection and provides fast and reliable transmission.

It Supports networking of a wide range of portable devices that work on low batteries. These devices include a mobile phone, mouse, keyboard, wireless speaker, wireless headset, tablet, laptop computer, and personal computer. The laptop computer has built-in Bluetooth but personal computers can use a Bluetooth adapter to communicate With Bluetooth devices.

v. Describe the functions of the following communication devices.

a) Router

b) Network Interface Card (NIC)

c) Switch / Access point

Ans:

a) Router:

The router is a communication device that is used when two networks have to be connected for communication. They send information from one network to another by selecting the best pathway available.

b) Network Interface Card (NIC):

A Network Interface Card (NIC) or simply a network card is used to connect computers together to create a computer network. It makes communication between computers possible.

It is a card that is installed on the motherboard. In modern computers, it is integrated to the motherboard.

c) Switch Access Point:

A switch/access point is used for connecting commuters together in a local area network (LAN). Switch is used in wired networks whereas an access point is used in wireless networks.

A switch/access point receives information from a computer in the network, inspects it, and then transmits it appropriately to the destination computer.

Select the best answer for the following MCQs.

i. In which type of data transmission start/stop bits are used?

A. Synchronous transmission             

B. Asynchronous transmission

C. Satellite transmission                                

D. Microwave transmission

ii. In which of the following transmission, the time interval between the characters is always the same?

A. Synchronous transmission             

B. Asynchronous transmission

C. Satellite transmission

D. Microwave transmission

iii. Which of the following transmission media uses light Waves for transmitting information?

A. Coaxial cable 

B. Twisted pair cable

C. Telephone line 

D. Fibre optic cable

iv. Which of the following is used for short-distance communication?

A. Radio signals 

B. Microwave

C. Infra-red  

D. Satellite communication

v. In which of the following impairment, the strength of the signal falls off with distance?

A. Distortion             

B. Attenuation

C. Cross talk             

D. Noise

vi. Which of the following impairment refers to undesired signals that enter the path of the transmitted signal due to electromagnetic radiation?

A. Distortion                                                  

B. Attenuation`

C. Crosstalk 

D. Noise

vii. Which of the following device is used for connecting computers together in a wireless local area network?

A. Dial-up modem 

B. Router

C. Switch 

D. Access point

viii. Which of the following device is used for connecting computer together in a wired local area network?

A. Dial-Up modem                                        

B. Router   

C. Switch                                                        

D. Access point

ix. Which of the following device forwards information from one network to another by selecting the best pathway available?

A. Dial-Up modem                                        

B. Router  

C. Switch                                                        

D. Access point

x. What represents the overall data transmission capacity of a computer network?

A. Data rate                                                     

B. Bandwidth

C. Signal strength 

D. Baud rate

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Chapter 5 Computer Networks