Class 9th Computer Science Notes Chapter 4 Data Communication Solved Exercise

Class 9th Computer Science Notes Chapter 4 Data Communication Solved Exercise

Class 9th Computer Science Notes Chapter 4 Data Communication Solved Exercise. 9th Class Computer Science Notes (Unit # 4). Class 9 / IX / SSC-I / Matric. Download PDF Guide / Key Book written / composed by Mujeeb ur Rahman. These notes are in accordance with the latest syllabus / courses recommended by the Mardan Board of Intermediate and Secondary Education (BISE) Mardan and all the Boards of KPK Province.

Class 9th Computer Science Notes Chapter 4 Data Communication Solved Exercise
Class 9th Computer Science Notes Chapter 4 Data Communication Solved Exercise

UNIT 4

DATA COMMUNICATION

SOLVED EXERCISE

Q.1 Fill in the blanks.

i. Data Communication is the exchange of data between devices (computers) via some form of transmission medium.

ii. The continuous signals in wave form are called analog signals.

  1. A set of rules that guides (or governs) data communication is called protocol.

Iv. In asynchronous transmission, data is transmitted one byte at a ‘time’.

  1. A fiber optic cable is made of glass or plastic and transmits signals in the form of light.
  2. Attenuation is the loss of energy as the signal propagates outwards.

‘ii. MODEM stands for Modulator-Demodulator.

viii. Router is intelligent device which routes data to destination computers.

ix. Data rate is the speed at which binary digits (bits) would be transmitted over a communications path.

x. Bandwidth is the information-carrying capability of a communications channel or line, expressed in cycles per second (Hertz or Hz).

Q.2 Select the correct choice for each question.

i. What are raw facts and figures given to the computer as input for processing called?

A. Information B. ✓Data

C. Network D. Output

ii. Which of the following is an electronic device that can convert the analog signal to digital and vice versa?

A. Keyboard B. Mouse

C. ✓Modem D. Scanner

iii. What is a device used in a communication system to send or transmit data to another device called?

A. Receiver B. ✓Sender

C. Medium D. Channel

iv. In which type of transmission, data is transmitted block-by-block or word-by-word simultaneously?

A. Parallel B. Serial

C. Asynchronous D. ✓Synchronous

v. Which of the following is an example of Guided Transmission Media?

A. Satellite B. Microwave

C. ✓Coaxial cable D. Infrared

vi. Which technology allows computing devices to communicate via short-range wireless signals?

A. Satellite B. Microwave

C. Cellular Radio D. ✓Infrared

vii. In which of the following transmission impairment the signal changes its shape and form?

A. Attenuation B. ✓Distortion

C. Noise D. Cross talk

viii. Which communication device is used in?

Networking environment to connect computers to the same network?

A. Switch B. Hub C. ✓Router D. Modem

ix. What is a unit of signaling speed?

A. ✓Baud B-: Kilometer C. Second D. Hertz

  1. Which of the following digital channels provide transmission speeds from 19200 bps to several billion bps?

A: Voice band B. Modalism band C. ✓Broad band D. Narrow band

SHORT QUESTIONS .AND ANSWERS

Q.3 Give short answers to the following questions. i. What is data communication?

Ans: Data Communication is the exchange of information from one entity (device) to the other using a transmission .medium. Such as wire cable, wireless system, • microwave system, satellite system etc.

The communicating devices must be the part of a communication system. The communication system may consist of hardware and software. In data communication, data. Is transmitted electronically from one system to other system using standard methods.

  1. Differentiate between analog signal and digital

signal.

Ans: Analog Signal:

  • n It is a continuous wave forth that changes smoothly over time as the wave moves from value ‘ A’ to value ‘B’, it passes through and
  • n It includes an infinite number of values along its path

Digital Signal:

  • A digital signal is discrete. It can have only a limited number of defined values, often as simple as is and Os
  • The transition, of a digital signal from value to value is instantaneous like a light being switched ON and OFF

iii. Define the following properties of a good communication system.

a. Delivery b. Accuracy c. Timeliness

Ans: The effectiveness of the communication system depends upon three fundamental characteristics.

  1. Delivery

The communication system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user

  1. Accuracy

The communication system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable. The data must be delivered accurately. If there is any error occurred during transmission, the data must be re-transmitted.

c. Timeliness

The communication system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission.

iv. Differentiate between guided and unguided transmission media.

Ans: Guided Transmission Media:

In this type of transmission media, communication devices are directly linked with each other via physical materials (like cables, etc.) for data communication. It is also called physical or wired transmission media. These types of transmission media are usually used in LAN.

Examples:

Twisted pair cable, Coaxial cable, Fiber optic cable Unguided Transmission Media:

In this type of transmission media, communication devices communicate with each other through the air or space using broadcast radio signals,, microwave signals and infrared signals. This transmission medium is used when it is impossible to install the cables. The data can be transmitted all over the world through this medium. It is also called wireless transmission media.

Examples:

Radio Waves, Cellular Radio, Microwave, infra-red, Satellite

  1. What is the purpose of communication devices?

Ans: Communication Device:

An electronic device that can send and receive data on the network is called the communication device.

Purpose of communication devices:

The communication devices are used on both ends of the connections. Most of the communication devices have the ability to convert the digital signal of computer into analog signal so that the signals can be transmitted on the communication line to another end. The reverse is also true.

Examples:

Dialup Modem, Network Interface card (NIC), Router,

Switch / Access Point

  1. What-is signal-to-noise ratio?

Ans: Signal to Noise Ratio:

Signal-To-NoiSe Ratio (S/N) is the ratio of the relative power levels of a voice or data communications signal and the noise on a line, expressed in decibels (dB).

SNR = Signal / Noise

SNR is actually the ratio•of what is wanted (signal) to what is not wanted (noise). A high SNR means the signal is less corrupted by noise; a low SNR means the signal is more corrupted by noise.

vii. How data rate and baud rate can be linked through formulae?

Ans: Formulae for Data rate and Baud rate:

Data rate (bps) and Baud rate (baud per second) have the following connection.

Data rate (bps) = Baud rate (baud per second) x the number of bit per baud

Baud rate (baud per second) = Data rate (bps) / the number of bits per baud

LONG QUESTIONS AND ANSWERS

Q.4 what is data communication? Explain the basic components of a communication system.

Ans: Data communication is the exchange of data between devices (computers) via some form of transmission medium such as wire cable, wireless system, microwave system, satellite system etc. The communicating devices must be the part of a communication system. The communication system may consist of hardware and software. In data communication, data is transmitted electronically from one system to other system using standard methods. A common example of Data Communications would be the personal computer (PC) connecting to the Internet with a Modem. In which users establish a Communications between a PC and many hundred computers on the Internet. Every time users click on a hyperlink, they are requesting information and it is presented to them in some form of Data which may be textual information, graphics, videos, sounds, etc.

Components of a Communication System

A data communication system is made up of five components which are as under.

1. Sender

2. Receiver

3. Message

4. Protocol

5. Transmission Medium

1. Sender

A device used in a communication system to send or transmit data to another device is called Sender, or Transmitter or Source. A sender may be a computer, workstation, telephone handset, video camera and mobile phone.

2. Receiver

A device used in a communication system 10 receive messages from another device (sender) is called Receiver or Sink. A receiver may be a computer, workstation, telephone handset, mobile phone, television set, printer, fax machine, and so on.

3. Message

The message is the information or data that is to be transferred from one location to another. It may consist of text, numbers, pictures, sounds, videos or any, combination of these.

4. Protocol

A set of rules that guides (or governs) data communication is called protocol. It represents an agreement between the communicating devices. Without a proper protoc6I, the devices may be connected but they cannot communicate with each other. For example, a person whose mother language is English cannot communicate with a person who can speak only Urdu without protocol.

5. Transmission Medium

Transmission Medium is a path or channel through which message is transmitted (sent) or received from one location to another in a communication system. The twisted wire, fiber optic, microwave, satellite system etc. are used as medium.

Q.5 Explain synChronous and asynchronous transmission modes wfth’examples. Ans: Modes of Data Communication:

There are. Two modes of data communication.

• Synchronat3

• Asynchronous

A. vnchronous Transmission;

In synchronous transmission, large volumes of information ‘can be transmitted at a time. In this type of transmission, data is transmitted block-by¬block or word-byword simultaneously. Each block may contain several bytes of data: In synchronous transmission, a special communication device known as synchronized clock is required to schedule the transmission of. information. With synchronous transmission, large blocks of bytes are transmitted at regular intervals without any start/stop signals. Synchronous transmission requires that both the sending and receiving devices be synchronized before data is transmitted. Synchronous transmission requires more expensive equipment but provides greater

speed and accuracy than asynchronous transmission.

B. Asynchronous Transmission

In ‘asynchronous transmission, data is transmitted one byte at a ‘time’. This type of transmission is most commonly used by microcomputers. The data is transmitted character-by-character as the user types it on a keyboard. In asynchronous transmission, transmission does not occur at pr.edeterrnined or regular intervals (i.e., not synchronized). A sending device can transmit bytes at any time, and the receiving device must be ready to accept them as they arrive. A start bit marks the beginning of a byte and a stop bit marks the end of the byte. An ‘additional bit called a parity bit is sometimes included at the end of each byte to allow for error checking. Asynchronous transmission usually involves communications in which data can be. Transmitted intermittently instead of lima steady stream

Q.6 what is guided transmission media? Explain different types of guided media with advantages and disadvantages of each.

Ans: Guided Transmission Media:

In this type of transmission media, communication device’s are directly linked with each other via physical materials for data communication. It is also called physical or wired transmission media. These types of transmission media are usually used in LAN (Local Area Network).

Examples:

  1. Twisted pair cable
  2. Coaxial cable
  3. Fiber optic cable

1. Twisted pair cable:

Twisted-pair cable is one of the most commonly used communication media for network cabling. It consists of two separate copper wires that are covered by insulating material such as plastic and are twisted together to form a cable. One of the wires is used to carry signals to the receiver, and other is used only as ground reference.

Advantages:

  • Cheaper and easier to join
  • Less prone to electrical interference caused by nearby equipment or wires.
  • Are less likely to cause interference themselves
  • Because it is electrically “cleaner”, STP wire

Can carry data at a faster speed.

2. Coaxial cable:

Coaxial cable is also referred to as Coax. It carries signals of higher frequency ranges than twisted- of light. A typical optical fiber consists of a very narrow strand or fiber of glass called the core (It is as thin as a human hair). The core is surrounded by a concentric layer of glass called Cladding.

The fiber-optic cable is becoming more popular. Now-a-days, telephone, Internet and television companies are replacing their existing cables with fiber-optic cables.

Advantages:

  • The data transmission speed is very high because fiber-optic cable uses light to transmit data. The data transmission speed is up to billions bits per second.

• It has high level of security.

• It is not affected by electromagnetic waves.

  • It is more reliable and has lower data transmission errors.
  • The disadvantages of fiber optic cable are:

• It is more costly.

• It is difficult to install and modify.

Q.7 Explain the following unguided transmission media.

  1. Radio waves

ii Cellular Radio

  1. Satellite

Ans:

  1. Radio waves:

It is a wireless transmission medium that is used to communicate information through radio signals in air, over long distance such as between cities and countries. In this medium, a transmitter is required to send messages (signals) and receiver is required to receive them. To receive the broadcast radio signal, the receiver has an antenna that is located in the range of signal. Some networks use a special device called transceiver used to send and to receive messages. in the form of radio signals. The data transmission speed of broadcast radio is up to 54Mbps (Megabits per second).

  1. Cellular Radio:

Cellular radio is a form of broadcast radio that is used for mobile communications such as cellular telephones and wireless modems. A cellular telephone is .a telephone device that uses high frequency radio waves to transmit voice and digital messages. Some mobile users connect their laptop computer or other mobile device to a cellular telephone to access the Web, send and receive email, etc. while away from a standard telephone line.

  1. Satellite:

A communication satellite is a space station that receives microwave signals from earth microwave station (earth based station). Transmitting a signal from ground or earth station to a satellite station in space is called up-linking and the reverse is called the down- linking.

Now-a-days, television and radio broadcast, global positioning systems and Internet also use the communication satellites. The communication satellite is launched about 22300 miles (or more) above the earth into ‘space. The communication satellite consists of solar powered, transceiver that receives and sends signals.

Q.8 what are transmission impairments? Explain different causes of transmission impairments.

Ans: Transmission Impairments:

Transmission Impairments is a condition that causes information to be lost. If the transmission media were perfect, the receiver could receive exactly the same signal that the transmitter sent. But communication lines are usually not perfect, so the receive signal is not the same AF the transmitted signal. What is sent is not what is received.

Causes of Transmission Impairments:

The causes of impairment are:

    1. Attenuation
    2. Distortion
    3. Noise
  1. Attenuation:

It is the loss of energy as the signal propagates outwards. The amount of energy depends on the frequency. If the attenuation is too much, the receiver may not be able to detect the signal at all. For reliable communication, the range of frequencies of transmission should be constant.

  1. Distortion:

The second transmission impairment is distortion. Distortion means that the signal changes its shape and form. This happens because a signal is composed of multiple frequencies and each frequency in a signal has different propagation speed through medium. Due to this they do not reach the destination at the same time, thus producing different shape of signal as compared to the shape at sending end.

  1. Noise:

Noise is another cause of impairment. Several types of noise, such as thermal noise, induced noise, crosstalk, and impulse noise, may corrupt the signal. Thermal noise is the random motion of electrons in a wire which creates an extra signal not originally sent by the transmitter. Induced noise comes from sources such as motors and appliances. These devices act as a sending antenna, and the transmission medium acts as receiving antenna. Crosstalk is the effect of one wire on the other. One wire acts as a sending antenna and the other as the receiving antenna.

Q.9 Explain any five communication devices.

Ans: Communication Device:

An electronic device that can send and receive data on the network is called the communication device. The communication devices are used on both ends of the connections. Most of the communication devices have the ability to convert the digital signal of computer into analog signal so that the signals can be transmitted- on the communication line to another end. The reverse is also true. The most important communication devices are:

I Dialup Modem

2. Network Interface card (NIC)

3. Router

4. Switch / Access Point

5. Bridge

1.Dialup Modem:

Modem stands for Modulator and Demodulator.

The Modem (dialup modem) is an electronic device that can convert the digital signals into analog signals and analog signals into digital signals. It is used on both ends of the connection for data communication between, computers through telephone line.

Data is communicated through telephone lines in the form of analog signals. So data in the form of digital signal from one computer must be converted into analog signals before to transmit it to another computer through telephone lines. Similarly, to receive the data from another computer through telephone lines in the form of analog signals must be converted to digital before to store into the computer.

2. Network Interface card (NIC)

It is also referred to as LAN adapter or simply LAN card. It is used in Local Area Network to establish the communication link between the devices (computers, printers and other devices) attached on the network. Usually, the personal computers use the network interface card (NIC) in Local Area Network (LAN).

The Ethernet card is the most common type of network interface card. The data transmission speed of Ethernet card is from 10 Mbps to 1Gbps. Some of the network interface cards also, have the combined features of Ethernet card and dialup modem card.

3 Router: Router is intelligent device which routes data to

Destination computers. It helps in connecting two different logical and physical networks together. Some routers also have built-in antivirus protection. Similarly, some routers also support wireless communications.

4. Switch / Access Point:

Switch is an important communication device. It is used in networking environment to connect computers to the same network. In the network every computer has a unique address for identification which is called MAC (Media Access Control) address. Switch uses MAC address for communication. It is also called Hub or Access Point.

5. Bridge:

The bridge is the simpler device provides a means of interconnecting similar LANs. The router is a more general-purpose device, capable of interconnecting a variety of LANs and WANs. The bridge is designed for use between local area networks (LANs) that use identical protocols for the physical and link layers (e.g., all conforming to IEEE802.3). Because the devices all use the same protocols, the amount of processing required at the bridge is minimal. More sophisticated bridges are capable of mapping from one MAC format to another.

0.10 What is bandwidth? Explain different types of bandwidths.

Ans: Bandwidth:

Bandwidth is the information-carrying capability of a communications channel or line, expressed in cycles per second (Hertz or Hz). Different communication systems use different band widths for different purposes.

Types of bandwidths:

There are three types of bandwidths.

1. Voice band or low speed channels

2. Medium band or medium speed channels

3. Broad band or high speed channel

1. Voice band or low-speed channels:

Voice band or low-speed channels allow data transmission rates from 110 to 9600 bps. These channels are voice grade communication lines commonly used for ordinary telephone communications.

2. Medium band or medium-speed channels:

Medium band or medium-speed channels use specially conditioned lines to handle data transmission speeds from 9600 bps to 256 Kbps.

3. Broad band or high-speed digital channels:

Broad band or high-speed digital channels provide transmission speeds from 19200 bps to several billion bps. They typically use microwave, fiber optics, or satellite transmission.

EXTRA QUESTIONS AND ANSWERS

Q.1 Explain the following terms.

a. Data

b. Data Transmission

Ans:

a. Data

In computing, data is any raw facts and figures given to the computer as input for processing. The processed form of data is called information. Data can be in the form of text, numbers, graphics, sounds and videos. In Communication data is translated into a form that is more convenient to move or process

b. Data Transmission:

Data transmission means sending and receiving data through transmission medium. The transmission mediums include cables (e.g. telephone lines or fiber optics) or wireless medium like microwave, infrared and satellite, etc. The data can be transmitted from one place to another in the form of electromagnetic or light waves through communication medium. The electromagnetic or light waves representing data are called signals. Data communication signals can be in analog or digital form.

Q.2 Write short note on the following unguided media.

a. Microwave

b. Infra-red

Ans:

a. Microwave

Microwaves are radio waves that provide a high speed transmission. In Microwaves transmission, data is transmitted from one station to another. Microwave station contains an antenna, transceiver (transmitter & receiver) and other equipment’s that are required for microwave communication. Microwave’ uses the line-of-sight transmission, which means that in microwave transmission system the data signals travel in a straight path and cannot bend.

Microwave stations or antennas are usually installed on the high towers or buildings. Thus microwave stations need to be placed within 20 to 30 miles of each other. Each microwave station receives signals from the previous stations. In this way, data is transmitted from one place to another. Fig 4.9 shows Microwave transmission.

b. Infra-red

Infrared technology allows computing devices to communicate via short-range wireless signals. With infrared, computers can transfer files and other digital data bi-directionally. Computer infrared network adapters both transmit and receive data. Infrared adapters are installed in many laptops, handheld personal devices and mobile phones. Infrared communications span very short distances within a few feet (not more than 5 meters). Unlike Wi-Fi and Bluetooth technologies, infrared network signals cannot penetrate walls or other obstructions and work only in the direct “line of sight.” It supports data rates from 100 Kbps to 4 Mbps.

Q.3 Define the following terms.

a. Data rate

b. Baud rate

Ans:

a. Data rate

Data rate or bit rate is the speed at which binary digits (bits) would be transmitted over a communications path. It is expressed in “bits per second” (bps). OR

Bit rate is the measure of the number of data bits (i.e. 0’s and l’s) transmitted in one second in a communication channel. For example 2400 bits per second means 2400 zeros or ones can be transmitted in one second.

b. Baud rate

Baud is a unit of signaling speed. Baud rate is the amount of times per second a signal within a communication channel changes state. For example, a 1000 baud rate means that it can change state a thousand times per second. In simple terms, baud rate is the speed at which data is transmitted. Baud rate is associated with modems, digital televisions, telephones and other such devices. A higher baud rate is preferred to send faster transmissions.

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