Fbise Notes-Computer

Data Communication CH# 04Questions and Answers

i. Differentiate between analog and digital signals.

Ans: Analog Signals:

Analog signal is in continuous form. It varies continuously within a range. It is represented by a sine wave. It is described by the amplitude, period, frequency and phase. It transmits data in the form of waves. Examples; human sound, temperature, etc.

Digital Signals:

Digital signals are not continuous. They switch between two discrete, low and high voltage levels. In digital computers, low voltage level represents binary 0 and high voltage represents binary 1. Information represented in digital form can be easily transmitted by series of “ON” and “OFF” signals by pulses of electricity. A pulse “ON” can represent 1 and “OFF” 0.

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ii. Why digital signals are used in computer systems?

Ans: Information represented in digital form can be easily transmitted by series of “ON” and “OFF” signals by pulses of electricity. A pulse “ON” can represent 1 and “OFF” 0.

Multiple bit (0,1) streams are used in a computer network. Digital data can be compressed relatively easily, thereby increasing the efficiency of transmission. That is why digital signals are used in computer systems.

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iii. Name the properties of a good communication system.

Ans: Characteristics or properties of a good communication system:

Following are the properties of a good communication system.

Delivery:

Data communication system must deliver the message to the correct destination. Message must be received by only the device or user to whom it is sent.

For Example: when e-mail is sent to a person, it is received only by the person to whom it is addressed. This is managed by the protocol used in the communication system.

Accuracy:

System must deliver the message accurately without any change. If incorrect data is transmitted by the system, it may not be useable by the receiver.

For Example: when data is transmitted over a long distance, it may get corrupted due to transmission errors. The data that is not correctly received at the destination is retransmitted from the source. This is ensured by the protocol used in the data transmission system.

Timeliness:

The system must deliver the data without significant delay in a timely manner. It is very important in real time transmission such as video conferencing that video or audio are delivered as soon as they are produced. Data delivered late may be useless. Some real time systems require immediate transmission of data within limited time.

For Example: a computerized real time system is used to monitor the temperature in an oil refinery. If the temperature is getting too high, it must be transmitted immediately otherwise there can be an explosion.

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

Ans: Guided medium is more reliable than unguided because of the following reasons;

i. It reduces cross talk and electromagnetic interference and make the transmission more reliable.

ii. It provides high quality transmission at extremely high speed. It can transmit trillions of bits per second.

iii. It is used for data transmission over long distance.

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v. What is meant by transmission impairment?

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

When a signal is transmitted over a communication medium, it may have different types of impairments. Impairments occur due to imperfect characteristics of communication medium. As a consequence, the received and the transmitted signals are not always the same.

Types of impairments;

i. Attenuation

ii. Amplification

iii. Distortion

iv. Cross talk

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vi. Differentiate between attenuation and distortion.

Ans: Attenuation:

Attenuation is the fall of signal strength with the distance as 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 change in shape or frequency of digital signal when it is transmitted over a communication line. Communication line delays the signal frequency by different amounts because different frequency components travel at different speed. Therefore various frequency components of a signal are received at different delays. This cause distortion in digital signals.

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vii. What is cross talk?

Ans: Cross Talk:

As signal is transmitted through a wire, undesired signals enter the path of the transmitted signals due to electromagnetic radiations. This is called cross talk. It is due to guided media. It is caused because of putting several wires together in a single cable.

Sometimes, user can hear another conversation in the background when talking on the phone. This happens by the coupling between two wires that are close to each other.

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viii. What is Dial-up modem? Why is it used?

Ans: Dial-up Modem:

Dial-up modem provides internet connection through telephone line. Maximum speed of this modem is 56 kbps which is very slow. It is being replaced by faster DSL connection for the internet.

Uses of Dial-up Modem:

A telephone line is used for voice transmission which is analog signal. A modem converts digital signal to analog form for transmission over telephone line. This process is called modulation.

Another modem at the receiving end converts the analog back to digital form. This is called demodulation. Modem is the abbreviation of Modulator-Demodulator.

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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 or megabits per second.

Baud Rate:

It is the rate of change of electrical signals per second during data communications. Electrical signal have two or more states to represent binary digits 0 or 1. In the case of two states the baud rate and the number of states per second are the same.

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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.

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