1Which layer of the OSI model is responsible for the transmission of raw bits over a communication channel?
A.Data Link Layer
B.Network Layer
C.Physical Layer
D.Transport Layer
Correct Answer: Physical Layer
Explanation:The Physical Layer is responsible for moving individual bits from one node to the next. It deals with the mechanical and electrical specifications of the interface and transmission medium.
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2In a periodic analog signal, what is the relationship between the period () and the frequency ()?
A.
B.
C.
D.
Correct Answer:
Explanation:Period and frequency are inversely related. The period is the time it takes for one full cycle, while frequency is the number of cycles per second.
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3Which of the following transmission impairments refers to the loss of signal energy due to the resistance of the medium?
A.Attenuation
B.Distortion
C.Noise
D.Jitter
Correct Answer: Attenuation
Explanation:Attenuation is the loss of energy as a signal propagates through a medium. To compensate for this, amplifiers are often used.
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4If a signal has a power of 10 mW at the sender and 1 mW at the receiver, what is the attenuation in decibels (dB)?
A.-10 dB
B.-20 dB
C.10 dB
D.100 dB
Correct Answer: -10 dB
Explanation:The formula for decibels is . Here, and . Thus, dB.
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5Which formula defines the theoretical maximum bit rate of a noiseless channel?
A.Shannon Capacity
B.Nyquist Bit Rate
C.Fourier Transform
D.Pascal's Limit
Correct Answer: Nyquist Bit Rate
Explanation:The Nyquist Bit Rate formula defines the theoretical maximum bit rate for a noiseless channel: , where is the number of signal levels.
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6Calculate the Shannon Capacity of a channel with a bandwidth of 3000 Hz and a Signal-to-Noise Ratio (SNR) of 3162 (approx 35 dB).
A.6000 bps
B.34,860 bps
C.12,000 bps
D.90,000 bps
Correct Answer: 34,860 bps
Explanation:Using Shannon's formula . . Since , bps.
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7Which of the following is considered a 'Guided Media'?
A.Radio waves
B.Infrared
C.Microwave
D.Coaxial Cable
Correct Answer: Coaxial Cable
Explanation:Guided media provide a physical conduit from one device to another (e.g., Twisted Pair, Coaxial Cable, Fiber Optic). The others are unguided (wireless).
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8In fiber optics, transmission relies on which physical phenomenon to keep the light inside the core?
A.Refraction
B.Total Internal Reflection
C.Diffraction
D.Absorption
Correct Answer: Total Internal Reflection
Explanation:Fiber optics work because the core is less dense than the cladding, and light hits the boundary at an angle greater than the critical angle, causing Total Internal Reflection.
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9Which cabling standard describes the wiring color code where the order is White/Orange, Orange, White/Green, Blue, White/Blue, Green, White/Brown, Brown?
A.T568A
B.T568B
C.RJ-11
D.RS-232
Correct Answer: T568B
Explanation:T568B is the standard termination pattern widely used in commercial structured cabling. T568A starts with White/Green.
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10In Digital-to-Digital conversion, what is the primary problem with the basic NRZ-L (Non-Return-to-Zero Level) encoding?
A.High bandwidth requirement
B.Baseline wander and synchronization issues
C.Complex implementation
D.Low data rate
Correct Answer: Baseline wander and synchronization issues
Explanation:NRZ-L can suffer from baseline wander (DC component builds up) and synchronization issues if there are long strings of 0s or 1s, as the receiver clock may drift.
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11Which line coding scheme guarantees a transition at the middle of each bit period, providing self-synchronization?
A.NRZ-L
B.NRZ-I
C.Manchester
D.AMI
Correct Answer: Manchester
Explanation:Manchester encoding combines the clock and data, ensuring a voltage transition in the middle of every bit, which helps in synchronization.
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12The process of converting an analog signal to a digital signal (A/D) using sampling and quantization is known as:
A.Pulse Amplitude Modulation (PAM)
B.Pulse Code Modulation (PCM)
C.Frequency Shift Keying (FSK)
D.Amplitude Shift Keying (ASK)
Correct Answer: Pulse Code Modulation (PCM)
Explanation:PCM is the standard method for converting analog signals into digital data involves Sampling, Quantization, and Encoding.
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13According to the Nyquist sampling theorem, to reproduce an analog signal without distortion, the sampling rate () must be:
A.
B.
C.
D.
Correct Answer:
Explanation:The sampling rate must be at least twice the highest frequency component of the original signal () to avoid aliasing.
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14In Digital-to-Analog conversion, which modulation technique varies the amplitude of the carrier signal to represent data?
A.FSK
B.PSK
C.ASK
D.QAM
Correct Answer: ASK
Explanation:ASK (Amplitude Shift Keying) changes the amplitude of the carrier wave to represent binary 1s and 0s, while frequency and phase remain constant.
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15Quadrature Amplitude Modulation (QAM) is a combination of which two modulation techniques?
A.ASK and FSK
B.ASK and PSK
C.FSK and PSK
D.AM and FM
Correct Answer: ASK and PSK
Explanation:QAM modifies both the amplitude and the phase of the carrier signal to increase the data rate.
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16What is the 'Baud Rate'?
A.The number of bits per second
B.The number of signal elements (symbols) transmitted per second
C.The bandwidth of the channel
D.The frequency of the carrier
Correct Answer: The number of signal elements (symbols) transmitted per second
Explanation:Baud rate refers to the rate at which the signal changes (symbols per second). It is distinct from bit rate if one signal element carries multiple bits.
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17If a signal element carries 4 bits of data, and the baud rate is 1000 baud, what is the bit rate?
A.250 bps
B.1000 bps
C.4000 bps
D.16000 bps
Correct Answer: 4000 bps
Explanation:. Therefore, bps.
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18Which multiplexing technique is primarily used for fiber optic communication to transmit multiple light beams of different frequencies?
A.FDM
B.TDM
C.WDM
D.CDM
Correct Answer: WDM
Explanation:WDM (Wavelength Division Multiplexing) is an analog multiplexing technique used in fiber optics to combine optical signals of different wavelengths (colors).
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19In Frequency Division Multiplexing (FDM), what is used to separate channels to prevent interference?
A.Time slots
B.Guard bands
C.Start bits
D.Sync pulses
Correct Answer: Guard bands
Explanation:Guard bands are unused strips of the frequency spectrum kept between active channels in FDM to prevent crosstalk/interference.
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20Which type of Time Division Multiplexing (TDM) allocates time slots dynamically based on demand, rather than fixed pre-assignment?
A.Synchronous TDM
B.Statistical TDM
C.Analog TDM
D.Wave TDM
Correct Answer: Statistical TDM
Explanation:Statistical TDM (or Asynchronous TDM) allocates slots only to devices that have data to send, improving bandwidth efficiency compared to Synchronous TDM.
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21What is 'Jitter' in the context of network performance?
A.The total time taken for a message to travel
B.The variation in packet arrival time
C.The loss of packets
D.The strength of the signal
Correct Answer: The variation in packet arrival time
Explanation:Jitter is the variation in the latency (delay) of received packets. High jitter can severely affect real-time applications like VoIP.
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22Which component is eliminated in a digital signal using Polar NRZ-L compared to Unipolar NRZ?
A.High frequency components
B.DC Component
C.Noise
D.Synchronization errors
Correct Answer: DC Component
Explanation:While NRZ-L still has some DC component issues, Polar schemes (using positive and negative voltages) generally reduce the average DC power compared to Unipolar (positive and zero only), though NRZ-L is not entirely DC-free.
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23What does a 'Constellation Diagram' represent?
A.Network topology
B.Amplitude and Phase of signal elements
C.Frequency spectrum allocation
D.Router hop count
Correct Answer: Amplitude and Phase of signal elements
Explanation:A Constellation Diagram is a graphical representation of a signal in the complex plane, showing the amplitude and phase of signal elements in modulation schemes like QAM or PSK.
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24In Analog-to-Analog conversion, FM stands for:
A.Frequency Mixing
B.Frequency Modulation
C.Fast Modulation
D.Frequency Multiplexing
Correct Answer: Frequency Modulation
Explanation:Frequency Modulation (FM) varies the frequency of the carrier signal in accordance with the instantaneous amplitude of the modulating signal.
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25Which unguided media typically operates in the frequency range of 3 kHz to 1 GHz and is omnidirectional?
A.Radio waves
B.Microwaves
C.Infrared
D.Visible light
Correct Answer: Radio waves
Explanation:Radio waves are generally omnidirectional and operate in lower frequency ranges (VLF to UHF). Microwaves are higher frequency and unidirectional.
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26What is the primary advantage of Twisted Pair cable twisting?
A.Increases bandwidth
B.Reduces crosstalk and electromagnetic interference
C.Makes the cable stronger
D.Increases transmission speed
Correct Answer: Reduces crosstalk and electromagnetic interference
Explanation:Twisting the pairs causes the electromagnetic waves from external sources to affect both wires equally (canceling out) and minimizes radiation from the cable itself, reducing crosstalk and EMI.
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27Which scrambling technique replaces a sequence of eight zeros with a specific pattern to ensure synchronization in long-distance communication?
A.HDB3
B.B8ZS
C.AMI
D.4B/5B
Correct Answer: B8ZS
Explanation:B8ZS (Bipolar with 8-Zero Substitution) is a scrambling technique used in North American T1 lines to replace 8 consecutive zeros with a pattern containing intentional violations to maintain sync.
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28Calculate the propagation time if the distance between two points is 12,000 km and the propagation speed is m/s.
A.20 ms
B.50 ms
C.5 ms
D.0.5 s
Correct Answer: 50 ms
Explanation:. . Time seconds = 50 ms.
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29In Pulse Code Modulation (PCM), if the number of quantization levels is increased, what happens to the PCM system performance?
A.Quantization noise increases
B.Quantization noise decreases
C.Sampling rate decreases
D.Bandwidth decreases
Correct Answer: Quantization noise decreases
Explanation:Increasing the number of levels () reduces the gap between levels (), which reduces the maximum quantization error (noise). However, it requires more bits per sample.
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30Delta Modulation (DM) is a simplified form of PCM where each sample is encoded as:
A.8 bits
B.4 bits
C.1 bit
D.16 bits
Correct Answer: 1 bit
Explanation:In Delta Modulation, the analog signal is tracked, and the output indicates only whether the signal has risen or fallen compared to the previous sample (1 bit).
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31Which of the following connector types is commonly used with Coaxial Cable?
A.RJ-45
B.BNC
C.MT-RJ
D.SC
Correct Answer: BNC
Explanation:BNC (Bayonet Neill–Concelman) connectors are standard for coaxial cables. RJ-45 is for twisted pair, SC/MT-RJ are for fiber.
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32What does 'Baseband' transmission mean?
A.Sending digital signals over an analog channel
B.Sending a signal over a channel without changing its frequency
C.Using a carrier frequency
D.Multiplexing multiple signals
Correct Answer: Sending a signal over a channel without changing its frequency
Explanation:Baseband transmission sends the digital signal directly on the wire without modulation (shifting to a higher frequency band), occupying the entire bandwidth.
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33Which block coding scheme transforms a 4-bit data group into a 5-bit code group?
A.2B1Q
B.8B/10B
C.4B/5B
D.MLT-3
Correct Answer: 4B/5B
Explanation:4B/5B is a block coding method used (often with NRZ-I) to ensure adequate transitions for synchronization by mapping 4 data bits to 5 transmission bits.
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34In the context of data communications, what is 'Throughput'?
A.The maximum theoretical capacity
B.The actual measurement of data transferred over time
C.The delay in the network
D.The frequency range of the medium
Correct Answer: The actual measurement of data transferred over time
Explanation:While bandwidth is the potential capacity, throughput is the actual rate at which data is successfully transmitted, often lower than bandwidth due to overhead and errors.
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35Phase Shift Keying (PSK) is generally more robust than ASK against which impairment?
A.Frequency drift
B.Noise/Amplitude interference
C.Phase distortion
D.Propagation delay
Correct Answer: Noise/Amplitude interference
Explanation:Noise typically affects the amplitude of a signal. Since PSK relies on phase changes rather than amplitude changes, it is less susceptible to amplitude noise than ASK.
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36What is the result of 'Crosstalk'?
A.A signal on one line creates an unwanted effect on another line
B.The signal loses strength over distance
C.The signal frequency shifts
D.The digital signal becomes analog
Correct Answer: A signal on one line creates an unwanted effect on another line
Explanation:Crosstalk occurs when the electromagnetic field from a signal on one wire induces a current in a nearby wire, causing interference.
Explanation:Microwaves travel in straight lines and do not penetrate solid objects well or follow the earth's curvature, thus requiring line-of-sight between antennas.
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38Spread Spectrum technology (like FHSS and DSSS) is primarily used to:
A.Increase data rate
B.Prevent jamming and eavesdropping
C.Reduce bandwidth usage
D.Simplify the receiver design
Correct Answer: Prevent jamming and eavesdropping
Explanation:Spread Spectrum spreads the signal over a wider bandwidth than necessary. This makes the signal harder to detect (security) and more resistant to interference/jamming.
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39In Frequency Hopping Spread Spectrum (FHSS):
A.The signal is expanded by a chipping code
B.The signal broadcasts on all frequencies simultaneously
C.The signal hops from frequency to frequency in a pseudorandom sequence
D.The amplitude hops between levels
Correct Answer: The signal hops from frequency to frequency in a pseudorandom sequence
Explanation:In FHSS, the carrier frequency changes rapidly according to a pseudorandom sequence known to both transmitter and receiver.
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40Which digital-to-analog encoding is most susceptible to noise?
A.PSK
B.FSK
C.ASK
D.QAM
Correct Answer: ASK
Explanation:ASK is the most susceptible to noise because noise usually manifests as voltage spikes, directly corrupting the amplitude-based data.
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41What is the minimum bandwidth required for an ASK signal transmitting at baud in half-duplex?
A.
B.
C.
D.
Correct Answer:
Explanation:The bandwidth for ASK (and PSK) is typically calculated as , where is the signal rate (baud) and is a factor related to modulation/filtering (between 0 and 1). In simple theoretical terms, it is proportional to the baud rate.
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42Which type of fiber optic cable has the largest core diameter?
A.Single-mode step-index
B.Multi-mode step-index
C.Multi-mode graded-index
D.Laser-optimized
Correct Answer: Multi-mode step-index
Explanation:Multi-mode fibers have larger cores (e.g., 50 or 62.5 microns) compared to single-mode (approx 9 microns) to allow multiple modes of light to propagate.
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43If the Signal-to-Noise Ratio (SNR) is infinite, the channel capacity is:
A.Zero
B.Infinite
C.1
D.Limited by bandwidth
Correct Answer: Infinite
Explanation:According to Shannon's capacity formula , if SNR approaches infinity, the capacity also approaches infinity (theoretically).
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44The transmission of multiple signals on a single medium where the medium's data rate is greater than the individual devices' data rate requirements implies the use of:
A.Modulation
B.Encoding
C.Multiplexing
D.Amplification
Correct Answer: Multiplexing
Explanation:Multiplexing allows the high capacity of a single link to be shared by multiple lower-speed devices.
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45In Synchronous TDM, if a source does not have data to send, what happens to its time slot?
A.It is allocated to another source
B.It remains empty
C.The frame size is reduced
D.The system crashes
Correct Answer: It remains empty
Explanation:In Synchronous TDM, time slots are pre-assigned. If a device has no data, its slot is transmitted empty, leading to inefficiency.
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46Which encoding scheme is known as 'Bi-phase' coding?
A.NRZ-L
B.Manchester
C.AMI
D.B8ZS
Correct Answer: Manchester
Explanation:Manchester encoding is often called bi-phase because the signal level changes in the middle of the bit interval.
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47The ratio of the power of the signal to the power of the noise is called:
A.Attenuation
B.SNR (Signal-to-Noise Ratio)
C.Distortion
D.Gain
Correct Answer: SNR (Signal-to-Noise Ratio)
Explanation:SNR is defined as .
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48Category 6 (Cat 6) cable is designed to support frequencies up to:
A.100 MHz
B.250 MHz
C.600 MHz
D.1000 MHz
Correct Answer: 250 MHz
Explanation:Cat 5e supports up to 100 MHz, while Cat 6 is standardized for performance up to 250 MHz.
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49Which phenomenon causes different light modes to arrive at the receiver at different times in multimode fiber, distorting the signal?
A.Attenuation
B.Modal Dispersion
C.Crosstalk
D.Phase Jitter
Correct Answer: Modal Dispersion
Explanation:Modal Dispersion occurs in multimode fiber because different modes (paths) travel different distances, spreading the pulse out over time.
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50In AM (Amplitude Modulation), the bandwidth required is approximately equal to:
A.The bandwidth of the modulating signal
B.Twice the bandwidth of the modulating signal
C.Half the bandwidth of the modulating signal
D.The carrier frequency
Correct Answer: Twice the bandwidth of the modulating signal
Explanation:AM generates two sidebands (upper and lower). Thus, .
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