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Communications MCQ Set 1

1. Protocol is a set of
a) Formats
b) Procedures
c) Formats & Procedures
d) None of the mentioned

View Answer

Answer: c [Reason:] Protocol is a set of procedures and formats that entities use to communicate information.

2. The time required to transmit frame depends on
a) Frame size
b) Channel capacity
c) Frame size & Channel capacity
d) None of the mentioned

View Answer

Answer: c [Reason:] The time to transmit frame is given by the ratio of frame size and channel capacity.

3. Window given the number of
a) Bytes
b) Frames
c) Bytes & Frames
d) None of the mentioned

View Answer

Answer: c [Reason:] Window gives the number of frames or bytes that can be in transit unacknowledged.

4. Routing is
a) Static
b) Dynamic
c) Static & Dynamic
d) None of the mentioned

View Answer

Answer: c [Reason:] Routing can be static and dynamic.

5. Routing is performed only centrally.
a) True
b) False

View Answer

Answer: a [Reason:] Routing is performed centrally and also in fully distributed way.

6. Which is connection oriented and which is connection-less?
a) Datagrams, virtual circuits
b) Virtual circuits, datagrams
c) Datagrams
d) None of the mentioned

View Answer

Answer: b [Reason:] Datagram is connection-less and virtual circuits are connection oriented.

7. Which uses UDP?
a) Echo
b) Time
c) Domain name server
d) All of the mentioned

View Answer

Answer: d [Reason:] The protocols using UDP are echo, time, domain name server, network file system etc.

8. Which uses TCP?
a) Simple mail transfer protocol
b) Simple network management protocol
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: a [Reason:] Some of the protocols using TCP are http, telnet, file transfer protocol, simple mail transfer protocol etc.

9. Which tells about low level transmission and framing?
a) V series
b) X series
c) G series
d) Q series

View Answer

Answer: c [Reason:] G series tells about level transmission, modulation and framing.

10. Which tells about signalling?
a) V series
b) X series
c) G series
d) Q series

View Answer

Answer: d [Reason:] Q series tells about signalling.

Communications MCQ Set 2

1. Pseudorandom signal ________ predicted.
a) Can be
b) Cannot be
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: a [Reason:] Random signals cannot be predicted whereas pseudorandom sequence can be predicted.

2. The properties used for pseudorandom sequence are
a) Balance
b) Run
c) Correlation
d) All of the mentioned

View Answer

Answer: d [Reason:] The three basic properties that can be applied for pseudorandom sequence are balance, run and correlation properties.

3. The shift register needs to be controlled by clock pulses.
a) True
b) False

View Answer

Answer: a [Reason:] The shift register operation is controlled by clock pulses.

4. A linear feedback shift register consists of
a) Feedback path
b) Modulo 2 adder
c) Four stage register
d) All of the mentioned

View Answer

Answer: d [Reason:] A linear feedback shift register consists of four stage register for storage and shifting, modulo 2 adder and feedback path.

5. If the initial pulse of 1000 is fed to shift register, after how many clock pulses does the sequence repeat?
a) 15
b) 16
c) 14
d) 17

View Answer

Answer: a [Reason:] If the initial pulse 1000 is given to shift register, the foregoing sequence repeats after 15 clock pulses.

6. The sequences produced by shift register depends on
a) Number of stages
b) Feedback tap connections
c) Initial conditions
d) All of the mentioned

View Answer

Answer: d [Reason:] The sequences produced by shift register depends on the number of stages, the feedback tap connections and initial conditions.

7. For maximal length sequence, the sequence repetition clock pulses p is given by
a) 2n + 1
b) 2n -1
c) 2n
d) None of the mentioned

View Answer

Answer: b [Reason:] For maximal length sequence, produced by n stage linear feedback shift register the sequence repetition clock pulses p is given by 2n -1 .

8. For any cyclic shift, the auto-correlation function is equal to
a) 1/p
b) -1/p
c) –p
d) p

View Answer

Answer: b [Reason:] For any cyclic shift the auto-correlation function is equal to -1/p.

9. Which method is better?
a) To share same bandwidth
b) To share different bandwidth
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: b [Reason:] If the jammer noise shares the same bandwidth, the result could be destructive.

10. Pulse jammer consists of
a) Pulse modulated excess band noise
b) Pulse modulated band-limited noise
c) Pulse width modulated excess band noise
d) Pulse width modulated band-limited noise

View Answer

Answer: b [Reason:] Pulse jammer consists of pulse modulated band-limited noise.

11. Which are the design options for anti jam communicator?
a) Time diversity
b) Frequency diversity
c) Special discrimination
d) All of the mentioned

View Answer

Answer: d [Reason:] The design options for anti-jam communicator are time diversity, frequency diversity and special discrimination.

12. The ratio (J/S)reqd gives the measure of
a) Vulnerability to interference
b) Invulnerability to interference
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: b [Reason:] The ratio (J/S)reqd gives the measure of how invulnerable the system is to interference.

13. The system should have
a) Larger (J/S)reqd
b) Greater system’s noise rejection capability
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] The system will be efficient if it has greater (J/S)reqd and larger system’s noise rejection capability.

14. The broadband jammer jams the entire
a) W
b) Wss
c) W & Wss
d) None of the mentioned

View Answer

Answer: b [Reason:] The broadband jammer or wide-band jammer is the one which jams the entire Wss with its fixed power.

15. To increase error probability, the processing gain should be
a) Increased
b) Decreased
c) Exponentially increased
d) Exponentially decreased

View Answer

Answer: a [Reason:] In a system, to increase the error probability the processing gain should be increased.

16. Which jamming method produces greater degradation?
a) Broadband jamming
b) Partial jamming
c) Broadband & Partial jamming
d) None of the mentioned

View Answer

Answer: b [Reason:] Greater degradation is possible more with partial jamming than broadband jamming.

17. The jammer which monitors a communicator’s signal is known as
a) Frequency follower jammers
b) Repeat back jammers
c) Frequency follower & Repeat back jammers
d) None of the mentioned

View Answer

Answer: c [Reason:] The smart jammers which monitors a communicator’s signals is known as frequency follower or repeat back jammers.

Communications MCQ Set 3

1. In public key cryptosystem _____ keys are used for encryption and decryption.
a) Same
b) Different
c) Encryption Keys
d) None of the mentioned

View Answer

Answer: b [Reason:] In conventional cryptosystem same keys are used for encryption and decryption where as in public key cryptosystem different keys are used.

2. In public key cryptosystem which is kept as public?
a) Encryption keys
b) Decryption keys
c) Encryption & Decryption keys
d) None of the mentioned

View Answer

Answer: a [Reason:] In public key cryptosystem, the encryption keys are kept as public where as decryption keys are kept as secret.

3. In a trapdoor function, the functions are easy to go in
a) One direction
b) Two directions
c) All directions
d) None of the mentioned

View Answer

Answer: a [Reason:] A trapdoor is a one way function. Such functions can go easily in only one direction.

4. Pretty good privacy program is used for
a) Electronic mails
b) File encryption
c) Electronic mails & File encryption
d) None of the mentioned

View Answer

Answer: c [Reason:] Pretty good privacy (PGP) privacy program is used for both electronic mails and file encryption.

5. PGP system uses
a) Private key system
b) Public key system
c) Private & Public key system
d) None of the mentioned

View Answer

Answer: c [Reason:] Pretty good privacy system uses both private key and public key based systems.

6. Private key algorithm is used for _____ encryption and public key algorithm is used for _____ encryption.
a) Messages, session key
b) Session key, messages
c) Can be used for both
d) None of the mentioned

View Answer

Answer: a [Reason:] Private key algorithm is used for encryption of messages and public key algorithm is used for encryption of session keys.

7. Which are called the block ciphers?
a) IDEA
b) CAST
c) Triple-DES
d) All of the mentioned

View Answer

Answer: d [Reason:] Some of the examples of block codes are triple-DES, CAST and IDEA.

8. Which has a key length of 128 bits?
a) IDEA
b) Triple-DES
c) IDEA & Triple-DES
d) None of the mentioned

View Answer

Answer: a [Reason:] Triple-DES uses 168 bit key size and IDEA and CAST uses 128 bits key length.

9. Which algorithm can be used to sign a message?
a) Public key algorithm
b) Private key algorithm
c) Public & Private key algorithm
d) None of the mentioned

View Answer

Answer: a [Reason:] Public key algorithms are used to sign a message and private key algorithms are used to encrypt the messages.

10. Examples of hash functions are
a) MD5
b) SHA-1
c) MD5 & SHA-1
d) None of the mentioned

View Answer

Answer: c [Reason:] Some examples of hash functions are MD5 and SHA-1.

11. A cryptographic hash function has variable output length.
a) True
b) False

View Answer

Answer: b [Reason:] A cryptographic hash function has fixed output length.

12. A set of numbers is called as super increasing if
a) Each element is greater than previous element
b) Each element greater than sum of all the previous elements
c) Each element greater than the average of all elements
d) Each element lesser than the sum of all the elements

View Answer

Answer: b [Reason:] A set of numbers is called as super increasing if each element is greater than the sum of all the numbers lesser than it.

13. Knapsack problem can be solved by
a) Public key cryptosystem
b) Private key cryptosystem
c) Public & Private key cryptosystem
d) None of the mentioned

View Answer

Answer: a [Reason:] The knapsack problem can be solved by public key cryptosystem system using knapsack vector and data vector.

14. Merkle hellman is a symmetric cryptosystem.
a) True
b) False

View Answer

Answer: b [Reason:] Merkell hellman cryptosystem is a public key asymmetric cryptosystem method.

15. In this Merkle Hellman method same key is used for encryption and decryption.
a) True
b) False

View Answer

Answer: b [Reason:] In Merkle hellman cryptosystem method, two separate private and public keys are used for encryption and decryption.

Communications MCQ Set 4

1. The signals which are obtained by encoding each quantized signal into a digital word is called as
a) PAM signal
b) PCM signal
c) FM signal
d) Sampling and quantization

View Answer

Answer: b [Reason:] Pulse code modulation is the name for the class of signals which are obtained by encoding the quantized signals into a digital word.

2. The length of the code-word obtained by encoding quantized sample is equal to
a) l=log(to the base 2)L
b) l=log(to the base 10)L
c) l=2log(to the base 2)L
d) l=log(to the base 2)L/2

View Answer

Answer: a [Reason:] The quantized sample which are digitally encoded into l bit value code-word. The length l can be calculated as l=log(to the base 2)L.

3. Quantization noise can be reduced by ________ the number of levels.
a) Decreasing
b) Increasing
c) Doubling
d) Squaring

View Answer

Answer: b [Reason:] The process of quantization replaces the true signal with approximation(quantization noise). By increasing the number of quantization level the quantization noise can be reduced.

4. In PCM encoding, quantization level varies as a function of ________
a) Frequency
b) Amplitude
c) Square of frequency
d) Square of amplitude

View Answer

Answer: b [Reason:] In linear PCM the quantization levels are uniform. But in normal PCM encoding the quantization level vary according to the amplitude, based of A-law of Myu-law.

5. What is bit depth?
a) Number of quantization level
b) Interval between two quantization levels
c) Number of possible digital values to represent each sample
d) None of the mentioned

View Answer

Answer: c [Reason:] One of the properties of PCM signal which determines its stream fidelity is bit depth which is the number of possible digital values that can be used to represent each sample.

6. Choosing a discrete value that is near but not exactly at the analog signal level leads to
a) PCM error
b) Quantization error
c) PAM error
d) Sampling error

View Answer

Answer: b [Reason:] One of the limitations of PCM is quantization error which occurs when we choose a discrete value at some near by value and not at the analog signal level.

7. In PCM the samples are dependent on ________
a) Time
b) Frequency
c) Quanization leavel
d) Interval between quantization level

View Answer

Answer: a [Reason:] The samples depend on time,an accurate clock is required for accurate reproduction.

8. DPCM encodes the PCM values based on
a) Quantization level
b) Difference betweent the current and predicted value
c) Interval between levels
d) None of the mentioned

View Answer

Answer: b [Reason:] Differential PCM encodes the PCM value based on the difference between the previous sample and the present sample value.

9. Delta modulation uses _____ bits per sample.
a) One
b) Two
c) Four
d) Eight

View Answer

Answer: a [Reason:] Delta modulation is used for analog to digital conversion and vice versa. It is a simple form of DPCM. Its uses 1 bit per sample. It also depends on the difference betweent he current and previous sample values.

10. Sample resolution for LPCM ____ bits per sample.
a) 8
b) 16
c) 24
d) All of the mentioned

View Answer

Answer: d [Reason:] Common sampling resolution for LPCM are 8, 16, 20, 24 bits per sample.

11. Adaptive DPCM is used to
a) Increase bandwidth
b) Decrease bandwidth
c) Increase SNR
d) None of the mentioned

View Answer

Answer: b [Reason:] Adaptive DPCM is used to decrease required bandwidth for the given SNR.

Communications MCQ Set 5

1. Spread spectrum is used for
a) Encrypting signal
b) Hiding signal
c) Encrypting & Hiding signal
d) None of the mentioned

View Answer

Answer: c [Reason:] Spread spectrum is used for hiding and encrypting signals.

2. Which is a quantization process?
a) Rounding
b) Truncation
c) Rounding & Truncation
d) None of the mentioned

View Answer

Answer: c [Reason:] Rounding and truncation are the examples of quantization process.

3. Quantization is a _____ process.
a) Few to few mapping
b) Few to many mapping
c) Many to few mapping
d) Many to many mapping

View Answer

Answer: c [Reason:] Quantization is a many to few mapping process.

4. Quantization is a _____ process.
a) Non linear
b) Reversible
c) Non linear & Reversible
d) None of the mentioned

View Answer

Answer: a [Reason:] Quantization is a non linear and irreversible process.

5. Which conveys more information?
a) High probability event
b) Low probability event
c) High & Low probability event
d) None of the mentioned

View Answer

Answer: b [Reason:] High probability event conveys less information than a low probability event.

6. If the channel is noiseless information conveyed is ___ and if it is useless channel information conveyed is ___
a) 0,0
b) 1,1
c) 0,1
d) 1,0

View Answer

Answer: d [Reason:] If the channel is noiseless information conveyed is 1 and if it is useless channel information conveyed is 0.

7. The mutual information between a pair of events is
a) Positive
b) Negative
c) Zero
d) All of the mentioned

View Answer

Answer: d [Reason:] The mutual information between a pair of events can be positive negative or zero.

8. The output of the source encoder is an analog signal.
a) True
b) False

View Answer

Answer: b [Reason:] The output of the source encoder is a sequence of binary digits. The conversion of source output to digital form is done here in source encoder.

9. The output of an information source is
a) Random
b) Deterministic
c) Random & Deterministic
d) None of the mentioned

View Answer

Answer: a [Reason:] The output of any information source is random.

10. When the base of the logarithm is e, the unit of measure of information is
a) Bits
b) Bytes
c) Nats
d) None of the mentioned

View Answer

Answer: c [Reason:] The unit of measure of information is determined based on the base of logarithm. If the base is e then the unit is nats( natural unit).