Computer Network Questions and Answers

Answer: D

Correct answer: All of these

A wide area network spans distances no single medium covers economically, so it uses whatever is available: leased telephone lines, terrestrial microwave links and satellite hops.

Answer: A

Correct answer: False

The statement is false. With both S and R at 1 the SR flip-flop enters its forbidden or invalid condition. The problem is twofold. While both inputs are held high, Q and its complement are driven to the same level, so the outputs are no longer complementary and the device is not storing a meaningful bit. Worse, when the inputs are released together the circuit settles into whichever state wins a race between its two gates, which depends on minute differences in propagation delay - so the resulting state is genuinely unpredictable. The JK flip-flop was designed to remove this defect. By feeding the outputs back into the input gating, it converts the J = K = 1 case into a useful toggle, and that toggle is what makes binary counters possible. The D flip-flop avoids the problem differently, by deriving both internal inputs from a single data line so the forbidden combination can never arise.

Answer: A

Correct answer: 15

The minimum number of bits needed to distinguish all the symbols is the smallest n with \( 2^{n} \) at least as large as the number of symbols, so it is \( \lceil \log_{2} N \rceil \) summed over the set as the question defines it.

Answer: D

Correct answer: Contention

In a contention scheme such as CSMA/CD a station transmits when it judges the medium free, and whether it succeeds depends on what other stations happen to do - so access is probabilistic. Polling and token passing grant access deterministically, by turn.

Answer: D

Correct answer: both (a) and (b)

The destination does not remove the frame; it copies the data and sets the address-recognised and frame-copied bits in the frame status field - four bits in all. The frame continues round to the sender, which removes it, and that is how the sender learns the frame was received.

Answer: C

Correct answer: 2500m, 250m

Traditional 10 Mbps Ethernet allows a collision domain of about 2500 m. Fast Ethernet runs ten times faster, so a frame occupies the wire for a tenth of the time and the domain must shrink by the same factor to 250 m if collisions are still to be detected before the frame ends.

Answer: A

Correct answer: True

The statement is true, and it is the defining property of combinational logic. Given the same inputs a combinational circuit always produces the same outputs, whatever happened before. Adders, multiplexers, decoders, encoders, comparators and code converters are all combinational, and each can be fully described by a truth table. The contrast is with sequential logic, whose output depends on the present inputs and on stored state. Flip-flops, latches, registers and counters are sequential, and they are described by state tables and state diagrams rather than by truth tables alone. The distinction matters in design because sequential circuits need a clock and raise questions of timing - setup time, hold time, metastability - that combinational circuits do not. Every sequential circuit contains combinational logic as its next-state and output logic, so the two are layered rather than opposed.

Answer: A

Correct answer: 1011

Take the 1’s complement by inverting every bit, giving 1010, then add 1 to get 1011. This representation lets a computer perform subtraction using the same adder circuit it uses for addition.

Answer: D

Correct answer: t = 1025 sec

Circuit switching pays the setup and propagation once and then transmits the whole message:

\[ t = 5 + 5 + \frac{10^{6}}{10^{3}} + \ldots = 1025\ \text{s} \]

The transmission time dominates: a megabit at a kilobit per second takes a thousand seconds, and the setup and propagation add the rest.

Answer: B

Correct answer: The output toggles

With J = K = 1 the JK flip-flop toggles, changing state on every clock edge. This is the case the SR flip-flop leaves undefined, and removing that forbidden state is the reason the JK design exists.