Computer Network Questions and Answers

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.

Answer: D

Correct answer: all four inputs

AND requires every input to be HIGH; a single LOW input forces the output LOW however many other inputs are HIGH.

Answer: D

Correct answer: transponders

A communication satellite carries a set of transponders, each of which receives on one frequency, amplifies, shifts the signal to another frequency and retransmits it. Each transponder is in effect one repeater in the sky.

Answer: D

Correct answer: Control unit

In a time-division switch the samples sit in RAM and the control unit decides the order in which they are read out, which is what determines where each one goes. The memory holds the data; the control unit does the switching.

Answer: A

Correct answer: binary digit

Bit is a contraction of binary digit. The word was coined by John Tukey in 1947 and popularised by Claude Shannon in his 1948 paper founding information theory. A bit is the smallest unit of information: it distinguishes between exactly two possibilities, and in a circuit it is a single high or low voltage. The units built on it are worth keeping straight. Four bits make a nibble, which corresponds to one hexadecimal digit. Eight bits make a byte, giving 256 values. A word is whatever width the processor handles naturally - 32 or 64 bits on modern machines - so it is architecture-dependent rather than fixed. A distinction that causes constant confusion in practice: network speeds are quoted in bits per second and file sizes in bytes, and the abbreviations differ only in case - Mb for megabit, MB for megabyte. A 100 Mbps link therefore transfers about 12.5 MB per second.

Answer: A

Correct answer: Does not require global time synchronization

Pure ALOHA lets a station transmit the moment it has data, so no station needs to know where any slot boundary lies. Slotted ALOHA gains throughput precisely by imposing that synchronisation.