Computer Network Questions and Answers

Answer: A

Correct answer: True

The statement is true, and it is the standard distinction between the two. A latch is transparent while its enable input is at the active level: as long as the enable is high, changes at the data input pass straight through to the output. A flip-flop responds only at the instant the clock changes - on the rising or falling edge - and ignores its input at every other moment. That difference matters greatly in synchronous design. Because a flip-flop samples at a single instant, its output is stable for a whole clock period, which makes timing analysis tractable: one need only check that data arrives before the setup time and holds past the hold time. A latch’s transparency window makes the same analysis far harder and can allow a signal to race through two stages in one cycle. Latches are still used where their transparency is wanted, and internally a flip-flop is often built as two latches in a master-slave arrangement.

Answer: C

Correct answer: UUCP

UUCP - Unix to Unix Copy - copies files between machines over a single link, and was the basis of early mail and news distribution. TFTP is a trivial transfer protocol and UART is a hardware device.

Answer: D

Correct answer: 2000

A single-stage crossbar needs one crosspoint for every input-output pair:

\[ 40\times 50 = 2000 \]

Answer: C

Correct answer: 8-12

Digits 8 to 12 identify the terminal, following the four-digit DNIC and the three-digit area code.

Answer: B

Correct answer: 12 cells

The burst is limited by the interval L and the peak cell rate, and the excess over what the line itself would deliver in that time works out at 12 cells for the figures given.

Answer: C

Correct answer: Poll

A secondary never transmits unbidden. It sends data only in response to a poll - the primary's invitation to do so. Select is the opposite direction, the primary announcing that it has data to send.

Answer: A

Correct answer: computer bus

A computer's internal bus runs at rates no external line approaches: it is short, parallel and driven at the processor's own clock. Telephone and leased lines are limited by the distance they must cover and by the medium available.

Answer: C

Correct answer: \( A + A = A \)

The idempotent law states that combining a variable with itself changes nothing: \[ A + A = A, \qquad A \cdot A = A. \] This is one of the clearest departures from ordinary arithmetic, where \( A + A = 2A \) and \( A \cdot A = A^{2} \). In a two-valued algebra there is no 2 and no square, so the operation simply returns the value unchanged. The other options are the remaining basic identities, each with its own name. \( A + \bar{A} = 1 \) is the complement law, with dual \( A \cdot \bar{A} = 0 \). \( A + 0 = A \) is the identity law, with dual \( A \cdot 1 = A \). And \( A + 1 = 1 \) is the null or annulment law, with dual \( A \cdot 0 = 0 \). Each pair is a dual of the other, obtained by exchanging AND with OR and 0 with 1 - a symmetry that runs through the whole of Boolean algebra and halves the amount to be memorised.

Answer: A

Correct answer: 625

Each line needs one write and one read per frame, so two memory accesses of 100 ns, and the whole frame period is available:

\[ \frac{125\ \mu\text{s}}{2\times 100\ \text{ns}} = \frac{125\times 10^{-6}}{2\times 10^{-7}} = 625 \]

Answer: C

Correct answer: multiplexer

A multiplexer combines several input streams onto one line and separates them again at the far end. A concentrator also shares a line but buffers and forwards rather than dividing it into fixed channels.