Computer Network Questions and Answers

Answer: C

Correct answer: placing a telephone call prior to a conversion

A virtual circuit is set up before any data flows and torn down afterwards, so the route is fixed for the duration - exactly as dialling establishes a path before the conversation begins. Nothing is physically switched into place, which is what makes the circuit virtual.

Answer: D

Correct answer: 93 db

Shannon's formula gives the required signal-to-noise ratio from the capacity and bandwidth:

\[ 1.544\times 10^{6} = 50{,}000\log_{2}\!\left(1+\frac{S}{N}\right) \Rightarrow \frac{S}{N} \approx 2^{31} \]

and \( 10\log_{10}(2^{31}) \approx 93\ \text{dB} \) - a ratio no real line could sustain, which is why T1 is not carried this way.

Answer: A

Correct answer: 0 to 63

A window of 63 requires 64 distinct sequence numbers, one more than the window, so that a full window cannot be confused with an empty one. Numbering from 0 gives the range 0 to 63.

Answer: C

Correct answer: presentation layer

The presentation layer deals with the representation of data - character encoding, compression and encryption - so that the two ends interpret it the same way. Encryption may also be applied elsewhere in practice, but in the OSI model it belongs here.

Answer: B

Correct answer: 1 / K - P

If each transmission fails with probability p independently, the number of attempts is geometric and its mean is \( 1/(1-p) \). The expression given is that quantity written with the question's own symbols.

Answer: A

Correct answer: source routing

In IBM's Token Ring the sending station discovers and carries the whole route in the frame, so the bridges simply follow the directions given rather than deciding for themselves. That is source routing, and it is what distinguishes Token Ring bridging from Ethernet's transparent bridging.

Answer: B

Correct answer: True

The statement is true. An OR gate outputs 1 when any of its inputs is 1, and 0 only when every input is 0. Its Boolean expression is \( Y = A + B \). Its truth table for two inputs runs: 0,0 gives 0; 0,1 gives 1; 1,0 gives 1; 1,1 gives 1. Only the first row gives 0, which is why the OR gate is sometimes described by what makes it low rather than what makes it high. The contrast is with the AND gate, whose output is 1 only when all inputs are 1, expressed as \( Y = A \cdot B \). The gate to distinguish it from is XOR, exclusive OR, whose output is 1 when the inputs differ - so 1,1 gives 0 rather than 1. The ordinary OR is sometimes called inclusive OR for that reason. Note that the symbol \( + \) in Boolean algebra means OR, not addition, so \( 1 + 1 = 1 \).

Answer: D

Correct answer: Either (b) or (c)

Both RS-232-C and RS-449 are physical-layer standards for the interface between a terminal and a modem; RS-449 was introduced to carry higher rates over longer distances, but either will serve.

Answer: C

Correct answer: the hubs

SNMP management is put where the traffic converges, so the agent is fitted to the hub, which sees every port on its segment. Putting it on a single node or PC would show only that machine's view.

Answer: B

Correct answer: True

NAND is functionally complete: a NOT is a NAND with its inputs tied together, an AND is a NAND followed by that inverter, and an OR follows from De Morgan’s theorem. NOR is the other functionally complete gate.