Computer Network Questions and Answers

Answer: B

Correct answer: 250

Crossbars are dimensioned on the observation that only about a quarter of the crosspoints are needed at once, since not every input is active and each active one uses a single crosspoint. For 1000 crosspoints that is 250.

Answer: D

Correct answer: 8

A decoder activates exactly one output for each combination of its inputs, so \( n \) input lines give \( 2^{n} \) outputs. With three inputs that is \[ 2^{3} = 8. \] Such a device is called a 3-to-8 decoder. Its principal use is address decoding: the address lines of a processor are fed to a decoder whose outputs act as chip-select signals, so that exactly one memory or peripheral device responds to any given address. Decoders usually have an enable input, which allows several to be cascaded to decode a larger address space. The inverse device is an encoder, which takes \( 2^{n} \) inputs and produces an \( n \)-bit code. A priority encoder resolves the case of several inputs being active at once by responding to the highest, which is how interrupt controllers work. A related device is the seven-segment decoder, which converts a four-bit BCD digit into the seven signals that drive a display.

Answer: C

Correct answer: modem

Telephone lines, coaxial cable and microwave systems all carry the signal, so each is a transmission medium. A modem is equipment at the end of the medium, converting the signal so it can travel.

Answer: B

Correct answer: 47

In hexadecimal the digit F stands for 15, so \(2F_{16} = 2 \times 16 + 15 = 47\). Hexadecimal is convenient because each digit maps onto exactly four binary bits.

Answer: C

Correct answer: manchester encoding

Ethernet uses Manchester encoding: each bit is sent as a transition in the middle of its interval, so the receiver recovers the clock from the data itself and no separate timing signal is needed. The price is twice the bandwidth.

Answer: B

Correct answer: MAU

The Multistation Access Unit holds the relays that close the ring: a station's connection is switched in when it is powered and bypassed when it is not, so one dead station does not break the ring.

Answer: C

Correct answer: Addition and subtraction of headers

A transceiver sits at the physical layer: it transmits and receives the signal, monitors the line voltage and detects collisions. Building and stripping headers is the data link layer's work.

Answer: A

Correct answer: 24 Mbps

Nyquist's formula for a noiseless channel with four levels:

\[ C = 2B\log_{2}V = 2\times 6\times 10^{6}\times \log_{2}4 = 24\ \text{Mbps} \]

Answer: C

Correct answer: Line discipline

Line discipline is the part of the data link layer that settles who may transmit and who must listen, by enquiry and acknowledgement or by poll and select.

Answer: D

Correct answer: all of these

An Ethernet frame carries destination and source addresses, a type or length field, the data, and a checksum. All three named fields are present, so none of them can be the exception.