Which of the following is not a transceiver function?
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.
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Television channels are 6 MHz. How many bits can be sent if four level digital signals are used (assume a noiseless channel)?
Answer: A
Correct answer: 24 Mbps
Nyquist's formula for a noiseless channel with four levels:
\[ C = 2B\log_{2}V = 2\times 6\times 10^{6}\times \log_{2}4 = 24\ \text{Mbps} \]
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Which of the following decides the role (sender or receiver) of a device on a network ?
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.
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A field in the Ethernet message packet is
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.
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The number of cross-points needed for 10 lines in a cross-point switch which is full duplex in nature and there are no self connection, is
Answer: B
Correct answer: 45
One full-duplex line serves both directions between a pair, and no line joins a station to itself:
\[ \binom{10}{2} = 45 \]
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Which of the following is a time - division switch?
Answer: D
Correct answer: both (a) and (b)
A time-slot interchanger and a TDM bus both switch by moving samples between time slots rather than by making a physical path, so both are time-division switches. A crosspoint makes a path and is space-division.
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In a broad sense, a railway track is an example of
Answer: B
Correct answer: half-duplex
A single railway track carries traffic both ways but only one way at a time, which is the definition of half duplex.
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A combinational circuit contains memory, so its output depends on past inputs as well as the present ones.
Answer: A
Correct answer: False
A combinational circuit has no memory: its output at any moment is determined entirely by the inputs present at that moment. Circuits whose output also depends on past inputs are sequential, and they achieve it with flip-flops.
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Which among the following signal is not standard RS-232-C signal?
Answer: A
Correct answer: VDR
RTS, CTS and DSR are all RS-232-C control signals - request to send, clear to send and data set ready. VDR is not among the standard's signals.
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The power dissipation, PD, of a logic gate is the product of the ________.
Answer: B
Correct answer: dc supply voltage and the average supply current
Power dissipation is
\[ P_D = V_{CC}\times I_{CC(avg)} \]
The average current is used because the current drawn varies as the gate switches; the peak value would overstate the power, and the supply is dc, not ac.
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