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:
\[ C = 2B\log_{2}V = 2\times 6\times 10^{6}\times \log_{2}4 = 24\ \text{Mbps} \]
Please log in or register to report this question.
What is the maximum burst length on an 155.52 Mbps ATM ABR connection whose PCR value 200,000 and whose L value is 25 msec ?
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.
Please log in or register to report this question.
Poll/select line discipline requires what to identify the packet recipient ?
Answer: C
Correct answer: Address
In a poll/select discipline the primary addresses each transmission to a particular secondary, so every frame carries an address and each station acts only on the frames bearing its own.
Please log in or register to report this question.
In sliding window flow control, if window size is 63, what is the range of sequence numbers ?
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.
Please log in or register to report this question.
For a sliding window of size n-1 (n sequence numbers), there can be maximum of how many frames sent but unacknowledged ?
Answer: A
Correct answer: n -1
With n sequence numbers the window is limited to n−1 frames. If it were n, a completely lost set of acknowledgements would leave the receiver unable to tell a retransmission from a new frame.
Please log in or register to report this question.
Select incorrect statement in error retransmission used in continuous ARQ method
Answer: C
Correct answer: Go-back-N has better line utilization
Selective repeat retransmits only the frame that failed, whereas go-back-N retransmits it and everything sent after it, so selective repeat makes the better use of the line. It pays for that with more buffering at the receiver and more complex logic, which is what the other statements record.
Please log in or register to report this question.
Collision domain can be compared to which distance data travels between two stations ?
Answer: B
Correct answer: Maximum
The collision domain is bounded by the greatest distance a frame may travel and still be detected as a collision by the sender before it finishes transmitting. It is therefore a maximum distance, and it shrinks as the data rate rises.
Please log in or register to report this question.
How many crosspoints are needed in a single-stage switch with 40 inputs and 50 outputs ?
Answer: D
Correct answer: 2000
A single-stage crossbar needs one crosspoint for every input-output pair:
\[ 40\times 50 = 2000 \]
Please log in or register to report this question.
In a time - division switch, which governs the destination of a packet stored in RAM?
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.
Please log in or register to report this question.
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:
\[ \binom{10}{2} = 45 \]
Please log in or register to report this question.
