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Compute the fraction of the bandwidth that is wasted on overhead (headers and retransmissions)
for protocol selective repeat on a heavily loaded 50-kbps satellite channel with data
frames consisting of 40 header and 3960 data bits. Assume that the signal propagation
time from the earth to the satellite is 270 msec. ACK frames never occur. NAK frames
are 40 bits. The error rate for data frames is 1%, and the error rate for NAK frames is
negligible. The sequence numbers are 8 bits.
asked in Computer Networks by Loyal (9.7k points) | 25 views

1 Answer

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With a 50-kbps channel and 8-bit sequence numbers, the pipe is always full. The number of retransmissions per frame is about 0.01. Each good frame wastes 40 header bits, plus 1% of 4000 bits (retransmission), plus a 40-bit NAK once every 100 frames. The total overhead is 80.4 bits per 3960 data bits, giving 80.4/(3960 + 80.4) = 1.99%.
answered by (11 points)

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