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Frames of 1000 bits are sent over a 1-Mbps channel using a geostationary satellite
whose propagation time from the earth is 270 msec. Acknowledgements are always
piggybacked onto data frames. The headers are very short. Three-bit sequence numbers
are used. What is the maximum achievable channel utilization for
(a) Stop-and-wait?
(b) go back n?
(c) selective repeat?
in Computer Networks by Boss (10.5k points) | 103 views

2 Answers

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where L is the frame size

BW is bandwidth

Tt and Tp are transmission delay and propagation delay respectively

by (133 points)
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L=1000 bits

B=1 Mbits/sec

Transmission Delay($T_{t}$)=$\frac{1000}{1*10^6}$=1 ms

Prpagation Delay($T_{p}$)=270 ms

a=$\frac{T_{p}}{T_{t}}=\frac{270}{1}$=270

Frame sequence number=3 bits

(a)  Stop & Wait Protocol

      Channel Utilization/Efficiency=$\frac{1}{1+2a}$=0.18 %

(b) Go-Back-N Protocol

    in GBN, window size of sender=$2^m-1$ where m=sequence number bits

    N=$2^3-1$=7

    Channel Utilization/Efficiency=$\frac{N}{1+2a}$=1.29%

(c) Selective Repeat Protocol

     Window size of sender=window size of receiver=half the available sequence numbers=$2^m/2=2^3/2=4$

     N=4

    Channel Utilization/Efficiency=$\frac{N}{1+2a}$=0.74%
by Active (5k points)

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