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A 3000-km-long T1 trunk is used to transmit 64-byte frames using Protocol GO back  N. If the
propagation speed is 6 μsec/km, how many bits should the sequence numbers be?(refer Tanenbaum)
in Computer Networks by Boss (10.5k points)
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The max window size could be N=1+2a

[it means 100% efficiency]

Bandwidth of T1 trunk=1.544 Mbits/sec

Ref-https://en.wikipedia.org/wiki/T-carrier

Transmission Delay($T_{t}$)=$\frac{Length-of-Frame}{Bandwidth}=\frac{64*8}{1.544*10^6}=0.331 ms$

Propagation delay

for 1 KM distance the propagation delay is 6 μsec

for 3000 KM propagation delay=$\frac{6*3000}{10^6}$=18 ms

$a=\frac{T_{p}}{T_{t}}=\frac{10}{0.331}=54.3$

1+2a=1+2*54.3=110

No. of bits in sequence number=$log_{2}110$=7

by Active (5k points)

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