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edited | 121 views

+1 vote

20 transmissions are required.

1 2 3 4 5 6 7 8 4 5 6 7 8 9 10 7 8 9 10 10

lost                  lost                lost

Numbers in bold indicate the lost packets. In GBN, even if first packet is lost, entire window is to be retransmitted as the corresponding packets in the window at that instant are also lost.

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Thanks
+1 vote

even best answer is also wrong

$1 2 3 {\color{Red} 4 5 6 7 {\color{Red} 8}}$

here first packet lost is 4th and next packet lost is 8th but sender do not notice it ( that is packet 8th is lost ) because as  soon as sender did not get the ack of 4th packet he will start sending the packet again from 4th

that is

$4 5 6{\color{Red} 7} 8 9$ $10$

now 7th packet will lost

so again sending

${\color{Red} 7} 8 9$ $10$

again  ${\color{Red} 7} 8 9$ $10$ this process repeat forever

edited
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Exactly I was thinking.

20 Packet need re-transmission.

Blue Marked - indicate current window packet.
1 2 3 45678  Go Back N in window from last transmitted packet. N = 5 Here

1 2 3 4 5 6 7 8 4 5 6 7 8 9 10  Go Back N in window from last transmitted packet. Here N != 5 , Then Go Back N , where N = current window size

1 2 3 4 5 6 7 8 4 5 6 7 8 9 10 7 8 9 10 Go Back N in window from last transmitted packet. Here N = current window size

1 2 3 4 5 6 7 8 4 5 6 7 8 9 10 7 8 9 10 10 Final Transmitted Packets