computer networks

Question

Station A needs to send a message consisting of 10 packets to station B using a sliding window of size 4. All packets are ready and can be transferred immediately. Selective repeat and GBN are used at 2 different times and every 5th packet get lost for both protocols. (ACK’s from B never gets lost). Let x and y be the number of transmissions that A has to make in selective repeat and GBN respectively to ensure safe delivery to B. Then x+y = ?

Ans given=31...........but i got 38(x=12 and y=26)

Comments

I think next 4 packets won't be resent rather all outstanding packets will be resent.

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@dileshwar sahu. You are correct

1  2  3  4  5  6  7  8  5  9  10  9 ------------------------- so x = 12

1  2  3  4  5  6  7  8  5  6  7  8  9  6  7  8  9  10  7  8  9  10  8  9  10  10 -------------------------- so y=26 

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yes i'm also getting x=12, y=26.

Answer 1

Answer 31 is correct as 1,2,3,4,5,6,7,8,5,6,7,8,6,7,8,9,8,9,10 resulting in 19 packets so 12 plus 19 equals 31

Comments

please explain in detail

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Window size is given as 4 and you put only 3 packets where 2 nd lost occurred wrong answer plz correct it