Sliding window protocol

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 get 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= ?

Comments

@Utkarsh , I think you have done some mistake while taking window size of 4.

Total no. of transmissions for GBN will be 26 and sequence will be like this :-

$1,2,3,4, (5*,6,7,8) ,5, (6*,7,8,9) ,6, (7*,8,9,10) ,7, (8*,9,10), 8,9, (10*), 10$

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Yes for go back n it should be 26

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@Mk Utkarsh bro could u once recheck what u wrote. I'm getting $26$ transmissions for $GBN$

Answer 1

In GBN,
First time 4,3,2,1 will be transmitted and received successfully.
Second time 8,7,6,5* will be transmitted and 5 will lost. so this along with the rest packets will be transmitted again.
Third Time 8,7,6*,5 will be transmitted and 6 will lost this time as it is the next fifth. So this along with the rest packets will be transmitted again.
Fourth time 9,8*,7,6 will be transmitted and 8 will lost as it is next fifth. so this along with the rest packets will be transmitted again.
Lastly 10,9,8 will be transmitted and reached successfully.
Therefore total 19 Transmissions in GBN.

In SR,
First time 4,3,2,1 will be transmitted and received successfully.
Second time 8,7,6,5* will be transmitted and 5 will lost and rest will reach. Third time 10,9* 5 will be transmitted and 9 will lost.
Lastly 9 will be transmitted and reaches successfully.
Therefore total 12 Transmissions in SR.

Then x+y = 31.

Comments

yeah 26 is correct for GBN and 12 for SR.

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Thanks so much.this helped a lot.

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in case of G0 BACK-N  ,i am getting 26 .

n case of SR   ,i am getting 12 .

total x+y=38

Answer 2

For GBN

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

* indicates every 5th packet.

Total 26.

Answer 3

31 is the correct answer

Comments

Wrong, you are recounting the frame which has been lost.

See explanation above the 5th packet will be 5,6,8 respectively.

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I am confused. Let me check again.

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your answer is totally wrong… @sumit