Madeesasy work book

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 what are the values of x and y?

for GBN i am getting 26 but it is given as 19….please check

Comments

oh yes, i'm too getting 26. and i think 26 is correct. let's see what others have to say about it.

actually, they have calculated taking into account the the GBN is using cumulative acknowledgement for which answer is 19.

how we have calculated is individual acknowledgement, for which answer is 26.

GBN uses both.

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WHICH ONE IS CORRECT?

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how it comes to be 19 using cumulative ack, it is repeated for 2 times, then the answer has to be even.

for GBN, using individual ack, answer is 13, hence for 2 different time it will be 26.