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Station A needs to send a message consisting of 15 packets to station ‘B’ using a sling window (window size 4) and go-back-N error control strategy. All packets are ready and immediately available for transmission. If every 6th packet that ‘A’ transmits gets lost (but no Acks from ‘B’ ever gets lost), then what is the number of packets that ‘A’ will transmit for sending the message to ‘B’ ?
(a) 29

(b) 33

(c) 27

(d) 25

3 Answers

Best answer
13 votes
13 votes

Since every 6th packet get lost : packets will be send like shown below

1 2 3 4 5 6 (lost) 7 8 9

                6 7 8 (lost) 9 10 11

                      8 9 10(lost) 11 12 13

                              10 11 12 (lost) 13 14 15 

                                         12 13 14(lost) 15

                                                    14 15

So , Total 33 packets . option B

selected by
7 votes
7 votes
1 2 3 4 5 6 7 8 9 6 7 8 9 10 11 8 9 10 11 12 13 10 11 12 13 14 15 12 13 14 15 14 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

$\Rightarrow\color{Red}{33}$

0 votes
0 votes
Answer is (b).

Assuming:
Number packets from 0 to 14.
(x) -> x packet is dropped.

0-1-2-3-4-(5)-6-7-8-5-6-(7)-8-9-10-7-8-(9)-10-11-12-9-10-(11)-12-13-14-11-12-(13)-14-13-14

Number of packets are 33.

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