# Station A needs to send a message consisting of 9

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Station A needs to send a message consisting of 9 packets to Station B using a  sliding window (window size 3) and go-back-n error control strategy. All packets are ready and immediately available for transmission. If every 5th packet that A transmits gets lost (but no acks from B ever get lost), then what is the number of packets that A will transmit for sending the message to B?
(A) 12
(B) 14
(C) 16
(D) 18

Ravi Garg edited question

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Ravindra Reddy (anonymous)

1,2,3,4,5,6,7[Time out],5,6,7,8,9[Time out],7,8,9,9

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Prasanna Lakshmi (anonymous)

is it b??

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Ravindra Reddy (anonymous)

16 is the answer m sure our coachin teacher solved it this question haunted me a lot

1234567 timme out since window size is 3 it can have 3 unacknowl frames therfore even 5 acknow. doesnt arrive 6n7 are sent and after 7 is sent timer for 5 expires causing it to send 567 in its window

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Sonali Kapoor (anonymous)
```Sender      Receiver
1
2            1
3            2
4            3
5            4
6
7            6
7
[Timeout for 5]

5
6            5
7            6
8
9
8
9
[Timeout for 7]

7
8            7
9            8

[Timeout for 9]
9
9```