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Last Modified: 2012-05-06
I am confused by the explanation of this book:


It's at the part when it says "For example, suppose LFR = 5 ......"

My confusion is that why is it when frame 6 arrived then the receiver acknowledges frame 8. Why is it frame 8 and not 7? What does acknowledges here mean?
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The ack for frame 8 means it has successfully received all frames up to 8. That way it isn't sending one ack for every packet received.


you mean for every frame received?

it is saying that after the last frame received was 5, 7 and 8 are received out of order and then 6 arrives at wich point the receiver sends an ACK where LFR = 8 indicating that the last frame received is 8. Even though they were out of order they are buffered an re-sequenced as long as the timer doesn't expire.

hope this helps,



so although the 6 came in late, the LFR is still 8 not 6?
6, 7, and 8 are in the buffer so the next frame needed is 9, LFR = 8 re-inforces that, if LFR = 6 the sender would resend 7 and 8 but that is unecessary because they are already in the buffer.

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ok.. I think I got it now...

glad to help,
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