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# sliding window question

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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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Commented:
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.

Commented:
you mean for every frame received?

Commented:
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,

-t

Commented:
so although the 6 came in late, the LFR is still 8 not 6?
Commented:
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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Commented:
ok.. I think I got it now...

Commented:
-t
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