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Posted on 2009-02-12
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I am confused by the explanation of this book:

http://books.google.com/books?id=XUkIKfJbFCUC&pg=PA103&lpg=PA103&dq=Frames+7+and+8+are+said+to+have+arrived+out+of+order&source=bl&ots=U9P8EsOUEh&sig=qeGnTxdIjB7xqumhSrg_MCT6rT4&hl=en&ei=ZHKUSdrXCNPGtgfq6JGkCw&sa=X&oi=book_result&resnum=1&ct=result#PPA103,M1

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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Question by:kuntilanak
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Expert Comment

by:Rick_O_Shay
ID: 23627377
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.
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Author Comment

by:kuntilanak
ID: 23628003
you mean for every frame received?
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Expert Comment

by:decoleur
ID: 23629856
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
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Author Comment

by:kuntilanak
ID: 23629884
so although the 6 came in late, the LFR is still 8 not 6?
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decoleur earned 2000 total points
ID: 23629942
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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Author Comment

by:kuntilanak
ID: 23629947
ok.. I think I got it now...
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Expert Comment

by:decoleur
ID: 23630018
glad to help,
-t
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