Why does TCP sometimes not acknowledge the packets it receives?

Posted by misteryes on Super User See other posts from Super User or by misteryes
Published on 2013-06-19T20:32:42Z Indexed on 2013/06/28 10:24 UTC
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networking

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tcp

I use firefox to visit a web server running on a computer on my LAN. I notice that sometimes TCP doesn't acknowledge the packets it receives. For example, in the following captured packets:

https://docs.google.com/file/d/0B-LaBUj9KtQhS0RYNXF1RjZTa2M/edit?usp=sharing

the 7th 9th and 11th packets are duplicated ACK, the browser receives TCP packets 6,8 and 10, but the browser TCP stack doesn't acknowledge the received packets, why?

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