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Re: Question about ACK number
From: Sake Blok <sake () euronet nl>
Date: Mon, 15 Apr 2013 09:25:09 +0200

Hello Amit,

Yes, this is normal. Before the data stream and after the data stream, there is 1 phantom byte. So the first data 
packets has a sequence number that is 1 higher than the initial sequence number and after the FIN, there is also one 
phantom byte. This makes it possible to make a certain that the FIN was seen and not just the last data byte.

See the RFC at http://tools.ietf.org/html/rfc793

Cheers,
Sake


On 15 apr 2013, at 09:10, Amit Aggarwal wrote:

Hello,
 
Please help to comment about ACK calculation in below scenario.
 
Frame100: Client ACKs the data received till now..  ACK= 10000
 
Frame 101:  Server sends client TCP Data ( 924 bytes) with FIN,PSH and ACK flags set.
 
Frame 102: Client sends ACK= 10925    à QUESTION ..Why is client sending 10925 and not 10924 .. Is it adding 1 for 
FIN received in Frame 101 ..?  Is it normal ?
 
Frame 103:  Client sends FIN,ACK == ACK = 10925
 
Best Regards
Amit
 
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