December 15th, 2007, 10:37 PM
How is corrupted TCP traffic dealt with?
I know about the three-way handshake to establish a TCP connection. If there are two hosts, "A" requesting information and "B" providing it, "A" sets the window size. Let's say that the window size will allow 3 frames to be transferred before "A" issues an ACK.
Assume that the connection has been establised and transfer of data occurs:
"B" sends frames 1, 2 and 3 to "A"
"A" sends an ACK, indicating that the next expected frame is 4
"B" sends frames 4, 5 and 6 to "A" but frame 5 is damaged
"A" sends an ACK, indicating that the next expected frame is 5 (rather than 7)
The question that I have is what happens next?
Does "B" send frames 5, 6 and 7 (even though 6 and 7 have been received by "A" correctly) and are the original frames 6 and 7 discarded?
When "A" sends the ACK, does it indicate that it only requires frame 5 and reduce the window size so that a further ACK will be issued after the single frame has been received correctly? If this happens, "A" will have to reassemble the data into the correct order and return the window size to what it was previously.
I hope that I've explained the question. I've done some googling but haven't come up with any solution. I guess that I could run a packet sniffer and look for retransmitted frames but that might be a long process going through the traffic to identify them.
Thanks for your time.
December 15th, 2007, 10:40 PM
IIRC it would just resend packet 5 and then continue with8,9, and 10 once it receives the ACK for 5.
December 15th, 2007, 11:10 PM
So does it mean that "A" reduces the window size to 1 and then back to 3 when frame 5 has been received correctly or is there something special about the request to resend a particular frame which doesn't need the window size to be changed?
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