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Reason for delay in Fast-Retransmission from Server

Hi Everyone,

I am trying to understand that after receiving 3 DUP ACKS from the client a few times, why Server sent the TCP Retransmission very late.

In Frame 531 we can see that the next sequence from the Server should be 499853 but the server sends a higher sequence number 501265 and TCP says that the previous segment is not captured. In frame 534, the Client sends the ACK 499583 and in 535, it sends the same ACK value 499853 as DUP ACK.

Then again, the Client sent 4 DUP ACKS starting 544-547. In Frame 548 again sent a higher sequence number of 516797. The client sent 3 Dup ACKS starting 551-553 and the server again sent a higher sequence number of 521033.

Finally, the client again sent 3 DUP ACKS from 557-559 and the Server sent the sequence number of 499583 as TCP FAST RETRANSMISSION in frame 560.

Can anyone explain to me the reason that why Server did not send the segment starting 499583 in frame 548 and rather it was sent in 560. I understand as per the Congestion algorithm Fast Retransmission should have been done as soon as 3 DUP ACKs were received.

I appreciate any insight on the same. Below is the link for the PCAP:-

https://easyupload.io/jzl28b

Reason for delay in Fast-Retransmission from Server

Hi Everyone,

I am trying to understand that after receiving 3 DUP ACKS from the client a few times, why Server sent the TCP Retransmission very late.

In Frame 531 we can see that the next sequence from the Server should be 499853 but the server sends a higher sequence number 501265 and TCP says that the previous segment is not captured. In frame 534, the Client sends the ACK 499583 and in 535, it sends the same ACK value 499853 as DUP ACK.

Then again, the Client sent 4 DUP ACKS starting 544-547. In Frame 548 again sent a higher sequence number of 516797. The client sent 3 Dup ACKS starting 551-553 and the server again sent a higher sequence number of 521033.

Finally, the client again sent 3 DUP ACKS from 557-559 and the Server sent the sequence number of 499583 as TCP FAST RETRANSMISSION in frame 560.

Can anyone explain to me the reason that why Server did not send the segment starting 499583 in frame 548 and rather it was sent in 560. I understand as per the Congestion algorithm Fast Retransmission should have been done as soon as 3 DUP ACKs were received.

I appreciate any insight on the same. Below is the link for the PCAP:-

https://easyupload.io/jzl28b

Password for the file - [email protected]