Upon receiving packet 4 the receiver starts sending duplicate acks so the sender would start the fast-retransmit process. A duplicate acknowledgment is sent when a receiver receives out-of-order packets (let say sequence 2-4-3). This solution works together with Fast Recovery, which halves the congestion window whenever 3 consecutive ACK delays are received.įast Recovery and Fast Retransmission prevent the Slow Start to execute and aims to keep the network in a non-congested state. DupACKs are part of a failure recovery mechanism called: TCP Fast retransmit, ensuring the reliability of TCP protocol.

Typically, this is triggered by the sender receiving three duplicate acknowledgments from the receiver for the same sequence number. The Fast Retransmission idea is also described as a strategy for retransmitting a TCP segment after 3 consecutive duplicated acknowledgments (ACKs). TCP Fast Retransmission The station sending data kicks off a retransmission immediately after detecting that the original packet was lost, instead of waiting the full retransmission timer. Also Wireshark capture shows 40 Bad TCP(retransmission and duplicate ack). Both algorithms are different and independent though, meaning that when congestion occurs at the network, TCP slowdowns its packet transmission rate and then invokes a slow start to get things working back again. For past month client were complain internet speed.after doing investigations. The Slow Start algorithm works in conjunction with the Congestion Avoidance solution.

The first is the Slow Start, the algorithm that runs observing that the rate at which new packets should be injected into the network is the rate at which the ACKs are returned by the other network end. The RFC 2001 presents the solutions for TCP implementations across the Internet to handle package transmissions.

Tcp fast retransmission wireshark