In TCP, every transmitted byte has an identifier. The concept of re-transmission is simple: data that was sent, was sent again. Senders should Fast Retransmit upon receipt of 3 Receive some packets which sequence number are bigger than theĪcknowledged packets. TCP Fast Retransmission - Occurs when the sender retransmits a packet before the expiration of the acknowledgement timer. TCP Retransmission - Occurs when the sender retransmits a packet after the expiration of the acknowledgement. Wireshark will detect and trigger display of interesting events for When this feature is enabled the sliding window monitoring inside Requirements of Wireshark but can be disabled if required. This feature should not impact too much on the run-time memory Measurements of packet-loss and retransmissions than is available inĪny other protocol analyzer. This allows much better and more accurate Some extra state information and memory to be kept by the dissectorīut allows much better detection of interesting TCP events such as , _retransmission and _retransmission, for the general case of packet loss check for _lost_segmentīy default Wireshark and TShark will keep track of all TCP sessionsĪnd implement its own crude version of Sliding_Windows.

In wireshark several filters can be applied to capture all types of inconsistencies in sequence numbers i.e.

The next expected sequence number is greater than the current sequence numberīeside TCP Retransmission this there is also TCP Spurious Retransmission and TCP Fast Retransmissionīasically a retransmission is only necessary if a package is lost.įor detecting this type of fault in wireshark the filter _lost_segment is used.

In the forward direction, the segment length is greater than zero or the SYN or FIN flag is set.

If the sequence number is higher than expected the packet is a retransmitted one ( TCP Analysis chapter of the wireshark docs,

For detecting a retransmission you have to keep track of the expected sequence number.

Tcp spurious retransmission wireshark