Wireshark TCP sequence analysis
Wireshark has a built-in filter, tcp.analysys.flags, that will show you packets that have some kind of expert message from Wireshark; tcp.analysis.flags is shown in the TCP section of the Packet Details pane. Under that, expand SEQ/ACK analysis then expand TCP Analysis Flags. This will tell you exactly what triggered tcp.analysis.flags. A few examples include:
TCP Retransmission
TCP Fast Retransmission
TCP DupACK
TCP ZeroWindow
TCP ZeroWindowProbe
TCP retransmission
TCP makes the transmission of segments reliable via sequence number and acknowledgement. When TCP transmits a segment containing data, it puts a copy on a retransmission queue and starts a timer; when the acknowledgment for that data is received, the segment is deleted from the queue. If the acknowledgment is not received before the timer runs out, the segment is retransmitted. During TCP retransmission, the sequence number is not changed until the retransmission timeout happens.
Open the example tcp-retransmission...