TCP Excessive Retransmissions
This occurs when a sequence number is either identical to a previous sequence number, or is less than a previous sequence number. This indicates that the packet is a duplicate of one previously sent. TCP retransmissions occur for a number of reasons, including the sending station did not receive an acknowledgment, the packet was lost, dropped or otherwise missing. The event is displayed when the percentage of retransmitted packets (by application and address pair) is above the critical value set in the Expert Thresholds. This value is the sum of all identified events in the TCP Events display.
Possible reasons for the event:
The receiving station was too busy to respond to the sending station.
Network traffic load was so high the original packet was lost, or the ACK was never received due to the high utilization.
A router dropped the packet, or was unable to forward the packet. This could be because the router is too busy, or is malfunctioning.
Bad cabling or a failing switch/hub is causing an intermittent network failure.