On Making TCP More Robust To Packet Reordering

Previous research indicates that packet reordering is not a rare event on some Internet paths. Reordering can cause performance problems for TCP’s fast retransmission al-gorithm, which uses the arrival of duplicate acknowl-edgments to detect segment loss. Duplicate acknowl-edgments can be caused by the loss of a segment or by the reordering of segments by the network. In this pa-per we illustrate the impact of reordering on TCP perfor-mance. In addition, we show the performance of a con-servative approach to “undo ” the congestion control state changes made in conjunction with spurious retransmis-sions. Finally, we propose several alternatives to dynami-cally make the fast retransmission algorithm more tolerant of the reordering observed in the network and assess these algorithms.