TCP-DCR: MAKING TCP ROBUST TO NON-CONGESTION LOSSES Sumitha Bhandarkar and A. L. Narasimha Reddy {sumitha,reddy}@ee.tam

1. Congestion Response Delay Timer End-to-End RTT No Retransmission or Window Reduction Wireless Link RTT Congestion Response Delay Timer Cancelled Sender 1 2 3 4 5 6 7 8 9 Base Station … Receiver 2 2 2 2 6 7 8 9 10 Link Level Retransmission of Packet 2 Packet Lost on Wireless Link Congestion Response Delay Timer End-to-End RTT No Retransmission or Window Reduction Congestion Response Delay Timer Cancelled 7 8 9 10 11 1 2 3 4 5 6 Sender … Receiver 2 2 2 2 2 7 8 9 10 11 12 Packet Delayed Causing Reordering Conclusions and Future Work • Simple, easy to implement, low overhead. • Packets reordered/delayed by more than  cannot be recovered. • Analyze the stability more rigorously. • One unified solution for a number of problems. • End-to-end semantics of TCP maintained. • Evaluate our current Linux implementation. We would like to thank Dr. Nitin Vaidya and Nauzad Sadry for their invaluable contributions towards evaluating TCP-DCR in wireless networks. More info at: http://ece.tamu.edu/techpubs/2003/TAMU-ECE-2003-04.pdf TCP-DCR: MAKING TCP ROBUST TO NON-CONGESTION LOSSESSumitha Bhandarkar and A. L. Narasimha Reddy {sumitha,reddy}@ee.tamu.edu Texas A&M University General Problem Application 2 : Wireless Channel Errors Results With No Non-Congestion Losses Loss of TCP Throughput for Non-congestion Events • Rely on local recovery through link level retransmission. • Delay of  = 1 RTT (> wireless link delay) sufficient for link level recovery • Delay of  = 1 RTT (< TCP RTO) avoids retransmission timeouts • TCP-DCR Behavior for Wireless Networks Proposed Solution(TCP-DCR) • Delay the congestion response for a short interval of time . • Allows underlying mechanisms to handle non-congestion events. • At the end of , treat unrecovered loss as a normal congestion event. • Retransmission Timer (RTO) limits delay to about 1 RTT. • Steady state analysis shows throughput is TCP-Friendly. Application 1 : Packet reordering • Packet reordering in Multipath routing, Parallel routers  TCP problems • TCP-DCR tolerates reordering delay upto . • Delay of  = 1 RTT (< TCP RTO) avoids retransmission timeouts • TCP-DCR Behavior for Packet Reordering Sample Result Sample Result