When TCP Friendliness Becomes Harmful Amit Mondal Aleksandar Kuzmanovic Northwestern University

A. Mondal When TCP Friendliness Becomes Harmful 2 Introduction Internet was designed for throughput – TCP probes for available b/w even if it causes packet losses – Interactive applications suffer! Telnet, ssh, games, chat all use TCP Telnet delay from typed character until echo – Includes transmission, propagation and queuing delay – It loss, TCP retransmits

A. Mondal When TCP Friendliness Becomes Harmful 3 data packets dummy packets strict priority TCP-fair rate Upgrading mice to elephants Padding misbehavior

A. Mondal When TCP Friendliness Becomes Harmful 4 Outline Source of the problem Related work Implication Padding-induced response time gain Sustainable countermeasures Conclusion

A. Mondal When TCP Friendliness Becomes Harmful 5 Outline Source of the problem Related work Implication Padding-induced response time gain Sustainable countermeasures Conclusion

A. Mondal When TCP Friendliness Becomes Harmful 6 Source of the problem How TCP detects packet loss? –Retransmission Timeout (RTO) (1 second) –Triple duplicate acknowledgment/Fast retransmit (~ ms ) How does it affect interactive applications? –Burst size (~ 1-2 packets) –Inter-burst time (~ seconds) Packet loss is detected by timeout, which degrades the response time in orders of magnitude

A. Mondal When TCP Friendliness Becomes Harmful 7 A deeper look RTO improvement A B CD Incentive for misbehavior!

A. Mondal When TCP Friendliness Becomes Harmful 8 Outline Source of the problem Related work Implication Padding-induced response time gain Sustainable countermeasures Conclusion

A. Mondal When TCP Friendliness Becomes Harmful 9 Related Work Packet marking & differential dropping [ Guo and Matta 01 ] Service differentiation [ Noureddine and Tobagi 02 ] Differential Congestion Notification [ Le et al. 04] Explicit congestion notification [Floyd 94] TCP smart framing [ Mellia et al. 05 ]

A. Mondal When TCP Friendliness Becomes Harmful 10 Outline Source of the problem Related work Implication Padding-induced response time gain Sustainable countermeasures Conclusion

A. Mondal When TCP Friendliness Becomes Harmful 11 Implication Packet switched => Circuit switched

A. Mondal When TCP Friendliness Becomes Harmful 12 Outline Source of the problem Related work Implication Padding-induced response time gain Sustainable countermeasures Conclusion

A. Mondal When TCP Friendliness Becomes Harmful 13 Quantifying padding induced-gain RTT RTO 2RTO RTO 2RTO 4RTO 1-p p p p 1-Q p p 1-p Q Correlated packet loss (FIFO) Random packet loss (RED) P = packet loss ratio Q = prob. packet loss is detected timeout

A. Mondal When TCP Friendliness Becomes Harmful 14 Modeling REDFIFO Upgrading interactive TCP flows to fully backlogged flows always pays-off

A. Mondal When TCP Friendliness Becomes Harmful 15 Simulations 1) Queuing delay plays a role 2) Consecutive packet losses can affect overall gain achieved

A. Mondal When TCP Friendliness Becomes Harmful 16 Outline Source of the problem Related work Implication Padding-induced response time gain Sustainable countermeasures Conclusion

A. Mondal When TCP Friendliness Becomes Harmful 17 Sustainable countermeasures (1) Differentiated minRTO –Application-limited flows use reduced value for minRTO parameter Short-term padding with dummy packets – Enable that a packet loss is detected via fast retransmit mechanism –Actual packet followed by three tiny dummy packets. A diversity approach – TCP sends k (k>1, k is a small integer) copies of the packet without violating congestion control mechanism –In reality k=2 is sufficient

A. Mondal When TCP Friendliness Becomes Harmful 18 Sustainable countermeasures (2) Short-term padding and diversity approaches outperform fully-backlogged approach Differentiated minRTO does not work

A. Mondal When TCP Friendliness Becomes Harmful 19 Sustainable countermeasures (3) REDFIFO Short-term padding and diversity approaches outperform fully-backlogged approach

A. Mondal When TCP Friendliness Becomes Harmful 20 Overhead and Sustainability RED FIFO Short-term padding and diversity approaches provide significantly friendlier environment Issue: What happens when everyone adopts our approach?

A. Mondal When TCP Friendliness Becomes Harmful 21 Conclusion TCPs loss recovery mechanism degrades response time of interactive applications relative to long flows during congestion. Incentive for padding misbehaviour and seriously degrades overall networks performance. Explored simple, sustainable and easily deployable solutions.

A. Mondal When TCP Friendliness Becomes Harmful 22 Questions?