MSWIM '01 Proceedings of the 4th ACM international workshop on Modeling, analysis and simulation of wireless and mobile systems
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TCP WestwoodNR is a sender-side modification of the TCP congestion window algorithm that improves upon the performance of TCP New Reno in wired as well as wireless networks. The improvement is most significant in wireless networks with lossy links, since TCP WestwoodNR relies on end-to-end bandwidth estimation to discriminate the cause of packet loss congestion or wireless channel effect) which is a major problem in TCP New Reno. The key idea of our improvement consists in increasing the throughput of the transmission by modifying the algorithm of congestion avoidance. The rationale of this strategy is simple: in contrast with TCP Reno, which reduce "blindly" to slow start threshold the congestion window after three duplicate ACKs, TCP WestwoodNR stabilize during a certain period the congestion window to new threshold larger then ssthresh, then it increases it linearly. The proposed mechanism is particularly effective over wireless links where sporadic losses due to radio channel problems are often misinterpreted as a symptom of congestion by current TCP schemes and thus lead to an unnecessary window reduction. Experimental studies reveal improvements in throughput performance, as well as in fairness. In addition, friendliness with TCP New Reno was observed in a set of experiments showing that TCP New Reno connections are not starved by TCP WestsoodNR connections.