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TCP In Conflict-Based Wireless Links
TCP's bidirectional traffic causes self-interference in contention-based wireless links as in IEEE 802.11 wireless LANs and results in the loss of TCP data segments and ACKs. The fast-recovery algorithm is the basis for congestion control in most TCP enhancements proposed to address wireless network characteristics. However we show in this paper, that fast-recovery worsens performance during self-interference by causing deadlock situations that only terminate with a timeout. Both Reno and New Reno are evaluated in comparison to the lesser-optimized TCP-Tahoe to demonstrate the degradation in performance during fast-recovery. The less-optimized TCP-Tahoe that forgets all outstanding packets soon after fast-retransmit, outperforms TCP-Reno with an 80% gain in throughput. For the minrto_ parameter set to 1 second, Tahoe outperforms New Reno by a significant margin. A key contribution in this paper is the visualization of TCP dynamics that capture MAC layer collisions due to self-interference, and the protocols' behavior during congestion control. The paper demonstrates the disadvantages of combined error and flow control and makes a sound case for cross-layer awareness in transport protocols over wireless networks.
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