Cross-Layer Explicit Link Status Notification to Improve TCP Performance in Wireless Networks

To alleviate the performance degradation of conventional TCP in wireless networks, many schemes have been proposed so far. One category of such schemes is the Explicit Loss Notification (ELN) scheme in which TCP senders are notified of wireless losses so as to avoid congestion control against those losses. Thus the key design factor of the ELN scheme is how to detect wireless losses accurately and rapidly. This paper proposes a new ELN scheme, in which wireless losses are detected by monitoring the operation of the wireless link layer. By exploiting such cross-layer design, the proposed scheme can detect wireless losses without additional transmission over the wireless link and thus achieves accurate detection with minimum delay. The proposed scheme additionally sends new information, that is, Explicit Retransmission Start Notification, in order to prevent spurious timeouts of the TCP senders. Furthermore, in order to handle packet reordering and avoid successive shrinking of a congestion window due to multiple packet drops, a new TCP modification is proposed. Through intensive simulations, it is demonstrated that the proposed scheme outperforms the other ELN schemes, and yields the throughput performance of more than 400% of TCP-Reno and 150% of Snoop in the considered environments