Abstract
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.
Highlights
In recent years, wireless networks become more common in real life and many services such as e-mail, web browsing, ecommerce, and so fourth are available in the current wireless networks
We use the built-in modules for Reno, NewReno [35], SACK [5], and Snoop, the open sources [36] for Transmission Control Protocol (TCP) Westwood, [37] for TCP-DCR [19], and add some modules for TCP Veno [12], TCP Jersey [13], Jitter-based TCP (JTCP) [14], TIBET [15], and LHP, with default parameter settings mentioned in the corresponding papers. (The version of TCP Westwood considered in the simulation is Westwood+.) Unless otherwise specified, LL-ELSN is used with ELN-capable SACK (ESACK)
Simulation is run for a period of 200 seconds and we average over 20 runs without LLARQ and 50 runs with Link Layer Automatic Repeat Request (LL-ARQ). (LL-ARQ increases link layer dynamics and we need more simulation runs with LL-ARQ to obtain stable results.) The TCP packet size is 1000 bytes
Summary
Wireless networks become more common in real life and many services such as e-mail, web browsing, ecommerce, and so fourth are available in the current wireless networks. A packet is lost in the wireless link, not by congestion, the TCP sender reduces its congestion window size because the packet loss assumes that it is due to congestion in the network Such TCP behavior results in significant throughput degradation and high interactive delay. LL-ELSN does not require additional transmission over a wireless link for loss notification and enables accurate detection with minimum delay This is achieved by exploiting cross-layer design. Along with ELN, the proposed scheme sends a new information, that is, Explicit Retransmission Start Notification (ERSN), which notifies the TCP sender of the start of the retransmission process at the wireless link layer, in order to prevent spurious timeouts at the TCP sender.
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