Abstract
This paper presents a sender side only TCP mechanism to prevent compromise for bandwidth utilization in IEEE 802.11 wireless networks. In absence of mechanism for accurate and immediate loss discrimination, the TCP sender unnecessarily reduces its Loss Window in response to the packet losses due to transmission errors. At the same time, frequent transmission losses and associated link retransmissions cause inaccuracy for available bandwidth estimate. The proposal, Adaptive TCP tackles the above issues using two refinements. First, sender estimates the degree of congestion by exploiting the statistics for estimated Round Trip Time (RTT). With this, it prevents unnecessary shrinkage of Loss Window and bandwidth estimate. Second, by concluding the uninterrupted evolution of its sending rate in recent past, the Adaptive TCP advances bandwidth estimate under favorable network conditions. This in turn, facilitates for quick growth in TCP’s sending rate after loss recovery and consequently alleviates bandwidth utilization. The authors implement the algorithm on top of TCP NewReno, evaluate and compare its performance with the wireless TCP variants deployed in current Internet. Through intensive simulations it is demonstrated that the Adaptive TCP outperforms other well-established TCP variants, and yields more than 100% of the throughput performance and more than 60% of improvement for bandwidth utilization, compared to TCP NewReno. The simulation results also demonstrated compatibility of Adaptive TCP in a shared wireless environment.
Highlights
Transmission Control Protocol (TCP) [1] is the most popular transport layer protocol used for reliable data transfer in Internet [2]
Few approaches in improving the performance of TCP over wireless networks largely focus either on increasing the size of Loss Window speedily based on the approval from intermediate node [16] [17] or adjusting TCP’s congestion control parameters after loss recovery (i.e. Loss Window, ssthresh) to an advance size based on network state or loss discrimination [6] [7] [18] [19]
When the estimated RTT prior to loss detection (RTTn) is equal to RTTmin, it represents the congestion-free state of the network (i.e. α is set to 1) and like other Loss Differentiation Algorithms (LDA) schemes, Adaptive TCP adjusts Loss Window to a size that corresponds to the maximum value of cwnd exercised prior to the loss detection
Summary
Transmission Control Protocol (TCP) [1] is the most popular transport layer protocol used for reliable data transfer in Internet [2]. With non-congestion RTO, the TCP sender resets Loss Window to a minimum size and loss recovery is followed by inferior transmission rate. The uncorrelated reduction in ssthresh causes quick termination of slow-start process and TCP sender prematurely enters into congestion-avoidance process This prevents sender to obtain usable share of network capacity quickly [15]. Few approaches in improving the performance of TCP over wireless networks largely focus either on increasing the size of Loss Window speedily based on the approval from intermediate node [16] [17] or adjusting TCP’s congestion control parameters after loss recovery (i.e. Loss Window, ssthresh) to an advance size based on network state or loss discrimination [6] [7] [18] [19].
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