Abstract
In heterogeneous wireless networks, random packet loss and high latency lead to conventional TCP variants performing unsatisfactorily in the case of competing communications. Especially on high-latency wireless links, conventional TCP variants are unable to estimate congestion degrees accurately for fine-grained congestion control because of the effects of random packet loss and delay oscillations. This paper proposes a TCP variant at the sender side to identify congestion degrees, namely TCP-WBQ, which quickly responses to the real congestion and effectively shields against random packet loss and oscillations of latency time. The proposed algorithm of congestion control firstly constructs a backlog-queue model based on the dynamics of the congestion window, and deduces the two bounds of the model which delimit oscillations of the backlog queue for non-congestion and random packet loss respectively. TCP-WBQ detects congestion degrees more accurately and thus implements the corresponding schemes of adjusting the congestion window, maintaining a tradeoff between high throughputs and congestion avoidance. The comprehensive simulations show that TCP-WBQ works efficiently in bandwidth utilization with single and multiple bottleneck scenarios, and achieves high performance and competitive fairness in heterogeneous wireless networks.
Highlights
Traffic Receiver (n-1)Satellite link:1Mbps High latency Receiver nAverage throughput (Mbps) Transmission Congestion Protocol (TCP)-WBQ (Mbps) TCP-WBQ Hybla NewrenoWestwood westwood-ekfTCP-WBQ Hybla Newreno Westwood westwood-ekfWireless link delay(a) Average throughput in moderate traffic (b) Average throughput in heavy traffic
In the dumbbell topology including the single bottleneck, we compare various TCP variants according to different metrics, including the average throughput, the real-time estimated bandwidth, the normalized backlog queue, and the competitive fairness
We can observe that TCP-WBQ attains significant performance gain, minimum backlog queue, and most competitive fairness over the wireless link with different latency and pl. These results prove TCP-WBQ effectively shields the impact of the random packet loss and high latency on the wireless link, so it is very suitable for heterogeneous wireless networks
Summary
Many TCP variants for congestion control are proposed for wireless networks. While receiving normal Acks and congestion signals, TCP-WBQ estimates the backlog queue size (q) in [3] to identify the congestion degree. TCP-WBQ constantly changes cwnd according to the congestion degree, i.e., the size of the backlog queue. Since the backlog queue is still unformed in the case of non-congestion, directly increasing cwnd to wmax can rapidly increase throughput, which is beneficial to the wireless links with random packet loss. In TCP-WBQ, wthresh is the reduced cwnd for the true congestion, and wmax is the expected maximum because it limits the max size of the backlog queue. Because wmax is often much more than two packets, the recovery time in TCP-WBQ is much faster and is just one Rtt to recover to wmax rather than several Rtts as in AIMD mechanism This is important to the TCP stream via the high-latency wireless link when it competes with other streams on superior wired links. These demonstrate that TCP-WBQ on wireless links maintains good fairness with other prevalent TCP variants
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