T. Edwan, L. Guan, G. Oikonomou, I. Phillips, "Higher Order Delay Functions for Delay-Loss Based TCP Congestion Control", in Proc. 6th Wireless Advanced, London, UK, pp. 1-6, 2010
TCP-Illinois aims to address TCP's low throughput when operating in high-speed, high-delay networks. Previous research has shown that, due to its linear increase behaviour and to its relatively long congestion epochs, TCP-Illinois exhibits sub-optimal scaling behaviour with an increasing path Bandwidth-Delay Product (BDP). This paper discloses our contributions towards improving the aggressiveness and responsiveness of loss-based TCP congestion control algorithms. We formally show that higher order versions (of power n) of the delay functions used by TCP-Illinois become more aggressive and responsive with an increasing value of n. Based on this finding, we propose three variants: i) a second order (quadratic) version of additive increase and multiplicative decrease (TCP-Q), ii) a second order multiplicative decrease only (TCP-Fq) and iii) a sub-linear multiplicative decrease only (TCP-Fs). By modifying the TCP-Illinois code in the GNU/Linux kernel, we obtained the three corresponding modules and used them for our simulations using the TCP/Linux patch for ns2. Based on standardised congestion control metrics, we conducted a comparative analysis between our variants and a number of relevant high speed TCP algorithms. Simulation results agree with our analytical findings; compared to TCP-Illinois, TCP-Q exhibits shorter congestion epochs and thus better responsiveness and convergence.
T. Edwan, L. Guan, G. Oikonomou, I. Phillips, "Understanding the Impact of Link Errors on TCP Congestion Control", in Proc. 26th UK Performance Engineering Workshop (UK PEW 2010), Coventry, UK, pp. 59-64, 2010
This paper presents a control-theoretic-like analysis of TCP congestion control mechanism. We extend previous analysis by considering two additional factors: i) wireless link errors and ii) general variable multiplicative decrease (MD). Wireless link errors are usually the cause for unnecessary TCP congestion window reductions and thus lower throughput. We also study the effects of those parameters on TCP's stability condition. In this paper, we present a modified TCP model and analyse it in the presence of delay. This is then linearised around an equilibrium point and re-analysed using a control-theoretic-like framework. The analysis verifies that non-congestive packet loss acts as a disturbance, as opposed to loss due to congestion, which is well within TCP's control.
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