Faculty Publications
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Item On the robustness of AQM mechanisms against non-responsive traffic(Institute of Electrical and Electronics Engineers Inc., 2017) Patil, S.D.; Tahiliani, M.P.Active Queue Management (AQM) mechanisms have come a long way, with an initial goal to avoid congestion to the recent most focus on reducing queue delay. The benefits of using AQM mechanisms at routers are being thoroughly studied nowadays, mainly to avoid the problem of bufferblaat. Although a lot of work has focused on analyzing the behavior of AQM mechanisms, the nature of traffic used while deriving inferences is mainly responsive (TCP), with small numbers of unresponsive flows (UDP) used in the background. The usage of UDP in Internet has increased significantly in the recent past, owing to a great demand for time sensitive multimedia applications. Since UDP flows do not respond to congestion signals, controlling the queue length at routers by using AQM mechanisms becomes a non-trivial task. In this paper, we study the robustness of popular AQM mechanisms in the presence of a large number of unresponsive UDP flows using ns-2. Further, we provide guidelines to effectively tune the AQM knobs and enhance their robustness against non-responsive UDP flows. © 2016 IEEE.Item FQ-PIE Queue Discipline in the Linux Kernel: Design, Implementation and Challenges(Institute of Electrical and Electronics Engineers Inc., 2019) Ramakrishnan, G.; Bhasi, M.; Saicharan, V.; Monis, L.; Patil, S.D.; Tahiliani, M.P.Proportional Integral controller Enhanced (PIE) is an Active Queue Management (AQM) mechanism to address the bufferbloat problem. AQM mechanisms tackle bufferbloat by dropping or marking packets before the buffers fill up, but typically do not ensure fairness between responsive and unresponsive flows that share the same bottleneck link i.e., unresponsive flows can starve responsive flows when they co-exist. Recently, there has been an active interest in integrating flow protection mechanisms with AQM mechanisms to collectively tackle the problem of bufferbloat and fairness. There exist two such algorithms: Flow Queue Controlled Delay (FQ-CoDel) and Flow Queue Proportional Integral Controller Enhanced (FQ-PIE) that integrate flow protection with AQM mechanisms. Flow protection is achieved by dividing the incoming flows into separate queues and then applying CoDel/PIE algorithm on respective queues. Although FQ-CoDel is available in the mainline of Linux, there does not exist a model for FQ-PIE. In this paper, we discuss the design and implementation of FQ-PIE in the Linux kernel. We test and evaluate our proposed model of FQ-PIE in different scenarios by comparing the results obtained from it to those obtained for PIE and FQ-CoDel. Besides evaluating the fairness among responsive and unresponsive flows, we also evaluate the fairness among different types of responsive flows, such as when CUBIC TCP shares the same bottleneck link as TCP BBR. We also assess the benefits of integrating flow protection with AQM mechanisms in terms of reducing the latency for thin, latency sensitive flows when they coexist with thick, latency tolerant flows. © 2019 IEEE.Item Towards a better understanding and analysis of controlled delay (CoDel) algorithm by using fluid modelling(Institution of Engineering and Technology journals@theiet.org, 2019) Patil, S.D.; Tahiliani, M.P.In this study, a modified fluid model is proposed to understand the design of controlled delay (CoDel) algorithm for active queue management (AQM) and analyse its sensitivity to parameter settings. CoDel significantly differs from other AQM algorithms because it operates at the head of the queue and adopts a deterministic packet drop strategy, unlike other algorithms that operate at the tail and adopt a probabilistic packet drop strategy. The correctness of the proposed fluid model is verified by comparing its results with those obtained from ns-2. Subsequently, using the model developed in this study, the authors analyse the performance of CoDel algorithm by changing its internal parameters and modifying its control law. They highlight the role of the internal parameters and control law on the ability of the CoDel algorithm to control queue delay. Their analysis shows that the CoDel algorithm is sensitive to its parameter settings and that its control law requires minor modifications to gain a better control over the queue delay. © The Institution of Engineering and Technology 2018.Item Minstrel PIE: Curtailing queue delay in unresponsive traffic environments(Elsevier B.V., 2019) Patil, S.D.; Tahiliani, M.P.Active Queue Management (AQM) algorithms aim to maintain a proper trade-off between queue delay and bottleneck link utilization. However, it is often noticed that this trade-off is not achieved convincingly when unresponsive UDP flows coexist with responsive TCP flows. This paper proposes an extension to Proportional Integral controller Enhanced (PIE) algorithm called Minstrel PIE, which adapts the reference queue delay to improve the trade-off between queue delay and link utilization when unresponsive flows share the same bottleneck queue as responsive flows. Extensive evaluations through simulations and real time experiments demonstrate that Minstrel PIE improves the performance of PIE in the presence of unresponsive flows, and delivers similar performance otherwise. Moreover, the Minstrel PIE algorithm does not introduce new knobs to improve the performance of PIE and hence, can be easily deployed without any additional complexity. © 2019 Elsevier B.V.