## Kunniyur, Srisankar S

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Publication End-to-End Congestion Control Schemes: Utility Functions, Random Losses and ECN Marks(2003-10-01) Kunniyur, Srisankar S; Srikant, R.We present a framework for designing end-to-end congestion control schemes in a network where each user may have a different utility function and may experience noncongestion-related losses. We first show that there exists an additive-increase-multiplicative-decrease scheme using only end-to-end measurable losses such that a socially optimal solution can be reached. We incorporate round-trip delay in this model, and show that one can generalize observations regarding TCP-type congestion avoidance to more general window flow control schemes. We then consider explicit congestion notification (ECN) as an alternate mechanism (instead of losses) for signaling congestion and show that ECN marking levels can be designed to nearly eliminate losses in the network by choosing the marking level independently for each node in the network. While the ECN marking level at each node may depend on the number of flows through the node, the appropriate marking level can be estimated using only aggregate flow measurements, i.e., per-flow measurements are not required.Publication Sensor Network Devolution and Breakdown in Survivor Connectivity(2004-06-27) Kunniyur, Srisankar S; Venkatesh, Santosh SAs batteries fail in wireless sensor networks there is an inevitable devolution of the network characterised by a breakdown in connectivity between the surviving nodes of the network. A sharp limit theorem characterising the time at which this phenomena makes an appearance is derived.Publication Congestion Controllers for High Bandwidth Connections with Fiber Error Rates(2004-06-20) Kavak, Egemen; Kunniyur, Srisankar SThe inefficiency of a TCP connection in the presence of high bandwidth links due to the constant multiplicative decrease factor has been well documented in recent literature. In this paper we look at the effect of fiber error rates on the throughput of a TCP connection. We propose a congestion controller that removes the ill-effects of fiber error rates on TCP throughput by lower bounding the marking probability. We show that this congestion controller can achieve extremely high utilizations in high bandwidth links. We also discuss the TCP friendliness of this congestion controller and present simulation results that validate our analysis.Publication Stability of Adaptive Congestion-Controllers for High Bandwidth Connections(2003-12-09) Kavak, Egemen; Kunniyur, Srisankar SIn this paper we use fluid-models to look at the adaptation of congestion-controllers to achieve higher throughputs and utilizations in high bandwidth connections. We first parameterize the congestion-controllers using a parameter called the multiplicative decrease parameter and study the adaptation of the congestion-controllers in terms of adapting this parameter. We then linearize the system to study the local stability properties and provide design rules for choosing the parameters of the congestion-controllers. We assume a general network topology and arbitrary round-trip delays in the analysis. Simulations that show the throughput increase that can be achieved using such adaptive congestion-controllers are also presented.Publication A Time-Scale Decomposition Approach to Adaptive Explicit Congestion Notification (ECN) Marking(2002-06-01) Kunniyur, Srisankar S; Srikant, R.Fair resource allocation in high-speed networks, such as the Internet, can be viewed as a constrained optimization program. Kelly et al. have shown that an unconstrained penalty function formulation of this problem can be used to design congestion controllers that are stable. In this paper, we examine the question of providing feedback from the network such that the congestion controllers derived from the penalty function formulation lead to the solution of the original unconstrained problem. This can be viewed as the decentralized design of explicit congestion notification (ECN) marking rates at each node in the Internet to ensure global loss-free operation of a fluid model of the network. We then look at the stability of such a scheme using a time-scale decomposition of the system. This results in two seperate systems which are stable individually, and we show that under certain assumptions the entire system is semiglobally stable and converges fast to the equilibrium point exponentially.Publication An Adaptive Virtual Queue (AVQ) Algorithm for Active Queue Management(2004-04-01) Kunniyur, Srisankar S; Srikant, R.Virtual queue-based marking schemes have been recently proposed for Active Queue Management (AQM) in Internet routers. We consider a particular scheme, which we call the Adaptive Virtual Queue (AVQ), and study its following properties: its stability in the presence of feedback delays, its ability to maintain small queue lengths, and its robustness in the presence of extremely short flows (the so-called web mice). Using a linearized model of the system dynamics, we present a simple rule to design the parameters of the AVQ algorithm. We then compare its performance through simulation with several well-known AQM schemes such as RED, REM, Proportional Integral (PI) controller, and a nonadaptive virtual queue algorithm. With a view toward implementation, we show that AVQ can be implemented as a simple token bucket using only a few lines of code.Publication AntiECN Marking: A Marking Scheme for High Bandwidth Delay Connections(2003-05-11) Kunniyur, Srisankar SIn this paper we describe a simple scheme that uses feedback from underutilized high capacity links to allow a TCP connection to aggressively increase its sending rate. The feedback is in the form of a single bit in the packet header and is given per packet. The scheme uses aggregate information to provide feedback and does not require the routers to maintain per flow state. We show through simulations that such a scheme allow TCP connections to efficiently utilize high capacity links without increasing the implementation complexity at the routers.