End-to-end congestion control schemes: utility functions, random losses and ECN marks

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.     

Stable, scalable, fair congestion control and AQM schemes that achieve high utilization in the Internet

Virtual queue-based active queue management schemes have been proposed to provide low-loss, low-delay service in the Internet. In an earlier work, we had proposed a particular scheme called the adaptive virtual queue (AVQ) algorithm where the capacity of the virtual queue is adapted to the traffic conditions to achieve a desired level of utilization in the network. Here, we study the choice of the parameters of the congestion-controllers at the sources and the AVQ scheme at the links that is required to ensure stability. In particular, we consider a system in which users with diverse round-trip delays and fairness requirements access a general topology network. For this system, we show that, by choosing the speed of adaptation at the sources and the links appropriately, one can guarantee the stability of the network.     

Dendrimer functionalized polysilane: An efficient and recyclable organocatalyst

Polysilane supported dendrimer was efficiently utilized as an organocatalyst for Knoevenagel condensation reaction. Polysilane support was synthesized by the polymerization of trichloromethylsilane. The polypropyleneimine (PPI) dendrimer was grafted on the polymer support by divergent method. The dendrimer was synthesized up to three generations (G3). The dendrimer functionalized polysilane (PS‐PPIG3) was found to contain high concentration of terminal amino groups. The catalytic activity of the PS‐PPIG3 dendrimer was generalized by conducting the Knoevenagel condensation reaction with diverse sets of substrates, and was found to be an efficient organocatalyst. The condensation product could be easily separated from the reaction medium because of the heterogeneous nature of the polymer support. The reaction conditions were optimized, and the catalyst was found to be reusable. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41593.     

A time-scale decomposition approach to adaptive explicit congestionnotification (ECN) marking

Fair resource allocation in high-speed networks, such as the Internet, can be viewed as a constrained optimization program. Kelly et al. (2000) 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 separate systems which are stable individually, and we show that under certain assumptions the entire system is semi-globally stable and converges fast to the equilibrium point exponentially     

Synthesis and application of polycarbosilane supported manganese ions as catalyst in mannich reaction

Polycarbosilane (PCS) with highly crosslinked structure and high surface area was synthesized by the polycondensation reaction between trimethoxyvinylsilane and trichloromethylsilane. The reaction was conducted in the presence of sodium metal. Manganese ion was supported on PCS. The immobilization of transition metal ions to polymer support leads to a number of advantages over homogeneous catalyst, viz easy product recovery, increased selectivity, etc. The catalytic activity of PCS supported manganese ion was studied by considering three‐component Mannich reaction. Reaction with diverse sets of aldehydes, amines, and ketones was examined. PCS‐supported manganese ion catalyst has been prepared for the first time and used successfully in Mannich reaction. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

An adaptive virtual queue (AVQ) algorithm for active queue management

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.     

Threshold Functions, Node Isolation, and Emergent Lacunae in Sensor Networks

A geometrically random network of sensors is obtained by modeling sensors as random points in the unit disc equipped with a local sensing capability and the ability to communicate with other sensors in their vicinity. Node extinctions in the network representing the finite battery lifetimes of the sensors are modeled as a sequence of independent random variables governed by a common probability distribution parametrized by the sensing and communication radii of the sensor nodes. Following its establishment, the devolution of the network with time is characterized by the appearance first of isolated nodes, then the growth of sensory lacunae or dead spots in the sensor field, and, eventually, a breakdown in connectivity between survivors. It is shown that these phenomena occur very sharply in time, these phase transitions occurring at times characteristic of the underlying probability law governing lifetimes. More precisely, it is shown that as the number of sensors grows there exists a critical point in time determined solely by the lifetime distribution at which the number of emergent lacunae of a given size is asymptotically Poisson