@conference {
	title = {Trust-Aware Network Utility Optimization in Multihop Wireless Networks with Delay Constraints},
	author = {Paraskevas, Evripidis., Jiang, Tao., Purkayastha, Punyaslok., Baras, John S.},
	year = {2016},
	month = {06/2016},
	abstract = {Many resource allocation problems can be formulated as a constrained maximization of a utility function. Network Utility Maximization (NUM) applies optimization techniques to achieve decomposition by duality or the primal dual method. Several important problems, for example, joint source rate control, routing, and scheduling design, can be optimized by using this framework. In this work, we introduce an important network security concept, {\textquotedblleft}trust{\textquotedblright}, into the NUM formulation and we integrate nodes{\textquoteright} trust values in the optimization framework. These trust values are based on the interaction history between network entities and community-based monitoring. Our objective is to avoid routing packets through paths with large percentage of malicious nodes. We also add end-to-end delay constraints for each of the traffic flows. The delay constraints are introduced to capture the imposed quality of service (QoS) requirements for each traffic flow.},
	address = {Athens, Greece},
	booktitle = {24th Mediterranean Conference on Control and Automation},
	pages = {pp. 593-598}
}
@conference {
	title = {Convergence Results for Ant Routing Algorithms via Stochastic Approximation and Optimization},
	author = {Purkayastha, Punyaslok., Baras, John S.},
	year = {2010},
	month = {04/2010},
	abstract = {In this paper, we provide convergence results for an Ant Routing (ARA) Algorithm for wireline, packet switched communication networks, that are acyclic. Such algorithms are inspired by the foraging behavior of ants in nature. We consider an ARA algorithm proposed by Bean and Costa [2]. The algorithm has the virtues of being adaptive and distributed, and can provide a multipath routing solution. We consider a scenario where there are multiple incoming data traffic streams that are to be routed to their destinations via the network. Ant packets, which are nothing but probe packets, are used to estimate the path delays in the network. The node routing tables, which consist of routing probabilities for the outgoing links, are updated based on these delay estimates. In contrast to the available analytical studies in the literature, the link delays in our model are stochastic, time-varying, and dependent on the link traffic. The evolution of the delay estimates and the routing probabilities are described by a set of stochastic iterative equations. In doing so, we take into account the distributed and asynchronous nature of the algorithm operation. Using methods from the theory of stochastic approximations, we show that the evolution of the delay estimates can be closely tracked by a deterministic ODE (Ordinary Differential Equation) system, when the step-size of the delay estimation scheme is small. We study the equilibrium behavior of the ODE in order to obtain the equilibrium behavior of the algorithm. We also provide illustrative simulation results.},
	address = {Stockholm, Sweden},
	booktitle = {Proceddings of the 13th International Conference on Hybrid Systems: Computation and Control (HSCC {\textquoteright}10)},
	pages = {pp. 201-210}
}
@conference {
	title = {Component Based Performance Modeling of Wireless Routing Protocols},
	author = {Baras, John S., Tabatabaee, Vahid., Purkayastha, Punyaslok., Somasundaram, Kiran K.},
	year = {2009},
	month = {06/2009},
	abstract = {We propose a component-based methodology for modelling and design of wireless routing protocols. Componentization is a standard methodology for analysis and synthesis of complex systems, or software. The feasibility of the component based design relies heavily on the compositionality property (i.e. system-level properties can be computed from properties of components). To provide a component based design methodology and to test compositionality for routing protocols, we have to develop a component-based model of the wireless network. We present the main components of the routing protocol that should be modelled and focus on three main components: neighborhood discovery, selector of topology information to disseminate, and the path selection components. For each component, we identify the inputs, outputs, and a generic methodology for modelling. Throughout the paper, we use the Optimized Link State Routing (OLSR) protocol as a case study to demonstrate the effectiveness of our approach. Using the neighborhood discovery component, we present our design methodology and design a modified enhanced version of this component, and compare its performance to the original OLSR design.},
	address = {Dresden, Germany},
	booktitle = {IEEE ICC 2009 Ad Hoc and Sensor Networking Symposium},
	pages = {pp.1-6}
}
@conference {
	title = {Loss Network Models and Multiple Metric Performance Sensitivity Analysis for Mobile Wireless Multi-Hop Networks},
	author = {Baras, John S., Perumal, Senni., Tabatabaee, Vahid., Somasundaram, Kiran K., Purkayastha, Punyaslok.},
	year = {2008},
	month = {11/2008},
	abstract = {We develop and evaluate a new method for estimating and optimizing various performance metrics of mobile wireless multi-hop networks, including MANETs. The method utilizes approximate (throughput) loss model that couples the physical, MAC and routing layers effects. The model provides quantitative statistical relations between the loss parameters that are used to characterize multiuser interference and physical path conditions on the one hand and the traffic rates between origin-destination pairs on the other. The model considers effects of the hidden nodes, node scheduling algorithms, MAC and PHY layer failures and unsuccessful packet transmission attempts at the MAC layer in~arbitrary time-varying network topologies where multiple paths share nodes. The method then applies Automatic Di{\textregistered}erentiation (AD) to these implicit performance models, to compute sensitivities of various performance metrics with respect to net- work parameters. We demonstrate the method by applying it to time-varying mobile network topologies, including reduced connectivity instances, with both random access MAC (contention mode of the 802.11) as well as reservation-based MAC (USAP TDMA based protocol). We analyze throughput, delay and packet loss as metrics and investigate metric optimization and tradeoff analysis. Finally, we provide numerical results for realistic mobile networks with time-varying topologies.},
	address = {Maui, Hawaii},
	booktitle = {Fourth International Wireless Internet Conference (WICON 2008)}
}
@conference {
	title = {A Policy-Based Routing Scheme for Multi-Robot Systems},
	author = {Purkayastha, Punyaslok., Hovareshti, Pedram., Baras, John S.},
	year = {2008},
	month = {06/2008},
	abstract = {In this paper, we consider a policy-based routing scheme for a wireless communication network consisting of a set of robots as nodes. Our scheme provides a communication infrastructure that enables the multi-robot system to accomplish its assigned tasks. Our scheme is adaptive and can be implemented in a distributed manner by the nodes of the network. The scheme makes estimates of link and path costs in the network and uses these estimates to construct probabilistic routing tables in the nodes. We use ideas from the literature on simulation methods for approximate dynamic programming to compute, in a distributed manner, the cost estimates.We propose two schemes that update the probabilistic routing tables at the nodes of the network. One of the schemes is an adaptation of the Linear Reward Inaction rule found in studies of stochastic learning automata. Our other scheme is a modification of an Ant-Based Routing algorithm. We assume a simple model of the link behavior in the wireless network - a message transmission on a wireless link is assumed to be successful with a certain probability and is lost otherwise. We also analyze our algorithms and show that our probabilistic update schemes direct packets along paths with low costs.},
	address = {Ajaccio, France},
	booktitle = {16th Mediterranean Conference on Control and Automation},
	pages = {pp. 970-975}
}
@conference {
	title = {Constrained Coalitional Games and Networks of Autonomous Agents},
	author = {Baras, John S., Jiang, Tao., Purkayastha, Punyaslok.},
	year = {2008},
	month = {03/2008},
	abstract = {We develop a unifying analytical and optimization based framework for the design, operation and performance evaluation of networks of dynamic autonomous agents. The fundamental view is that agents in such a network are dynamic entities that collaborate because via collaboration they can accomplish objectives and goals much better than working alone, or even accomplish objectives that they cannot achieve alone at all. Yet the benefits derived from such collaboration require some costs (e.g. communications), or equivalently, the collaboration is subject to constraints. Understanding and quantifying this tradeoff between the benefits vs the costs of collaboration, leads to new methods that can be used to analyze, design and control/operate networks of agents. Although the inspiration for the framework comes from social and economic networks, the fundamental ideas and in particular the methodology of dynamic constrained coalitional games (DCCG) can unify many concepts and algorithms for networks in various areas: social networks, communication networks, sensor networks, economic networks, biological networks, physics networks. We then analyze a specific instance of such tradeoffs arising in the design of security-aware network protocols. We extend network utility maximization (NUM) so as to encompass security metrics such as {\textquotedblleft}trust{\textquotedblright}. The trust values assigned to nodes are based on interaction history and community-based monitoring. The effect of these trust values on the resulting protocols is that in routing and media access scheduling node trustworthiness is automatically considered and used. We develop a distributed algorithm for the joint physical-MAC-routing protocol design. Our extension to NUM with security concerns leads to resilient networks.},
	address = {St. Julians, Malta},
	booktitle = {Third International Symposium on Communications, Control and Signal Processing},
	pages = {pp. 972-979}
}
@conference {
	title = {Convergence Results for Ant Routing Algorithms via Stochastic Approximation and Optimization},
	author = {Purkayastha, Punyaslok., Baras, John S.},
	year = {2007},
	month = {12/2007},
	abstract = {"Ant algorithms" have been proposed to solve a variety of problems arising in optimization and distributed control. They form a subset of the larger class of {\textquotedblleft}Swarm Intelligence{\textquotedblright} algorithms. The central idea is that a {\textquoteleft}swarm{\textquoteright} of relatively simple agents can interact through simple mechanisms and collectively solve complex problems. Instances that exemplify the above idea abound in nature. The abilities of ant colonies to collectively accomplish complex tasks have served as sources of inspiration for the design of {\textquotedblleft}Ant algorithms{\textquotedblright}. Examples of {\textquotedblleft}Ant algorithms{\textquotedblright} are {\textquotedblleft}Ant Routing{\textquotedblright} algorithms that have been proposed for communication networks. We analyze in this paper an Ant-Based Routing Algorithm for packet-switched wireline networks. The algorithm is an attractive multiple path probabilistic routing scheme, that is fully adaptive and distributed. Using methods from adaptive algorithms and stochastic approximation, we show that the evolution of the link delay estimates can be closely tracked by a deterministic ODE system. A study of the equilibrium points of the ODE then gives us the equilibrium behavior of the routing algorithm, in particular, the equilibrium routing probabilities, and mean delays in the links under equilibrium. We also show that the fixed-point equations that the equilibrium probabilities satisfy are actually the necessary and sufficient conditions of an appropriate optimization problem. Simulations supporting the analytical results are provided.},
	address = {New Orleans, Louisiana},
	booktitle = {46th IEEE Conference on Decision and Control},
	pages = {pp. 340-345}
}
@article {
	title = {Convergence Results for Ant Routing Algorithms via Stochastic Approximations},
	author = {Purkayastha, Punyaslok., Baras, John S.},
	year = {2013},
	month = {04/2013},
	abstract = {In this article, we provide convergence results for an Ant-based Routing Algorithm (ARA) for wireline, packet-switched communication networks, that are acyclic. Such algorithms are inspired by the foraging behavior of ants in nature. We consider an ARA algorithm proposed earlier by Bean and Costa [2005]. The algorithm has the virtues of being adaptive and distributed and can provide a multipath routing solution. We consider a scenario where there are multiple incoming data traffic streams that are to be routed to their respective destinations via the network. Ant packets, which are nothing but probe packets, are introduced to estimate the path delays in the network. The node routing tables, which consist of routing probabilities for the outgoing links, are updated based on these delay estimates. In contrast to the available analytical studies in the literature, the link delays in our model are stochastic, time-varying, and dependent on the link traffic. The evolution of the delay estimates and the routing probabilities are described by a set of stochastic iterative equations. In doing so, we take into account the distributed and asynchronous nature of the algorithm operation. Using methods from the theory of stochastic approximations, we show that the evolution of the delay estimates can be closely tracked by a deterministic ODE (Ordinary Differential Equation) system when the step size of the delay estimation scheme is small. We study the equilibrium behavior of the ODE system in order to obtain the equilibrium behavior of the routing algorithm. We also explore properties of the equilibrium routing probabilities and provide illustrative simulation results.},
	pages = {pp. 1-34},
	volume = {Vol.  8},
	number = {Issue 1, Article 3},
	journal = {ACM Transactions on Autonomous and Adaptive Systems (TAAS)}
}
@techreport {
	title = {Convergence Results for Ant Routing Algorithms via Stochastic Approximation},
	author = {Purkayastha, Punyaslok., Baras, John S.},
	year = {2009},
	month = {10/2009},
	abstract = {In this paper, we provide convergence results for an Ant-Based Routing (ARA) Algorithm for wireline, packet-switched communication networks, that are acyclic. Such algorithms are inspired by the foraging behavior of ants in nature. We consider an ARA algorithm proposed by Bean and Costa [2]. The algorithm has the virtues of being adaptive and distributed, and can provide a multipath routing solution. We consider a scenario where there are multiple incoming data traffic streams that are to be routed to their respective destinations via the network. Ant packets, which are nothing but probe packets, are introduced to estimate the path delays in the network. The node routing tables, which consist of routing probabilities for the outgoing links, are updated based on these delay estimates. In contrast to the available analytical studies in the literature, the link delays in our model are stochastic, time-varying, and dependent on the link traffic. The evolution of the delay estimates and the routing probabilities are described by a set of stochastic iterative equations. In doing so, we take into account the distributed and asynchronous nature of the algorithm operation. Using methods from the theory of stochastic approximations, we show that the evolution of the delay estimates can be closely tracked by a deterministic ODE (Ordinary Differential Equation) system, when the step-size of the delay estimation scheme is small. We study the equilibrium behavior of the ODE system in order to obtain the equilibrium behavior of the routing algorithm. We also explore properties of the equilibrium routing probabilities, and provide illustrative simulation results.}
}
@article {
	title = {An Optimal Distributed Routing Algorithm using Dual Decomposition Techniques},
	author = {Purkayastha, Punyaslok., Baras, John S.},
	year = {2008},
	month = {01/2008},
	abstract = {We consider the routing problem in wireline, packet-switched communication networks. We cast our optimal routing problem in a multicommodity network flow optimization framework. Our cost function is related to the congestion in the network and is a function of the flows on the links of the network. The optimization is over the set of flows in the links corresponding to the
various destinations of the incoming traffic. We separately address the single commodity and the multicommodity versions of the routing problem. We consider the dual problems and using dual decomposition techniques, we provide primal-dual algorithms that converge to the optimal solutions of the problems. Our algorithms, which are subgradient algorithms to solve the corresponding dual problems, can be implemented in a distributed manner by the nodes of the network. For online, adaptive implementations of our algorithms, the nodes in the network need to utilize {\textquoteleft}locally available information{\textquoteright} like estimates of queue lengths on outgoing links. We show convergence to the optimal routing solutions for synchronous versions of the algorithms, with perfect (noiseless) estimates of the queueing delays. Every node of the network controls the flows on the outgoing links using the distributed algorithms. For both the single commodity and multicommodity cases, we show that our algorithm converges to a loop-free optimal solution. Our optimal solutions also have the attractive property of being multipath routing solutions.},
	pages = {pp. 277-302},
	volume = {Vol. 8},
	number = {Issue 3},
	journal = {Communications in Information and Systems, Brockett Legacy Issue, International Press}
}
