Satyajit Banerjee

Symmetric key based authenticated querying in wireless sensor networks

Wireless Sensor Networks (WSNs) enabled with authenticated querying [1] allows only the authorized users to inject queries into the network and get responses thereof. Queries from unauthorized users are silently dropped. Providing authenticated querying for WSN is especially very challenging since the nodes are very much resource constrained and vulnerable to physical captures by the adversary. We present a fully symmetric key based solution for the above problem and analyze the same.

Designing Reliable Architecture for Stateful Fault Tolerance

Performance and fault tolerance are two major issues that need to be addressed while designing highly available and reliable systems. The network topology or the notion of connectedness among the network nodes defines the system communication architecture and is an important design consideration for fault tolerant systems. A number of fault tolerant designs for specific multi-processor architecture exists in the literature, but none of them discriminates between stateless and stateful failover. In this paper, we propose a reliable network topology and a high availability framework which is tolerant up to a maximum of k node faults in a network and is designed specifically to meet the needs of stateful failover. Assuming the nodes in the network are capable of handling multiple processes, through our design we have been able to prove that in the event of k node failures the load can be uniformly distributed across the network - ensuring load balance. We also provide an useful characterization for the network, which under the proposed framework ensures one hop communication between the required nodes

Efficient Load Balancing on a Cluster for Large Scale Online Video Surveillance

In this paper we present a new load distribution strategy tailored to real-time, large scale surveillance systems with the objective of providing best effort timeliness of on-line automated video analysis on a cluster of compute nodes. We propose a novel approach to fine grained load balancing, modeled as a makespan minimization problem to reactively minimize the tardiness of processing individual camera feeds. The proposed approach is also robust in the sense that it is not dependent on either the estimates of future loads or the worst case execution requirements of the video processing load. Simulation results with real-life video surveillance data establish that for a desired timeliness in processing the data, our approach reduces the number of compute nodes by a factor of two, compared to systems without the load migration heuristics.

Contention-free many-to-many communication scheduling for high performance clusters

In the context of generating efficient, contention free schedules for inter-node communication through a switch fabric in cluster computing or data center type environments, all-to-all scheduling with equal sized data transfer requests has been studied in the literature [1, 3, 4]. In this paper, we propose a communication scheduling module (CSM) towards generating contention free communication schedules for many-to-many communication with arbitrary sized data. Towards this end, we propose three approximation algorithms - PST, LDT and SDT. From time to time, the CSM first generates a bipartite graph from the set of received requests, then determines which of these three algorithms gives the best approximation factor on this graph and finally executes that algorithm to generate a contention free schedule. Algorithm PST has a worst case run time of O(max (Δ|E|, |E| log (|E|))) and guarantees an approximation factor of 2H2Δ-1, where |E| is the number of edges in the bipartite graph, Δ is the maximum node degree of the bipartite graph and H2Δ-1 is the (2Δ - 1)- th harmonic number. LDT runs in O(|E|2) and has an approximation factor of 2(1 + τ), where τ is a constant defined as a guard band or pause time to eliminate the possibility of contention (in an apparently contention free schedule) caused by system jitter and synchronization inaccuracies between the nodes. SDT gives an approximation factor of 4 log (wmax) and has a worst case run time of O(Δ|E| log (wmax)), where wmax represents the longest communication time in a set of received requests.

Video surveillance with PTZ cameras: the problem of maximizing effective monitoring time

The effectiveness of the surveillance (monitoring a set of mobile targets with a set of cameras) depends on the resolution of the monitored images and the duration for which the targets are monitored. PTZ cameras are a natural choice to maintain a desired level of resolution for mobile targets. Maintaining resolution by controlling the camera parameters above a desired threshold value, however, implies that the field of regard of a camera cannot be arbitrarily broadened to include multiple targets. Camera for each target needs to be judiciously chosen to ensure monitoring for prolonged time interval. In this paper we propose a metric viz. average effective monitoring time (AEMT), towards capturing the effectiveness of video based surveillance. To achieve enhanced AEMT, we formulate an optimization problem in terms of associating cameras with the targets based on an appropriate weight function and design an efficient distributed algorithm. Simulation results show that our approach contributes significantly towards improving AEMT.

Efficient Algorithms for Variants of Weighted Matching and Assignment Problems

Abstract.Obtaining a matching in a graph satisfying a certain objective is an important class of graph problems. Matching algorithms have received attention for several decades. However, while there are efficient algorithms to obtain a maximum weight matching, not much is known about the maximum weight maximum cardinality, and maximum cardinality maximum weight matching problems for general graphs. Our contribution in this work is to show that for bounded weight input graphs one can obtain an algorithm for both maximum weight maximum cardinality (for real weights), and maximum cardinality maximum weight matching (for integer weights) by modifying the input and running the existing maximum weight matching algorithm. Also, given the current state of the art in maximum weight matching algorithms, we show that, for bounded weight input graphs, both maximum weight maximum cardinality, and maximum cardinality maximum weight matching have algorithms of similar complexities to that of maximum weight matching. Subsequently, we also obtain approximation algorithms for maximum weight maximum cardinality, and maximum cardinality maximum weight matching.

The Double Digest Problem: finding all solutions

The strongly NP-complete Double Digest Problem (DDP), for physical mapping of DNA, is now used for efficient genotyping. Existing methods: are inefficient in tackling large instances; produce only one solution while an instance may have multiple distinct solutions. In this paper, we employ the notion of equivalence among the distinct solutions to obtain almost all of them. Our method comprises two phases: finding a representative from each equivalence class using an elitist Genetic Algorithm (GA); for each representative generating the entire class efficiently. Experimental results tally for known instances. Significant reduction in search space provides notable efficiency.

A New Threshold Certification Scheme Based Defense Against Sybil Attack for Sensor Networks

Security is a major concern for a large fraction of sensor network applications. Douceur first introduced the notion of Sybil attacki?ź[5], where a single entity node illegitimately presents multiple identities. As the nodes in sensor networks can be physically captured by an adversary, Sybil attack can manifest in a severe form leading to the malfunction of basic operational protocols. It is also pointed out ini?ź[5] that Sybil attack could be prevented if each honest identity possesses an unforgeable certificate issued by a trusted authority. The identity is mandated to produce the certificate as a proof of authenticity before it takes part in any network activity. Since ordinary certification schemes are not suitable for sensor networks due to some typical incompatibility features, we propose a symmetric key based threshold certification scheme specially designed to defend Sybil attack in sensor networks.

Genetic algorithm for double digest problem

The strongly NP-complete Double Digest Problem (DDP) for physical mapping of DNA, is now used for efficient genotyping. An instance of DDP has multiple distinct solutions. Existing methods produce a single solution, and are slow for large instances. We employ a type of equivalence among the distinct solutions to obtain almost all of them. Our method comprises of first finding a solution from each equivalence class by an elitist genetic algorithm, and then generating entire classes. Notable efficiency was achieved due to significant reduction in search space.