Sridhar Radhakrishnan

PMAC: an adaptive energy-efficient MAC protocol for wireless sensor networks

We propose a novel adaptive MAC protocol for wireless sensor networks. In existing protocols such as SMAC, the sensor nodes are put to sleep periodically to save energy. As the duty cycle is fixed in such protocols, the network throughput can degrade under heavy traffic, while under light loads, unwanted energy consumption can occur. In the proposed pattern-MAC (PMAC) protocol, instead of having fixed sleep-wakeups, the sleep-wakeup schedules of the sensor nodes are adaptively determined. The schedules are decided based on a nodes own traffic and that of its neighbors. Our analytical and experimental results show that in comparison to SMAC, PMAC achieves more power savings under light loads, and higher throughput under heavier traffic loads. Furthermore, unlike SMAC, only the sensor nodes involved in communication wake up frequently in PMAC and hence energy is conserved in other sensor nodes.

Measurement and analysis of worm propagation on Internet network topology

There has been a constant barrage of worms over the Internet during the recent past. Besides threatening network security, these worms cause an enormous economic burden in terms of loss of productivity at the victim hosts. In addition, these worms create unnecessary network data traffic that causes network congestion, thereby hurting all users. To develop appropriate tools for thwarting quick spread of worms, researchers are trying to understand the behavior of the worm propagation with the aid of epidemiological models. In this study, we apply the classical SIS model and a modification of SIR model to simulate worm propagation in two different network topologies. Whereas in the SIR model once a node is cured after infection it becomes permanently immune, our modification allows this immunity to be temporary, since the cured nodes may again become infected, maybe with a different strain of the same worm. The simulation study also shows that time to infect a large portion of the network vary significantly depending on where the infection begins. This information could be usefully employed to choose hosts for quarantine to delay worm propagation to the rest of the network

A framework for fast RFID tag reading in static and mobile environments

A framework for reducing the average reading time of passive RFID tags in dense environments is introduced. The proposed framework termed Accelerated Frame Slotted ALOHA (AFSA) can be used in conjunction with almost all RFID tag reading protocols that are based on frame slotted ALOHA. It is shown that AFSA reduces the tag reading time by avoiding the wastage in bit times due to collisions and idle slots. The implementation of AFSA in conjunction with two different ALOHA protocols - one with unlimited frame sizes and the other with limited frame sizes is discussed. For both these protocols, extensions of AFSA to read passive tags in a mobile setting are described. Simulation results show that AFSA reduces the average tag reading time by up to 40% with respect to the stand alone ALOHA protocols under both static and mobile settings.

DST-A routing protocol for ad hoc networks using distributed spanning trees

A dynamic ad hoc network consists of a collection of mobile hosts with frequently changing network topology. We propose a distributed algorithm that adapts to the topology by utilizing spanning trees in the regions where the topology is stable, and resorting to an intelligent flooding-like approach in highly dynamic regions of the network. Routing is performed using the spanning trees based on a hold-and-forward or shuttling method. We introduce the notion of connectivity-through-time and holding time to quantify the performance of the routing algorithms for various network connectivity scenarios. Using simulation, we study the throughput, reachability and message-reachability ratio of the proposed network under various connection/reconnection rates and holding times.

Online energy aware routing in wireless networks

Online energy aware routing in wireless networks is the problem of finding energy efficient routes that maximize the network lifetime without the knowledge of future message flows. To maximize network lifetime, the paths for message flows are chosen in such a way that the total energy consumed along the path is minimized while avoiding energy depleted nodes. Finding paths which consume minimum energy and finding paths which do not use energy depleted nodes lead to conflicting objectives. In this paper, we propose two-phased energy aware routing strategies that balance these two conflicting objectives by transforming the routing problem into a multi-metric widest path problem. We find that the proposed approaches outperform the best-known algorithms in the literature. We also demonstrate a simple but insightful relationship between the total energy required along a path and the minimum remaining energy of a node along the path. We further exploit this relationship to show that staying within the solution space of paths with high residual energy and low total energy provides much improved lifetimes in general.

Error control and concealment for image transmission

In the practical transmission of compressed still images, bit errors may occur, which probably result in desynchronization and packet loss. In packet-switched networks, network congestion also results in packet loss. This survey article reviews the error resilience factors that must be faced by a robust image encoder and decoder (codec). The article begins with the enumeration of the different kinds of impact noisy channels and congested networks have on block-coded images. Then we present different techniques that can be applied to combat the degradation of the images introduced by the noisy channel and network congestion. These techniques include resynchronization strategies, post-processing error concealment algorithms, and preprocessing error control techniques. All these techniques can be either used directly or extended to robust video transmission.

Protocol for dynamic ad-hoc networks using distributed spanning trees

A dynamic ad-hoc network consists of a collection of mobile hosts with frequently changing network topology. We propose a distributed algorithm that adapts to the topology by utilizing spanning trees in the regions where the topology is stable, and resorting to an intelligent flooding-like approach in highly dynamic regions of the network. Routing is performed using the spanning trees based a hold-and-forward or shuttling mechanisms. We introduce the notion of connectivity-through-time and the parameter holding-time as new fundamental concepts that can be used by ad-hoc routing algorithms. For various network connectivity scenarios we evaluate the impact of these concepts on the performance of ad-hoc routing algorithms. Using simulation, we study the throughput, reachability and message–reachability ratio of the proposed schemes under various connection/disconnection rates and holding times.

Towards SDN-based fog computing: MQTT broker virtualization for effective and reliable delivery

Performance of data analytics in Internet of Things (IoTs) depends on effective transport services offered by the underlying network. Fog computing enables independent data-plane computational features at the edge-switches, which serves as a platform for performing certain critical analytics required at the IoT source. To this end, in this paper, we implement a working prototype of Fog computing node based on Software-Defined Networking (SDN). Message Queuing Telemetry Transport (MQTT) is chosen as the candidate IoT protocol that transports data generated from IoT devices (a:k:a: MQTT publishers) to a remote host (called MQTT broker). We implement the MQTT broker functionalities integrated at the edge-switches, that serves as a platform to perform simple message-based analytics at the switches, and also deliver messages in a reliable manner to the end-host for post-delivery analytics. We mathematically validate the improved delivery performance as offered by the proposed switch-embedded brokers.

Relay network design in freight transportation systems

Abstract This paper provides techniques, heuristics, and algorithms for the location of a minimal number of relay points on a highway network that satisfies the driver-distance constraint––a driver leaving a distribution center does not travel for more than t miles before which he/she returns back to the originating point or rests before moving on further. Straight Route and Detour versions are considered. Empirical evaluations of the proposed heuristics on road networks are performed. The results indicate that the Straight Route version is computationally efficient but locates a larger number of relay points than the Detour versions.

Interference aware multi-path routing in wireless networks

We can improve the end-to-end throughput between a sender and receiver in a wireless network using multiple paths which do not interfere with each other. Given that the problem of finding such paths is computationally hard, the paper focuses on finding multiple paths which may have interference between them, but still are able to obtain the maximum possible throughput. It is achieved by observing that the pattern of interference is more important than the number of interfering links. The nature of path sets with non-destructive interference is discussed and based on these observations, combinatorial techniques for finding interference aware disjoint paths in a wireless network are presented. Simulation results indicate that the proposed solutions achieve throughputs that are significantly higher than the established theoretical results.