Sonia Fahmy

Bio: Sonia Fahmy is an academic researcher from Purdue University. The author has contributed to research in topics: Asynchronous Transfer Mode & Wireless sensor network. The author has an hindex of 39, co-authored 217 publications receiving 11177 citations. Previous affiliations of Sonia Fahmy include Ohio State University & Hewlett-Packard.

Sleep/wake scheduling for multi-hop sensor networks: Non-convexity and approximation algorithm

Abstract: We investigate the problem of sleep/wake scheduling for low duty cycle sensor networks. Our work differs from prior work in that we explicitly consider the effect of synchronization error in the design of the sleep/wake scheduling algorithm. In our previous work, we studied sleep/wake scheduling for single hop communication, e.g., intra-cluster communication between a cluster head and cluster members. We showed that there is an inherent trade-off between energy consumption and message delivery performance (defined as the message capture probability). We proposed an optimal sleep/wake scheduling algorithm, which satisfies a given message capture probability threshold with minimum energy consumption. In this work, we consider multi-hop communication. We remove the previous assumption that the capture probability threshold is already given, and study how to decide the per-hop capture probability thresholds to meet the Quality of Services (QoS) requirements of the application. In many sensor network applications, the QoS is decided by the amount of data delivered to the base station(s), i.e., the multi-hop delivery performance. We formulate an optimization problem to set the capture probability threshold at each hop such that the network lifetime is maximized, while the multi-hop delivery performance is guaranteed. The problem turns out to be non-convex and hence cannot be efficiently solved using standard methods. By investigating the unique structure of the problem and using approximation techniques, we obtain a solution that provably achieves at least 0.73 of the optimal performance. Our solution is extremely simple to implement.

Forwarding devices: From measurements to simulations

Abstract: Most popular simulation and emulation tools use high-level models of forwarding behavior in switches and routers, and give little guidance on setting model parameters such as buffer sizes. Thus, a myriad of papers report results that are highly sensitive to the forwarding model or buffer size used. Incorrect conclusions are often drawn from these results about transport or application protocol performance, service provisioning, or vulnerability to attacks. In this article, we argue that measurement-based models for routers and other forwarding devices are necessary. We devise such a model and validate it with measurements from three types of Cisco routers and one Juniper router, under varying traffic conditions. The structure of our model is device-independent, but the model uses device specific parameters. The compactness of the parameters and simplicity of the model make it versatile for high-fidelity simulations that preserve simulation scalability. We construct a profiler to infer the parameters within a few hours. Our results indicate that our model approximates different types of routers significantly better than the default ns-2 simulator models. The results also indicate that queue characteristics vary dramatically among the devices we measure, and that backplane contention can be a factor.

Synergy: An overlay internetworking architecture and implementation

Abstract: A multitude of overlay network designs for resilient routing, multicasting, quality of service, content distribution, storage, and object location have been proposed. Overlay networks offer several attractive features, including ease of deployment, flexibility, adaptivity, and an infrastructure for collaboration among hosts. In this paper, we explore cooperation among co-existing, possibly heterogeneous, overlay networks. We discuss a spectrum of cooperative forwarding and information sharing services, and investigate the associated scalability, heterogeneity, and security problems. Motivated by these services, we design Synergy, a utility-based overlay internetworking architecture that fosters overlay cooperation. Our architecture promotes fair peering relationships to achieve synergism. Results from Internet experiments with cooperative forwarding overlays indicate that our Synergy prototype improves delay, throughput, and loss performance, while maintaining the autonomy and heterogeneity of individual overlay networks.

HEED: a hybrid, energy-efficient, distributed clustering approach for ad hoc sensor networks

Abstract: Topology control in a sensor network balances load on sensor nodes and increases network scalability and lifetime. Clustering sensor nodes is an effective topology control approach. We propose a novel distributed clustering approach for long-lived ad hoc sensor networks. Our proposed approach does not make any assumptions about the presence of infrastructure or about node capabilities, other than the availability of multiple power levels in sensor nodes. We present a protocol, HEED (Hybrid Energy-Efficient Distributed clustering), that periodically selects cluster heads according to a hybrid of the node residual energy and a secondary parameter, such as node proximity to its neighbors or node degree. HEED terminates in O(1) iterations, incurs low message overhead, and achieves fairly uniform cluster head distribution across the network. We prove that, with appropriate bounds on node density and intracluster and intercluster transmission ranges, HEED can asymptotically almost surely guarantee connectivity of clustered networks. Simulation results demonstrate that our proposed approach is effective in prolonging the network lifetime and supporting scalable data aggregation.

Topology Control in Wireless Ad Hoc and Sensor Networks

Abstract: Topology Control (TC) is one of the most important techniques used in wireless ad hoc and sensor networks to reduce energy consumption (which is essential to extend the network operational time) and radio interference (with a positive effect on the network traffic carrying capacity). The goal of this technique is to control the topology of the graph representing the communication links between network nodes with the purpose of maintaining some global graph property (e.g., connectivity), while reducing energy consumption and/or interference that are strictly related to the nodes' transmitting range. In this article, we state several problems related to topology control in wireless ad hoc and sensor networks, and we survey state-of-the-art solutions which have been proposed to tackle them. We also outline several directions for further research which we hope will motivate researchers to undertake additional studies in this field.