Maneesh Varshney

SQualNet: a scalable simulation framework for sensor networks

We have developed a scalable sensor network simulation framework called sQualnet [1]. sQualnet is based on the well-known Qualnet simulator; it benefits from Qualnet’s greater scalability, realistic and detailed propagation models, and support for easing model development. sQualnet features a rich suite of detailed and accurate sensor network specific models, including: sensing and radio channels, sensor protocols (MAC, routing), battery and power consumption models, support for multi-tiered sensor network evaluations. The observed network performance is highly dependent on the model accuracy, as shown in [2]. Besides, sQualnet provides real code simulation capability for motes [3]. Specifically, it allows the use of unmodified TinyOS applications (written in NesC) and SOS applications (written in C), thereby enabling easy transition between simulation and real experimentation on a deployed sensor network. Through the aforementioned features, sQualnet overcomes limitations of existing sensor network evaluation tools. Compared to common wireless network simulators (e.g., ns-2, OPNET, Qualnet) and other sensor-specific simulators (e.g., SensorSim), sQualnet has the additional capability for real-code simulation. With its support for accurate radio propagation models, it also addresses a key limitation of existing real-code simulators (e.g., TOSSIM) and hardware emulators (e.g., ATEMU). In addition, sQualnet offers hybrid simulation capability to support varying degrees of integration of real and simulated network components, which can aid in system development and enable large-scale evaluations in a cost-effective manner. Using this capability, one can model a network where some nodes are simulated while the rest are real physical nodes, or where some layers of the network

SenQ: a scalable simulation and emulation environment for sensor networks

Although there is growing interest in the use of physical testbeds to evaluate the performance of applications and protocols for sensor platforms, such studies also encounter significant challenges that include the lack of scalability and repeatability, as well as the inability to represent a diverse set of operational scenarios. On the other hand, simulators can typically address the preceding problems but often lack the high degree of fidelity available to the analysts with physical testbeds. In this paper, we present the design and implementation of SenQ - an accurate and scalable evaluation framework for sensor networks that effectively addresses the preceding challenges. In particular, SenQ integrates sensor network operating systems with a very high- fidelity simulation of wireless networks such that sensor network applications and protocols can be executed, without modifications, in a repeatable manner under a diverse set of scalable environments. SenQ extends beyond the existing suite of simulators and emulators in four key aspects: first, it supports emulation of sensor network applications and protocols in an efficient and flexible manner; second, it provides an efficient set of models of diverse sensing phenomena; third, it provides accurate models of both battery power and clock drift effect which have been shown to have a significant impact on sensor network studies; and finally it provides an efficient kernel that allows it to run experiments that provide substantial scalability in both the spatial and temporal contexts.

iMASH: interactive mobile application session handoff

Mobile computing research has often focused on untethering an in-use computing device, rather than enabling the mobility of the computation task itself. This paper presents an architecture, implementation, and experimental evidence that together validate a new continuous computing concept, application session handoff. The iMASH architecture leverages previous work on proxies, content adaptation, and client awareness to provide a unique, middleware-enable capability for continuous computing. Implementation in both socket- and RPC-based environments shows that very fast, secure session handoff of non-trivial client/server applications across heterogeneous client devices and network is feasible: experiments on a number of applications yielded handoff latencies ranging from 0.5s to 2s.

Detailed models for sensor network simulations and their impact on network performance

Recent trends in sensor network simulation can be divided between less flexible but accurate emulation based approach and more generic but less detailed network simulator models. We offer an approach with the flexibility of network simulators and provides the accuracy comparable to emulation based approaches. We describe the design and architecture of sensor network simulator which provides a rich suite of following models: sensing stack to model wave and diffusion based sensor channels, an accurate battery model, processor power consumption model, energy consumption model and sensor network based traffic model. We also present our study on the effects of detailed modeling on the performance of higher layer protocols. We describe the impact of using accurate models for battery, processor power consumption and traffic models on the network layer statistics as network lifetime and availability, throughput and routing overhead. Our results show there is high sensitivity of model accuracy on network and application level statistics. In extreme cases we have noticed an inversion of results with our accurate models as compared with previous generation of abstract models.

WHYNET: a hybrid testbed for large-scale, heterogeneous and adaptive wireless networks

We present an overview of the WHYNET (Wireless HYbrid NETwork) testbed, currently being developed for realistic and scalable evaluation of next-generation wireless network protocols and applications. WHYNET framework enables seamless integration of physical, simulation and emulation components in a single framework, and allows the use of any combination of those components when evaluating a target wireless network scenario. In this article, we describe the rationale behind our hybrid testbed approach, and give an overview of the architectural components of the hybrid testbed and key technical challenges addressed in its design. Further, we present several case studies to demonstrate the value of the hybrid testbed for realistic and scalable evaluation of a broad range of wireless network scenarios, focusing on cross-layer interactions, heterogeneous and large-scale wireless networks.

Modeling environmental mobility and its effect on network protocol stack

In this paper we address the effects of environmental mobility, that is, the ambient motion of entities like people and vehicles in the vicinity of wireless communication, on the channel characteristics and wireless network performance. We present a three step process of measurements, modeling and network simulations to quantify the significance of environmental mobility. Our field experiments show that presence of people not only cause deep fades but also distorts the fading distribution. We model the shadowing loss by three knife-edge diffraction model and propose a two-state Markov process channel fading behavior. The models are validated against measurement data and implemented in a network simulator. The models are scalable and incur execution overhead less than 15%. We also show the impact of environment mobility on protocol performance by means of two simulation case studies. We show that MAC layer data rate adaptation behavior is sensitive to environmental mobility and can result in 40% packets being delivered at lower rates. Second study on ad-hoc network performance show the throughput is decreased by 20%. We have identified that with environmental mobility the links are more sensitive to interference and the routes are less stable

A Live-Virtual-Constructive (LVC) framework for cyber operations test, evaluation and training

Current simulations supporting the Net-Centric Test battlespace do not accurately represent the impact of cyber threats and information operations. When cyber threats are considered, they are typically limited to a small number of isolated physical devices. To further limit consideration, insufficient attention is paid to cyber attacks launched on the basis of passive threats like the eavesdroppers or the coordinated threats. Further, the test technologies are typically limited to incorporation of threats that can be realized physically, which limits both the scale and sophistication of representing such attacks; a Live-Virtual-Constructive (LVC) paradigm for modeling of threats is missing. Lastly, for threats such as jamming, wormhole attacks, large-scale Denial of Service attacks, use of physical threats is expensive, since specialized equipment and manpower is required to realize these threats. The net consequence of these deficiencies is to leave a major gap in the DoD test infrastructure with respect to our ability to realistically test the vulnerabilities and resiliency of Blue Force communication architectures to sophisticated cyber attacks, particularly in networks that include both current force & Future Force communication infrastructure. In this paper, we present StealthNet, a Live-Virtual-Constructive (LVC) framework that provides a real-time, hardware-in-the-loop capability for simulation of cyber threats to the entire net-centric infrastructure. It also provides the ability to evaluate the effectiveness of the threats in disrupting Blue Force communications via key performance indicators, i.e. bandwidth, reliability, delay and quality of service metrics. The StealthNet framework provides models for accurate cyber threat simulation at all layers of the networking stack to include passive, active, coordinated and adaptive attacks on networks with hundreds to thousands of wired and wireless components. The LVC technology can stimulate physical Networked-System Under Test (NSUT) with simulated cyber threats that span all the protocol stack layers for real-time testing. Additionally, the framework enables composability with existing Test and Evaluation (T&E) architecture and tools (TENA, SBE environments, etc) to facilitate transition to other T&E programs.

Performance Implication of Environmental Mobility in Wireless Networks

Environmental mobility refers to the ambient motion of people, vehicles and other objects in the vicinity of wireless communication. Whereas the effect of mobility of transmitting and receiving radios has been widely researched, the impact of environmental mobility has been relatively unexplored in wireless networks. In this paper, we present a systematic study to analyze the effect of environmental mobility on wireless link behavior and protocol performance using measurement, analysis, and simulations. Measurement data from channel traces was collected to isolate and quantify the effects of environmental mobility on the channel performance. Efficient models were developed to explain the observed behavior and integrated with network simulation to enable protocol level analysis under such dynamics. We found that the class of protocols that maintain state or have memory but are otherwise agnostic of the channel operations fare poorly by acquiring incorrect information about the channel and are not able to adequately exploit durations where channel conditions are good. Two case studies at different layers of protocol stack are used to quantify such behavior to show that protocol perform maybe as much as 20-50% below their expected performance. To remedy this situation we present a cross layer optimization scheme, called Recovery from Earlier Good State (REGS), that allows protocols to become aware of the underlying channel operations. We show that use of REGS together with existing optimizations can improve throughputs in the presence of EM by more than 100%.

WHYNET: a framework for in-situ evaluation of heterogeneous mobile wireless systems

The design and implementation of wireless systems has been impeded by the lack of an evaluation framework that can provide an accurate understanding of middleware and application performance in the context of their interactions with system hardware and software, network architecture and configuration and wireless channel effects. In this paper we present a novel evaluation paradigm wherein the applications, middleware or sub-networks can be evaluated in-situ, in other words, as operational software that interfaces with the operating system and other applications, thus offering a fidelity equivalent to physical deployment. The physical environment in which such systems operate is modeled using high-fidelity simulations. This approach combines the fidelity of physical test beds with the benefits of scalability, repeatability of input parameters, and comprehensive parameter space evaluation - the known limitations of a physical test-bed. The framework design is extensible in that it allows configuring the desired components of a system with different modalities to suit a particular evaluation criterion. The implementation also addresses the key challenges in the interaction of the framework sub-components: seamless interfaces, time synchronization and preserving causality constraints. The benefits and applicability of the framework to diverse wireless contexts is demonstrated by means of various case studies in diverse wireless networks. In one case study, we show that a design exhibiting 4X improvement in network metrics may be actually degrading the application metric by 50%.

High-fidelity application-centric evaluation framework for vehicular networks

This paper proposes an evaluation framework for vehicular networks to achieve accurate, scalable, flexible and repeatable performance studies through the utilization of a hybrid emulation testbed and incorporation of high fidelity protocol and environment models. The proposed framework not only addresses the unique challenges of vehicular networks but also enables new types of network analyses via the capability of conducting application-centric evaluation. Compared to traditional network-centric evaluation, case studies show scenarios where network-level statistics do not clearly discriminate between the two routing protocols while significant performance differences were observed using the application-level metrics. The paper also identifies future research directions that are enabled by the evaluation framework.