1315797
Correctness of Component-Based Adaptation
Long running applications often need to adapt due to changing requirements or changing environment. Typically, such adaptation is performed by dynamically adding or removing components. In these types of adaptation, components are often added to or removed from multiple processes in the system. While techniques for such adaptations have been extensively discussed in the literature, there is a lack of systematic methods to ensure the correctness of dynamic adaptation. To redress this deficiency, in this paper, we propose a new method, based on the concept of proof lattice, for verifying correctness of dynamic adaptation in a distributed application. We use transitional-invariant lattice to verify correctness of adaptation. As an illustration of this method, we show how correctness of dynamic adaptation is obtained in the context of a message communication application.
1711572
Designing masking fault-tolerance via nonmasking fault-tolerance
Masking fault-tolerance guarantees that programs continually satisfy their specification in the presence of faults. By way of contrast, nonmasking fault-tolerance does not guarantee as much: it merely guarantees that when faults stop occurring, program executions converge to states from where programs continually (re)satisfy their specification. In this paper, we show that a practical method to design masking fault-tolerance is to first design nonmasking fault-tolerance and to then transform the nonmasking fault-tolerant program minimally so as to achieve masking fault-tolerance. We demonstrate this method by designing novel fully distributed programs for termination detection, mutual exclusion, and leader election, that are masking tolerant of any finite number of process fail-stops and/or repairs.
6279302
A line in the sand: a wireless sensor network for target detection, classification, and tracking
Intrusion detection is a surveillance problem of practical import that is well suited to wireless sensor networks. In this paper, we study the application of sensor networks to the intrusion detection problem and the related problems of classifying and tracking targets. Our approach is based on a dense, distributed, wireless network of multi-modal resource-poor sensors combined into loosely coherent sensor arrays that perform in situ detection, estimation, compression, and exfiltration. We ground our study in the context of a security scenario called "A Line in the Sand" and accordingly define the target, system, environment, and fault models. Based on the performance requirements of the scenario and the sensing, communication, energy, and computation ability of the sensor network, we explore the design space of sensors, signal processing algorithms, communications, networking, and middleware services. We introduce the influence field, which can be estimated from a network of binary sensors, as the basis for a novel classifier. A contribution of our work is that we do not assume a reliable network; on the contrary, we quantitatively analyze the effects of network unreliability on application performance. Our work includes multiple experimental deployments of over 90 sensor nodes at MacDill Air Force Base in Tampa, FL, as well as other field experiments of comparable scale. Based on these experiences, we identify a set of key lessons and articulate a few of the challenges facing extreme scaling to tens or hundreds of thousands of sensor nodes.
52887342
Low-cost fault-tolerance in barrier synchronizations
We show how fault-tolerance can be effectively added to several types of faults in program computations that use barrier synchronization. We divide the faults that occur in practice into two classes, detectable and undetectable, and design a fully distributed program that tolerates the faults in both classes. Our program guarantees that every barrier is executed correctly even if detectable faults occur, and that eventually every barrier is executed correctly even if undetectable faults occur. Via analytical as well as simulation results we show that the cost of adding fault-tolerance is low, in part by comparing the times required by our program with that required by the corresponding fault-intolerant counterpart.
37856387
Collision-Free Communication in Sensor Networks
In this paper, we provide a stabilizing solution for collision-free diffusion in sensor networks. Such diffusions are often necessary in sensor networks when information from one sensor needs to be communicated to other sensors that satisfy certain geographic properties. Our solution deals with several difficulties, e.g., unidirectional links, unreliable links, long links, failed sensors, and sensors that are sleeping in order to save energy, that occur in sensor networks. It also ensures that there are no collisions during the diffusion and that the time required for the diffusion is O(D) where D is the diameter of the network. Moreover, while the solution can be applied to an arbitrary topology, it is more suitable for a commonly occurring topology, a two-dimensional grid. 
 
We show how our solution for collision-free diffusion can be used for time-division multiplexing (TDM) in sensor networks. TDM ensures that the message communication (other than the messages sent by diffusion) among sensors is also collision-free. While collision-free diffusion and time-division multiplexing are interdependent, we show how both these properties can be achieved simultaneously. Our algorithms are stabilizing fault-tolerant, i.e., collision-free diffusion and time-division multiplexing are restored even if the system reaches an arbitrary state where the sensors are corrupted or improperly initialized.
12287966
Complexity issues in automated synthesis of failsafe fault-tolerance
We focus on the problem of synthesizing failsafe fault-tolerance where fault-tolerance is added to an existing (fault-intolerant) program. A failsafe fault-tolerant program satisfies its specification (including safety and liveness) in the absence of faults. However, in the presence of faults, it satisfies its safety specification. We present a somewhat unexpected result that, in general, the problem of synthesizing failsafe fault-tolerant distributed programs from their fault-intolerant version is NP-complete in the state space of the program. We also identify a class of specifications, monotonic specifications, and a class of programs, monotonic programs, for which the synthesis of failsafe fault-tolerance can be done in polynomial time (in program state space). As an illustration, we show that the monotonicity restrictions are met for commonly encountered problems, such as Byzantine agreement, distributed consensus, and atomic commitment. Furthermore, we evaluate the role of these restrictions in the complexity of synthesizing failsafe fault-tolerance. Specifically, we prove that if only one of these conditions is satisfied, the synthesis of failsafe fault-tolerance is still NP-complete. Finally, we demonstrate the application of monotonicity property in enhancing the fault-tolerance of (distributed) nonmasking fault-tolerant programs to masking.
6063474
PAC learning with generalized samples and an application to stochastic geometry
In this paper, we introduce an extension of the standard PAC learning model which allows the use of generalized samples. We view a generalized sample as a pair consisting of a functional on the concept class together with the value obtained by the functional operating on the unknown concept. It appears that this model can be applied to a number of problems in signal processing and geometric reconstruction to provide sample size bounds under a PAC criterion. We consider a specific application of the model to a problem of curve reconstruction, and discuss some connections with a result from stochastic geometry.
38081004
A high-speed 32-bit parallel correlator for spread spectrum communication
This paper describes a high speed 32-bit pipelined digital parallel correlator implemented in a Lattice field programmable gate array (FPGA). The parallel correlator is of use in CDMA and spread spectrum transceivers for the continuous calculation of correlation between an incoming data stream with a PN sequence. The maximum frequency of operation of the FPGA based correlator is 87 MHz providing a throughput of one 32-bit correlation every 11.5 ns resulting in considerable improvement over commercially available correlators in terms of speed as well as number of bits. The high speed of operation of the correlator coupled with its ability to handle up to 32 chips per data bit alleviates the problem of low information bit rates due to signal encoding in spread spectrum communication systems. A CMOS integrated circuit implementation of the parallel correlator is presented.
7360646
Upper bounds to transport capacity of wireless networks
We derive upper bounds on the transport capacity of wireless networks. The bounds obtained are solely dependent on the geographic locations and power constraints of the nodes. As a result of this derivation, we are able to conclude the optimality, in the sense of scaling of transport capacity with the number of nodes, of a multihop communication strategy for a class of network topologies.
11400186
On probably correct classification of concepts
We consider the problem of classifying an unknown concept into one of two subclasses of concepts. Specifically, if C is a concept class and Co and Cl are two disjoint subsets of C, given an unknown c E Co U Cl we wish to decide whether c c Co or c E Cl based on a set of random examples. We consider both uniform and non-uniform probably correct classification for which the number of samples is or is not required to be independent of c, respectively. For both cases, we obtain necessary and sufficient conditions on Co and Cl that allow probably correct classification. The conditions obtained are in terms of separability and/or coverability conditions on the classes Co and Cl. Furthermore, in the non-uniform case we show that this is equivalent to classification in the limit. Several examples of the applicability of our results are also provided.
15475360
Estimating correspondence in digital video
This paper addresses several estimation problems involving correspondence in digital video. We present three cases, in order of increasing complexity: affine transformations, projective transformations, and general correspondence. We review some recent research in the first two cases and present a new framework for discussing the third case. We also discuss how to use the formalism of correspondence graphs to ensure that any estimated correspondence is physically valid.