1431008
Polynomial time synthesis of Byzantine agreement
We present a polynomial time algorithm for automatic synthesis of fault-tolerant distributed programs, starting from fault-intolerant versions of those programs. Since this synthesis problem is known to be NP-hard, our algorithm relies on heuristics to reduce the complexity. We demonstrate that our algorithm is able to synthesize an agreement program that tolerates a Byzantine fault.
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.
11497337
Secret instantiation in ad-hoc networks
Abstract In this paper, we focus our attention on the problem of assigning initial secrets to users in ad-hoc network (respectively, sensors in a sensor network) so that they can use those secrets to ensure authentication and privacy during their communication. The goal of this assignment is to ensure that any two users can communicate securely with each other even though each user maintains only a small number of secrets. With this motivation, we present a protocol that maintains O ( n ) secrets per user where n is the number of users in the system. We show that our secret distribution protocol suffices for privacy and authentication as well as secure multihop communication between two users. Furthermore, we show that the number of secrets maintained in this protocol is within a constant factor of the optimal. For the case where user capability prevents them from maintaining the necessary secrets, we propose two probabilistic protocols that maintain O(log n) secrets and where the probability of security compromise between two users is inversely proportional to the number of secrets they maintain. Thus, our protocols provide a continuum where the level of privacy and authentication depends upon user requirements and capabilities.
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.
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.
14885154
On-line learning of functions of bounded variation under various sampling schemes
We consider the problem of learning of an arbitrary function selected from the non-smooth class of functions that are of bounded variation. Bounds on the prediction errors resulting from sequential type algorithms are achieved for various scenarios. It is shown that for any algorithm there exists a sequence of samples and a function that results in a unit error at each step. If the samples are i.i.d. uniform then there exists an algorithm such that for any function of bounded variation the expected error is less than O(log n/n). Furthermore, for any algorithm there exists a function such that the expected error is greater than 0(1/n). We then introduce a mixed sampling setting in which an adversary can choose points but the actual samples are drawn uniformly from a 6 neighborhood of his selection. We show that there exists an algorithm such that for any function of bounded variation and for any sequence of adversarychosen points the expected cumulative error is less than 0(+ log n). Finally, results are derived for the uniform sampling case with noisy observations. We show that the order of growth of the expected error with noise sequences in Z1 remains unaltered. However, for i.i.d. zero mean and finite variance noise there exists an algorithm with expected error less than 0(1/n*), and for i.i.d. Gaussian noise any algorithm has expected error of at least o(l/@). Permission to copy without fee all or part of this material is granted provided that the copies ars not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying IS by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. ACM COLT ’93 171931CA, USA @ 1993 Acfvf 0.89791-61 ~-5/93 /o(307/0439... $1 .50
5710059
Universal variable-to-fixed length source codes
A universal variable-to-fixed length algorithm for binary memoryless sources which converges to the entropy of the source at the optimal rate is known. We study the problem of universal variable-to-fixed length coding for the class of Markov sources with finite alphabets. We give an upper bound on the performance of the code for large dictionary sizes and show that the code is optimal in the sense that no codes exist that have better asymptotic performance. The optimal redundancy is shown to be H log log M/log M where H is the entropy rate of the source and M is the code size. This result is analogous to Rissanen's (1984) result for fixed-to-variable length codes. We investigate the performance of a variable-to-fixed coding method which does not need to store the dictionaries, either at the coder or the decoder. We also consider the performance of both these source codes on individual sequences. For individual sequences we bound the performance in terms of the best code length achievable by a class of coders. All the codes that we consider are prefix-free and complete.
15091862
A physical design tool for built-in self-repairable static RAMs
A novel physical design tool, BISRAMGEN, that generates layout geometries of parametrized built-in self-repairable SRAM modules, producing significant improvement in testability, reliability, production yield and manufacturing cost of ASICs and microprocessors with embedded RAMs, is presented.
7170748
Efficiently synthesizing virtual video
Given a set of synchronized video sequences of a dynamic scene taken by different cameras, we address the problem of creating a virtual video of the scene from a novel viewpoint. A key aspect of our algorithm is a method for recursively propagating dense and physically accurate correspondences between the two video sources. By exploiting temporal continuity and suitably constraining the correspondences, we provide an efficient framework for synthesizing realistic virtual video. The stability of the propagation algorithm is analyzed, and experimental results are presented.
325979
Recursive propagation of correspondences with applications to the creation of virtual video
This paper is concerned with the efficient temporal propagation of correspondences between frames of two video sequences, an integral component of many video processing tasks. The main contribution is a framework for the recursive propagation of these correspondences. The propagation consists of a time update step and a measurement update step. The time update depends only on the dynamics of the rotating source cameras, while the measurement update can be tailored to any member of a general class of image correspondence algorithms. Using these results, the correspondence between points of each frame pair can be propagated and updated in a fraction of the time required to estimate correspondences anew at every frame. We discuss an application of the recursive correspondence propagation framework to the creation of virtual video. Previous virtual view algorithms have been used to generate synthetic video of a static scene, in which objects seem frozen in time. In contrast, the algorithms described here allow the creation of "true" virtual video, in the sense that the synthetic video evolves dynamically along with the scene. While virtual video is our motivating application, the recursive correspondence propagation framework applies to any two-camera video application in which correspondence is difficult and prohibitively time-consuming to estimate by processing frame pairs independently.