Emerging Industrial Internet-of-Things systems require wireless solutions to connect sensors, actuators, and controllers as part of high data rate feedback-control loops over real-time flows. A key challenge is to provide predictable performance and agility in response to fluctuations in link quality, variable workloads, and topology changes. We propose WARP to address this challenge. WARP uses programs to specify a network's behavior and includes a synthesis procedure to automatically generate such programs from a high-level specification of the system's workload and topology. WARP has three unique features: (1) WARP uses a domain-specific language to specify stateful programs that include conditional statements to control when a flow's packets are transmitted. The execution paths of programs depend on the pattern of packet losses observed at runtime, thereby enabling WARP to readily adapt to packet losses due to short-term variations in link quality. (2) Our synthesis technique uses heuristics to improve network performance by considering multiple packet loss patterns and associated execution paths when determining the transmissions performed by nodes. Furthermore, the generated programs ensure that the likelihood of a flow delivering its packets by its deadline exceeds a user-specified threshold. (3) WARP can adapt to workload and topology changes without explicitly reconstructing a network's program based on the observation that nodes can independently synthesize the same program when they share the same workload and topology information. Simulations show that WARP improves network throughput for data collection, dissemination, and mixed workloads on two realistic topologies. Testbed experiments show that WARP reduces the time to add new flows by 5 times over a state-of-the-art centralized control plane and guarantees the real-time and reliability of all flows.

Future Industrial Internet-of-Things (IIoT) systems will require wireless solutions to connect sensors, actuators, and controllers as part of high data rate feedback-control loops over real-time flows. A key challenge in such networks is to provide predictable performance and adaptability in response to link quality variations. We address this challenge by developing RECeiver ORiented Policies (Recorp), which leverages the stability of IIoT workloads by combining offline policy synthesis and run-time adaptation. Compared to schedules that service a single flow in a slot, Recorp policies share slots among multiple flows by assigning a coordinator and a list of flows that may be serviced in the same slot. At run-time, the coordinator will execute one of the flows depending on which flows the coordinator has already received. A salient feature of Recorp is that it provides predictable performance: a policy meets the end-to-end reliability and deadline of flows when the link quality exceeds a user-specified threshold. Experiments show that across IIoT workloads, policies provided a median increase of 50% to 142% in real-time capacity and a median decrease of 27% to 70% in worst-case latency when schedules and policies are configured to meet an end-to-end reliability of 99%.

Hand washing is an effective countermeasure to the spread of many types of infection. Recently, sensing technology has automated the sampling and study of hand hygiene rates. Surprisingly, many questions about the area are unresolved, motivating further exploration based on wrist-worn commodity sensors (accelerometer and MEMS gyroscope). This paper describes initial work on techniques for measuring the duration of washing events and classifying different scrubbing motions. The work compares different sensor types and their fusion, compares sensing from one wrist to measuring both wrists, and explains results of experiments on a range of hand washing motions in a variety of subject populations, some in clinics of a teaching hospital. Machine learning is used to explore such questions: the paper investigates numerous features extracted from sensor data, looking at sampling rates, windowing, and platform details that affect classification. In training and classification experiments, data collection starts on the wrist, activated by a message from a disinfectant dispenser; data is then transferred by radio to a base station for subsequent reduction, analysis and characterization. Results show that hand hygiene motions can be classified with up to 93% accuracy.

We present DESALalpha, a realization of the dynamic embedded sensor-actuator language for Telos-based devices. The platform provides native support for: (i) rule-based programming; (ii) synchronized action scheduling; (iii) neighborhood management; and (iv) distributed state sharing. We describe the design and implementation of DESALalpha, present examples that illustrate its use, and summarize the resource requirements of compiled applications. Finally, we present lessons learned based on our use of DESALalphaduring the past year.

A goal of peer-to-peer applications is to share files between users themselves rather than downloading files from file servers. Self-downloading protocols have the property that, eventually, every user downloads only from other users. Self-downloading is problematic if users disconnect from the system upon completing file downloading, because they only share with other users while connected. Yet, if users continue to arrive at a sufficient rate, self-downloading protocols are possible. One vulnerability of file sharing between users is the possibility that files or segments could be counterfeit or corrupt. Protocols that are d -safe tolerate some number of instances of faulty segments in a file being downloaded, because each segment is downloaded d times before being shared. This article shows that d -safe self-downloading is possible for a sufficiently large arrival rate of users to the system. Upper and lower connectivity and sharing bounds are given for d = 2, and simulation results show effects of relaxing assumptions about arrival rates and bandwidth.

Project ExScal (for extreme scale) fielded a 1000+ node wireless sensor network and a 200+ node peer-to-peer ad hoc network of 802.11 devices in a 13km by 300m remote area in Florida, USA during December 2004. In comparison with previous deployments, the ExScal application is relatively complex and its networks are the largest ones of either type fielded to date. In this paper, we overview the key requirements of ExScal, the corresponding design of the hardware/software platform and application, and some results of our experiments.

No abstract available.

The ability of a system to recover from unexpected change in its environment or disruptions to its internal state is an indication of robust design and autonomous control. Recovery can be constrained by service availability requirements, so that even during periods of recovery, new service requests should be admitted and processed in a timely manner. Given that complex systems are constructed from many components, it is sensible to investigate how individual components can facilitate recovery and also satisfy availability requirements. The component presented is a search tree data structure that can recover from any disruption: it is a self-stabilizing data structure. No matter how severe the damage to its internal state, new operations on the data structure behave properly and the responses to operations are accurate indicators of any change to the search tree, even as the search tree recovery is underway. This paper resolves, for the first time, issues of dynamic allocation and pointer organization in a stabilizing data structure. After any sequence of O(m) operations in an arbitrary initial search tree of m nodes, the tree becomes balanced, all operations have O(lg n) running time, and free chains are adequate to supply new nodes for insertions. To meet availability constraints, operations have O(lg K) running time during periods of recovery, where K is the maximum number of items that the data structure can contain.

Phase clocks are synchronization tools that implement a form of logical time in distributed systems. For systems tolerating transient faults by self-repair of damaged data, phase clocks can enable reasoning about the progress of distributed repair procedures. This paper presents a phase clock algorithm suited to the model of transient memory faults in asynchronous systems with read/write registers. The algorithm is self-stabilizing and guarantees accuracy of phase clocks within O(k) time following an initial state that is.

No abstract available.

. Self-stabilization provides a non-masking approach to fault tolerance. Given this fact, one would hope that in a self-stabilizing system, the amount of disruption caused by a fault is proportional to the severity of the fault. However, this is not true for many self-stabilizing systems. Our paper addresses this weakness of distributed self-stabilizing systems by introducing the notion of fault containment. Informally, a fault-containing self-stabilizing algorithm is one that contains the effects of limited transient faults while retaining the property of self-stabilization. The paper begins with a formal framework for specifying and evaluating fault-containing self-stabilizing protocols. Then, it is shown that self-stabilization and fault containment are goals that can conflict. For example, it is shown that imposing a O(1) bound on the worst case recovery time from a 1-faulty state necessitates added overhead for stabilization: for some tasks, the O(1) recovery time implies stabiliz...

Two aspects of reliability of distributed protocols are a protocol's ability to recover from transient faults and a protocol's ability to function in a dynamic environment. Approaches for both of these aspects have been separately developed, but have drawbacks when applied to an environment that has both transient faults and dynamic changes. This paper introduces definitions and methods for addressing both concerns in the design of systems. A protocol is superstabilizing if it is (i) self-stabilizing, meaning that it is guaranteed to respond to an arbitrary transient fault by eventually satisfying and maintaining a legitimacy predicate, and (ii) it is guaranteed to satisfy a passage predicate at all times when the system undergoes topology changes starting from a legitimate state. The passage predicate is typically a safety property that should hold while the protocol makes progress towards re-establishing legitimacy following a topology change. Specific contributions of the paper inc...

An adaptive program is one that changes its behavior base on the current state of its environment. This notion of adaptivity is formalized, and a logic for reasoning about adaptive programs is presented. The logic includes several composition operators that can be used to define an adaptive program in terms of given constituent programs; programs resulting from these compositions retain the adaptive properties of their constituent programs. The authors begin by discussing adaptive sequential programs, then extend the discussion to adaptive distributed programs. The relationship between adaptivity and self-stabilization is discussed. A case study for constructing an adaptive distributed program where a token is circulated in a ring of processes is presented.>