In the emerging area of sensor-based systems, a significant challenge is to develop scalable, fault-tolerant methods to extract useful information from the data the sensors collect. An approach to this data management problem is the use of sensor database systems, exemplified by TinyDB and Cougar, which allow users to perform aggregation queries such as MIN, COUNT and AVG on a sensor network. Due to power and range constraints, centralized approaches are generally impractical, so most systems use in-network aggregation to reduce network traffic. Also, aggregation strategies must provide fault-tolerance to address the issues of packet loss and node failures inherent in such a system. An unfortunate consequence of standard methods is that they typically introduce duplicate values, which must be accounted for to compute aggregates correctly. Another consequence of loss in the network is that exact aggregation is not possible in general. With this in mind, we investigate the use of approximate in-network aggregation using small sketches. Our contributions are as follows: 1) we generalize well known duplicateinsensitive sketches for approximating COUNT to handle SUM (and by extension, AVG and other aggregates), 2) we present and analyze methods for using sketches to produce accurate results with low communication and computation overhead (even on low-powered CPUs with little storage and no floating point operations), and 3) we present an extensive experimental validation of our methods. 1

Underwater Sensor Networks (UWSNs) are significantly different from land-based sensor networks. In UWSNs, the new features: low bandwidth, high latency, high network dynamics, high error probability, and 3-dimensional space, bring big challenges to network protocol design. In this technical report, we tackle one fundamental problem in UWSNs: scalable and energy efficient routing. We propose a novel routing protocol, called vector-based forwarding (VBF) to address these new challenges. VBF is scalable and energy efficient. In VBF, no state information is required on the sensor nodes and only a small fraction of the nodes are involved in routing. Moreover, we develop a localized and distributed self-adaptation algorithm to enhance the performance of VBF. The self-adaptation algorithm allows the nodes to weigh the benefit to forward packets and reduce energy consumption by discarding the low benefit packets. We evaluate the performance of VBF through extensive simulations. Our experiment results show that for networks with small or medium node mobility (2 m/s-10 m/s), VBF can effectively accomplish the goals of energy efficiency, high success of data delivery and low end-to-end delay.

Abstract — Wireless mesh networks hold promises to provide robust and high-throughput data delivery to wireless users. In a mesh network, high-speed Access Points (HAPs), equipped with advanced antennas, communicate with each other over wireless channels and form an indoor/outdoor broadband backhaul. This backbone efficiently forwards user traffic to a few gateway APs (GAPs), which additionally have high-speed connections to the wired Internet. In this paper, we describe ROMER, a resilient and opportunistic routing solution for mesh networks. ROMER balances between long-term route stability and shortterm opportunistic performance. It builds a runtime, forwarding mesh on a per-packet basis that offers a set of candidate routes. The actual forwarding path by each packet opportunistically adapts to the dynamic channel condition and exploits the highestrate wireless channels at the time. To improve resilience against lossy links, HAP failures or HAPs under DoS attacks, ROMER delivers redundant data copies in a controlled and randomized manner over the candidate forwarding mesh. We evaluate the effectiveness of ROMER through both simulations and analysis. I.

Several anomalies can occur in wireless sensor networks that impair their desired functionalities i.e., sensing and communication. Different kinds of holes can form in such networks creating geographically correlated problem areas such as coverage holes, routing holes, jamming holes, sink/black holes and worm holes, etc. We detail in this paper different types of holes, discuss their characteristics and study their effects on successful working of a sensor network. We present state-of-the-art in research for addressing the holes related problems in wireless sensor networks and discuss the relative strengths and short-comings of the proposed solutions for combating different kinds of holes. We conclude by highlighting future research directions.

Node compromise poses severe security threats in wireless sensor networks. Unfortunately, existing security designs can address only a small, fixed threshold number of compromised nodes; the security protection completely breaks down when the threshold is exceeded. In this paper, we seek to overcome the threshold limitation and achieve resiliency against an increasing number of compromised nodes. To this end, we propose a novel location-based approach in which the secret keys are bound to geographic locations, and each node stores a few keys based on its own location. The location-binding property constrains the scope for which individual keys can be (mis)used, thus limiting the damages caused by a collection of compromised nodes. We illustrate this approach through the problem of report fabrication attacks, in which the compromised nodes forge non-existent events. We evaluate our design through extensive analysis, implementation and simulations, and demonstrate its graceful performance degradation in the presence of an increasing number of compromised nodes.

Abstract. The directed flood-routing framework (DFRF) for wireless sensor networks is introduced in this paper that allows the modeling and rapid development of application specific routing protocols based on directed flooding. Flood-routing protocols are probabilistic methods that make only the best effort to route data packets. The presented family of protocols can route regular sized data packets via broadcast messages according to customizable, state machine based routing policies that govern the way intermediate nodes rebroadcast messages. The framework supports automatic data packet aggregation, and allows in-network data packet filtering and alteration. 1

Denial of service (DoS) attacks can cause serious damage in resourceconstrained, wireless sensor networks (WSNs). This paper addresses an especially damaging form of DoS attack, called PDoS (Path-based Denial of Service). In a PDoS attack, an adversary overwhelms sensor nodes a long distance away by flooding a multihop end-to-end communication path with either replayed packets or injected spurious packets. This paper proposes a solution using one-way hash chains to protect end-to-end communications in WSNs against PDoS attacks. The proposed solution is lightweight, tolerates bursty packet losses, and can easily be implemented in modern WSNs. The paper reports on performance measured from a prototype implementation. 1.

We introduce a simple ad-hoc routing scheme that operates in the true spirit of ad-hoc networking, i.e., in a modeless fashion, without neighborhood discovery or explicit point-to-point forwarding, while offering a high (and tunable) degree of reliability, fault-tolerance and robustness. Being aimed at truly tiny devices (e.g., with 1KB of RAM), our scheme can automatically take advantage of extra memory resources to improve the quality of routes for critical nodes. In contrast to some popular low-cost solutions, like ZigBee, TM our approach involves a single node type and exhibits lower resource requirements. The presented scheme has been verified in an industrial deployment with stringent quality of service requirements. 1.

There is a fundamental difference between wireless and wired networks, since the latter employ point-to-point communication while the former use broadcast transmission as the communication primitive. In this paper, we describe an algorithm, called self-selection, which takes advantage of broadcast communication to efficiently implement the basic operation of selecting a node possessing some desired properties among all the neighbors of the requestor. Self-selection employs a prioritized transmission back-off delay scheme in which each node’s delay of transmitting a signal is dependent on the probability of the node’s ability to best perform a pertinent task and in turn, enables the node to autonomously select itself for the task. We demonstrate the benefits of self-selection in two basic wireless ad hoc network communication algorithms: flooding and routing. By relating back-off delay to the signal strength of a received packet, we design an efficient variant of conventional flooding named Signal Strength Aware Flooding. By using distance-to-destination to derive back-off delay, we design a novel and fault-tolerant wireless ad hoc network routing protocol named Self-Selective Routing.

This paper presents the results of implementation of a novel protocol, Self-Healing Routing (SHR) for opportunistic multi-hop wireless communication, on MicaZ sensor motes. The protocol uses broadcast communication and a prioritized transmission back-off delay scheme to empower a receiving mote to use its hop distance from the destination to decide autonomously whether to forward a packet. When severed routes are encountered, the protocol dynamically and locally re-routes packets so they traverse the surviving shortest route. We have implemented this protocol on a set of MicaZ motes as well as in the SENSE sensor network simulator and conducted field testing with different mote and network configurations. We also tested scenarios with the motes turned off (modeling permanent failures) and in simulation also temporarily off line (modeling transient failures). We compared SHR with two traditional protocols: MintRoute and AODV. The results, as shown by experimental measurement and simulations reported in the paper, demonstrate that Self-Healing Routing is an efficient fault-tolerant protocol that performs well even with spontaneous network topology changes.