Showing papers by "Bhaskaran Raman published in 2008"

Brimon: a sensor network system for railway bridge monitoring

Abstract: Railway systems are critical in many regions, and can consist of several tens of thousands of bridges, being used over several decades. It is critical to have a system to monitor the health of these bridges and report when and where maintenance operations are needed. This paper presents BriMon, a wireless sensor network based system for such monitoring. The design of BriMon is driven by two important factors: application requirements, and detailed measurement studies of several pieces of the architecture. In comparison with prior bridge monitoring systems and sensor network prototypes, our contributions are three-fold. First, we have designed a novel event detection mechanism that triggers data collection in response to an oncoming train. Next, BriMon employs a simple yet effective multi-channel data transfer mechanism to transfer the collected data onto a sink located on the moving train. Third, the BriMon architecture is designed with careful consideration of the interaction between the multiple requisite functionalities such as time synchronization, event detection, routing, and data transfer. Based on a prototype implementation, this paper also presents several measurement studies to show that our design choices are indeed quite effective.

Censor networks: a critique of "sensor networks" from a systems perspective

Abstract: This writeup presents a critique of the field of "Wireless Sensor Networks (WSNs)". Literature in this domain falls into two main, distinct categories: (1) algorithms or protocols, and (2) applicationcentric system design. A striking observation is that references across these two categories are minimal, and superficial at best. We argue that this is not accidental, and is the result of three main flaws in the former category of work. Going forward, an applicationdriven, bottom-up approach is required for meaningful articulation and subsequent solution of any networking issues in WSNs.

On the Feasibility of the Link Abstraction in (Rural) Mesh Networks

Abstract: Outdoor community mesh networks based on 802.11 have seen tremendous growth in the recent past. The current understanding is that wireless link performance in these settings in inherently unpredictable, due to multipath delay spread. Consequently, researchers have focused on developing intelligent routing techniques to achieve the best possible performance. In this paper, we are specifically interested in mesh networks in rural locations. We first present detailed measurements to show that the PHY layer in these settings is indeed stable and predictable. There is a strong correlation between the error rate and the received signal strength. We show that interference, and not multipath fading, is the primary cause of unpredictable performance. This is in sharp contrast with current widespread knowledge from prior studies. Furthermore, we corroborate our view with a fresh analysis of data presented in these prior studies. Based on our results, we argue that outdoor rural mesh networks can indeed be built with the link abstraction being valid. This has several design implications, and opens up a fresh perspective on a wide range of technical issues in this domain.

Emulation-based Evaluation of an Architecture for Wide-Area Service Composition

Abstract: Service composition provides a flexible way to quickly enable new application functionalities using component services. We focus on the scenario where next generation portal providers “compose” the services of other providers. We have developed an architecture based on an overlay network of service clusters to provide failure-resilient composition of services across the wide-area Internet: our algorithms detect and recover quickly from failures in composed client sessions. In this paper, we present an evaluation of our architecture whose overarching goal is quick recovery of client sessions. The evaluation of an Internet-scale system like ours is challenging. Simulations do not capture true workload conditions and Internetwide deployments are often infeasible. We have developed an emulation platform for our evaluation – one that allows a realistic and controlled design study. Our experiments show the effectiveness of our recovery mechanisms: over 90% of the client sessions are restored within 1sec after failure detection in Internet paths. We collect trace data to show that failure detection itself can be tight on wide-area Internet paths – within about 2sec. Failure detection and recovery within these time bounds represents a significant improvement over existing Internet path recovery mechanisms that take several tens of seconds to a few minutes [12]. Furthermore, the control overhead involved in implementing our recovery mechanism is minimal in terms of network as well as processor resources; minimal additional provisioning is required for this.