Design of Hierarchical, Mobile, Multi-Sink Routing for Low-Power and Lossy Networks

Abstract

Wireless Sensor Network (WSN) devices are small, low-powered sensors that are deploy- able for long-periods of time to provide information on the local evironment to the world at large. These devices are designed to be deployed and operated for extended periods of time with a minimum amount of maintenance. These inexpensive devices open up a new eld in computing, providing the ability for small groups to gather data on their environment for use in myriad tasks. This work presents the Hierarchical network of Observable devices with Itinerant Sinks Transporting data (HOIST), a WSN architecture I designed to alleviate the e ects of the disadvantages that lie within a WSN deployment. I began this design by dividing the traditional sender-sink model into a three-tier hierarchial model. This model separates the senders and the ultimate destination sink into tiers joined together by a series of bridging sinks. These bridging devices each control a smaller fragment of the collectors, enabling downward routing to a larger degree than otherwise possible with a traditional single DAG, while also coordinating the transmission of data between the collectors and the destination sink. Furthermore, HOIST adds in mobility to the model, allowing the highest tier sink to move about the deployment area, minimizing any set of bridging sinks from being the sole route burdened with relaying the messages of all of the devices on the network to the sink. This architecture further de nes the role of the bridges to coordinate their local collectors to send data one device at a time, enabling the expansion in network tra c to increase logarithmically with respect to the increase in the number of collectors. HOIST also allows further scaling by using the rst mobile sink, designated as the messenger, to travel between geographically segregated deployment areas to enable each cluster to send their data without having to create unnecessary lines of devices to connect the elds together. Furthermore each of the collectors is designed to locally store all of their data until the messenger next arrives, when it will receive a dump of all collected data before leaving. In this manner, a central data processing facility would be able to send the messenger to each of the remote deployment areas and receive back all of the collected data for processing. Further extending this design, I have added the ability to use a second mobile sink, designated as an observer, to perform live collection on the local cluster it is in, allowing a responsible party to perform a spot-check of the environment. The architectural design required signi cant modi cations to the open-source, commonly used Contiki operating system. These modi cations fall within the guidelines of the routing protocol speci cations and represent un nished aspects of Contiki's implementation. Additional mod cations were also made beyond the protocol speci cation to further allow the operating system the capabilities to properly manage general, multiple-sink routing networks. The objective of this work is to assess, design, and implement modi cations for the Con- tiki operating system to enable the validation and implementation of the designed HOIST architectural framework. The operating system modi cations serve as a standalone compo- nent of this work to enable generalized multiple sink routing applications.