Sensor Networks Storage Sanket Totala Sudarshan Jagannathan

Outline  Introduction  Storage Mechanisms  Multi-Resolution Storage  Two-Tier Storage  Conclusion

Introduction  Sensor Nodes Low Memory Low Power Low processing capability Inapproachability  Sensor Networks Efficiency requirements Highly dense

Introduction  Sensor Storage Large number of events Query handling capability required Streaming data Aging mechanism Data organization

Sensor Network Storage - Mechanism  Centralized Storage Central server  Ample power  Sufficient storage  Single point of failure Fast Query processing High communication Sparse Networks  Infrequent events  Low Data Transfer Scalability problems

Sensor Network Storage - Mechanism  Distributed Storage Storage at each node Local computation Scalable Dense Networks  Frequent events  High Data Transfer Slower Query processing  Flooding  Distributed Indexing  Drill-down querying

Multi-Resolution Storage  Multi-Resolution summarization Construct data summaries Hierarchy construction  Drill-down query evaluation Narrowing search space Spatio-temporal compression  Data aging Efficient storage utilization Data Degradation

Multi-Resolution summarization  Temporal Summarization Exploits Temporal redundancy Computation overhead No communication overhead  Spatial Summarization Exploits Spatial redundancy Data Summarization every level Hierarchy construction

Drill-down query evaluation  Spatial compression Finer data view with every level. Reduced search cost  Query routing Sub region selection More accurate result

Data Aging  Long deployment  Limited storage  Efficient resource utilization  Fast query processing  Accuracy  Higher level, Higher time periods

Data Aging – Algorithms  Omniscient Algorithm Data sets available Full global knowledge required Query specific  Training Algorithm Data sets available Data set partitioned  Training data (available during sensor deployment)  Test data  Greedy Algorithm Data set unavailable Assigns weights to data summaries

Outline – Two Tier Sensor Storage  Design Considerations and Principles  System Design Architecture Data structures  Data Storage  Sensor Network Data Summarization  Conclusion

Design Consideration and Principles  The Three-Tier Model Bottom tier - Untethered sensor nodes Middle tier - Tethered sensor proxies Upper tier - Applications and user terminals

Design Consideration and Principles  Principles Store locally, access globally Distinguish data from metadata Provide data-centric query support

Data Structures Used  Skip Graph Ordered index In-place indexing Log n height Probabilistic balance Redundancy and resiliency

Data Structures Used  Interval Skip Graph Extends skip graphs to store intervals Allows efficient searches Complexity of search is O(log n) Insertion cost of O(n)  Sparse Interval Skip Graph

Data Storage  Local Storage at Sensors Archival Stores: Collection of records Interval skip graphs used Efficient routing and query handling Operations: Create, Read & Delete

Sensor Data Summarization  Data summaries – bind the storage at the remote sensor and the index at the proxy  Each update from a sensor to the proxy includes The summary Time period corresponding to the summary The start and end offsets for the flash archive

Sensor Summarization  Adaptive Summarization Balances the cost of sending updates against the cost of false positives Summarization Parameters  The interval over which summaries of the data are constructed and transmitted to the proxy  The size of the application specific summary.

Conclusion  Multi-tier nature of sensor networks  Large amounts of events and data Lossy Approach Two-Tiered Approach  Low overheads Decentralized and Hierarchical storage  Possible Solution Combine lossy nature of Multi-resolution with routing techniques of Two-tiered approach.