Network Architecture for General-purpose Sensor Networks Omprakash Gnawali gnawali@usc.edu http://enl.usc.edu/ CSSE March 17, 2009

Sensor Network Network of small form-factor sensors Resource constraints CPU (<10 MHz) RAM (<10 KB) Low power Embedded in the physical world Wireless communication

Building Vibrations Forced Vibration Testing at the Four Seasons Building in Los Angeles

Bridge Vibrations

Pursuit Evasion

Habitat Imaging James Reserve, Riverside, CA

Sensor Network Applications Examples Industrial space Environment Infrastructure Hardware and Software Optimizations Components Scenarios

Outline Sensor Network Programming a Sensor Network Tenet: A General-purpose Sensor Network

Programming a SensorNet Programming Abstraction Services

Programming Abstraction Node-level API “Node x: execute program y” Reasoning and Debugging Challenging Program the network “Network: Collect light readings” No fine-grained control Network and Node Services

Collection Routing Collect data from the network Challenges From all the nodes To a small number of “sinks” Challenges Link estimation Dynamics Tree Routing CTP, MultihopLQI

Collection

Reliable Transport Prevent data-loss End-to-end retransmission Used with Collection Challenges Limited RAM Congestion

Congestion Collapse Four Seasons building deployment Some packets took more than an hour to recover while collecting 10 minutes worth of data Loss recovery latency 14

Dissemination Delivers data to every node in a network Challenges Rate “Broadcast storm” Many uses Reconfiguring a network Injecting queries and tasks Substrate for more complex protocols

Timing Timestamps for sensor readings Globally synchronized time Challenges Different clock rates on the nodes Wireless Approaches Hardware: GPS Software: FTSP

Sensing and Actuation Sensors Actuators Portable abstraction Light, Temperature, Accelerometer Actuators LED, Relays Portable abstraction

Data Processing Services Raw data not always needed Data filters Specify (un)wanted data Data processing Statistics Transforms, Coefficients

General-purpose API Provides Services Collection routing Reliable transport Dissemination Timing Sensing and Actuation Data processing Allows flexible composition of services

Outline Sensor Network Programming a Sensor Network Tenet: A General-purpose Sensor Network

repeat(1s)->sense(LIGHT)->send(RELIABLE) Tenet Masters and Motes Tasks and Responses Linear data-flow programs repeat(1s)->sense(LIGHT)->send(RELIABLE)

Tenet Services

Tenet Programs Linear data flow language natural choice for sensor data processing Tasklets specify elementary actions sense(), set_leds(), avg() Tasklets can be composed to form a task sense(LIGHT,10 samples)avg(LIGHT)send() repeat(10 mins)get(ROUTING_PARENT)send() No branches

Executing Tenet Programs Applications run on masters, and masters task motes Motes produce, process data, and return responses 24

Tenet Performance Tenet applications perform comparably with software optimized for a particular application.

Deployments

Conclusion Deployments Looking ahead Software reuse No performance penalty Looking ahead General-purpose radio duty-cycling