CS 425 Distributed Systems “Sensor Networks”Some questions…Sensors!Slide 4Sensor NodesExample: Berkeley “Motes” or “Smart Dust”Example HardwareExamplesTypes of SensorsI2C bus – simple technologyTransmission MediumSlide 12Summary: Sensor NodeSensor-node Operating SystemTinyOS design pointProgramming TinyOSSteps in writing and installing your NesC appTinyOS component modelA Complete TinyOS ApplicationTinyOS FactsSlide 21Slide 22TinyOS: More Performance NumbersTinyOS: SizeTinyOS: SummaryDiscussionSystem RobustnessScalabilityEtceteraOther ProjectsCivilian Mote Deployment ExamplesSlide 32CS 425Distributed Systems “Sensor Networks”Indranil GuptaLecture 21November 1, 2007Reading: Links on websiteSome questions…•What is the smallest transistor out there today?•How would you “monitor”: a) a large battlefield (for enemy tanks)? b) a large environmental area (e.g., movement of whales)? c) your own backyard (for intruders)?Sensors!•Coal mines have always had CO/CO2 sensors•Industry has used sensors for a long timeToday…•Excessive Information–Environmentalists collecting data on an island–Army needs to know about enemy troop deployments–Humans in society face information overload•Sensor Networking technology can help filter and process this information (And then perhaps respond automatically?)Growth of a technology requiresI. HardwareII. Operating Systems and ProtocolsIII. Killer applications–Military and CivilianSensor Nodes•Motivating factors for emergence: applications, Moore’s Law, wireless comm., MEMS (“micro electro mechanical systems”)•Canonical Sensor Node contains1. Sensor(s) to convert a different energy form to an electrical impulse e.g., to measure temperature2. Microprocessor3. Communications link e.g., wireless4. Power source e.g., batteryLaser diodeIII-V processPassive CCR comm.MEMS/polysiliconSensorMEMS/bulk, surface, ...Analog I/O, DSP, ControlCOTS CMOSSolar cellCMOS or III-VThick film batterySol/gel V2O5Power capacitorMulti-layer ceramic1-2 mmExample: Berkeley “Motes” or “Smart Dust”Can you identify the 4 components here?Example Hardware•Size–Golem Dust: 11.7 cu. mm–MICA motes: Few inches•Everything on one chip: micro-everything–processor, transceiver, battery, sensors, memory, bus–MICA: 4 MHz, 40 Kbps, 4 KB SRAM / 512 KB Serial Flash, lasts 7 days at full blast on 2 x AA batteriesExamplesSpec, 3/03 •4 KB RAM• 4 MHz clock• 19.2 Kbps, 40 feet• Supposedly $0.30MICA: State of the Art (xbow)Similar i-motes by IntelTypes of Sensors•Micro-sensors (MEMS, Materials, Circuits)–acceleration, vibration, gyroscope, tilt, magnetic, heat, motion, pressure, temp, light, moisture, humidity, barometric, sound•Chemical–CO, CO2, radon•Biological–pathogen detectors•[Actuators too (mirrors, motors, smart surfaces, micro-robots) ]I2C bus – simple technology•Inter-IC connect–e.g., connect sensor to microprocessor•Simple features–Has only 2 wires –Bi-directional–serial data (SDA) and serial clock (SCL) bus •Up to 3.4 Mbps•Developed By PhilipsTransmission Medium•Spec, MICA: Radio Frequency (RF)–Broadcast medium, routing is “store and forward”, links are bidirectional•Smart Dust : smaller size => RF needs high frequency => higher power consumption => RF not good Instead, use Optical transmission: simpler hardware, lower power–Directional antennas only, broadcast costly–Line of sight required–However, switching links costly : mechanical antenna movements–Passive transmission (reflectors) => wormhole routing–Unidirectional linksBerkeley Family of MotesSummary: Sensor Node•Small Size : few mm to a few inches•Limited processing and communication–MhZ clock, MB flash, KB RAM, 100’s Kbps (wireless) bandwidth•Limited power (MICA: 7-10 days at full blast)•Failure prone nodes and links (due to deployment, fab, wireless medium, etc.)•But easy to manufacture and deploy in large numbers•Need to offset this with scalable and fault-tolerant OS’s and protocolsSensor-node Operating SystemIssues–Size of code and run-time memory footprint•Embedded System OS’s inapplicable: need hundreds of KB ROM–Workload characteristics•Continuous ? Bursty ?–Application diversity•Reuse sensor nodes–Tasks and processes•Scheduling•Hard and soft real-time–Power consumption–CommunicationTinyOS design point–Bursty dataflow-driven computations–Multiple data streams => concurrency-intensive–Real-time computations (hard and soft)–Power conservation–Size–Accommodate diverse set of applications TinyOS: –Event-driven execution (reactive mote)–Modular structure (components) and clean interfacesProgramming TinyOS•Use a variant of C called NesC•NesC defines components•A component is either –A module specifying a set of methods and internal storage (~like a Java static class) A module corresponds to either a hardware element on the chip (i.e., device driver for, e.g., the clock or the LED), or to a user-defined software module Modules implement and use interfaces–Or a configuration , a set of other components wired (virtually) together by specifying the unimplemented methods invocation mappings•A complete NesC application then consists of one top level configurationSteps in writing and installing your NesC app(applies to MICA Mote)•On your PC–Write NesC program –Compile to an executable for the mote–Debug on your PC (using TOSSIM)–Plug the mote into the parallel port through a connector board–Install the program•On the mote–Turn the mote on, and it’s already running your applicationTinyOS component model•Component specifies:•Component invocation is event driven, arising from hardware events•Static allocation avoids run-time overhead•Scheduling: dynamic, hard (or soft) real-time•Explicit interfaces accommodate different applicationsInternal StateInternal TasksCommands EventsA Complete TinyOS ApplicationRFMRadio byteRadio Packeti2cTempphotoMessaging LayerclocksbitbytepacketRouting Layersensing applicationapplicationHWSWADCmessagingroutingTinyOS Facts•Software Footprint 3.4 KB •Power Consumption on Rene PlatformTransmission Cost: 1 µJ/bitInactive State: 5 µAPeak Load: 20 mA•Concurrency support: at peak load CPU is asleep 50% of time•Events propagate through stack <40 µSEnergy – a critical resource•Power saving modes:–MICA: active, idle, sleep•Tremendous variance in energy supply and
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