Fault Tolerant Event Specification in Heterogeneous Sensor Networks
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Transcript of Fault Tolerant Event Specification in Heterogeneous Sensor Networks
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Fault Tolerant Event Specification in Heterogeneous Sensor Networks
Ortmann, Steffen
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2/23Outline
• Introduction & Motivation
• Related work
• Shortcomings and open issues
• Fault tolerant event specification
• Conclusion
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3/23Motivation
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4/23Introduction
• Ubiquitous systems are ambient intelligent environments build by cooperating autonomous devices
• Computing devices are to be embedded on everyday objectWatching and serving us at any place and any time
• Supposed to substitute today’s computers and information technology
• Reliable and fault tolerant ubiquitous systems are potentially capable of executing mission- and safety-critical applications
Healthcare- and structural monitoringHomeland securityEmbedded systemsAvionic and deep space applications
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5/23Sensor networks
• Sensor networks are one of the first real world examples
of ubiquitous systems
• Tiny autonomous devices that are assembled to fulfill common tasks
• Structure:
Main challenge: Devices and systems are prone to failures
Low cost devices, rare resources, strict energy constraints
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6/23Tmote Sky sensor node from Moteiv
• Main Features:
250kbps 2.4GHz IEEE 802.15.4 Wireless Transceiver
8MHz Texas Instruments MSP430 microcontroller
10k RAM, 48k Flash
Integrated ADC, DAC, Supply Voltage Supervisor, DMA Controller
Onboard antenna with 50m range indoors / 125m range outdoors
Integrated Humidity, Temperature, and Light sensors
Programming and data collection via USB
Ultra low current consumption
Fast wakeup from sleep (<6μs)
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7/23Related Work
• Most reliability enhancing approaches for sensor networks
focus on data gathering and data transmission
• Events are predefined states based on certain measurements
Usually defined by threshold values
• Exploit the effect of redundancy on mean time to failure
Strongly depends on the density in the network
• Main approach: collective distributed data evaluation by voting
Neighbored nodes compare their results to decide about events
Many different voting algorithms are presented so far
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8/23Distributed event evaluation
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9/23Voting
• Based on redundant devices in certain areas of the network
Cluster, position-based, n-hop neighborhood etc.
• Majority Voting [1]
All nodes within the region of event possess the same weights
Fusion center analyzes and combines all values
• Distance Weighted Voting [2]
Voting weight decreases with distance to the center of the event
• Confidence Weighted Voting [2]
Grants higher weights to sensors that are more likely to be correct
Every nodes assigns a confidence value
Best implemented in the TIBFIT [3] protocol
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10/23Shortcomings and open issues
• Voting is sufficient enough to provide an enhanced reliability
Currently done on predefined event regions
Not adaptable to different tasks and network conditions
• Consider heterogeneous sensing capabilities
Almost all sensor network applications are handmade and customized
• Take care on energy dissemination
Varying tasks demand different overhead for fault tolerance
Exploit reactive algorithms that vote on demand only!
• Vision: adaptable multi-tasking sensor networks
Miscellaneous fine-grained multi-event detection
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11/23Event Specification Language for Sensor Networks
• Idea: Enable complete events specifications by an uniform description language
Get rid of custom-built sensor networks!
• Combine heterogeneous sensing capabilities
Enable more precise and complex event detection capabilities
• Fine-grained configuration of fault tolerant event evaluation
Configure voting conditions explicitly for any single event
• Specify execution intervals and associate appropriate event handlers
Online configuration of sensor networks without physical access to every node!
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12/23<EVENT> element
• Structure of an events specification
<EVENT id=“fire.001" priority="high">
<SENSOR-DATA> … </SENSOR-DATA>
<VOTING> … </VOTING>
<EXECUTION> … </EXECUTION>
<CONSEQUENCE> … </CONSEQUENCE>
</EVENT>
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13/23<SENSOR-DATA> element
• List sensing capabilities
e.g. <temperature>, <smoke>, <humidity> etc.
• Configure corresponding threshold values
Exact threshold values as <equal> element
Scopes of threshold values by <atleast> or <atmost>
• Correlate threshold values by logic operations
<AND/>, <OR/>, <NOR/>, <NAND/> etc.
<SENSOR-DATA> element is analyzed to a Boolean value during evaluation of sensor readings
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14/23<SENSOR-DATA> example
<SENSOR-DATA>
<AND>
<temperature>
<atleast> 353 </atleast>
<kelvin/>
</temperature>
<smoke>
<atleast> 1.1 </atleast>
<percent/>
</smoke>
</AND>
</SENSOR-DATA>
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15/23<VOTING> element (1)
• Customizes preconditions for distributed event evaluation
Precisely configures conditions for voting
• Determines which other devices are allowed to vote
Defines the legal size of the event evaluation region
All nodes within this area are allowed to vote
• <DISTANCE> element defines a radius around initiating sensor node
Using quantifying elements like <atmost>
• Other preconditions are to be considered too
e.g. all nodes within 1-hop neighbourhood
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16/23<VOTING> element (2)
• Number of necessary voting devices can be fixed or limited
Stated by <NUMBER_OF_DEVICES> element
Enables n-modular redundancy
• Specification of further abort criteria (called Exceptions)
Listed by the <EXCEPTION> element
Deadline criteria
Keeps timing constraints for safety-critical applications!
Other criteria imaginable
<no_devices_available>
• All listed criteria can be concatenated by logic operations
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17/23<VOTING> example
<VOTING><CONDITION>
<DISTANCE><atmost> 5 </atmost><meters/>
</DISTANCE></CONDITION><NUMBER OF DEVICES>
<atleast> 3 </atleast><NUMBER OF DEVICES><EXCEPTION>
<OR><DEADLINE>
<equal> 3 </equal><seconds/></DEADLINE><no_devices_available></OR>
</EXCEPTION></VOTING>
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18/23<EXECUTION> element
• Configuration of demand-oriented execution intervals
Precisely adaptation to varying requirements
• Implicitly considers energy consumption of the sensor node
Manages active and sleep periods of the sensor node
Can be quantified by acceptable time periods or exact time slots
• Example:
<EXECUTION>
<INTERVAL>
<equal> 60 </equal>
<seconds/>
</INTERVAL>
</EXECUTION>
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19/23<CONSEQUENCE> element
• Connects procedures to an event
Procedures are called event handlers
<CONSEQUENCE> element holds a list of event handlers
• Every event handler links a certain procedure
Attribute id holds the respective identifier
All listed handlers are successively executed if an event occurs
• Example:
<CONSEQUENCE>
<TRIGGER HANDLER id="send-fire-alert">
</CONSEQUENCE>
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20/23Conclusion
• Reliable and fault tolerant sensor networks are in great demand
Enable mission- and safety-critical applications
• Current approaches and solutions revealed several shortcomings
• Idea: Define events by an uniform event specification language
Regards heterogeneous sensing capabilities
Allows for fine-grained event-related fault tolerance
Provides miscellaneous task execution
Improves maintenance capabilities and enables online configuration of sensor networks
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21/23Outlook
• Finish definition of event specification language
• Implement pre-parser for event specifications
Parses specification into tree that can be send through the network
• Implement interpreter for the sensor node side
Using network (OMNet++) and algorithm simulator (Castalia)
• Comprehensive test procedures on simulator
Different network density
Different event specification containing varying voting conditions
Measure and compare energy consumption
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22/23References
[1] B. Krishnamachari and S. S. Iyengar. Efficient and fault-tolerant feature extraction in sensor networks. In 2nd Workshop on Information Processing in Sensor Networks, IPSN’03, Palo Alto, California, April 2003
[2] T. Sun, L.-J. Chen, C.-C. Han, and M. Gerla. Reliable sensor networks for planet exploration. In L.-J. Chen, editor, Proc. IEEE Networking, Sensing and Control, pages 816–821, Tucson, USA, 2005
[3] M. Krasniewski, P. Varadharajan, B. Rabeler, S. Bagchi, and Y. Hu. Tibfit: trust index based fault tolerance for arbitrary data faults in sensor networks. In Proc. International Conference on Dependable Systems and Networks DSN 2005, pages 672–681, 2005
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23/23Discussion
Thanks for your attention.
Any questions?