International Graduate School Cottbus / IHP microelectronics Im Technologiepark 25 15236 Frankfurt...
-
Upload
timothy-cooper -
Category
Documents
-
view
217 -
download
2
Transcript of International Graduate School Cottbus / IHP microelectronics Im Technologiepark 25 15236 Frankfurt...
International Graduate School Cottbus / IHP microelectronicsIm Technologiepark 2515236 Frankfurt (Oder)
Germany
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
Fault Tolerant Event Specification in Heterogeneous Sensor Networks
Ortmann, Steffen
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
2/23Outline
• Introduction & Motivation
• Related work
• Shortcomings and open issues
• Fault tolerant event specification
• Conclusion
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
3/23Motivation
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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)
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
8/23Distributed event evaluation
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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!
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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>
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
14/23<SENSOR-DATA> example
<SENSOR-DATA>
<AND>
<temperature>
<atleast> 353 </atleast>
<kelvin/>
</temperature>
<smoke>
<atleast> 1.1 </atleast>
<percent/>
</smoke>
</AND>
</SENSOR-DATA>
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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>
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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>
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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>
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
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
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2008 - All rights reserved
23/23Discussion
Thanks for your attention.
Any questions?