1. Elham Hormozi & Razieh Asadi
e.hormozi@ustmb.ac.ir & Rzh_asadi@yahoo.com
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2. Outline
 Review of Wireless Sensor Network
 Fault Tolerance in WSNs
 Fault Detection
 Fault Recovery
 Relay Node Placement in Wireless Sensor Networks
 Hop-by-Hop TCP for Sensor Networks
 Conclusion
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3. Review of Wireless Sensor Network
 A WSN is a self-organized network that consists of a large number
of low-cost and low powered sensor devices, called sensor nodes
 Can be deployed on the ground, in the air, in vehicles, on bodies,
under water, and inside buildings
 Each sensor node is equipped with a sensing unit, which is used to
capture events of interest, and a wireless transceiver, which is used
to transform the captured events back to the base station, called
sink node
 Sensor nodes collaborate with each other to perform tasks of data
sensing, data communication, and data processing
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4. Type of failure in WSNs
 Energy depletion
 Have very limited energy and their batteries cannot usually be recharged or
replaced, due to hostile or hazardous environments
 Hardware failure
 A sensor node has two component: sensing unit and wireless transceiver
 Usually directly interact with the environment, which is subject to variety of physical,
chemical, and biological factors.
 Communication link errors
 Even if condition of the hardware is good, the communication between sensor
nodes is affected by many factors, such as signal strength, antenna angle,
obstacles, weather conditions
 Malicious attack
It results in low reliability of performance of sensor nodes.
Therefore, fault tolerance is one of the critical issues in WSNs
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5. Fault Detection:
 Centralized Approach
• Sympathy
• Secure Locations
 Distributed Approach
1. Node Self-detection
2. Clustering Approach( MANNA)
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6. Sympathy[4]
 Using a message-flooding approach to pool event data and current
states (metrics) from sensor node
 Nodes periodically send metrics back to a sink to detect failures and
cause of failure
 Given sensor hardware and network limitations, these transmitted
metrics must be minimized
 Insufficient data at the sink implies failure; sufficient data at the sink
implies acceptable network behavior
 Based on these metrics, it detects which nodes or components have
not delivered sufficient data and infers the causes of failures
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7. Secure Locations[5]
 Work on location-aware sensor networks
 Introduces a scalable trust-based routing protocol (TRANS)
 Select trusted paths that do not include misbehaving
nodes by identifying the insecure locations and routing
 Include two parts:
1. trust routing
2. insecure location discovery and isolation
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8. Secure Locations (cont’d)
 Select a secure path and avoid insecure locations
 All destination nodes use TESLA, to authenticate all requests
1. sink creates a message with( source location, destination
location, authentication message)
2. encrypts this message with its share key and broadcasts it.
3. neighbors who know its shared key will be able to decrypt the
request
4. trusted neighbor decrypts the request, adds its location,
encrypts the message with its share key and sends it to
neighbors
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9. Secure Locations (cont’d)
 Use Expanding TTL Search (ETS).
1. Sink marks data packets with increasing hop-count
2. Each intermediate node decrements the hop-count before
forwarding
3. When hop count reaches zero node sends ACK to the
source informing it of its location is safe
4. The source identifies that part of the path as safe and
increases the hop count in subsequent packets.
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10. Advantage & Disadvantage of Centralize
Approaches
 The centralized approach is efficient and accurate to identify
the network faults in certain ways
 Resource-constrained sensor networks can not always afford
to periodically collect all the sensor measurements and states
in a centralized manner
 Central node easily becomes a single point of data traffic
concentration in the network, as it is responsible for all the
fault detection and fault management
 This subsequently causes a high volume of message traffic and
quick energy depletion in certain regions of the network,
especially the nodes closer to the base station
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11. Advantage & Disadvantage of Centralize
Approaches(cont’d)
 This approach will become extremely inefficient and expensive
in consideration of a large-scale sensor network
 Multi-hops communication of this approach will also increase
the response delay from the base station to faults occurred in
the network
 Therefore, we have to seek a localized and more
Computationally efficient fault detection model
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12. Distributed Approach & Node Self-detection
 Use flexible circuit acts as a sensing layer around a node,
capable of sensing the physical condition of a node.
 Detect physical faults requires the use:
1. Hardware interface consists of a
sensing layer(wraps around the node).
1. Software interface reads the sensors,
Figure 1: SYS25 node.
and transmits the data to the Sink
 Use TinyOS( have very small footprint, energy-aware, event-based )
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13. Distributed Approach & Clustering
Approach MANNA
 Design for event-driven WSN
 Clustering use for building scalable and energy balanced applications
for WSNs
 Distribute fault management into each cluster
 Management agents execute in the cluster-heads
 This mechanism decreases the information flow and energy
consumption as well
 A manager is located externally to the WSN has a global vision
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14. Distributed Approach & Clustering
Approach MANNA
 Management application is divided into two phases:
 Installation
 Occurs as soon as the nodes are deployed in the network.
 Each node report its position and energy to the agent located in the
cluster-head.
 Agent sends a LOCATION TRAP and ENERGY TRAP to the
manager
 Manager build topology map model and the WSN energy model
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15. Distributed Approach & Clustering
Approach MANNA
 Management application is divided into two phases:
 Operation
 Each node report its energy level and position to the agent
whenever there is a state change (another ENERGY TRAP or
LOCATION TRAP)
 Manager rebuild topology map model and energy model
 Manager sends GET operations in order to retrieve the node
state
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16. Fault Recovery
 WSN restructured or reconfigured, in such a way that
failures or faulty nodes do not impact further on network
performance
 The most commonly used technique for fault recovery is
replication or redundancy of components that are prone
to be failure
 When some nodes fail to provide data, the base station still
gets sufficient data if redundant sensor nodes are deployed in
the region
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17. Fault Recovery(cont’d)
 Relay Node Placement in Wireless Sensor Networks
 Two-Tiered Wireless Sensor Networks
 Hop-by-Hop TCP for Sensor Networks
 RideSharing: Fault Tolerant Aggregation
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18. Relay Node Placement in Wireless Sensor
Networks(Two-Tiered Wireless Sensor Networks)
 Improving reliability and prolonging lifetime of WSNs
 Energy consumption is proportional to d for transmitting over
distance d, where is a constant in the interval , long distance
transmission in WSNs is costly
 Employs some powerful relay nodes whose main function is to
gather information from raw data from sensor nodes and relay the
information to the sink
 Relay nodes serve as a backbone of the network
 The relay nodes are more powerful than sensor nodes ( energy
storage, computing, and communication capabilities)
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19. Two-Tiered Wireless Sensor Networks
 Each cluster has only one cluster head and each sensor
belongs to at least (backup cluster heads)
 Receiver of a relay node fails
 Data sent by the sensors will be lost
 Sensor to be reallocated to other cluster heads
 Handle general communication faults
 There should be at least two node-disjoint paths between each
pair of relay nodes in the network
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20. Two-Tiered Wireless Sensor Networks
 An intuitive objective of relay node placement in two-tiered
WSNs is to place the minimum number of relay nodes, such
that some degree of fault tolerance can be achieved.
 There are other works that study placement of sensor nodes
to make a sensor network k-connected
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21. Hop-by-Hop TCP for Sensor Networks
 Why conventional TCP protocol can not be used?
 Communication links in a sensor network are unstable
 TCP protocol over a high loss rate will suffer from severe
performance degradation
 Sensor may not have sufficient computing power to implement
the entire TCP/IP protocol
 Hop-by-Hop TCP for Sensor Networks
 Aiming to accelerate reliable packet delivery
 Minimizing end-to-end packet delivery time without too much
throughput degradation
 Minimizing the number of retransmissions
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22. Hop-by-Hop TCP for Sensor Networks
 Every intermediate node execute a light-weight local
TCP
 Include two part:
1. End-to-End TCP
 Working on the source and destination nodes
2. One-Hop TCP
 Working on every node
 The sender module of a One-Hop TCP is working at the
sender end of a link, and the receiver module is working at the
receiver end.
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23. Hop-by-Hop TCP for Sensor Networks
Figure2. Protocol Stack Hop by Hop TCP
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24. End-to-End TCP
 Reuse an existing popular TCP protocol, NewReno, with
several modifications
1. Sender module forwards packets to the One-Hop TCP
module
2. Receiver module receives packets from the One-Hop TCP
module
3. One-Hop TCP in each node forwards data packets hop by
hop
4. End-to-End ACKs, are forwarded to the source node using
One-Hop TCP in the opposite direction
5. Set a larger initial RTO value
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25. One-Hop TCP
 A light-weight version of TCP running on each node to
forward received packets reliably
 Many TCP features, such as packetization and congestion
control, are removed
1. Add the IP address of current node to the packet header
(receiver knows where to send Local ACK)
2. Set CWND to 1
3. Set the upper threshold for the number of
retransmissions.
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26. RideSharing: Fault Tolerant Aggregation
 Aggregation use for filter redundancy and reduce communication
and energy consumption
 Multipath routing can overcome losses by duplicating and
forwarding each sensor measurement
 One or more other sensors have correctly overheard the packet
 Some aggregate functions, such as SUM, COUNT, are duplicate-
sensitive
 Use RideSharing (RS) scheme for fault-tolerant, duplicate-sensitive
aggregation
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27. RideSharing: Fault Tolerant Aggregation
 Edges are classified into three types: primary, backup, and side
edges
 Using a small bit vector that each parent attaches to each data
message it sends
 Parents detect link errors
when one or more children
are missing from the bit vector
Figure3. Track Topology
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28. Cascaded RideSharing
 Each parent broadcasts children ids and their bit positions
inside its bit vector
 When an error occurs, each backup parent decides whether
or not to correct the error based on its order in a correction
sequence(parent with smallest id)
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29. References
 [1] Hai Liu, Amiya Nayak, and Ivan Stojmenovi ' Fault-Tolerant Algorithms/Protocols in
Wireless Sensor Networks' Department of Computer Science, Hong Kong Baptist
University, Springer-Verlag London Limited 2009
 [2] M.Yu, H.Mokhtar, and M.Merabti, 'A Survey on Fault Management in Wireless Sensor
Networks' School of Computing & Mathematical Science Liverpool John Moores
University, 2007
 [3] Farinaz Koushanfar1, Miodrag Potkonjak2, Alberto Sangiovanni-Vincentelli1, ' FAULT
TOLERANCE IN WIRELESS SENSOR NETWORKS'1Department of Electrical Engineering
and Computer Science Univeristy of California, Berkeley , CA, US 94720, 2Department of
Computer Science Univeristy of California, Los Angeles Los Angeles, CA, US 90095
 [4] Nithya Ramanathan, Kevin Chang, Rahul Kapur, Lewis Girod, Eddie Kohler, and eborah
Estrin,' Sympathy for the Sensor Network Debugger' UCLA Center for Embedded Network
Sensing, ACM 2005
 29

30. References(cont’d)
 [5] Jessica Staddon, Dirk Balfanz, Glenn Durfee' Efficient Tracing of Failed Nodes in
Sensor Networks ', September 28, 2002, Atlanta, Georgia, USA,ACM.
 [6] Sapon Tanachaiwiwat1, Pinalkumar Dave1, Rohan Bhindwale2, Ahmed Helmy1,'
Secure Locations: Routing on Trust and Isolating Compromised Sensors in Location-Aware
Sensor Networks ' 1. Department of Electrical Engineering – Systems 2. Department of
Computer Science University of Southern California, ACM 2003
 [7] Gaurav Gupta1, Mohamed Younis2, ' Fault-Tolerant Clustering of Wireless Sensor
Networks ', Dept. of Computer Science and Elec. Eng. Dept. of Computer Science and
Elec. Eng. University of Maryland Baltimore County University of Maryland Baltimore
County 2003 IEEE
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31. References(cont’d)
 [8] Jinran Chen, Shubha Kher, and Arun Somani,' Distributed Fault Detection of Wireless
Sensor Networks' Dependable Computing and Networking Lab Iowa State University
Ames, Iowa 50010, 2006 IEEE

 [9] Sameh Gobriel, Sherif Khattab, Daniel Moss´e, Jos´e Brustoloni and Rami Melhem,’
RideSharing: Fault Tolerant Aggregation in Sensor Networks Using Corrective Actions’,
Computer Science Department, University of Pittsburgh,2006

 [10] Weiyi Zhang, Guoliang Xue and Satyajayant Misra,'Fault-Tolerant Relay Node
Placement in Wireless Sensor Networks', Department of Computer Science and
Engineering at Arizona State University, IEEE INFOCOM 2007

 [11] S Harte1, A Rahman1, K M Razeeb2 'FAULT TOLERANCE IN SENSOR NETWORKS
USING SELF-DIAGNOSING SENSOR NODES', 1 University of Limerick, Ireland 2 Tyndall
National Institute, Ireland,2005
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