Elham Hormozi & Razieh Asadi University of Science & Technology Mazandaran Babol

1. Fault Tolerance in Wireless Sensor Network ElhamHormozi & RaziehAsadiUniversity of Science & Technology Mazandaran Babol Elham.Hormozi@gmail.com & Rzh_asadi@yahoo.com

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

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

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

5. Fault Detection: • Centralized Approach • Sympathy • Secure Locations • Distributed Approach • Node Self-detection • Clustering Approach( MANNA)

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

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: • trust routing • insecure location discovery and isolation

8. Secure Locations (cont’d) • Select a secure path and avoid insecure locations • All destination nodes use TESLA, to authenticate all requests • sink creates a message with( source location, destination location, authentication message) • encrypts this message with its share key and broadcasts it. • neighbors who know its shared key will be able to decrypt the request • trusted neighbor decrypts the request, adds its location, encrypts the message with its share key and sends it to neighbors

9. Secure Locations (cont’d) • Use Expanding TTL Search (ETS). • Sink marks data packets with increasing hop-count • Each intermediate node decrements the hop-count before forwarding • When hop count reaches zero node sends ACK to the source informing it of its location is safe • The source identifies that part of the path as safe and increases the hop count in subsequent packets.

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

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

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: • Hardware interface consists of a sensing layer(wraps around the node). • Software interface reads the sensors, and transmits the data to the Sink • Use TinyOS( have very small footprint, energy-aware, event-based ) Figure 1: SYS25 node.

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

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

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

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

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

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)

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

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

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

22. Hop-by-Hop TCP for Sensor Networks • Every intermediate node execute a light-weight local TCP • Include two part: • End-to-End TCP • Working on the source and destination nodes • 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.

23. Hop-by-Hop TCP for Sensor Networks Figure2. Protocol Stack Hop by Hop TCP

24. End-to-End TCP • Reuse an existing popular TCP protocol, NewReno, with several modifications • Sender module forwards packets to the One-Hop TCP module • Receiver module receives packets from the One-Hop TCP module • One-Hop TCP in each node forwards data packets hop by hop • End-to-End ACKs, are forwarded to the source node using One-Hop TCP in the opposite direction • Set a larger initial RTO value

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 • Add the IP address of current node to the packet header (receiver knows where to send Local ACK) • Set CWND to 1 • Set the upper threshold for the number of retransmissions.

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

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

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)

29. References • [1] Hai Liu, AmiyaNayak, 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] NithyaRamanathan, Kevin Chang, RahulKapur, Lewis Girod, Eddie Kohler, and eborahEstrin,' Sympathy for the Sensor Network Debugger' UCLA Center for Embedded Network Sensing, ACM 2005

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

31. References(cont’d) • [8] Jinran Chen, ShubhaKher, and ArunSomani,' Distributed Fault Detection of Wireless Sensor Networks' Dependable Computing and Networking Lab Iowa State University Ames, Iowa 50010, 2006 IEEE • [9] SamehGobriel, SherifKhattab, Daniel Moss´e, Jos´eBrustoloni and RamiMelhem,’ RideSharing: Fault Tolerant Aggregation in Sensor Networks Using Corrective Actions’, Computer Science Department, University of Pittsburgh,2006 • [10] Weiyi Zhang, GuoliangXue and SatyajayantMisra,'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