Fault Management in Mobile Ad-Hoc Networks by Tridib Mukherjee

Transient Faults in Mobile Ad-Hoc Networks Mobility of the Nodes Error Prone Medium Link Failures Low Battery Power Node Corruption

Fault Tolerance Ability of a system to perform its function correctly even in the presence of internal faults. Makes the network system more dependable. Hides the faults from the user. Two basic kinds of Fault Tolerance : Proactive and Reactive.

Self Stabilization Stabilizes a Distributed System to a legitimate state from any arbitrary initial state. Used as a Proactive Fault Tolerant Scheme. There are 2 properties : Closure and Convergence.

Self-stabilizing Multicast Routing Protocols For Mobile Ad-Hoc Networks Shortest Path Spanning Tree (SPST) Used in this project Maintains Shortest Path from source to destination. Beacon Messages provide information about neighbors. Recreates the tree in case of faults. Unnecessarily propagates limited faults across the network.

Fault Containment Contains the fault in the region where it has occurred Improves stabilization time Considerably. Increases Computational and Communication Overhead. Does not contain faults in all the desired cases in Mobile Ad-Hoc Networks. Tradeoff needed for optimal Energy Efficiency while managing the faults.

Fault-containment Algo. can_stabilize :

Propose for Adaptation Adapt to the changing Fault Scenarios. Use Self Stabilization where Fault Containment can not contain the faults. Use Fault Containment where it can contain the faults.

Fault Classification Fault-Containable (FC) Faults Fault can be contained using Fault Containment Non-Fault-Containable (NFC) Faults Fault Containment can not contain the faults Self-stabilization and Fault-containment have same performance Fault-containment executes self-stabilization internally Fault-containment adds computational overhead

Valid SPST Tree R A X M Y Level 0 Level 1 Level 2 Level 3 Level 4

M moves out R A C X D M Y Level 0 Level 1 Level 2 Level 3 Level 4 can_stabilize(Y) is false can_stabilize(X) is false can_stabilize(C) is false can_stabilize(D) is false

This is NFC fault R A X Y Level 2 Level 3

Neighborhood of Y is different R A C X D M Y Level 0 Level 1 Level 2 Level 3 Level 4 can_stabilize(Y) is true can_stabilize(A) is false can_stabilize(C) is false can_stabilize(D) is false

FC faults The scenario of the previous slide Faults occurred due to corruption are FC faults Both NFC and FC faults can occur in multiple nodes simultaneously For NFC faults, self stabilization is executed internally

Two FC faults within 2 hops RM X AYB Level of A gets corrupted to 6 M moves out and X becomes the parent of Y Both the FC faults become Non-containable Distance of 2 hops is named as Containability Limit (CL)

Reason G p (Y) and G p (A) are true Can_stabilize(Y) and Can_stabilize(A) are false So Fault Containing Algorithm executes self-stabilization internally FC faults becomes NFC if they occur within CL

Improved_Can_Stabilize  Check if local action can nullify G p in all the two hop neighbors instead of one hop neighbors as in the original algorithm  Otherwise check if local actions in all the one hop neighbors can eradicate fault in all the two hop neighbors

Improved Fault-containment

Reasoning G p (Y) and G p (A) are true Can_stabilize(Y) and Can_stabilize(A) are also true Fault Containing Algorithm executes self- stabilization internally only if faults are NFC Containability Limit is 0

Simulation Simulation is done in NS2 Comparison between Self-stabilization, Fault-containment and Improved Fault- containment Simulation is done for NFC and FC faults as well as multiple FC faults occurring within CL Performance is measured in terms of Beacon Intervals

NFC Fault Simulation Result

FC faults with distance greater than CL

FC faults with distance less than CL

Advantages & Disadvantages If a fault can be contained, it is contained regardless of its occurrence in the network Costs more communication overhead if a fault is not containable

References Sukumar Ghosh, Arobinda Gupta, Sriram V. Pemmaraju. ”Fault-containing network protocols”. Proceedings of the 1997 ACM symposium on Applied computing, p , April 1997, San Jose, California, United States. Sukumar Ghosh, Arobinda Gupta, T. Herman, Sriram V. Pemmaraju. Faultcontaining Self- Stabilizing Algorithms”. 15th Annual ACM Symposium on Principles of Distributed Computing, 1996, pp

References (Contd…) Sandeep K. S. Gupta, Pradip K. Srimani. ”Self-stabilizing multicast protocols for ad hoc networks”. Journal of Parallel and Distributed Computing 63(1): (2003)

Questions?