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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.
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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 Level 0 R Level 1 A M X Level 2 Y Level 3 Level 4
M moves out Level 0 R A Level 1 M X Level 2 Y Level 3 C D can_stabilize(Y) is false can_stabilize(X) is false can_stabilize(C) is false can_stabilize(D) is false Level 4
This is NFC fault R A X Level 2 Y Level 3
Neighborhood of Y is different Level 0 R A Level 1 M X Level 2 Y Level 3 C D can_stabilize(Y) is true can_stabilize(A) is false can_stabilize(C) is false can_stabilize(D) is false Level 4
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 R M Y A B X 0 1 2 3 4 5 • 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 • Gp(Y) and Gp(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 Gp 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
Reasoning • Gp(Y) and Gp(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
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.431-37, 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. 45-54.
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): 87-96 (2003)