CSE-591: Term Project Self-stabilizing Network Algorithms by Tridib Mukherjee ASU ID :

Self-stabilization Introduced by Dijkstra in 1974 Brings the system back to a valid state from any arbitrary initial state Used for tolerating intermittent and unpredictable transient faults Network Algorithms Token Rings Spanning Trees Network Resets

Top Level State Diagram Self-stabilization (Closure) Faults in the network Self- stabilization (Convergence) Invalid System State Valid System State System Start-up Self- stabilization (Convergence)

Diajkstra’s Definition Privilege Boolean predicate which is true in at least one process in the system Authorizes a process to make a move Action Legal system (global) state There must be at least one privilege in the system During an infinite time every process should be able to receive a privilege an infinite number of times

Network Algorithms Network Spanning Trees The basic network architecture for routing and token passing Broadcasting, Multicasting Operation A privileged action is executed if a fault occurs in a node Multicast trees for mobile ad-hoc networks Counter Flushing Used for network resets Can be used in token Rings or trees using PIF

Valid Spanning Tree Level 1 Level 2 Level 3 Level 4 Root Node (Source Node) Leaf Nodes (Group Members)

Invalid Spanning Tree Root Node (Source Node) Leaf Nodes (Group Members)

First Step of Stabilization Root Node (Source Node) Leaf Nodes (Group Members) Level 1

Subsequent Stabilization Step (Constitutes the valid tree in this case) Root Node (Source Node) Leaf Nodes (Group Members) Level 1 Level 2 Level 3 Level 4

Practical Issues Stabilization Time Can be reduced by proper scheduling Optimized by the use of Fault-containment Contains the effect of faults Scheduling is implicit Service Unavailable during the time of stabilization Increases end-to-end latency for the network service Effects of faults are unnecessarily propagated through the network Mobile Ad hoc networks & Sensor Networks Energy Efficiency Periodic information exchange can expensive

Questions??