Autonomous Virtual Mobile Nodes Shlomi Dolev Seth Gilbert Elad Schiller Alex Shvartsman Jennifer Welch

Challenges Locality Nodes only send messages to nearby nodes Global coordination is expensive Locality Unreliable nodes Mobile nodes fail, go to sleep, and get turned off.

Challenges Locality Unreliable nodes Irregular motion Nodes travel wherever they want to go Locality Unreliable nodes Mobile nodes fail, go to sleep, and get turned off.

Opportunities Broadcast Wireless broadcast is a powerful primitive. Allows a node to reach all nearby nodes, Ensure they receive the same messages.

Opportunities Broadcast Time & Geography Nodes are physical entities –physical time & location Use GPS and/or algorithms for synchronization / location

Related work Existing protocols Flooding Distributed structure –E.g., TORA [PC97] Compulsory movement of nodes – [HP99, CNS01]

Related work Existing protocols Random walk Random walk of a single agent Coping with chaos by chaos

Related work Existing protocols Random walk Virtual nodes Geo-Quorums [DGL03] Virtual Stationary Automata –[DGL05] Virtual Mobile Node [DGL04]

Autonomous Virtual Mobile Node Automaton New programming abstraction A virtual general-purpose computing entity.

Autonomous Virtual Mobile Node Automaton New programming abstraction Distinct location at any time Implemented by “real’’ mobile nodes that happens to be near.

Autonomous Virtual Mobile Node Automaton New programming abstraction Distinct location at any time Communicates with: other virtual nodes, and “real” mobile nodes.

Autonomous Virtual Mobile Node Automaton Reliability Fault recovery The group emulation enhances robustness: some may fail, or move out of range. Automaton Reliability Fault recovery Self-stabilization Tolerate any starting state: maybe several (undesired) copies, or none at all. Automaton Reliability Autonomous On-line movement decision: –current state, and –sensor/environment input. Example 1 If north-east area appears deserted go south-west

Autonomous Virtual Mobile Node Automaton Reliability Autonomous On-line movement decision: –current state, and –sensor/environment input. Example 2 Hitchhike with the traffic, or Go in the opposite direction

Application Domain Vehicular networks Traffic control and safety –E.g., ad hoc traffic light

Application Domain Vehicular networks Traffic control and safety –E.g., ad hoc traffic light

Application Domain Vehicular networks RFID tags Very small, cheap and wireless tagging network. Limited power supply. –Photoelectric gate Use flash light to activate the net The AVMN follows the light E.g., count the number of items find an expired item Use microwave instead of light.

Application Domain Vehicular networks RFID tags Swarm computing Multiple virtual nodes –Hierarchically originated –Performing different task Collaborating or competing

Implementation Exactly 1 instance Three different schemes 1.Virtual Stationary Automaton alive messages to known location of a stationary node (VSA) VSA keeps track of the AVMN No message for too long create a new AVMN VSA eliminates duplicates

Implementation Exactly 1 instance Three different schemes 1.Virtual Stationary Automaton 2.Send alive messages Send alive messages in a random walk fashion. If a real node doesn’t receive an alive message for too long generates a formation token carries ids and traverses in a random walk fashion If tokens collide: merge ids’ lists If containing more than (N+1)/2 creates a new AVMN

Implementation Exactly 1 instance Three different schemes 1.Virtual Stationary Automaton 2.Send alive messages 3.Nodes alive messages Real nodes periodically send stay alive messages random walk to AVMN in order to survive AVMN must collect at least (N + 1)/2 messages.

Implementation Exactly 1 instance Self-stabilization Every emulating real node –Keeps a replica of the AVMN –Ensures identical replica Buffer input events waiting to be applied to the state. At a fixed interval, sends replica to all. Predetermined function resolves conflicts.

Implementation Exactly 1 instance Self-stabilization Mobility Where and when to move? –Can be decided by current state –Ensure the right order of events –Ensure nodes´ proper join/leave x1x1 x2x2 x3x3 move to x 2 on t 2 move to x 3 on t 3 Esure that: Old nodes remain participants Enough nodes near the new location can receive notification And, mobile nodes can join

Discussion Described how to implement a single AVMN – Can implement multiple AVMNs using the same techniques. There are a number of ways to optimize – Use min amount of power to reach everyone. – Use nodes that are closer to the new AVMN centrum. – If possible, take advantage of nodes movement.

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