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RE-Pair

RE-Pair. Self-Repairing Mobile Node Network. Disabled Sensors. In James Bond movies, you often see him disabling sensors and cameras and sneaking into the secret hideout. So what’s wrong with this picture?

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RE-Pair

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  1. RE-Pair Self-Repairing Mobile Node Network

  2. Disabled Sensors • In James Bond movies, you often see him disabling sensors and cameras and sneaking into the secret hideout. • So what’s wrong with this picture? • If the bad guys can spend millions buying sharks with fricken lasers, then why can’t they buy better security?

  3. Mobile Nodes • What does mobility give us? • Self-deployment • Self-repair • We consider a sparse deployment of nodes • Depth vs Breadth • Each node has to maintain a connection to the base station

  4. Applications • Providing reliable wireless access • Quick, automated deployment • Fast repair, adaptive • Intrusion detection • Self-repairing perimeter allows recovery from damage • Monitor environment

  5. Challenges • Death of a node bisects the graph • 2 Ways to repair link (distributed vs centralized) • Nodes detect break and repair on their own • Base station/Master node redeploys the nodes to optimally cover the area • 2 Goals of repair • Reconnect all nodes • Maximize coverage

  6. Challenges cont. • Repair with nodes • Possible to reconnect network • Tough for nodes to cooperatively find the total slack in the network • Repair with master node • Able to calculate best dispersal with nodes it has • Can not reach separated nodes to issue deployment orders

  7. Re-Pair • Separate link repair into two stages • Stage 1 • Individual nodes detect break and repair link • Requires knowledge of node locations and node deaths • Stage 2 • Master node calculates a new deployment once it determines how many nodes it has left

  8. Keep-Alives • Nodes broadcast a keep-alive advertising their status and location • Optimization: filter out keep-alives that contain only old information • Reduces packet traffic • Assign pairs of neighboring nodes • Responsible for announcing death of paired node • Store locations and status in a table per node • Not necessary for correctness but for performance

  9. Pair 2 & 3 2 3 4 5 1 Pair 3 & 4 Paired Nodes

  10. Stage 1 • Node’s death detected by its neighboring pairs (network is now split in two) • Death announced to connected and disconnected nodes • Disconnected neighbor heads toward the location of the node preceding the dead node • Repeats until its reconnected or has reached the base station • Allows the network to retain coverage during repair

  11. Pair 2 & 4 4 2 5 1 2 announces death of 3 4 announces death of 3 2 3 4 5 1 Death Detection

  12. Stage 2 • Master node listens for changes in the network • Requests Update from nodes to get accurate count and locations • Sends a redeployment packet once nodes have reconnected to use existing slack in the network • Improves coverage

  13. LISTEN WAIT WAIT UPDATE Death/New/Arrival Timer (update) Death/New/Arrival Death Timer (deploy) Figure 1: Finite state machine for master node FSM for Master Node

  14. Deployment • Graph divided into linear sets • Nodes expand to cover the area assigned to set in case of loss • Extra nodes in a set are reassigned to sets without enough nodes to maintain coverage • At the very start, all the nodes are in the same set and are located at the base station

  15. Node Movement: Line

  16. Node Movement: Star

  17. Node Movement: Box

  18. Coverage: Box

  19. Future Work • Tweaks • Use distances to calculate timing parameters for state transitions • New applications • Coordinated movement to perform sweep-search • Allow nodes to search areas, use rendezvous to share search results and report progress

  20. Summary • Mobile nodes enable self-repair and self-deployment • Re-Pair • Use 2 stages to reconnect network and maximize coverage

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