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  1. 1. RE-Pair Self-Repairing Mobile Node Network
  2. 2. Disabled Sensors <ul><li>In James Bond movies, you often see him disabling sensors and cameras and sneaking into the secret hideout. </li></ul><ul><li>So what’s wrong with this picture? </li></ul><ul><li>If the bad guys can spend millions buying sharks with fricken lasers, then why can’t they buy better security? </li></ul>
  3. 3. Mobile Nodes <ul><li>What does mobility give us? </li></ul><ul><ul><li>Self-deployment </li></ul></ul><ul><ul><li>Self-repair </li></ul></ul><ul><li>We consider a sparse deployment of nodes </li></ul><ul><ul><li>Depth vs Breadth </li></ul></ul><ul><ul><li>Each node has to maintain a connection to the base station </li></ul></ul>
  4. 4. Applications <ul><li>Providing reliable wireless access </li></ul><ul><ul><li>Quick, automated deployment </li></ul></ul><ul><ul><li>Fast repair, adaptive </li></ul></ul><ul><li>Intrusion detection </li></ul><ul><ul><li>Self-repairing perimeter allows recovery from damage </li></ul></ul><ul><li>Monitor environment </li></ul>
  5. 5. Challenges <ul><li>Death of a node bisects the graph </li></ul><ul><li>2 Ways to repair link (distributed vs centralized) </li></ul><ul><ul><li>Nodes detect break and repair on their own </li></ul></ul><ul><ul><li>Base station/Master node redeploys the nodes to optimally cover the area </li></ul></ul><ul><li>2 Goals of repair </li></ul><ul><ul><li>Reconnect all nodes </li></ul></ul><ul><ul><li>Maximize coverage </li></ul></ul>
  6. 6. Challenges cont. <ul><li>Repair with nodes </li></ul><ul><ul><li>Possible to reconnect network </li></ul></ul><ul><ul><li>Tough for nodes to cooperatively find the total slack in the network </li></ul></ul><ul><li>Repair with master node </li></ul><ul><ul><li>Able to calculate best dispersal with nodes it has </li></ul></ul><ul><ul><li>Can not reach separated nodes to issue deployment orders </li></ul></ul>
  7. 7. Re-Pair <ul><li>Separate link repair into two stages </li></ul><ul><ul><li>Stage 1 </li></ul></ul><ul><ul><ul><li>Individual nodes detect break and repair link </li></ul></ul></ul><ul><ul><ul><li>Requires knowledge of node locations and node deaths </li></ul></ul></ul><ul><ul><li>Stage 2 </li></ul></ul><ul><ul><ul><li>Master node calculates a new deployment once it determines how many nodes it has left </li></ul></ul></ul>
  8. 8. Keep-Alives <ul><li>Nodes broadcast a keep-alive advertising their status and location </li></ul><ul><ul><li>Optimization: filter out keep-alives that contain only old information </li></ul></ul><ul><ul><ul><li>Reduces packet traffic </li></ul></ul></ul><ul><ul><li>Assign pairs of neighboring nodes </li></ul></ul><ul><ul><ul><li>Responsible for announcing death of paired node </li></ul></ul></ul><ul><ul><li>Store locations and status in a table per node </li></ul></ul><ul><ul><ul><li>Not necessary for correctness but for performance </li></ul></ul></ul>
  9. 9. Paired Nodes Pair 2 & 3 1 2 3 4 5 Pair 3 & 4
  10. 10. Stage 1 <ul><li>Node’s death detected by its neighboring pairs (network is now split in two) </li></ul><ul><li>Death announced to connected and disconnected nodes </li></ul><ul><li>Disconnected neighbor heads toward the location of the node preceding the dead node </li></ul><ul><ul><li>Repeats until its reconnected or has reached the base station </li></ul></ul><ul><ul><li>Allows the network to retain coverage during repair </li></ul></ul>
  11. 11. Death Detection 1 2 3 4 5 2 announces death of 3 4 announces death of 3 Pair 2 & 4 1 2 4 5
  12. 12. Stage 2 <ul><li>Master node listens for changes in the network </li></ul><ul><li>Requests Update from nodes to get accurate count and locations </li></ul><ul><li>Sends a redeployment packet once nodes have reconnected to use existing slack in the network </li></ul><ul><ul><li>Improves coverage </li></ul></ul>
  13. 13. FSM for Master Node WAIT WAIT UPDATE LISTEN Timer (deploy) Timer (update) Death/New/Arrival Death/New/Arrival Death Figure 1: Finite state machine for master node
  14. 14. Deployment <ul><li>Graph divided into linear sets </li></ul><ul><li>Nodes expand to cover the area assigned to set in case of loss </li></ul><ul><ul><li>Extra nodes in a set are reassigned to sets without enough nodes to maintain coverage </li></ul></ul><ul><li>At the very start, all the nodes are in the same set and are located at the base station </li></ul>
  15. 15. Node Movement: Line
  16. 16. Node Movement: Star
  17. 17. Node Movement: Box
  18. 18. Coverage: Box
  19. 19. Future Work <ul><li>Tweaks </li></ul><ul><ul><li>Use distances to calculate timing parameters for state transitions </li></ul></ul><ul><li>New applications </li></ul><ul><ul><li>Coordinated movement to perform sweep-search </li></ul></ul><ul><ul><li>Allow nodes to search areas, use rendezvous to share search results and report progress </li></ul></ul>
  20. 20. Summary <ul><li>Mobile nodes enable self-repair and self-deployment </li></ul><ul><li>Re-Pair </li></ul><ul><ul><li>Use 2 stages to reconnect network and maximize coverage </li></ul></ul>