Download - RE-Pair
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RE-Pair
Self-Repairing Mobile Node Network
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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?
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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
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Applications
• Providing reliable wireless access• Quick, automated deployment• Fast repair, adaptive
• Intrusion detection• Self-repairing perimeter allows recovery
from damage
• Monitor environment
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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
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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
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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
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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
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Paired Nodes
Pair 2 & 3
1 2 3 4 5
Pair 3 & 4
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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
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Death Detection
1 2 3 4 5
2 announces death of 3
4 announces death of 3
Pair 2 & 4
1 2 4 5
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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
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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
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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
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Node Movement: Line
Node Movement: Line
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Distance Moved
CDF
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Node Movement: Star
Node Movement: Star
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Distance Moved
CDF
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Node Movement: BoxNode Movement for Box Topology
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Distance Moved
CDF
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Coverage: BoxCoverage: Box
89.00%
90.00%
91.00%
92.00%
93.00%
94.00%
95.00%
96.00%
97.00%
1 2 3 4 5
Lost Nodes
Coverage
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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
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Summary
• Mobile nodes enable self-repair and self-deployment
• Re-Pair• Use 2 stages to reconnect network and
maximize coverage