Cut detection


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Cut detection

  2. 2. Topics for discussion Introduction  Sensor network  Architecture of sensor network.  Applications of sensor network.  Challenges of sensor network. Cuts in sensor networks. Detection of cuts. Distributed cut detection algorithm. Conclusion. Future aspects. References.
  3. 3.  Sensor Network: It is a group of specialized transducers with a communication infrastructure intended to monitor and record conditions at diverse location, it may be temperature, pressure humidity wind direction and speed etc… It consists of multiple detection station called nodes, which is small, lightweight and portable.
  4. 4. Contd…
  5. 5. Contd…
  6. 6. Architecture of WSNs Transducer generates electrical signals. Microcomputer processes and stores Sensor output. Transceiver receives the commands from central computer, transmits data to that computer. Power from battery.
  7. 7. Applications Industrial monitoring.  Machine health monitoring.  Data logging.  Industrial sense and control applications. Automated and smart homes. monitoring the activities performed in a smart home is achieved using wireless sensors embedded within everyday objects forming a sensor network. Medical device monitoring.
  8. 8. Contd… Monitoring of weather conditions. Air traffic control. Robot control. Air pollution monitoring. Forest fire detection. Natural disaster prevention.
  9. 9. Challenges One of the challenge in the successful use of WSNs come from limited energy of the individual sensor nodes. WSNs consist of large number of small, low cost sensor nodes distributed over large area. WSNs have emerged as a promising new technology to monitor large regions. Node failure is expected to be quite common. this is true for sensor networks deployed in harsh and dangerous fields such as forest fire monitoring and in defense applications.
  10. 10. Cuts in sensor networks WSNs can get separated into multiple connected components due to failure of some of its nodes, which is called “cut”. So here we consider the problem of detecting cuts. Two nodes are said to be disconnected if there is no path between them.
  11. 11. Contd…
  12. 12. Contd… In the figure, filled circles represents active nodes and unfilled circles represent failed node. Solid lines represents the edges, and dashed lines represent the edges that existed before the failure of node. the hole in (d) is indistinguishable from the cut in (b) to nodes that lie outside the region R
  13. 13. Detection of cuts Nodes that detect the occurrence and approximate the locations of the cuts can then alert the source node or base station. If the node were able to detect the occurrence of cut it could simply wait for the network to be repaired and eventually reconnected, which saves on-board energy of multiple nodes and prolongs their lives. The ability to detect cuts by both the disconnected node and source node will lead to increase in the operational lifetime of the network as a whole.
  14. 14. Distributed cut detection algorithm This algorithm allows each node to detect DOS(Disconnection frOm Source) events and subset of node to detect CCOS(connected but cut occurred somewhere) events. The algorithm is distributed and asynchronous. It involves only local communication between neighboring nodes and is robust to temporary communication failure between node pairs. A key component of the DCD algorithm is a distributed iterative computational step through which the nodes compute their electrical potentials.
  15. 15. Distributed cut Detection Definition and problem statement Time is measured with a discrete counter k=∞,…., - 1,0,1,2,….. We model the sensor network as a time varying graph ( ) = ( (k )ℰ(k)), whose node set V(k) represents the sensor nodes active at time k and the edge set ℰ( ) consist of pairs of nodes (u,v) such that nodes u and v can directly exchange the message between each other at time k. By an active nodes we mean a nodes that has not failed permanently .
  16. 16. Contid… All graphs considered here are undirected i.e (i,j)=(j,i). The neighbors of node i is the set of nodes connected to i i.e. = { |( , ) ∈ ℰ}. The numbers of neighbors of i, | |, is called its degree, which is denoted by di. A path from i to j is sequence of edges connecting i and j. A graph is called connected if there is a path between every pair of nodes. A component Gc of the graph is maximal connected sub graph of G.
  17. 17. Contid… A cut is formally defined as the increase of the number of components of a graph due to the failure of subset of nodes. The number of the cuts associated with a cut event is the increase in the number of components after the event.
  18. 18. Contid… The problem we seek to address is two fold  First we want to enable every node to detect if it is disconnected from source.  Second we want to enable nodes that lie close to the cuts but are still connected to the source.
  19. 19. Contid… The DCD algorithm is based on the following electrical analogy. Imagine the wireless sensor network as an electrical circuit where the current is injected at the source node and extracted out of a common fictitious node that is connected to every node of sensor network. Each edge is replaced by the 1 Ω resistor. When a cut separates certain nodes from source node, the potential of each of those nodes becomes 0, since there is no current injection into their components. The potential is computed by an iterative scheme which only requires periodic communication among the neighboring nodes.
  20. 20. Contid…DOS detection• When node u is disconnected from the source, we say that a disconnected from source event has occurred for u.• The algorithm allows each node to detect DOS events.• The nodes use the computed potentials to detect if DOS event have occurred .• The approach here is if the state is close to 0 then the node is disconnected from the source , otherwise not.
  21. 21. Contid… DOS detection part consist of steady state detection, normalized state computation and connection/separation detection.
  22. 22. Contid…CCOS detection When a cut occurs in the network that does not separate a node u from the source node, connected but a cut occurred somewhere (CCOS) event has occurred for u. Detection of CCOS events by the nodes close to a cut, and approximate location of cut means location of one or more active nodes that lie at the boundary of cut and that are connected to source.
  23. 23. Contid… To detect the CCOS event the algorithm uses the fact that the potential of nodes that are connected to source node changes after the cut and also using probe messages. Probe messages that are initiated by the certain nodes that encounter failed neighbors, and are forwarded from one node to another node in a way that if short path exist around a hole created by node failures, the message will reach initiating nodes.
  24. 24. Contid… Each probe message contains the following information: A unique source ID Source node ID S Destination node, path traversed, and angle traversed by probe message.
  25. 25. Conclusion The DCD algorithm we propose here enables every node of a wireless sensor network to detect disconnected from source event if they occur. Second it enables the subset of nodes that experiences CCOS event to detect them and estimate the approximate location of the cut in the form of a list of active nodes that lie at the boundary of the cut/hole.
  26. 26. Future Aspect Application of DCD algorithm to detect the node separation and reconnection to the source in mobile networks.
  27. 27. references http:// ut.pdf - United States networks
  28. 28. THANK YOU