A framework of distributed indexing and data
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A framework of distributed indexing and data



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    A framework of distributed indexing and data A framework of distributed indexing and data Presentation Transcript

    • A Framework of Distributed Indexing and Data Dissemination in Large Scale Wireless Sensor Networks [Author Yingshu Li] [Presenter Harsh Achrekar]
    • Proposal
      • Integrated distributed Connected dominating set Based Indexing (CBI) data dissemination scheme
        • Handling of large amount of sensing data
        • Min. usage [ limited n/w computational resources ]
        • providing timely responses to queries
        • scalability , load balance and adaptivity during dynamic changes .
    • Connected Dominating Set [CDS] Concept
      • For a graph G(V,E), a Dominating Set S of G is a subset of V where each node in V S is adjacent to at least one node in S.
      • Connected subgraph of G
      • Nodes in C are dominators ,
      • the others are dominatees .
      • Candidate for virtual backbones in WSNs.
      • Routing tasks - dominators
      • A k-hop dominating set D in G is a set of nodes such that every node in G is at most k hops away from at least one of the nodes of D.
      • Fig. (b) shows 2-hop
      • dominating set.
      k-Hop Dominating Set [k-hop DS] Concept
    • Broadcast v/s data dissemination framework
      • Without CDS
        • A node broadcasts the packet whenever it first receives one
      • With CDS
        • All dominatees only need to send packets to their closest dominator(s )
        • dominators forward the packets towards their destinations.
      • Storage nodes
        • Sensing data is collected and stored close to sensing nodes
        • to decrease the communication cost
        • form a k-hop dominating set of the whole network .
      • Index nodes
        • Information of high level semantically rich data are pushed and maintained
        • formed by a connected m-hop dominating set .
      • Queries are routed to the appropriate index nodes instead of flooding into the whole network.
      • Storage and index nodes usually do not sense raw data
    • A Layered Approach
      • Bottom layer - sensing nodes - monitor the targets to generate raw sensing data.
      • Middle layer - storage nodes - store the high level semantically rich data.
        • max. dist(sensing nodes ,storage nodes )<= k hops.
        • raw data need not travel across the entire n/w.
      • Top Layer – index nodes - store the index information for those high level semantically rich data
        • use connected m-hop dominating set as index node set to dominate the storage nodes .
        • According to property of connected m- hop dominating set, max. dist (storage nodes ,index nodes) <= m hops
        • index node set is strictly connected.
    • Storage Nodes Determination
      • Query Injection time from sink to index node
        • Query_inject_time(sink ,index )<=(k+m) hops (constant) .
      • construct k-hop DS of n/w - obtain storage node set
      • Randomly select a node(usually a center of n/w) as a root. Initialize BFS search on root .
      • Every/All node exchanges info with its k-hop neighbors about the level[?], degree[?] and ID[?] . {? – explain}
      • To obtain Storage node of small size
        •  subgraph composed by all storage nodes have small diameter
        •  any leaf node should not be a storage node
      • if (L1 < L2) or (L1 = L2 && D1 > D2) or (L1 = L2 && D1 = D2 && ID1 < ID2)
      • then ( L1,D1, ID1) >(L2,D2,ID2)
      • At first, Leaf node u =smallest (Level,Degree,ID) among its neighbors sends a DOMINATING message to its exact k-hop away Parent node v =largest (Level,Degree,ID) to request v become a dominator (storage node).
      • When v receives this DOMINATING message, it becomes Black and broadcasts a BLACK message to all of its k-hop neighbors
      • On receiving a BLACK message from its parent, u becomes Gray and broadcasts a GRAY message to all of its k-hop neighbors .
      • Next node with smallest(Level,Degree,ID) among its k-hop neighbors that have not decided its status start this procedure.
      • Terminate - root ={ Gray,Black}.
      • Node 26 ,a leaf nodes with variable (4,1,26) sends a DOMINATING message to Node 7 with largest (Level,Deg, ID) within Node 26’s 2-hop neighbors. Node 7 becomes Black and broadcasts a BLACK message.
    • Index Nodes Determination
      • Construct connected m-hop dominating set I to dominate all storage nodes only and use all the nodes in I as index nodes.
      • Form new graph G’ of all the storage nodes and their parents in G .
      • Construct a connected m-hop dominating set .
      • - all the storage nodes should be dominatees
      • Add connectors to connect the red nodes which are index nodes.
    • Index Construction
      • Each index node stores one copy index of its dominatees (storage nodes).
      • Flood query to all index nodes for query result
      • flood overhead is much lower
        • size (index node set)< size( nodes in whole n/w)
      • When a query is injected into the sink (Node 29) it is forwarded to the Storage Node 4 which stores the data for Node 29.
      • Then, the query is flooded to all the index nodes. After that, the query result is returned to the sink after getting the result.
    • Results