Introduction Problems: ◦ Limited data communication capability and energy in WSN ◦ Routing queries to events based on short hops and minimized ◦ No global coordinate system ◦ Difficult to determine exactly geographic location of a node 3
Contribution Present a method for routing queries to nodes based on the event observed Not based on an unique id Not based on Geographic location of a node Node are densely distributed Allows data to be retrieved from the network keyed on the event Concentrates on data routing instead of naming based schemes 4
Possible Solutions Query flooding: ◦ Number of transmission: independent of the number of events ◦ Useful when number of events is higher number of queries Event flooding: ◦ Number of transmission: independent of the number of queries ◦ Efficient when number of events is higher number of queries 5
Rumor Routing Method Basic idea: ◦ Two lines in a bounded rectangle have a 69% chance of intersecting ◦ Create a set of straight line gradients from event, then send query along a random straight line from source 6
Rumor Routing Method (1) Use agents to create paths leading to each event when the event happens, and later to route queries along these paths. To join the path, the queries are first sent on a random walk in the network. Rumor Routing - a logical compromise between query and event flooding. 8
Rumor Routing Method (3) Use agents to create paths leading to each event when the event happens, and later to route queries along these paths. To join the path, the queries are first sent on a random walk in the network. Rumor Routing - a logical compromise between query and event flooding. 10
Rumor Routing Method (4) All nodes maintain a neighbor list and an event table. When it observes an event, the event is added with distance 0. Agents are actually long-lived packets traversing in the network. Creating aggregate path as they cross a path leading to another event 11
Rumor Routing Method (6) 13 Agent Path: ◦ Agent tries to travel in a “somewhat” straight line. Maintains a list of recently seen nodes. When it arrives at a node adds the node’s neighbors to the list. For the next tries to find a node not in the recently seen list. When agent finds a node with longer path than its own to the same event, it updates the routing table with the shorter path.
Rumor Routing Method (8) 15 Query Path: A query originates from source, and is forwarded along until it reaches the target Forwarding Rules: ◦ If a node has seen the query before, it is sent to a random neighbor ◦ If a node has a route to the event, forward to neighbor along the route ◦ Otherwise, forward to random neighbor using straightening algorithm
Experimental Results 16 Energy Comparison: Rumor Routing (1000 queries) ◦ Es + Q*(Eq + N*(1000-Qf)/1000) ◦ Es = avg. energy to set up path ◦ Eq = avg. energy to route a query ◦ Qf = successful queries ◦ Q queries are routed Query Flooding ◦ Q*N Event Flooding ◦ E*N
Conclusions Pros: ◦ Provides a good method for delivering queries to events in large networks ◦ Designed to be tunable to different application requirements, and be adjusted to support different query to event ratios. Cons: ◦ Optimal parameters depend heavily on topology ◦ Does not guarantee delivery ◦ There are no clear guidelines for parameter tuning. ◦ Simulation results in a particular environment. 18
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