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Directed Diffusion: A Scalable and Robust Communication Paradigm for Sensor Networks Intanagonwiwat, Govindan, Estrin USC, Information Sciences Institute, UCLA Carl Hartung CSCI 7143: Secure Sensor Networks

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Overview Directed Diffusion Conventions and Terms Interest Propagation Data Propagation Reinforcement Summary Evaluation of Directed Diffusion Impacts of node failures, etc..

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Directed Diffusion A Data Driven routing protocol The basics: A node (sink) broadcasts out Interests If a node measures something of interest, send it back to interested node. Every node thinks all neighbors are End Points Localized repair and reinforcement Multi-path delivery for different sinks

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Naming Task descriptions are named by Attribute-Value pairs Query/interest: 1. Type=four-legged animal// detect animal location 2. Interval=20ms (event data rate)// send back events every 20 ms 3. Duration=10 seconds// for the next 10 seconds 4. Rect=[-100, 100, 200, 400]// from sensors within rectangle Reply: 1. Type=four-legged animal// type of animal seen 2. Instance = elephant// instance of this type 3. Location = [125, 220]//location of node sensing 4. Intensity = 0.6// signal amplitude measure 5. Confidence = 0.85// confidence 6. Timestamp = 01:20:40// event generation time

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Interests and Gradients Interests injected into network by (possibly arbitrary) node– now called sink. Interests are cached by all nodes for time=duration, then purged Interests are periodically refreshed by the sink. Low initial data rate Higher if found something of interest

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Interests cont’d Nodes cache many interests Cached interests do not contain info about the sink – only node it received interest from Interest entry contains possibly many gradient fields

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Gradients Contain a data rate field requested by the specified neighbor Also contains timestamp and expiresAt One per neighbor per Interest Each interest can have many gradients (one per neighbor)

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Interest Propagation (flooding) A B C D F E G

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Sink Interests A B C D F E G

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Interest Propagation (flooding) Sink Interests A B C D F E G

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Interest Propagation (flooding) Sink Interests A B C D F E G

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Interest Propagation (flooding) Sink Interests A B C D F E G

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Data Propagation Sink Sensed something that matched an interest A B C D F E G

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Data Propagation Sink A B C D F E G

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Data Propagation Sink A B C D F E G

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Data Propagation (ignored) Sink A B C D F E G

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Data Propagation (ignored) Sink A B C D F E G

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Reinforcement Sink Re-send Interest with smaller interval A B C D F E G

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Reinforcement Sink Re-send Interest with smaller interval A B C D F E G

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Reinforcement Sink Primary path A B C D F E G

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Design Choices Diffusion ElementDesign Choices Interest Propagation Flooding Constrained or directional flooding based on location Directional Propagation based on previously cached data Data Propagation Reinforcement to single path delivery Multipath Delivery with selective quality along different paths Multipath delivery with probabilistic forwarding Data caching and aggregation For robust data delivery in face of node failure For coordinate sensing and data reduction For directing interests Reinforcement Rules for deciding when to reinforce Rules for how many neighbors to reinforce Negative reinforcement mechanisms and rules

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Summary Data-centric communication All communication neighbor to neighbor, not end-to-end All neighbors appear to be ‘end’ to each node Routes are established ‘on demand’ Message cache used to avoid loops

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Analysis Used 2 metrics to measure Average dissipated energy Measures the ratio of total dissipated energy per node in the network to the number of distinct events seen by sinks Average Delay Measures the average one-way latency observed between transmitting an event and receiving it at the sink Simulation uses a 1.6Mbps 802.11 MAC layer

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Analysis Compared Directed Diffusion to 2 other protocols Flooding All events are flooded to every node in the network Omniscient Multicast Each source transmits events along shortest-path multicast tree to all sinks

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Average Dissipated Energy

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Average Delay

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Average Dissipated Energy (w / node failures)

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Average Delay (w / node failures)

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Event Delivery Ratio (w / node failure)

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Problems? Interest timeouts while data is en-route to sink. Congested network? Can the network satisfy small event data intervals? Multiple? Security – nodes temporarily disabled cause data to loop? Cache size / Timeouts

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Conclusion Directed Diffusion has potential for significant energy efficiency Robust in dynamic sensor networks Self Configuring A good start Need better evaluation

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