Wireless Sensor Network Protocol: Directed Diffusion

This protocol for WSN is a data centric query-based protocol where sink floods a query into the network through several routes between the sink and source. The sink supports one of those routes and receives data from that path within shorter time interval. Therefore, multipath delivery can be realized and significant achievement can be attained by adapting subset of network. 

The four features of directed diffusion routing protocol include Interests, data, gradients and reinforcement. The query that determines the user’s requirements is the Interest. Processed information is the data. The direction state of node that gets the Interest is the gradient. Multiple gradient paths are used to transmit events from originators of interest. The attribute value pairs that are used to name task descriptions are 
example:             type=wheeled vehicle                   //vehicle location
                              interval=20 ms                           //event sent every 20ms
                              duration=10s                              //next 10s duration
                              rect=[-100,100,200,400]            // sensors inside rectangle

Directed diffusion protocol builds path on need-basis and stores the data in attribute value pairs. Interest messages are broadcast (flooded) when sink requires data. This is added to neighbor’s interest cache and each neighboring node has gradients corresponding the ones that transmitted the interest. When a node generates data matching that interest, it is sent back to sink using gradients. The sink then reinforces shortest path and the intermediate nodes send the reinforcement by checking the local cache of the sent messages.

Advantages

  • It is data centric. The communication uses interests to identify named data. 
  • It performs neighbor to neighbor communication without node addressing mechanism. Every node specifies an end in the sensor network thus eliminating the need of routers and every node interprets data and interest messages. 
  • Each node is capable of performing caching and aggregation along with sensing thus saving energy and reducing delay substantially. Unlike IP-based sensor network, where a collection of specialized servers collect and process the sensor data, the network with directed diffusion protocol performs coordinated sensing close to the sensed phenomena thus providing robustness and scalability. 
  • Nodes require to distinguish between neighbors but are independent of unique addresses or identifiers. 
  • Global network topology is not required here and directed diffusion routing protocol is energy efficient.

Limitations

Data progressing takes place in intermediate nodes thus increasing the transmission latency in the directed diffusion protocol. Energy utilization is high in the protocol with respect to flooding and data processing. It uses directional flooding to set multiple paths. Data messages are transmitted redundantly through those paths. It then observes the path performance and reduces the path multiplicity. Thirdly, loop-free paths are not guaranteed through gradient setup mechanisms.

References

Handziski V., Köpke A., Karl H., Frank C., Drytkiewicz W. (2004) Improving the Energy Efficiency of Directed Diffusion Using Passive Clustering. In: Karl H., Wolisz A., Willig A. (eds) Wireless Sensor Networks. EWSN 2004. Lecture Notes in Computer Science, vol 2920. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-24606-0_12

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