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Wireless Sensor and Actuator Networks: Algorithms and Protocols for Scalable Coordination and Data Communication by Ivan Stojmenovic, Amiya Nayak

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5.1 MULTICASTING

In a multicasting task, the same message is routed from one single source node to a fixed number of destinations whose locations are potentially scattered in the network. In the context of sensor and actuator networks, this routing scheme is usually applied by sensors to report their data to several actuators (as illustrated in Fig. 5.1).

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Figure 5.1 Multicasting from a sensor S to actuators A1, A2, A3.

More formally, given a graph G = (V, E), a source sV, and a set of destinations DV, the multicast problem consists in finding a set of relay nodes RV, such that sFR is connected in G. The main idea behind multicast is to try to reduce R as much as possible (share a maximum of the links to send as few duplicate packets as possible). In most of the algorithms, this path sharing consists in building an overlay tree whose root is the source and leaves are destinations (destinations may also act as relay nodes, though). This is however not always the case, some algorithms rather build a mesh overlay, which better tolerate the failure of links, thanks to redundancy. Also, when the positions of destinations are known beforehand, the multicast task can be achieved without using any overlay structure. In this latter case, the paths may also form trees or meshes, but these structures are built on the fly and not memorized. The present section reviews these different ...

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