Current problems at the network layer can be classified into three categories: topology control, routing, and coordination. Their coverage follows.

1.14.1 Topology Control

A well-organized network topology can not only prolong the lifetime of a network, but also enhance data communications. Topology control problems can be subdivided into neighbor discovery problems and network organization problems. Neighbor discovery problems are defined as problems in detecting and discovering neighbors which are located within the transmission range. In the network organization problems, each node chooses its neighbors and constructs local topology by either adjusting its transmission power or setting its status, such as sleep and active modes. There are some protocols that achieve desired network topology by movement control on nodes. For example, the localized mobility control protocol in Das et al. (2007) constructs a biconnected network from a connected network through the movement of nodes. In this and a number of other protocols, topology control is used to create fault-tolerant networks for reliable communication protocols.

The most important topology control, especially for power-critical sensor networks, is to place as many possible sensor (and similarly actor) nodes into a sleep mode as possible. All nodes that are not essential for communication or area coverage can be placed in sleep mode for prolonged periods, synchronously or asynchronously. ...

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