Topology Control - Topology Construction and Maintenance

Topology Construction and Maintenance

Lately, topology control have been divided into two subproblems: topology construction, in charge of the initial reduction, and topology maintenance, in charge of the maintenance of the reduced topology so characteristics like connectivity and coverage are preserved.

This is the first stage of a topology control protocol. Once the initial topology is deployed, specially when the location of the nodes is random, the administrator has no control over the design of the network; for example, some areas may be very dense, showing a high number of redundant nodes, which will increase the number of message collisions and will provide several copies of the same information from similarly located nodes. However, the administrator has control over some parameters of the network: transmission power of the nodes, state of the nodes (active or sleeping), role of the nodes (Clusterhead, gateway, regular), etc. By modifying this parameters, the topology of the network can change.

Upon the same time a topology is reduced and the network starts serving its purpose, the selected nodes start spending energy: The "optimal" reduced topology stops being it at the first second of full activity. After some time being active, some nodes will start to run out of energy. Especially in wireless sensor networks with multihoping, it is a fact that nodes that are closer to the sink spend higher amounts of energy that those farther away due to packet forwarding. The network must restore the reduce network periodically in order to preserve connectivity, coverage, density and any other metric that the application requires.