Topology management is a key component of network management of wireless sensor networks. The primary goal of topology management is to conserve energy while maintaining network connectivity. Topology management consists of knowing the physical connections and logical relationships among the sensors and at the same time creating a subset of nodes actively participating in the network, thus creating less communication and conserving energy in nodes. Networks require constant monitoring in order to ensure consistent and efficient operations. The primary goal of topology management is to maintain network connectivity in an energy-efficient manner. Topology management is one of the key aspects of configuration management, which entails initial set-up of the network devices and continuous monitoring and controlling of these devices. The main objective of this chapter is to throw a light on the recent developments and future directions of research in these directions.
One primary goal of network management in sensor networks is that it be autonomous. This is especially important in fault and configuration management. Configuration management includes the self-organization and self-configuration of the sensor nodes. Since WSN’s involve very little human intervention after deployment, it is imperative that the areas of fault management be self diagnostic and self-healing. Another important issue to consider in fault management of WSN’s is that a single node failure should not impact the operation of the network, unlike a traditional network device failure causing impact to several users to potentially the entire network. There are several new functional areas of network management in sensor networks. Apart from topology management there are still new functional areas introduced for network management of WSN’s are energy management and program management.
In (Akyildiz et al., 2002) energy management the most common way to conserve energy in WSN’s is to power off a node when idle, but there have been many proposals in existing algorithms and protocols as well as establishing new protocols in order to be more energy efficient.
Program or code management (Wattenhoffer & Zollinger, 2004) is another aspect of network management in WSN’s. The traditional method of updating a program in a sensor node is to attach the node to a programming interface of a laptop or PDA. This is not feasible in many WSN deployments. Transmitting an entire new program version to all sensors in a WSN is not practical as it consumes too much energy and will lead to a short network lifetime. There needs to be a way to transmit minimal packets to all nodes requiring the update while ensuring appropriate nodes receive the update reliably. There have been several proposals in the area of code update/management and it continues to be an active research area.
To begin with topology management (Zhang et al., 2009) there is six properties that should exist in the topology of WSN’s: 1) symmetry, 2) connectivity, 3) spanner, 4) sparseness, 5) low degree, and 6) low interference. It is often observed the case that two properties, connectivity and sparseness conflict with each other. Despite all conflicts, the objective of topology management is to provide a backbone to various routing protocols so that there is an energy-efficient communication of the data. The algorithms responsible for building up the backbone may be categorized into three types (1) topology discovery, (2) sleep cycle management, and (3) clustering.
Initialization Phase (Topology discovery Phase): In this phase, nodes discover themselves and use their maximum transmission power to build the initial topology.
Sleep cycle management: To conserve energy, in a node is to only have it powered on when necessary; the node would be powered off or put to sleep all other times.
Clustering: Clustering algorithms are used to decrease the number of nodes that transmit data to the base station (BS). These algorithms arrange the nodes deployed in the WSN into groups or clusters. One node in each cluster is identified as the leader of the cluster or the cluster head (CH). The nodes that are in a cluster, but are not cluster head, become member nodes of that cluster. The member nodes will transmit their data to their cluster head, which is typically within only a short distance thus consuming less energy.
Over the entire life of the network topology control cycle will repeat many times until the energy of the network is depleted.
Topology discovery involves a network management station, or a base station, determining the organization or topology of the nodes in the sensor network. The physical connectivity and/or the logical relationship of nodes in the network are reported to the management station, which maintains a topology map of the WSN. The base station, or network management station, will send a topology discovery request to the network. Each node in the network will respond with its information. There are three basic approaches taken for topology discovery: