# A Robust and Energy-Efficient Weighted Clustering Algorithm on Mobile Ad Hoc Sensor Networks +
## 4 Communication and Topology Maintenance  
### Topology Maintenance  
Topology maintenance is based on the fault nodes detection and CHs backup mechanism. Once finds fault nodes or failure \(CH\) nodes, then it needs to cluster again. From this perspective, the network of clustering is not periodic but on demand. However, because of node's mobility, if the network is normal after a certain period of time, the topology maintenance process is automatically conducted. The timing sequence of our protocol is presented as Figure 6 shows. In set up phrase, cluster formation process is to be conducted, that is, our proposed protocol is executed at this period. Actually, the time consumed is relied on the moment that the cluster formation accomplishes. If the energy of the whole network is extremely little and all nodes are going to die, the clustering formation will be longer for the greater times of iteration. In steady phrase, nodes are occupied with collecting data and transmission. Apparently, in this time phrase \(CH\) will consume much energy for the routing of nodes' message. Due to the mobility of nodes, the routing is a hard problem. However, after the cluster formation considering group mobility, the topology will relatively stable. Therefore, the overhead of routing will be reduced. During the period of _time_fn1_, fault detection algorithm will be implemented. In _time_fn2_, topology maintenance is executed. The time overhead is not stable which is dependent on the different application. If network is deployed in a well environment, the lifetime of each node will be longer than those malicious or bad environment. The fault detection algorithm can exclude \"dead\" node form the network. Here, \"dead\" nodes are relatively fewer. We mainly consider how to reduce the network partition and nodes failure. This consideration is also a way of topology maintenance. A stable topology will benefit decreasing overhead of routing and clustering. Of course, our proposed clustering algorithm mainly focuses on the clustering algorithm, however, in order to demonstrate routing problem with our protocol, we also need to clarify the reasonability of the proposed algorithm in routing finding aspects. Algorithm 4 gives the detailed process description of cluster maintenance algorithm. Through topology maintenance process, the cluster topology is relatively stable and the performance of the whole network can be guaranteed, such as throughput, lifespan and so forth. The network does not paralyze for the \(CH\) fault or nodes failure. The QoS of the network can be enhanced through a robust \(CH\) and stable topology. Actually, the fault detection can extend into a secure field for the similarity of the trust value of nodes. Currently, the trust value computing is a common method to estimate whether a node is good or bad. The realization of this kind of trust estimation, which can enhance the security of the network, is implemented through sensing among nodes or interception [24; 28; 41]. ```
Step 1: When cluster members finish sending packets, network fault detection process begins, if cannot detect any problems, then go to step 5; otherwise execute sequentially. Step 2: If finds the \(CH\) failure, then go to step 4; otherwise execute sequentially. Step 3: The RE\({}^{2}\)WCA algorithm is conducted according to the information of all cluster members. If fault node is backup \(CH\), backup \(CH\) is obliged to be elected again according to weight value among cluster members. Then jump to step 5. Step 4: Backup \(CH\) takes over the duty of \(CH\) firstly and broadcasts messages overall the network. If \(CH\) is permanent fault node, the ID will be deleted from the network; otherwise to be cluster member. Then, the RE\({}^{2}\)WCA algorithm is conducted to make sure the network re-cluster again. Then, jump to step 5. Step 5: Withdraw from topology maintenance process. ```  
**Algorithm 4** Cluster Maintenance Algorithm  
The robustness of the network is enhanced when the fault detection and backup \(CH\) mechanism are introduced.