# Efficient Actor Recovery Paradigm for Wireless Sensor and Actor Networks
## 4 Problem Statement and Optimized Deterministic Actor Recovery System Model
### Optimized Deterministic Actor Recovery System Model  
The network consists of multiple actors and sensor nodes that are structured with the hierarchical structure of the nodes. The hierarchical structure of the nodes provides an efficient, fast and logical packet forwarding patterns. It also determines the features of all nodes connected with WSANs. Another advantage of the hierarchical structure is that it helps to start with little multiplexing process for intra-domain routing. As the packets travel further from the source node the model helps to develop higher degree of multiplexing. The nodes of different categories in WSAN as depicted in Figure 3 possess the assorted nodes types. The network aims to use the resources efficiently for each packet forwarded by an actor node. In addition, it reduces the latency while keeping the network more stable. **Definition 4**. : _Critical actor node is the actor node which its failure cause network partitioning._  
**Definition 5**. : _Non-critical nodes (NCNs) are regular actor nodes._  
Figure 3: Nodes Types in EAR. Definition 6: Cut Vertex Nodes (CVNs) are nodes which have a cut-vertex link with a critical node, i.e., neighbors of critical node. Definition 7: The Critical Backup Nodes (CBNs) are actor nodes that are assigned to be the backup nodes for a critical node. The EAR consists of actor nodes, sensor nodes, and base station. Actor node can be critical or non-critical. Critical actor node is the actor node which its failure causes network partitioning. Non-critical nodes are regular actor node. Sensors node are used to monitor the network for event detection. In this topology, Cut Vertex Nodes (CVNs) are responsible for the removal of the paths that lead to the critical nodes. When the actor node becomes a critical node, then it is necessary to redirect the traffic of the neighbor nodes to the non-critical nodes. Thus, this task is done by removing the vertex (a path leading to critical nodes) and redirecting the traffic, as it further helps improving the throughput performance and reduces the latency. The Critical Backup Nodes (CBNs) replace the actor nodes when the actor nodes become the critical nodes. We assume that the number of critical backup nodes are more than actor nodes in the network. If all the actor nodes become critical nodes, then replacement should be much easier to avoid any kind of interruption or data loss. There could a possibility of disconnecting the direct communication links of the actor nodes towards the backup nodes when the actor nodes start moving. Thus, we also assume that the links of the actor nodes lead to the backup nodes are always stable despite the mobility. Therefore, there is a high possibility to easily replace the critical nodes with CVNs. The actor node has a privilege to collect the data from event-monitoring nodes (sensor nodes), then it forwards the packets to either base station or sensor /actor nodes in the network. On the other hand, the least degree Non Critical Nodes (NCNs) are preferred to be labeled as backup nodes for event-monitoring nodes. A neighbor node that is available in Node Distance range (ND) has a similar Cut Vertex Node Distance (CVND). This helps reduce the recovery time and overhead which is important for resource-constrained mission-critical applications. In the network, each actor node maintains its 2-hop neighbors' information using heartbeat messages. This information helps to maintain the network state, defining critical actor; as well as assigning backup node for the critical actor. Each actor node saves its neighbors information which includes node ID, RSSI value, number of neighbors which is denoted by the degree of node, node criticality (critical actor/non-critical actor), and node distance. Once a critical node is detected, the backup assignment process is executed in-order to assign a backup node for this critical node. The 2-hop node information is used in the process of backup node selection.