# Inverse Coupled Simulated Annealing for Enhanced OSPF Convergence in IoT Networks
## 2 Main Contribution
### OSPF Interval Synchronization and Node State Propagation Mechanism  
In the OSPF protocol, unifying the configuration of the Hello Interval (\(T_{h}\)) and Dead Interval (\(T_{d}\)) parameters for all nodes within the same segment is essential for ensuring the stable establishment and continuous maintenance of neighbor relationships. Hello packets primarily facilitate neighbor discovery and fault monitoring. Inconsistent parameter configurations can lead to asymmetries in neighbor state perception, adversely affecting the correct establishment of adjacency relations and timely fault detection. Additionally, parameter consistency synchronizes the time window for fault detection, preventing delays or misjudgments due to variations in \(T_{d}\). This unification also enables the synchronous propagation of topological state information within the segment, minimizing delays in topology updates. Consequently, this section introduces the OSPF interval synchronization mechanism to ensure parameter consistency among all nodes, providing foundational support for the deployment of the reverse coupled annealing algorithm, as illustrated in Figure 4.  
The specific steps of the OSPF interval synchronization mechanism are as follows:  
* When the Designated Router (DR) calculates the new parameters for \(T_{h}\) and \(T_{d}\) (assumed to be 10 s and 40 s, respectively), the DR appends its \(T_{h}\) and \(T_{d}\) parameters to the Hello message and broadcasts it to all neighbors in the subnet.
* The Backup Designated Router (BDR) and other non-DR routers have their previous \(T_{h}\) and \(T_{d}\) values assumed to be 7 s and 28 s, respectively.
* Once the BDR or other routers receive the Hello message from the DR containing \(T_{h}\) and \(T_{d}\), they will immediately update their \(T_{h}\) and \(T_{d}\) to 10 s and 40 s, respectively. At the same time, the nodes will adjust their Hello message sending timers and failure detection timers accordingly. As shown in Figure 4, due to the timer adjustments, the sending of Hello messages is delayed by 3 s compared to before. When the next Hello message sending cycle begins, the node will send a Hello message containing the new parameters.  
Figure 3: Link state diagram.  
* When the DR receives the Hello messages sent by the BDR or other routers, it can detect that these nodes' \(T_{h}\) and \(T_{d}\) have been updated to 10 s and 40 s, thereby achieving global synchronization of \(T_{h}\) and \(T_{d}\) across the entire subnet.  
Additionally, this section designs a node state propagation mechanism, which transmits the node state by mapping it to the Priority field in the Hello message. This approach not only optimizes the DR election process based on the Priority field--allowing nodes with higher node state to be prioritized as DR or BDR--but also ensures that nodes with superior states take on critical roles within the network, enhancing stability and routing efficiency. Furthermore, since the OSPF protocol lacks a native mechanism for propagating node state, this mechanism enables nodes to share node state information in real-time among neighbors.