# Multihop Latency Model for Industrial Wireless Sensor Networks Based on Interfering Nodes
## 4 Simulations  
To carry out the validation of the analytical model, simulations have been performed with different deployment configurations of a WSN network. As there is a wide variety of possible configurations, given that the interfering nodes in each hop can vary, the experiments have been limited to a maximum number of three hops (\(H=3\)), while the maximum number of interfering nodes in any given hop reaches a maximum of fifteen nodes. These configurations give enough information to be able to validate the accuracy of the model, covering a wide range of applications for industrial scenarios, where the number of devices is usually between 10 and 30 nodes [14]. The configuration of the protocol stack, as well as the different variations of each of the simulated configurations, have been carried out using the Contiki NG operating system, as it includes the Cooja simulator with which to deploy networks based on TSCH and RPL. Figure 4 shows one of the topologies under study, where the newly deployed node has ID 15, and is located three hops away from the root node (node 1), so it must relay its messages through nodes 3 and 2. The communication between node 15 and node 3 has ten interfering nodes, including node 2 and nodes 6 to 14. For the communication between node 3 and node 2, there would be five interfering nodes, including node 1 and nodes 4 to 7. The last hop, having no other node within the coverage area, has no interfering node. To validate the behaviour of this type of multi-hop network with sufficient repeatability, the selection of routes has been limited so that the same type of multi-hop network is always formed, while varying the number of interfering nodes at each stage up to the root. Simulations were performed for \(11\) different configurations, the topology of which is shown in Figure 5 in which the new node is one hop away from the root, Figure 6 in those in which it is located two hops away, and Figure 7 for those configurations in which the new node is deployed three hops away from the root. Each of these simulations was repeated 10 times, using different seeds for each of the simulations. Figure 4: Example of topology of one of the configurations under study. Figure 5: Simulated configurations with a single hop and different interfering nodes. The procedure followed in each of the simulations begins by deploying an initial network, based on the configurations presented above. The deployment of this initial network and its convergence before connecting the node under consideration, aims to normalize all simulations under the same initial conditions. Once the initial network is deployed, both the TSCH synchronization and the RPL topology, a new node is added at the location planned in each of the configurations. The simulation ends when the DAO message is received from the root. To analyse the time required to send and forward the multi-hop message, the processes at MAC layer are taken into account. Through the Cooja simulator, it is possible to check the cases of retransmissions due to interference and the time needed to send the control message along the path to the root node. Table 2 shows the basic configuration of some parameters of the selected communications architecture. For scheduling, we have used the Orchestra autonomous scheduling, which allows us to configure slotframes dedicated to different traffic planes. Since we want to evaluate the behaviour of downstream route shaping only, RPL will use a single slotframe to transmit all its control messages, whether multicast or unicast. In order to maintain a constant level of interference in all simulations, a constant traffic of multicast DIO messages has been generated, instead of using the period set by the Trickle Timer. This will allow the results to be as homogeneous as possible and will only affect the number of interfering nodes and the number of hops to the root. Figure 6: Simulated configurations with two hops and different interfering nodes. Figure 7: Simulated configurations with three hops and different interfering nodes.