# A Joining Procedure and Synchronization for TSCH-RPL Wireless Sensor Networks
## 5 Simulations and Testbeds  
The different mechanisms that are frequently used for synchronization and routing are prone to show very different behaviours, which impact on the network's formation time. Therefore, it is interesting to make a comparison of the different results in terms of the probability of synchronization/connection success, the amount of messages that are generated, energy consumption estimates of different devices, and above all the network's synchronization and connection speed. Different simulations have been carried out for this purpose using the Cooja simulator that is included in the Contiki OS, which allows us to compare the operation of different parameter configurations. A network that is formed by a grid of 16 nodes has been defined, in which only one of them takes on the role of coordinator (node 1 in Figure 6). This node, which is located in the upper left corner, is responsible for initiating the synchronization process by disseminating the EBs and RPL control messages. The configuration parameters for the simulation are shown in Table 1. In this topology, nodes are separated by a fixed distance of 40 m, forcing the creation of a multi-hop topology. This allows us to observe the impact of synchronization on the furthest nodes from the coordinator. The duration of the simulations is limited to 15 min, considering that the objective is to test the agility of the process; so, this amount of time is enough and longer times are not acceptable for deployment personnel. This limit matches the assumption that nodes need no more than 2 min for the next level to connect, \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Physical Parameters**} \\ \hline Min. number of Neighbors & 2 \\ Max. number of Neighbors & 4 \\ Min. number of hops (node 16) & 6 \\ Distance between neighbors & 40 m \\ Max. Simulation duration & 15 min \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The configuration’s main parameters. Figure 6: The physical topology. thus needing 12 min for all six levels to connect correctly. For different topologies and scalability issues, longer simulation times may be required. In order to have a point of reference for comparison, the behaviour of a configuration that uses TSCH as it is defined in the standard, with a fixed beacon transmission period (that is, the method described in Sections 4.1 and 4.2), is simulated. The configuration that combines TSCH with RPL is also used to modify the beacon transmission period according to the result of the RPL Trickle Timer (that is, the method described in Section 4.3). All simulations use Orchestra-based TSCH resource planning [10] in order to control the resources that are given to RPL individually. From these base configurations, different combinations of parameters that influence the synchronization and connection process are simulated. The aim is to reach an optimal configuration that improves the synchronization and connection process and the time it takes to complete this process. Table 2 shows the parameters that have been modified to perform the following simulations. For the energy consumption analysis, the parameters in Table 3 have been taken into account, corresponding to the consumption of the radio transceiver CC2420 datasheet, which is the hardware that is used by the Zolertia Z1 node model that was chosen to perform the different simulations.