# Bell-X, An Opportunistic Time Synchronization Mechanism for Scheduled Wireless Sensor Networks
## 3 Related Work
[23] perform different simulations, in which the density of nodes and the transmission beacon period varies, showing that a random period improves the connection process. [PERSON] et al. [24] analyse, when considering the entire protocol stack, the problems of the synchronization process in TSCH networks, comparing the minimal configuration proposed by 6 TSCH group and their proposed dynamic resource management algorithm. In [25], a dynamic EB period is proposed, sending more advertising messages, based on the number of joined nodes. In [6], the authors introduced a mechanism that was developed to facilitate the deployment of a WSN network, addressing possible issues during synchronization and connection phases when joining the network, and the influence of the TSCH and RPL parameters. This work proposes a mechanism that improves connection time and success probability, while significantly reducing energy consumption. This is achieved by allowing for the Beacons transmission period to be increased once the initial network set-up is finished and the network is in stable condition. This proposal is based on the analysis of results that were obtained by the methods described as \"Fixed EB\" and \"RPL trickle timer\". Using a Fixed EB, to achieve adequate synchronization and connection times, low periods must be used, with the consequent increase in energy consumption. Using the \"RPL trickle timer\", as in the proposal used in Contiki, poor synchronization and connection results are obtained, since this mechanism, valid for CSMA-CA (Carrier sense multiple access collision avoidance) RPL networks, does not take the particularities of TSCH networks into account. To address this, the Custom Trickle timer was developed in [6], which allowed for the high synchronization and connection probabilities of using a fixed and small EB transmission period to be matched with a low energy consumption, similar to that used with high periods (penalized with very poor connection results). The designed mechanism is valid during the set-up of a network, but did not address the problem of reconnection or connection of new nodes to the network after a long period of operation. A possible solution contemplates the use of an active mechanism, such as the one based on the sending of DIS messages to restart the timers. However, these RPL messages are discarded by the TSCH layer, as they are not yet synchronized. In this paper, the software of these layers was modified to allow for the real transmission of these messages. However, the chances of success of receiving this message before synchronizing is 1%-2%, as seen for the active scanning method, which implies a low impact in successfully joining the network, but with high impact in energy cost. Therefore, to achieve an adequate synchronization and connection rate, it is necessary to develop a mechanism that, depending on the scenario, determines the highest acceptable time for synchronization and connection, the lowest possible energy consumption, and modifies the behaviour and parameters of the network, to ensure these results.