# Implementation of a Topology Independent MAC (TiMAC) Policy on a Low-Cost IoT System
## 6 Conclusions  
In this work, a MAC policy independent of the underlying topology (TiMAC) was implemented in a small IoT network consisting of low-cost devices based on Arduino and 433 MHz RF modules. A decentralized method was used for synchronizing the nodes' clocks as required from the underlying TDMA policy. Experiments were conducted in a full graph topology network under increased network traffic load. The conducted experiments confirm in practice the theoretical expectations from TiMAC as all of the results were within the expected boundaries in terms of throughput and successful transmissions per frame. These results suggest that policies that are independent of the underlying network topology could be considered when designing an IoT system, as they offer a means of node deployment without the usual considerations of traditional TDMA schemes (physical location combined with particular slot assignment), which could prove to be easier due to the nature of this type of networks and still could meet the strict time constraints of various delay-sensitive applications. The decentralized synchronization method used here also proved to be successful. At the same time, the fact that a particular experimental setup was close to the theoretical maximum expected values suggests that the proposed policy can be improved if unique characteristics of particular polynomial sets are taken into account before assigning them to network nodes. Future work should experiment with larger sensor networks so that TiMAC may be tested in multi-hop environment. Moreover, cybersecurity and resilience will have to be taken into account, as both of them are crucial parts of IoT, while their performance on low-cost devices is questionable. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Polynomial Set** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** & **11** \\ \hline Node A & 0x + 0 & 1x + 2 & 0x + 1 & 0x + 4 & 1x + 0 & 0x + 1 & 0x + 3 & 0x + 1 & 0x + 2 & 0x + 1 & 2x + 1 \\ \hline Node B & 0x + 1 & 1x + 3 & 0x + 4 & 1x + 1 & 1x + 3 & 0x + 4 & 1x + 0 & 0x + 2 & 0x + 3 & 2x + 0 & 2x + 4 \\ \hline Node C & 0x + 2 & 2x + 0 & 2x + 0 & 1x + 2 & 1x + 4 & 2x + 2 & 2x + 4 & 0x + 4 & 2x + 4 & 2x + 3 & 3x + 0 \\ \hline Node D & 0x + 3 & 2x + 2 & 2x + 2 & 2x + 0 & 3x + 3 & 3x + 3 & 3x + 1 & 1x + 0 & 3x + 2 & 2x + 4 & 3x + 4 \\ \hline Node E & 0x + 4 & 3x + 0 & 2x + 3 & 3x + 2 & 4x + 4 & 4x + 4 & 4x + 1 & 4x + 1 & 4x + 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The particular polynomial sets used in the experiments. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Polynomial Set** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** & **11** \\ \hline Node A & 495 & 203 & 101 & 100 & 301 & 200 & 100 & 300 & 298 & 98 & 202 \\ \hline Node B & 423 & 399 & 200 & 101 & 300 & 199 & 102 & 200 & 201 & 194 & 300 \\ \hline Node C & 500 & 193 & 258 & 398 & 400 & 300 & 200 & 206 & 200 & 400 & 198 \\ \hline Node D & 396 & 275 & 302 & 99 & 198 & 200 & 200 & 97 & 198 & 195 & 200 \\ \hline Node E & 396 & 102 & 398 & 99 & 99 & 200 & 200 & 99 & 102 & 195 & 200 \\ \hline Total & 2210 & 1172 & 1259 & 797 & 1298 & 1099 & 802 & 902 & 999 & 1082 & 1100 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Successful transmissions per node for each polynomial set. **Funding:** This research received no external funding. **Acknowledgments:** This work was supported in part by project \"A Pilot Wireless Sensor Networks System for Synchronized Monitoring of Climate and Soil Parameters in Olive Groves\" (MIS 5007309), which is partially funded by European andNational Greek Funds (ESPA) under the Regional Operational Program \"Ionian Islands 2014-2020\". In addition, this work was supported in part by the European Commission as part of the ReCRED project (Horizon H2020 Framework Program of the European Union under GA number 653417), by the Chair of Excellence UC3M--Santander Program and by the National and Kapodistrian University of Athens (S.A.R.G.).