# 3 MSF: A Multi-Modal Adaptation of the 6 TiSCH Minimal Scheduling Function for the Industrial IoT
## 5 Simulations and Results
### Scenario 1: Two Nodes  
Figure 14 illustrates the first scenario, which consisted of two nodes, a root (#1) and a non-root node (#2), separated by 50 m. The network operated under normal conditions for 10 min to reach a steady state. Then, from the 10 min mark, we blocked all sub-GHz communication modes between nodes #1 and #2 in both directions in order to emulate \begin{table}
\begin{tabular}{l c l} \hline \hline
**Parameter** & **Value** & **Notes** \\ \hline MinHopRankIncrease & 1 (128) & Carries over from [6] \\ \hline MaxRankIncrease & 7 (896) & “ \\ \hline MAX\_PATH\_COST & 256 (32,768) & Carries over from [23] \\ \hline MAX\_LINK\_METRIC & 8 (1024) & “ \\ \hline PARENT\_SWITCH\_THRESHOLD & 1.5 (192) & “ \\ \hline MaxFrameRetries & 3 & Carries over from [2] \\ \hline MaxBe & 4 & “ \\ \hline MinBe & 0 & “ \\ \hline \(ETX_{initial}\) & 6 (768) & See Figure 12 \\ \hline FROZEN\_SWITCH\_THRESHOLD & 0.5 (64) & “ \\ \hline \(S\) & 8 (1024) & “ \\ \hline \(W_{off}\) & 0.2 & “ \\ \hline \(IL_{max}\) & 3 & “ \\ \hline \(IL_{div}\) & 4 & “ \\ \hline  & & Towards same neighbor: \\ Unicast Tx buffer size & 64 packets & \(\begin{array}{l}\leq\)64 normal packets, \\ \(\leq\)4 priority packets, \\ \(\leq\)64 packets total \\ \end{array}\) \\ \hline MaxNumCells & 64 & Carries over from [7] \\ \hline LimNumCellsUsedHighUp & 48 & Inspired by [7] \\ \hline LimNumCellsUsedLowUp & 16 & “ \\ \hline LimNumCellsUsedHighDown & 30 & “ \\ \hline LimNumCellsUsedLowDown & 16 & “ \\ \hline  & & Only with different neighbors \\ Maximum \# of concurrent 6P & 2 & or towards the same neighbor \\ transactions & & if opposite directions and \\  & & \(\geq\)1 CLEAR transaction \\ \hline
3 MSF slotframe length & 75 & \(\forall\) 5 slotframes \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Overview of 6 TiSCH configuration parameters common to all simulation scenarios unless noted otherwise. If a secondary value is presented in brackets, it is the 16-bit representation of that same value (as used by RPL). adversities impacting all interface-modes that operated in the same frequency range (on all channels of that range), such as wide-band interference/jamming. Figure 15 characterizes the (virtual) link between nodes #2 and #1 based on the data gathered from a single simulation run and only serves to illustrate several key mechanisms of our 6 TiSCH implementation in action. As can be observed, the first normalized metric for #1 was equal to \(ETX_{init}\), meaning #2 received a packet (most likely an EB) on all interface-modes it shared with #1 (which was all of them) prior to transmitting a unicast packet to #1 on any of them. The relatively high \(ETX_{init}\) value was required because we found that the odds of successfully transmitting a unicast packet on (shared) autonomous Tx supercells were generally lower than the odds of doing so on (dedicated) probing/negotiated Tx supercells. As such, the high \(ETX_{init}\) value prevents a newly discovered node and/or a node with newly discovered interface-modes from becoming the preferred parent only to immediately have its inferred metrics (and by extension, normalized metric and path cost) increase significantly upon initiating a 6P ADD transaction for the probing Tx supercell towards it (the traffic of which is all sent on autonomous supercells), which would lead to instability. However, it is important, especially during the network startup phase, that the ETX of all frozen interface-modes along the path to the root decreases quickly enough (from \(ETX_{init}\), where applicable). Otherwise, newly discovered nodes with worse virtual links but shorter paths to the root than the theoretically ideal preferred parent (i.e., in steady state) would weak havoc on network convergence speed. The normalized metric bump around the 640 s mark shows the frozen interface-mode switching mechanism in action. At that point, all inferred metrics to #1 were below the metric threshold, so #1's normalized metric equated to its frozen interface-mode's inferred metric.