## 6 Performance Evaluation
### Reliability in the Network
#### 6.5.2 Data Delivery Ratio in Case of Lossy Network  
In this section, we evaluate the behavior of the D-MSR and the WirelessHART routing mechanisms in terms of reliability. In the second experiment, we assume that the edges can only have two states, namely working or failed. We first increase the percentage of broken edges in the network and then measure the number of connections (from the 29 connections that were defined in the previous section) that are still working, _i.e._, connect the sensors to the actuators. Figure 25 shows that in the WirelessHART network, thanks to its multipath routing scheme, more than 50% of the connections are still usable upon increasing the percentage of broken edges to 30%. In contrast, for D-MSR we have around the same, 50% loss of end-to-end connections, when only 10% of edges are broken. However, thanks to the distributed nature of D-MSR, it can cope faster with interference (or edge failures) than WirelessHART, which uses the centralized approach. There is, therefore, a trade-off in  
Figure 24: Data delivery ratio differences in case of internal interference. Figure 25: Reliability of the end-to-end connections. applying the multipath routing in WirelessHART and in applying the distributed scheme to cope with the interference. In the third experiment, we evaluate the relationship between packet delivery ratio and increased interference in the network. To do so, we forward the CBR traffic (periodic sensor data) from sensors towards actuators, for all the 29 connections. At the destinations/actuators we then measure the number of received packets. Unlike in the earlier experiment outlined above, we now assume that the quality of edges may vary from 0% to 100%. In this experiment, we gradually increase the interference regions in the network in six steps (each step takes 2,000 seconds). These six steps of applying interference in the network are shown in Figure 26 and listed in Table 4. In each region, we randomly apply a different interference value to the edges between the nodes. This is because in a realistic harsh environment, each device may experience various packet loss ratios during the communication with each of its neighbors, which may be caused by external interference, non-line of sight connections, multipath fading or the shadowing effect. In this experiment, we assume that the more interference applied to an edge, the higher the chance that the packets will get lost. We define two scenarios in D-MSR. In the first scenario (D-MSR s1), we gradually increase interference in the network in six steps, while the sensor data are forwarded between the sensor and \begin{table}
\begin{tabular}{c c} \hline
**Interference Steps** & **Affected Edges** \\ \hline Step-i & 19–10, 19–18, 19–20, 19–28, 19–29, 19–30, 21–12, 21–11, 21–20, 21–31, 21–32, 21–22 \\ Step-ii & 9–6, 9–8, 9–3, 9–10, 9–18, 9–17, 34–23, 34–35, 34–45, 34–44, 34–43, 34–33 \\ Step-iii & 31–30, 31–32, 31–40, 31–41, 24–14, 24–25, 24–36, 24–35, 24–23, 24–13 \\ Step-iv & 16–17, 17–27, 27–28, 28–37, 37–38, 26–25, 25–36, 36–35, 35–45, 45–44 \\ Step-v & 39–38, 39–29, 39–30, 39–40, 42–41, 42–32, 42–33, 42–43 \\ Step-vi & 22–12, 22–13, 22–23, 22–33, 22–32, 20–11, 20–10, 20–31, 20–30 \\ \hline \end{tabular}
\end{table} 
Table 4: Interference steps details. Figure 26: Applying interference incrementally in six steps. actuators pairs. Following this, we measure the packet delivery ratio of all the connections between the sensor and actuator pairs. In this scenario, in order to assess the worst-case scenario, D-MSR deliberately does not attempt to re-construct the routes and re-schedule communication. In contrast, in the second scenario (D-MSR s2), the routing layer adjusts the affected routes, the D-SAR protocol releases the previous allocated resources on the affected paths and reserves new resources along the new path. Meanwhile, the data are being forwarded through the connections and the packet delivery ratio of all the connections between the sensor and actuator pairs are being measured.