## 6 Performance Evaluation
### Reliability in the Network
#### 6.5.2 Data Delivery Ratio in Case of Lossy Network
For WirelessHART we define three scenarios. The first scenario (WH s1) operates under similar conditions as that of D-MSR s1 to also assess the worst-case scenario in WirelessHART. To this end, the WirelessHART network manager does not adjust the affected routes and each node selects its next hop randomly based on the WirelessHART protocol. In the second scenario (WH s2), we assume that the condition of the poor interfered edge will be reported to the network manager conform the WirelessHART protocol. The network manager re-establishes new graphs through the least affected edges, releases the previously reserved resources on the old path, and then reserves new resources along the new graph/route. These instructions are forwarded towards the network devices upon filling the communication tables of the devices. In this scenario, each node selects the next-hop neighbor on the given graph in a random manner, in line with the WirelessHART protocol. In the third scenario (WH s3), similarly to the second scenario, we assume that the network manager re-establishes new graphs. However, to pursue better data delivery ratios, each node chooses the best next-hop neighbor based on local information on the packet loss ratio of each neighbor. This mechanism is used in each node during data delivery, while the network manager is collecting information on the edges health status, re-establishing new routes, re-constructing new communication schedule, forwarding the new instruction to the network, and after the maintaining process is finished during normal operation of network. Those five scenarios (D-MSR s1, D-MSR s2, WH s1, WH s2, and WH s3) are shown in Figure 27 D-MSR s2, in which the routes are repaired and resources are re-allocated, performs better than WH s2, in which the network manager re-constructs the interfered graphs and nodes select the next hop in a random manner and even better than WH s3, in which the nodes select their best next-hop neighbors based on their local information (an action which is not listed in the WirelessHART protocol). For instance, after three interference steps have been applied in the network, the data delivery ratio measured is around 7.5% more for D-MSR s2 compared to WH s3 and 41% more compared to WH s2. This large difference between D-MSR s2 and WH s2 can be explained by two facts. Firstly, in WirelessHART more edges are defined in the uplink and downlink graphs to increase their reliability. If the interference in question is extensive in the network, the repaired graphs still may include some poor edges as well. Therefore, if the nodes randomly choose the next hop, these poor edges may also be selected by them. Secondly, the centralized nature of WirelessHART requires more delay and overhead to fix the problem in the network that greatly affects the data delivery ratio. However, WH s3, in which the nodes select their best next-hop neighbors based on their local information, outperforms the WH s2 regarding packet delivery ratio. Figure 27 does not consider the overhead of the repairing phase in terms of delays and the number of required communications. As is shown in Figure 27, the performance of WH s1, in which the network manager does not repair the interfered edges and in which each node selects the next hop randomly, nearly matches that of D-MSR s1, in which the interfered edges and routes are not repaired. The fact that in WirelessHART more edges are defined in the uplink and downlink graphs, does not increase the probability of success in delivering the data in the case of extensive interference and random selection of next hop. In summary, in the worst case scenario when the two protocols do not attempt to re-construct routes and re-schedule communication, D-MSR s1 performs close to the WirelessHART multipath routing mechanism (in WH s1). However, in the second scenario, the distributed approach (D-MSR s2) assures a higher data delivery ratio than WirelessHART (WH s2 and WH s3).