# Vortex: Network-Driven Opportunistic Routing for Ad Hoc Networks
## 4 Performance Evaluation
### Simulation Results
Therefore, we conclude that VORTEX has met the research objectives stated in Section 1 from the following perspectives. * As for route discovery/route maintenance, VORTEX omits any of them for packet forwarding by using the network itself as a guide for packet forwarding. * As for information gathering for the routing procedure, VORTEX only uses topological information that can be gathered from neighboring terminals for packet forwarding. * As with the handling terminal participation and leave, VORTEX handles terminal participation and leaves so as not to impact the existing hierarchy for the first time and a periodical hierarchy update procedure re-arranges the hierarchy according to the topological characteristics of the participated/leave terminals. We also conclude that VORTEX has acceptable reliability and efficiency in various environments. In other words, VORTEX has a flexible adaptation ability to various environments maintaining its routing performance, especially reliability and efficiency. However, VORTEX still has a limitation in adapting to topology changes especially when the terminal moving speed becomes higher same as the conventional routing protocols. Therefore, every performance metric degrades as the moving speed increases. Although more stable guide selection in such environments is required to overcome the issue as described in [29], it is beyond the scope of this paper and remains a future study. For the future development of these research achievements, we are now researching ORs in heterogeneous environments of IoT (Internet of Things) [30]. This is because that heterogeneous environments generally consist of various kinds of communication media, and it requires a rendezvous point for mutual communication between the media. However, the communication environments change from time to time, and difficult to specify the optimal end-to-end route with conventional routing protocols. In addition to that, the heterogeneity also affects the symmetry of the communication range of terminals and the link bandwidth, namely, an increase in unidirectional communication is inevitable, which greatly affects the routing performance. Therefore, handling the asymmetry is an important issue in OR for heterogeneous networks and we have proposed a flag-based symmetry confirmation-based OR [31]. Another use-case for ORs can be found in the field of WMNs (wireless mesh networks), and some studies introduce network coding to WMNs using ORs [32]. This is a similar application of ORs in underwater wireless sensor networks [33; 34], and both applications are designed to collect packets in a single location. Thus, an important issue for ORs in the fields is path diversity and it is not required to address some issues that VORTEX has done in this paper. However, network-driven forwarding in VORTEX can also be applied to the fields and may have sufficient performance if the strategy of VORTEX is modified to be able to handle their communication characteristics. Moreover, we are now researching an OR that can handle link bandwidth asymmetry to maximize available network traffic. By combining the achievements of the research, we believe that communication in the IoT can become more flexible and efficient. Furthermore, routing protocols are not only used to establish end-to-end routes but can also be applied to other research areas. For example, our research team is applying routing protocols for ad hoc networks to route construction for UAVs [35; 36; 37; 38] and ORs may also be applicable for such environments when flexible route construction is required. Thus, the concept of ORs can be applied to any kind of graph to design routes, especially when dynamic topology and communication environment changes occur.