## 6 Discussion  
In this section, we discuss how this work accelerates the pace of research on IoUT. In Section 2, we first introduced numerous potential IoUT applications that are attractive to researchers. Then, in Section 3, we pointed out that a number of challenges exist. The challenging issues are attractive to researchers as well. Because reliability is one of the major concerns of IoUT, we investigated the UWSN channel models to calculate the reliability for IoUT in Section 4. The channel models provide a systematic way to compute the reliability between a pair of sensor nodes over IoUT. In Section 5, we conducted simulations to validate each part of the channel models, and confirmed that the models are applicable to underwater environments. We expect that the efforts would add value to the future research on IoUT.  
Following the previous sections, this section provides an extra example to demonstrate how the channel models help researchers investigate the design of the reliable IoUT communication protocols as follows. We take the IoUT routing protocol as an example. By definition, a routing protocol needs to specify how to select routes (i.e., paths) to forward data in communication networks. Accordingly, an IoUT routing protocol needs to select the appropriate paths to forward data from a source sensor node to a sink in UWSNs. A delay-sensitive routing protocol may select the shortest path for data transmission. However, for wireless communications, the shortest path is often different from the most reliable path. Figure 6 shows a typical example. In Figure 6a, the shortest path from the source sensor node (i.e., node G) to the sink (i.e., any sink on the surface of the water) is: node G, node F, node E, and then sink D. The distance of the shortest path is: 200 m + 200 m + 400 m = 800 m. However, as shown in Figure 6b, the most reliable path in the same UWSN is a different path: node G, node C, node B, and then sink A. This is because the reliability of the most reliable path is: 70% \(\times\) 70% \(\times\) 70% = 34.3%. This is one simple example to point out the importance of the reliability between a pair of sensor nodes in UWSNs. Without the information of the link reliability, it would be very difficult for a routing protocol to select the most reliable path. Using reasonable underwater channel models, researchers can calculate the reliabilities of links (as described in Section 4), and thereby design a reliable routing or communication protocol for IoUT.  
In addition, after studying many IoUT related works, we find that some of the early related works did not fully take the practical applications, challenges, and channel models into account. For instance, some of the related works evaluated the performance of the proposed IoUT communication protocols by using the traditional territorial channel models. By replacing the territorial channel models with the practical underwater channel models, the researchers may discover new issues regarding the existing IoUT protocols. From this point of view, we believe that this work would assist some existing IoUT protocols to be refined.  
Figure 6: Example of the routing paths in UWSNs with: (**a**) the information of link distance; and (**b**) the information of link reliability.