# Designing a Vertical Handover Algorithm for Security-Constrained Applications
## 4 Performance Evaluation and Results Discussion
As we see, the MIH standard does not consider the priority of the applications and is thus affected by frequent handovers. Additionally, breaking the connection during security-constrained applications is also risky and thus MUs may not trust the future of using security-constrained applications on such networks and connections. The throughput during the VHO process is important to compute for critical applications. In the case of the MIH standard, the throughput is computed for an entire VHO process. Therefore, in the case of the proposed algorithm, we also computed the throughput to show the performance in comparison with the MIH standard. As we can see in Figure 5, the VHO throughput of the proposed algorithm is significantly high compared to the MIH standard. There are two main reasons for this significant VHO throughput, namely (1) less frequent handovers and (2) connection to a network for a longer time. We noticed, during the experiments, that the MU in the case of the proposed algorithm is connected for a longer time to a network. One of the reasons for this is that as soon as an MU opens a security-constrained application, it switches to the UMTS network, which provides a higher coverage area compared to the Wi-Fi network. However, in the case of the MIH standard, the MU switches frequently between the available networks and thus causes frequent disruption during the transfer of connection. Figure 3: VHO delay is required by an MU during various handovers. We showed the packet loss during the VHO process. The International Telecommunication Union (ITU) defines the standard of packet loss during the VHO process as less than 3%; otherwise, the connection will break between the two parties. Therefore, we computed the VHO packet loss to show the performance of the proposed system. In the case of the proposed algorithm, the VHO packet loss is always less than the defined threshold of 3%. This is shown in Figure 6. The proposed system is connected for a longer time to a network; therefore, the VHO packet loss is significantly less compared to the MIH standard. The disconnection of the network due to the frequent network always selects an inappropriate network for VHO. This rises the number of frequent handovers as the MU is  
Figure 4: Total VHO time required by an MU during various handovers. Figure 5: Analysis of throughput during VHOs. always searching for the best network. However, RSS-based VHO triggering will always select inappropriate networks due to the many reasons discussed in [52]. Frequent handovers always affect the VHO process. For instance, if an MU using a security-constrained applications experiences a sudden disruption to connection, this may cause delay and even reinitiate the entire process. Therefore, we tested both the MIH standard and our proposed algorithm for frequent handovers. As we can see in Figure 7, the number of frequent handovers is significantly less compared to the MIH standard. One of the main reasons for this significantly a smaller number of frequent handovers is that the proposed algorithm always provides a stable enough connection time for a security-constrained application to finish. In general, security-constrained applications always require less time to complete compared to other applications, such as video streaming, etc. Additionally, in the case of frequent handovers, the MU always tries to establish connection to a new AP or BS, which is one of the main causes of high VHO delay in the MIH standard. Our proposed algorithm mainly considers user centricity during the VHO process. However, in the case of the MIH standard, the stability of the connection mainly relies on the RSS strength from the source AP or BS. Therefore, closed contact of the MU with the surrounding environment will always lead to frequent handovers if the VHO is based on the RSS value. Similarly, the number of failed VHOs will also increase if the RSS values from the target AP or BS change frequently.