# Designing a Vertical Handover Algorithm for Security-Constrained Applications
## 2 Related Works
In [48], a secure procedure to enhance VHO security during the execution phase was presented, taking into account the following parameters: security and signaling cost. The numerical analyses results show that security is successfully improved by 20%, whereas signaling cost is maintained as in the non-proposed procedure. The MIH and the IP multimedia subsystem (IMS) standards were established by the IEEE group and 3 GPP, respectively, to facilitate the seamless transfer of connection among heterogeneous networks, such as Wi-Fi, GSM, and UMTS, by leveraging these interconnected standards to aid and supplement their work [34]. In [25], the VHO approaches proposed in the literature were classified into four categories based on MIH and IMS standards: the MIH-based VHO category; the IMS-based VHO category; the MIP under the IMS-based VHO category; and the MIH and IMS combination-based VHO category, to show their objectives are performing seamless VHO. According to [25], the MIH standard is more flexible and has a higher performance when providing seamless VHO than the IMS standard; thus, the majority of techniques in the literature were based on the MIH standard. The MIH standard distinguishes two types of entities [34], namely point of service (PoS) and point of attachment (PoA). Using the MIH standard, the PoS is in charge of establishing communication between the network and the MU. The PoA is the RAT access point. Additionally, the MIH standard has three main services [34]: media independent event service (MIES); media independent command service (MICS); and media independent information service (MIIS). The MIES is responsible for reporting the events after detection, such as link up on the connection (established), link down (broken), and link going down (breakdown imminent) [34]. The MIIS is in charge of gathering the necessary information to determine the requirements for VHO and distributing it to the MUs, such as available networks, locations, capabilities, and cost [34]. The MICS is in charge of issuing orders based on the information gathered by the MIIS and MIES, such as MIH handover initiate, MIH handover prepare, MIH handover commit, and MIH handover complete [34]. The MIH standard is tested in NS2.29 v3. Initially, the MIH standard had many problems; however, with the passage of time, many of them were resolved and incorporated into the final version. A VHO process is always affected by using inappropriate parameters for triggering and network selection phase. For instance, using the RSS value to trigger a handover process may lead to the wrong selection of the target network. For instance, in [49], the authors showed how a VHO process may be affected by using the RSS value to trigger a handover process. The authors suggested the use of data rate to trigger a handover process. For instance, if the author is moving on a high-speed train and not using mobile equipment, then there is no need for a handover. However, if the MU is using an application with high priority, then it is necessary to switch to a target network that provides a high data rate. Similarly, in [50], the authors use a neural network model incorporating a number of parameters, such as maximum transmission rate, minimum delay, signal to interference and noise ratio (SINR), bit error rate, user moving speed, and packet loss rate, to select the trigger and the target network. However, using a neural network may lead to exhaustive processing during the VHO process; therefore, it might increase the VHO delay. In [51], the authors suggest triggering the handover process based on the data rate of the current application running on the MU equipment. If the data rate for all the applications on the MU equipment drops below a particular threshold, the MU triggers a handover. Similarly, the selection of the target network is performed based on the end-to-end delay, jitter, bit error rate, and packet loss of the available networks.