# Evaluation of VoIP QoS Performance in Wireless Mesh Networks
## 3 Experimental Setup  
There are several methods to evaluate and measure the performance of services offered over various types of computer networks. These methods and approaches are mainly analytical,  
Figure 4: WMN small-scale military operations scenarios: (**a**) Squad line formation, in which a small number of nodes could be used to support a military operation; (**b**) infantry platoon formation, where three squads’ communication could be facilitated by WMNs to support a military operation. Figure 3: Examples of urban and rural mesh network deployments: (**a**) urban mesh network where homes, public buildings, and private offices could be serviced by WMNs and the network can adapt based on nodes addition and removal; (**b**) a rural area where homes, police, hospitals, and schools could be connected with WMNs. real implementation, and network simulation [55]. Among these methods, the use of network simulators for conducting experiments which involve multiple parameters is a workable and preferred method. This method allows us to investigate the configuration of various parameters over different types of network deployments, various communication standards and protocols. In our experiments, we use the QualNet simulation software to simulate VoIP application in various scenarios and to evaluate how a set of standards and protocols integration can affect the VoIP quality in WMNs. One of the main challenges in VoIP applications in WMNs is the call quality as perceived by the VoIP call initiator (caller) and receiver (listener), which is usually measured with MOS based on the ITU-T standard and E-model [25; 39]. The model defines subjective and objective MOS measurement; subjective MOS measurement involves humans, while the objective MOS measurement could be automated using simulation software. Hence, in our research we consider objective MOS values, which are further supported by the analysis of delay, jitter, and packet loss factors. While ITU-T defines the MOS values as integers, measuring with points between the ranges with decimal values is also allowed, as shown in Table 2, and mostly used in simulation tools, as described in [17; 56]. The MOS values of the initiating node and receiving node can vary depending on the traffic condition in the network. There are several factors that can affect the MOS factor, but delay, jitter, and packet loss are considered the main factors affecting the MOS values [25]. As discussed in Section 1, the loss incurred by all these factors is called the \"VoIP total loss probability\" in QualNet simulation software; this indicates the percentage probability of a VoIP application packet being lost during transmission as the result of obstacles and other factors in the real environment and the configuration of this parameter affects the MOS values. In real scenarios, there is always a percentage of such loss that affects the VoIP quality. The VoIP total loss probability range could be any value from 1 (a few minor obstacles) to 100 (many large obstacles). The default value in QualNet simulation software is 5% and the same is used in our simulation scenarios, which is the maximum loss a VoIP application can tolerate [57]. The purpose of considering a 5% total loss probability in our scenarios is to simulate total loss due to various factors including loss incurred by terrain profiles in real scenarios. As a consequence, setting this parameter to 5% yields MOS rating values that are always below the value of 4. In order to investigate VoIP performance in various WMN scenarios, we have chosen five scenarios from those that were introduced in the previous section. The list of the scenarios selected for our experiments is in Table 3. There are five main scenarios; each of them is investigated under six different sub-scenarios with variations in the physical layer, data link layer, and presentation layer. The main scenarios are different in terms of area size, nodes mobility model, and distance between the nodes.