# Evaluation of VoIP QoS Performance in Wireless Mesh Networks
## 1 Introduction
The third type of WMN is a mixture of the first and second types, which comprises a mesh of wireless routers that form the backbone and a mesh of clients that form the access layer of a hierarchical network, as shown in Figure 1c. In this type of network, the nodes can form a mesh network among themselves and the mesh router could be a supportive component of the mesh network to connect mesh nodes to external networks. This type of network is called heterogeneous mesh (HetMesh) [7] and requires the mesh routers to be equipped with dual radio links in order to establish and maintain redundant links with the mesh routers and to service the mesh clients as their gateways to other mesh segments or external networks, e.g., the Internet. Since ad hoc networks increase delay, jitter, and packet loss, VoIP services offerings in such networks are challenging [12; 13]. There are several methods to investigate and measure the performance of VoIP and its service quality. In [14] methods such as mathematical proofs, real implementation and simulation are discussed to evaluate the performance of scenarios that involves multiple variables. The author uses OMNet++ simulation software to measure multiple variables which involves a wide range of parameters across multiple OSI model layers. There exist several network simulators such as OMNet++, NS-2, NS-3, EstiNet, QualNet, OPNET modeler, and JSim [15], in this research we use the QualNet simulation software in order to evaluate the performance of VoIP in various scenarios using multiple types of parameters for the reasons given below. The QualNet simulation software enables us to conduct experiments that are almost identical to real-life scenarios [16]. It also saves time in configuring, experimenting, collecting data and analyzing multiple scenarios using various parameters. Among several features for configuring VoIP profiles, generating VoIP traffic and evaluating the service performance, the configuration of the \"Total VoIP loss probability\" percentage parameters enables us to set the estimated VoIP loss probability percentage to mimic a real network scenario. This parameter's setting directly affects the mean opinion score (MOS) rating scale values obtained in simulation results. The MOS rating scale is defined by ITU-T as a 5-point rating scale where 5 is rated as \"Excellent\", 4 as \"Good\", 3 as \"Fair\", 2 as \"Poor\" and 1 as \"Bad\" [17]. The motivation behind this research is to provide an insight into VoIP application with recommendations on the best ways to combine standards, protocols and codecs to improve VoIP quality in various scenarios considering ad hoc mesh network implementations using selected IEEE 802.11 standards. Since ad hoc networks are self-formed and do not require any prior setup nor existing infrastructure, this makes it an interesting type of network compared to the first and third types explained above. On the other hand, one of the challenges in this research domain is the applicability of VoIP on wireless mesh networks and how it could be offered with improved service quality. Below we highlight our contributions towards this challenge:  
* We integrate and experiment 802.11g/n with 802.11s/e IEEE standards together with G.711 and G.729 voice codecs using AODV and HWMP routing protocols in order to extensively evaluate how VoIP service performs, which can help us to make informed choices about standards, codecs and protocols in WMN implementations. To the best of our knowledge, research dealing with the combination of these standards, codecs, and protocols in the specific type of scenarios considered in this work has not been reported before. * We investigate the performance of VoIP deployment in five main scenarios (three scenarios with mobility and two scenarios with no mobility). We evaluate how the mobility models(e.g., waypoint mobility and random waypoint mobility) and different area sizes can affect the VoIP performance.