# Evaluation of VoIP QoS Performance in Wireless Mesh Networks
## 1 Introduction  
Wireless mesh networks (WMNs), which are defined in standards such as IEEE 802.11s for Wi-Fi [1], IEEE 802.15.4 for Bluetooth [2] and IEEE 802.16j for WiMAX [3], are suitable platforms for many critical and non-critical services. Such types of networks own high availability features, self-formation and self-organization capabilities [4]. They are also considered self-healing and dynamic types of networks. WMNs can provide solutions for various applications including emergency relief efforts, urban, rural, military fields [5], mines and temporary setups [6], etc. In most of such applications, implementing a wired infrastructure or traditional wireless solution is either too expensive or is challenging due to environmental issues and/or the scenarios' specific requirements. There might even be cases for which other traditional solutions would be infeasible (in terms of e.g., air-to-air communication, mobility, right of way, immediate deployments, high availability, etc.). There are various standards and technologies available that can be used to form WMNs, in particular, WLAN and WPAN are mostly used to form client mesh networks and WiMAX mesh is used to establish infrastructure mesh network using wireless routers. The focus of this research paper is on the IEEE 802.11 standard (i.e., the Wi-Fi technology) using client nodes to form a mesh networks called client or ad hoc mesh network. WMNs could be one of three types, namely, backbone mesh, clients mesh, or a mix thereof [7,8]. The first type, backbone mesh [9], is formed by connecting at least three routers with each other in such a way that each mesh router has a direct path to the other two routers, as shown in Figure 1a. If a path through one router fails, each router has the possibility to send traffic through the other available routers in the network topology. A backbone mesh is usually formed by WiMAX technology, which uses the IEEE 802.16 standard, especially in large installations mainly due to interference, long range features and frequency allocation issues. A Wi-Fi backbone mesh of routers, which uses the IEEE 802.11 family of standards, could also be used in small/medium scale installations where interference is not a major concern, e.g., in remote areas where these bands are not crowded. In this type of mesh topology, the backbone mesh routers are responsible for providing redundant backbone paths to their clients. Usually, backbone mesh routers are considered as fixed network components. In this case, the wireless clients are not forming a mesh topology; instead, they are only serviced by mesh routers in an infrastructure-based wireless network using dual radio links. Figure 1: Three types of wireless mesh networks: (**a**) Backbone mesh with each router supporting a separate service set and clients connected in infrastructure mode with the routers; (**b**) ad hoc or clients mesh (MANETs), where the network is formed without dependency to any wireless router or access point; (**c**) backbone and clients mesh in which nodes can roam and connect to any available mesh node or router in any cell. The second type of WMN is the clients mesh. In this type of topology, all the clients form the mesh network; they all participate in the formation of the mesh network backbone and are usually referred to as mesh nodes/points; the type of topology is then called ad hoc, as shown in Figure 1b where the nodes a, b, c,..., i form a mesh network without any wireless router or access point's help. This type of network can use the IEEE 802.11 and 802.15 standards. In such types of mesh networks, each mesh node can act as a client, server and router. Each node's role can change based on the type of service offered over the WMN, but the nodes will always have to play either a client or a router role, while the server's role depends on the type of application offered using such network platforms. Ad hoc network with mobile nodes are usually referred to as mobile ad hoc networks (MANETs) [10; 11].