1.1. Wireless Mesh Network (WMN)
Wireless Mesh Networks (WMNs) is one among the novel networking standard. In WMN, every interacting node creates and retains interconnection between itself and surrounding nodes, and hence considered as self-systematizing and self-configuring network. WMN is a dynamic network and has lower cost of maintenance. WMN needs to sustain every new generation media application like Voice over IP (VoIP) and Video On-Demand (VOD) by adjusting to the new requirements. The media applications necessitate Quality of Service (QoS) in terms of reduced bandwidth and higher end to end delay (Kone et al., 2007). A WMN consists of internet gateways, mesh routers and mesh clients. In WMN, each node has to route data packets to the surrounding nodes. When a node does not have access to the backbone network, it can still transfer packet to the destination by transferring data to the neighbor node, which has connection with the backbone (Zhao et al., 2010).
WMN problems give rise to issues related to security, breakage in the paths causing packet loss and unfulfilled QoS metrics (Zhao et al., 2010). Figure 1 depicts a wireless mesh network with internet, gateway, mesh router and mesh clients.
1.2. Multicasting in Wireless Mesh Networks
Multicasting is a process of packet transfer to a set of host nodes recognized by the same destination address. Multicasting is suitable for dynamic network, where the node can enter or exit the group as per its requirement and the computation is group based (Junhai et al., 2008).
During multicasting of data, the link bandwidth consumed is less and delay in data delivery is also low, resulting in minimized communication expenditure. Multicasting also lowers the transmission overhead at the source side and also at the intermediate node side and it also increases the rate of data delivery at the destination node (Chi et al., 2010).
The Multicast routing protocols are classified into two groups: tree based and mesh based. In case of tree based multicast routing protocol, there exists only a single route from the source to the destination. This topology provides good efficiency. In case of mesh based multicast routing protocol, there exists multiple routes from the source to the destination. This topology is more reliable as well as robust (Sihai et al., 2012).
Network multicast schemes are classified into two categories. They are shortest path multicast tree and core-base tree. In case of shortest path multicast tree method, path that is shortest from the source to the destination is chosen and an individual tree has to be built by every source. Hence, the network consists of several trees. In the core-based tree method, the shortest route between the source and destination need not be chosen and a single tree needs to be built for every group. Hence, this network consists of very few trees (Junhai et al., 2008). MAODV, ODMRP and CAMP are the protocols built to sustain ad hoc multicast routing (Saghir et al., 2006).
But, the QoS feature of adhoc communication is not considered by these protocols. In WMN, the difficulty in consistent multicasting is handled by managing the node movement even at times of data packet forwarding. Few nodes may get disconnected from the neighboring nodes and hence may lose the multicasted packets, due to this movement (Saghir et al., 2006).