Chapter 1
INTRODUCTION
Wireless Mesh Networks (WMNs) [1, 2] is a new generation of networks that has appeared recently. The elements of a WMN are wireless mesh hosts, wireless mesh routers and access points (or gateways) that act both as wireless mesh routers and Internet routers, as shown in Figure 1. The mesh routers in a WMN are stationary; they set up the wireless mesh backbone, which provides multi-hop connectivity from mesh hosts to either other mesh hosts or the Internet via access points. While that mesh hosts can be mobile or stationary; they can form a mobile ad-hoc network (MANET) or a wireless local area network (WLAN), The mesh routers allow mesh hosts to communicate with the outside world. What distinguishes WMN that it is self-configured and self-organized with nodes in the network, and therefore these features brings many avails to WMNs such as self-management, low installation cost, large-scale deployment and reliability. We illustrate in Figure 2 a typical application of WMNs deployed in a new town. The wireless mesh routers are installed anywhere on the streets and buildings to cover the town. However a WMN incurs a much lower installation cost. Also a WMN deployed in a rural area, as shown in Figure 3 where it is very hard to build a wired network due to the mountains and the rugged nature. Furthermore, WMN is deployed easily.
Figure 1.1: Architecture of a WMN
Figure 2: WMN in a city
Figure 3: WMN in a rural area [2]
Multicasting is a technology that reduces the traffic in wireless network by delivering a stream of packets to a group of receivers simultaneously. Lots of multicast applications such video conferencing, shared workspaces, distributed interactive simulation (DIS), software upgrading, session schedules, stock prices, interactive distance learning, multi-layer gaming, chat groups, shared editing, collaboration and multimedia conferencing. Creating a method of multicasting in WMN is difficult because multicast protocol must consider some critical factors such as scalability and reliability, load balancing among channels and nodes, cross layer optimization, guarantee Quality of Services (QoS), availability of multi-channels & availability of static mesh routers infrastructure backbone.
1.1 MOTIVATIONS
In wireless mesh network, a multicast routing protocol is an important problem and facing many challenges, traditional protocols are not capable of addressing some of the new challenges posed by the necessity of multicast applications. Many problems have to be addressed while applying multicasting protocol in WMN, such as load balancing among channels and nodes, scalability, reliability, cross layer heuristic, guaranteed QoS (Quality of Services. One important problem also is no traditional protocols are capable of addressing the optimality of the problems which mentioned before. In addition to that, no technique or framework acts the connectivity between WMN backbone and Internet, finally the previous studies in multicast protocol consider only one or some factors which are necessary to build a multicast protocol rather than optimal multicast protocol, whereas, we need to apply all factors mentioned above while creating a multicast routing protocol.
1.2 RESEARCH OBJECTIVE
The overall objective of this thesis is to provide optimization of multicast routing protocols in WMNs. In this thesis, we define five main problems of multicast optimization in WMNs. Therefore, the research objective presented in this thesis is to make the multicast routing protocols optimized.
• To design and Implement a sufficient and scalable multicast routing protocol named MESHSPT (shortest path tree algorithm for wireless mesh network). The MESHSPT protocol builds source-based trees based on the network topology. It prevents flooding and the implosion and exposure problems while constructed of the tree and while joining, leaving the nodes.
• To design and Implement a reliable multicast protocol named MRMP (Mesh Reliable Multicast protocol). This protocol proves the effectiveness of cross layer optimization in Wireless Mesh Network through two important layers network layer and transport layer.
• To design and Implement a new Multi-objective model for optimization multicast load balancing in Wireless Mesh Network named called Path-Mesh Router-Gateway load balancing (PMRGLB), which aims to achieve four objectives, i.e. minimizing path length, minimizing path interference, minimizing the total cost of the network, , and minimizing gateway load balancing.
• To design and Implement a QoS multicast routing protocol using multiple trees (M-trees) called MTQOSM (Multiple trees Quality of Services multicasting) which maintains the maximum node-disjoint by using a distributed online heuristic. This protocol guarantees the QoS in a multicast routing.
• To design a framework allows for linking networks in efficient way. Design a Framework to support multicasting routing between wired Internet and wireless mesh networks .The proposed structure work in an appropriate way between the two networks.
1.3 CONTRIBUTIONS
To fulfil the research objectives stated earlier, the key contributions of this dissertation are stated as follows:
• A protocol named Mesh Shortest Path Tree algorithm for Wireless Mesh networks (MESHSPT) for efficient and scalable multicast routing inside the mesh backbone of a WMN. This protocol avoids the most problems in multicast technique: flooding and the problems of implosion and exposure during a tree constructed and during the joining, leaving nodes
• A cross layer reliable & multicast protocol named Mesh Reliable Multicast Protocol (MRMP). A recovery tree built dynamically which is joining with the multicast routing tree. The packet losses are repaired locally by using tree recovery.
• A new Multi-Objective model for optimization multicast load balancing in wireless mesh network named Path-Mesh-Router-Gateway load balancing (PMRGLB), which aims to achieve four objectives, i.e. minimizing gateway load balancing, minimizing path length, minimizing the total cost of the network and minimizing path interference. A meta-heuristic method used simultaneously with this optimization problem.
• A new protocol to optimize the QoS based on Multiple Trees (M-Trees) called (MTQoSM) Multiple Trees Quality of services Multicast which maintains the maximum node-disjoint by using a distributed online heuristic.
• A Framework supports the connectivity between Mesh backbone and Internet and allows for linking networks in efficient way
1.4 THESIS OUTLINE
The remainder of the thesis is organized as follows. Chapter 2 provides a literature survey of the existing multicast routing protocols. Chapter 3 illustrates technical background. Chapter 4 presents the MESHSPT protocol for multicast routing in a mesh backbone. Chapter 5 explains the cross layer protocol. Chapter 6 explains multicast load balancing optimization. Chapter 7 explains QoS multicast optimization. Chapter 8 explains interactive Framework between mesh backbone and Internet. Chapter 9 concludes the thesis and outlines some directions for future work.