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CHAPTER ONE

INTRODUCTION

1.1     BACKGROUND OF THE STUDY

Multicast sessions are expected to be a common form of traffic in emerging mobile ad hoc networks. However, the recently developed theory for fair resource allocation in Mobile Ad Hoc Networks (MANETs) (Lin & Shroff 2004; Eryilmaz & Srikant 2005, 2006; Stolyar 2005, 2006; Neely et al. 2005) only addresses the case of unicast flows. Other than developing appropriate notation, it is somewhat straightforward to extend the theory to multicast sessions if one assumes that data is delivered to all the receivers in a multicast group at the same rate. Such a form of multicast is called single-rate multicast. On the other hand, there are many video applications which allow layered-transmission so that different receivers can subscribe to different numbers of layers and receive different qualities of the same video, depending upon the congestion level in their respective neighborhoods. Moreover, in wireless networks, due to varying signal strengths at different receivers, it may not be desirable or feasible to deliver data at the same rate to all the receivers in a multicast group. Thus, it is important to extend the optimization-based theory to handle multi-rate multicast sessions, i.e., multicast sessions where different receivers are allowed to receive at different rates. Such an extension is not immediate as in the case of single-rate multicast. In the last few years there has been significant growth in the area of wireless communication. Institute of Electrical and Electronics Engineering (IEEE) 802.16 (WiMAX) is the network which is designed for providing high speed wide area broadband wireless access. It consists of a base station (BS) and multiple subscriber station (SSs). BS transmits data to the SSs through broadcast channel. The SSs are linked to BS through multiple access channels. IEEE 802.16 standard utilize new nodes called relay stations (RSs). The RSs relay data between the BS and the SSs in upward and downward direction. WiMAX is an emerging wireless technology for creating multi-hop Mesh network.

Future generation networks will be characterized by variable and high data rates, Quality of Services (QoS), seamless mobility both within a network and between networks of different technologies and service providers. A technology is developed to accomplish these necessities is regular by IEEE, is 802.16, also called as WiMAX (Worldwide Interoperability for Microwave Access). WiMAX supports Long range connectivity, High data rates, High security, Low power utilization and Excellent Quality of Services and squat deployment costs to a wireless access technology on a metropolitan level. Due to broadcast nature of the wireless medium, multicasting do not need more resources compared to unicasting. Multicast is used to transmit the data from the source to multiple receivers. It is useful because it allows the construction of truly distributed application, and provides important performance optimizations over unicast transmission.

There are a number of existing applications for real-time audio and video conferencing which can make good use of a multicast service when it is available. Due to heterogeneous channel conditions, each recipient may experience different bit error rates and the amount of resources required may vary for each recipient. Most modern technologies utilize adaptive modulation and coding scheme to suit the channel conditions. When there are more recipients to serve, the sender tends to consume more resources. Since the wireless medium has limited resource, it is not always possible to provide multicast services for all the subscriber stations. Within the resource budget of a multicast service, resource utilization should be done to serve as many recipients (i.e., SSs) as possible. WiMAX provides better platform for Multicast. When a network only consists of a BS and SSs, this maximization can be done by allocating the entire resource budget to the BS. However, if RSs are considered, this problem becomes much difficult because resource should be allocated among the BS and RSs.  
1.2   PROBLEM STATEMENT OF THE STUDY
However, the time-varying nature of the wireless environment, coupled with different channel conditions for different users, poses significant challenges to allocate shared resource in a fair manner among users. Moreover, the lack of availability of channel and arrival statistics further complicates the solution.  
1.     Unlike Ethernet, most traffic in 802.11 is sent reliably using ACKs and NACKs so that radio interference doesn't cause unbearably high packet loss. However, multicast packets are sent once and are not acknowledged, so they are subject to much higher loss rates.  
2.     Another issue with multicasting is that multicast frames experience lower quality of service. With 802.11 networks, lower throughput will definitely be the case when one or more of the wireless clients are using the 802.11.  
1.3   AIM OF THE STUDY
The aim of this study is to develop a system that would allocate resources evenly over a wireless network during multicast sessions.  
1.4   OBJECTIVES OF THE STUDY  
·           To solve routing issues that arises during the sending of multicast packets over a wireless network.
·           To develop a wireless network that reduces congestions during multicast sessions.
·           To reduce minimum power multicasting problems.
·           To allocate resources fairly using a resource algorithm during multicast sessions.
·           To improve the quality of service during multicast sessions.  
1.5   SIGNIFICANCE OF THE STUDY
This study aims to use multicasting, meaning delivery of information using multicast packets, to conserve the bandwidth of a network because only the transmission of a single packet is necessary rather than sending packets individually addressed to each node. This is especially important with wireless networks having limited throughput available.  
1.6   SCOPE OF THE STUDY
This study covers the allocation of resources over a wireless network, during multicast sessions; it does not include wired networks and other routing sessions.

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