Investigation Of Quality Of Service Mechanisms For Multimedia Services In Wireless Networks

A mobile Ad hoc wireless network is a new kind of wireless networks which has no infrastructure. It has high reliability and flexibility. Consequently, they are widely used in some emergent application environments or when the wired network is not available, such as battlefield communications, disaster recovery, occasional conferences, etc. In recent years, multimedia applications are more and more popular, and Ad hoc networks are widely used in commercial environments. So, it is crucial for Ad hoc networks to support Quality-of-Service. However, some distinct characters of Ad hoc networks, such as the constrained bandwidth, shared channel, dynamic topology and poor link quality, make it very difficult. Then, many elements should be investigated, including QoS architectures, QoS resource reservation signaling, QoS routing and QoS medium access control. As a result, the research on this subject is very slow.This thesis researches on how to provide the QoS in Ad hoc wireless networks where the topology is dynamic and the bandwidth is constrained. Towards to providing QoS, the work investigates several mechanisms design and setting, such as media access control, transmission and congestion control. And some original schemes are propposed.First, the Differentiated Services network is introduced, and the key component in the Differentiated Services networks, RIO queue management scheme, is investigated. The impact of setting and configurations of RIO parameters on the performance of Assurance Services is analyzed through a number of network simulations. Simulations results are helpful for future research to apply RIO and the Differentiated Services mechanisms to Ad hoc networks.Second, two major classes of QoS schemes for Ad hoc networks in MAC layer and network layer are compared respectively. Based on the observations, a new hybrid scheme is proposed, which is able to support QoS of real-time applications. Third, an analytical model is developed to calculate the throughput achieved by individual Two-windows TCP flows. Extensive simulations validate the model. Since the Two-windows TCP is effective on solving the bandwidth guarantee and fairness issues, it is possible that a new protocol of transport layer in Ad hoc networks could be designed based on the idea of Two-windows TCP. Last, the performance of TFRC in Ad hoc networks is investigated. Through a number of network simulations, the problems of TFRC used in Ad hoc networks are shown. Subsequently, the reasons are analyzed. Furthermore, the revised TFRC is proposed according to the revised TCP and by use of the open circuit feedback mechanism.