Pursuing Credibility in Performance Evaluation of VoIP over Wireless Mesh Networks
Edjair Mota, Edjard Souza Mota, Leandro Silva Galvão de Carvalho, Andréa Nascimento, Christian Hoene · InTech eBooks · 2011
There has been an increasingly interest in real-time multimedia services over wireless networks in the last few years, for the most part due to the proliferation of powerful mobile devices, and the potential ubiquity of wireless networks. Nevertheless, there are some constraints that make their deployment over Wireless Mesh Networks (WMNs) somewhat difficult. Due to the dynamics of WMNs, there are significant challenges in the design and optimization of such services. Impairments like packet loss, delay and jitter affects the end-to-end speech quality (Carvalho, 2004). Experimenters have been proposing solutions to the challenges found so far, and comparing them before implementation is a mandatory task. There exists a necessity of designing efficient tools for enhancing the computational effort of the performance modeling and analysis of VoIP over WMNs. Structural complexity of such highly dynamic systems causes that in many situations computer simulation is the only way of investigating their behavior in a controllable manner, allowing the experimenter to conduct independent and repeatable experiments, in addition to the comparison of a large number of system alternatives. Stochastic simulation is a flexible, yet powerful tool for scientifically getting insight into the characteristics of a system being investigated. However, to ensure reproducible results, stochastic simulation imposes its own set of rules. The credibility of a performance evaluation study is greatly affected by the problem formulation, model validation, experimental design, and proper analysis of simulation outcomes. Therefore, a fine-tuning of the parameters within a simulator is indispensable, so that it closely tracks the behavior of a real network. However, the lack of rigor in following the simulation methodology threatens the credibility of the published research (Pawlikowski et al., 2002; Andel & Yasinac, 2006; Kurkowski et al., 2005). The aim of this chapter is to provide a detailed discussion of these aspects. To do so, we used as a starting point the observation that the optimized use of the bandwidth of wireless networks definitely affects the quality of VoIP calls over WMN. Since the payload size of VoIP packets is usually smaller than the header size, much network resource is spent for conveying control information instead of data information. Hence, VoIP header compression is an alternative to reduce the use of the bandwidth needed to transmit control information, thereby increasing the percentage of bandwidth used to carry payload information. 9