Voice over IP is considered as the application as it is expected to be a low cost and thereby, a popular communication system in the next generation communication networks. Also with 4G mobile networks coming up, the performance of the integrated WLAN-WiMAX network is also evaluated and compared with the existing WLAN and WiMAX technologies. Hence, a study of the performance of the widely researched WiMAX network is performed under varying terrain and environmental conditions for various propagation models in this thesis. The path of propagation being wireless, the performance of the network is affected consequently by the topology and the environmental conditions of the area where the network is deployed. With wireless communication becoming an integral part of human life, the improvement of the performance of any wireless network has become a topic of keen interest of the researchers. Exhaustive simulation results have been provided. Finally, it is observed and concluded that the WiMAX-WLAN integrated network provides improved and optimal performance over WLAN and WiMAX network with respect to network capacity and quality of service. Quality of the service is critically analysed with parameters like jitter, MOS and delay for various voice codecs in the aforesaid networks for both fixed and mobile scenario. As OPNET 14.5.A provides a real life simulation environment, we have opted OPNET as the simulation platform for all performance studies in this work. Hence, an integrated network using WiMAX backbone and WLAN hotspots has been developed and VoIP application has been setup. WiMAX having higher bandwidth provides higher capacity but with degraded quality of service while WLAN provides low capacity and coverage. The objective of this paper is to analyse the VoIP performance among the most competing next generation wireless networks like WiMAX, WLAN and its integrated frameworks etc. Voice over IP is expected to be very promising application in the next generation communication networks.

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