A handover mechanism defines the steps involved in the transfer of all the information and resource allocation enabling a mobile terminal to remain connected to the wireless network infrastructure. A large number of handover mechanisms have been reported in the literature. We carry out a comprehensive QoS performance study of the handover mechanisms as proposed in the literature and a performance evaluation of various buffer management schemes used to compensate for service disruption caused during the handover phase. A detailed simulation model has been developed allowing us to set up parameters such as the speed and motion path of the mobile terminal. The performance metrics of interest are: the overall response time of the handover mechanism, the length of the disruption time caused by the handover mechanism and the number of lost packets caused by the handover mechanism. In our simulation study, we have made use of MPEG-4 video sources to evaluate the various buffer management mechanisms. The video is encoded using a layered coding scheme. Under the scenario under consideration, the handover using multicasting mechanism and the push-out buffer management mechanism exhibit the best results.