The advance of computer network technologies such as IEEE 802.11 Wireless Local Area Network enables users to connect to Internet almost anywhere. A mobile node is likely to move between different base stations while running applications. The IETF defines the Mobile IP (MIP) allowing mobile nodes to maintain their communication uninterrupted while roaming across different IP subnets. However, the mechanisms defined in MIP may cause undesired connection disruption or packet loss which will significantly degrade the quality of real-time applications. It is important yet challenging to support researches on seamless handoff management. To achieve seamless handoff, we propose a unified scheme to address application quality degradation. Our main contribution is the concept and implementation of utilizing buffering and resending method. It helps keep the end-to-end delay of real-time traffic flow in an acceptable value and eliminates the packet loss for accomplishing seamless handoff. The NS-2 simulation results also show that our proposed scheme can maintain application quality effectively for layer-2 and layer-3 handoff of a mobile node.