Design and Implementation of Cross-layer Architecture for Seamless VoIP Handover

In the near future, wireless local area networks (WLANs) will overlap to provide continuous coverage over a wide area. In such ubiquitous WLANs, a mobile node (MN) freely moves between WLANs with different IP subnets during VoIP communication. In such situations, since an MN experiences several handovers, the communication quality is degraded. In previous studies, in order to solve this problem, we proposed a seamless handover scheme based on frame retransmissions and demonstrated its effectiveness through simulation experiments. However, no existing scheme has demonstrated the effectiveness of cross-layer architecture exploiting the number of frame retransmissions on a real system. In the present paper, therefore, we design and implement a handover scheme based on the number of frame retransmissions. In our implementation, we propose a cross-layer architecture using a shared memory to pass the information, i.e., the number of frame retransmissions, from MAC layer to Transport layer. Finally, we show preliminary results in a real wireless environment and evaluate the performance of the proposed prototype system in a simple topology.