In the mobile IP-enabled wireless LAN (WLAN), packet flows are corrupted due to the handoff of a mobile node at the link and network layers, which results in burst packet losses. This transient behavior hurts time-critical streaming media applications so much. Many solutions have been suggested to address this handoff-related problem. However, even with recent low-latency and smooth handoff options, seamless streaming (i.e., without any playback disruption due to the handoff) is not easy to achieve in the practical situation. Since no packet will be delivered to the mobile node during the handoff process, this can cause temporary packet underflows at the streaming client. Thus, to avoid packet underflows, one has to pre-buffer the streaming client sufficiently before the handoff. Note that the required level of pre-buffering depends on the efficiency of adopted link-/IP-layer handoff options. In this paper, we are targeting seamless MPEG-4 streaming over the mobile IP-enabled WLAN. For this, we are introducing a seamless media streaming framework by estimating the accurate pre-buffering level to compensate the handoff latency and proposing a combination of schemes as a preliminary version of the proposed framework. We utilize a Layer 2 (L2) trigger (event) about a change of an associated access point (AP) with a wireless network interface to reduce the agent discovery time in total handoff latency. A packet forwarding with buffering mechanism is also realized at the foreign agent (FA). With these two options, we can nearly eliminate packet losses during the handoff period. Then, we perform pre-buffering adjustment based on handoff latency experimentally measured and analytically obtained by the handoff transient time analysis (9). The experimental results show that the proposed approach can eliminate packet losses during the handoff period and provide the feasibility of seamless MPEG-4 video streaming over the mobile IP-enabled WLAN.
