適用於無線網路快速交遞協定中的改良式暫存區管理

Abstract

近年來隨著無線網路技術的發達，人們對於通訊品質的要求也日益提升。在目前的網際網路中，結合IEEE 802.11無線區域網路和Mobile IP的技術，可以提供使用者在網域間漫遊的服務。藉由快速交遞協定(Fast handover)與階層式Mobile IP(Hierarchical Mobile IP)的幫助，大幅縮短了Mobile IP在交遞基地台的過程。由於在交遞的過程中，使用者會有短暫的時間無法接收資料，Fast handover協定中採用了暫存區來保存這部分的封包。不過在Fast handover協定中，卻缺少了一個有效的暫存區管理機制。當使用者數目增加的時候，通訊品質會無法保障。 在本篇論文中，我們提出了一個適用於Fast handover協定的暫存區管理機制。藉由同時使用交遞過程中的兩個路由器，我們可以提高網路中路由器內的暫存器的使用量。而針對不同資料流採取相對應的暫存機制，則提供了在交遞過程中保護重要資料的能力。另外，此方法也提供使用者在任意交遞過程中，要求路由器暫存資料的機制。同時由於大部分的控制訊息都是附加於原本Fast handover 協定上，因此並沒有增加過多的訊息負擔。透過ns-2程式的模擬，我們驗證了此機制的效能，證明其確實可提升交遞時的速度與品質。

With the quickly development of wireless technology, the requirement on communication quality also arises. Today, users have the ability to roaming between subnets with the cooperation of IEEE 802.11 wireless LAN and Mobile IP technologies. The combination of Hierarchical Mobile IP and Fast handover protocol greatly reduces the handoff delay in Mobile IP. Since a mobile host suffers a temporary disconnection from network during the handoff process, a buffer is used in the Fast handover protocol. However, there is no efficient buffer management mechanism in the protocol, thus service quality cannot be guaranteed when there are too many users. We propose an enhanced buffer management mechanism for Fast handover protocol in the thesis. With the cooperation of both access routers during the handoff process, the buffer utilization in the network can be improved. The proposed method also supports QoS service. High priority packets are protected from dropping and the real-time packets are protected by minimizing the delay time during a handoff process. Moreover, buffering operations during a link layer handoff is supported. Since most of the control messages are piggybacked on the original fast handover protocol, the proposed method does not involve additional signaling overhead. We evaluate the performance of the proposed method using the ns-2 simulator, and it is proven that our method really improves the quality of communications during a handoff process.