隨著線網路技術的蓬勃發展，使得以IEEE 802.11 為基礎的無線區域網路被廣泛的架設在許多公共的地方。它提供了移動式的設備一個非常方便的方法與網際網路接軌；也讓使用者可以在多個無線網路間漫遊。加上移動式協定 (Mobility Protocol) 的支援 (例如移動式的網際網路協定(Mobile IP 或Mobile IPv6, MIP6))，使用者可以在無線網路間漫遊而不會造成網路層的連線的中斷。然而使用移動式的網際網路協定所造成的換手延遲 (Handover Latency) 卻有可能讓使用者感到使用上的不便。因此，為了支援無縫式的換手服務 (seamless handover)，相關研究[13]提出了「快速換手的移動式網際網路協定 (Fast Handover for Mobile IPv6, FMIPv6)」。此外，為了提供更好的服務品質以及減少換手時所造成的換手延遲，整合IEEE 802.11 無線網路協定及移動式網際網路協定看來是必要的趨勢。然而，不幸的是，當我們試著將IEEE 802.11 無線網路協定整合至快速換手的移動式網際網路協定中時，快速換手的移動式網際網路協定通常無法使用
預先式的換手程序來完成換手服務的工作，取而代之的是使用被動式的換手程序來完成。這主要是由於IEEE 802.11 無線網路協定的本身的運作方式的缺點以及IEEE 802.11 無線網路協定與快速換手的移動式網際網路協定間並無存在任何的相互關聯。再者，由於使用快速換手的移動式網際網路協定之移動式設備，在送出快速繫結更新 (Fast Binding Update, FBU) 到原來的存取路由器(Original Access Router, OAR)後，便無法在原來的網路中，再接收到要送給它的資料。如此一來便會造成不必要的資料遺失。如果要強行使用預先式的換手服務，會造成
比被動式換手服務更多的資料遺失。這些情況都會造成服務品質的下降，而且會使得即時性的應用變的更加地不可行。在這篇論文中，我們主要提出了一個整合IEEE 802.11 無線網路協定與快速換手的移動式網際網路協定的想法。它是一個以快速換手的移動式網際網路協定為核心的想法，加上一個相容於IEEE 802.11無線網路協定相容的主動式作法來達成。因此，它保留了大部份的快速換手的移動式網際網路協定所帶來的優點；而且由於主動式IEEE 802.11 無線網路協定的支援，它還能減少換手時不必要的封包遺失。除此之外，主動式的作法，還能有效地避免IEEE 802.11 無線網路協定標準中，換手程序較費時的階段，使得換手的延遲可以被有效地減小。

IEEE 802.11-based wireless local area networks (WLANs) have been set up in many public places in last few years. It provides convenient network connectivity to mobile nodes (MNs) and allows users moving from one wireless network to another. With mobility protocol support, such as Mobile IPv6 (MIPv6), people can roam across wireless IP subnets without loss of network-layer connectivity. However, the handover latency may make users feel uncomfortable in MIPv6. To support seamless handover, an enhanced MIPv6 scheme, Fast Handovers for Mobile IPv6 (FMIPv6)[13], was been proposed. In order to further reduce the handover latency, integrating the lower layer procedure with the upper layer procedure is necessary. Unfortunately, when integrating the IEEE 802.11-based standard with FMIPv6, FMIPv6 always fails to perform predictive handover procedure. This may make the handover procedure result in reactive handover. It is because of the protocol nature of IEEE 802.11 and the weak relation between IEEE 802.11 and FMIPv6. Furthermore, a MN can’t receive packets destined to it when it sends the Fast Binding Update (FBU) to the original access router (OAR). This would cause unnecessary packet loss and make the redictive
handover have more packet loss then reactive. Those issues will cause quality of services degradation and make real-time applications unreachable. In this dissertation, a low-latency MIPv6 handover scheme will be proposed. It is a FMIPv6-based scheme
which is assisted by an active-scan link layer scheme. It has the advantage of FMIPv6 and can reduce unnecessary packet loss when the handover occurs. Also, with the assistance of the active scheme, it can avoid the longest phase that IEEE 802.11 will
enter, and can lower the handover latency.

中文摘要 IV
ABSTRACT VI
CHAPTER 1 INTRODUCTION 1
1.1. Motivation and Objectives 1
1.2. Summary of the Dissertation 5
1.3. Organization of the Dissertation 7
CHAPTER 2 RESEARCH BACKGROUND 8
2.1 Link-Layer Handover Procedures 10
2.2 Mobility Protocols 15
2.3 Other Upper-Layer Handover Procedures 19
CHAPTER 3 ACTIVE-SCAN LINK-LAYER HANDOVER SCHEME 21
3.1 A Selective Channel Probing Scheme 22
3.2 Active-Scan Link Layer 25
3.2.1 The Power Saving Mode 27
3.2.2 The START_PROBE Threshold 28
3.2.3 The Algorithm and the Enhancement 29
3.3 Overhead Discussion 32
3.4 Simulations and Analysis 35
3.4.1 Signal Quality Experiment 36
3.4.2 The START_PROBE Threshold 38
3.4.3 UDP Transmission Experiment 40
3.4.4 TCP Transmission Experiment 42
3.5 Discussion 44
3.5.1 Compatibility and Flexibility 45
3.5.2 Advantages and Disadvantages 46
CHAPTER 4 ENHANCED FMIPV6 48
4.1 Observations 48
4.2 Link Layer Assisted Method for FMIPv6 50
4.3 Two-Step FMIPv6 and the Problem of Early Start FMIPv6 53
4.4 Integrate the Active Scheme and FMIPv6 55
4.5 Simulations and Analysis 57
4.4.1. The Setting in the Active Scheme 58
4.4.2. Handover Latency 59
4.4.3. Discussions 62
CHAPTER 5 CONCLUSION 64
REFERENCES 67

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