近幾年來，各種無線通訊系統持續地蓬勃發展，然而，不同的通訊系統中皆有所屬的網路涵蓋範圍，這些擁有不同涵蓋範圍的網路結合起來便形成了一個階層式的重疊網路，當使用者在不同的網路中漫遊時，就需要一個垂直式交遞的機制來提供使用者在移動中能繼續保持網路連線的功能。
現存的垂直式交遞的機制中之最大問題在於必須要修改網路的基本架構，這點通常是無法達到的。在本篇論文中，我們提出了一個無接縫的重直式交遞機制，此機制將可以整合不同的重疊網路而形成一個高服務可利用性的網路系統，這個機制，是利用TCP Migration 的概念來達成垂直式交遞，只須修改欲進行溝通的兩個網路主機即可，因此可以保持網路的基本架構不變。為了驗證這個方法的正確性及可行性，我們在Linux上實作了一個雛形系統，實驗的結果顯示執行垂直式交遞所需的時間是在大多數的應用程式之容忍範圍內。

In the last decade, many new wireless communication systems have been developed. Those communication systems have different extents of network coverage, thus formed a hierarchical overlay networks. When moving between those networks, a vertical handoff mechanism is needed to handle the handover between different hierarchies of networks.
The problem of current vertical handoff approaches is that the network infrastructures needed to be modified, which is almost impossible. In this thesis, we propose a seamless vertical handoff approach that can integrate the overlay networks to achieve high service availability. Our approach only modifies the two end nodes of a communication path so that we can keep the network infrastructure unmodified. It performs vertical handoff through TCP migration. To verify the feasibility of our approach, we implement a prototype system on Linux. The experiment results show that the time for vertical handoff performed by the system is short and acceptable for most of the applications.

論 文 摘 要 i
Abstract ii
Acknowledgement iii
Table of Contents iv
List of Figures v
List of Tables vi
Chapter 1 Introduction 1
1.1 Overlay Networks 1
1.2 Vertical Handoff 2
1.3 Organization of the Thesis 4
Chapter 2 Related Works 5
2.1 Icomera Gateway 5
2.2 SONaccess 6
2.3 Vertical Handoff by Multicast, U. C. Berkeley 6
2.4 Handoff between WLAN and GPRS, University of Oulu 8
Chapter 3 Background 12
3.1 TCP Three-Way Handshaking 12
3.2 TCP Migration 13
3.2.1 TCP Connection Creation and Migration 15
Chapter 4 Design and Implementation 18
4.1 System Architecture of VHOST 18
4.2 TCP Options 20
4.3 Migration Monitor 21
4.4 Implementation 22
4.4.1 Socket 23
4.4.2 Suspensible TCP Core 23
4.4.3 Resumption Module 25
4.4.4 Migration Monitor 26
4.4.5 Wireless Link Adaptation 28
Chapter 5 Experiment 30
5.1 Experimental Results 31
Chapter 6 Conclusion and Future Work 34
6.1 Conclusion 34
6.2 Future Work 34
References 36

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