網路演進的趨勢已使我們可以不受到有線網路所限制住，不論在室內還是戶外皆可隨時隨地透過無線網路來瀏覽各種資訊，而在行動通訊裝置的普遍使用之下，無線網路的發展有了迫切的需求，所以漸漸的有越來越多種無線網路標準以及介面被設計了出來。

異質性網路(Heterogeneous Network)現在已融入我們所處的環境當中，也就是說有我們身邊有多種網路混合共存的情形，已經是一件非常稀鬆平常的事情，這讓使用者可以因應各種不同的情況來使用著不同的網路存取方式，而SCTP建立關聯(Association)時能夠同時配置一個以上的IP位址來作使用，對於現在異質性網路的環境下，擺脫了TCP協定只得使用單一IP位址的連線限制，並利用了此多重定址的特性達到故障轉移(Failover)的實現。

而由於標準SCTP上的故障轉移機制有著網路無法使用的空窗期存在，因此本論文提出一個在SCTP上運用同步多路徑傳輸來做為故障轉移評估的機制，並藉著同步多路徑傳輸的限制，一方面利用此限制做預估以讓同步多路徑傳輸作最大的利用，一方面利用同步多路徑傳輸來做其他路徑資訊的探測，並在結束評估階段時作出路徑選擇的決策，這使得整體傳輸行為有了中間的過渡時期，不會被空窗期所終止，並能在評估時期結束後藉由充足的資訊來決定出一條良好的路徑做後續的傳輸使用。

Nowadays, we can no longer be restricted by the wired due to the development of network technique. No matter we are indoor or outdoor, we can search any information via wireless network anytime. On the use of the mobile communication device, there is a high demand for the development of wireless network, so the more and more wireless standards have been developed for this situation.
Therefore, it is very common that there are multiple ubiquitous network around our world, so-called “Heterogeneous Network.” Users can choose any different network interface to fit what situation they are facing in. And the transport layer protocol –Stream Control Transmission Protocol (SCTP), can set up multiple IP address to use while creating the association. In the current situation with heterogeneous network, SCTP with the multiple IP address can also implement the “Failover” feature, and is more suitable than TCP which is restricted in using only single IP address.
Due to the failover drawback that of the standard SCTP where there is an empty period let user not to access the network temporarily, our research proposes a new failover evaluation mechanism using the concurrent multiple transfer (CMT). We exploit the restriction of CMT to reach the maximum use of CMT, and we also collect the information of all transmission path to decide next primary path when the end of evaluation. Therefore, it can avoid the transmission suffering from the empty period, and selecting a suitable path with sufficient information to do a better transmission.

第一章 導論 1
1.1 前言 1
1.2 研究動機 2
1.3 論文架構 3
第二章 相關背景與研究 4
2.1 異質性網路 4
2.2 WIFI(WIRELESS FIDELITY)技術簡介 4
2.2.1 訊框間隔(Interframe Space, IFS)與延遲(Backoff)機制 4
2.2.2 RTS/CTS與四段交握 6
2.3 串流控制協定(SCTP)的介紹 7
2.3.1 SCTP基本簡介 7
2.3.2 SCTP封包格式 11
2.3.3 SCTP 擁塞控制機制 17
2.3.4 SCTP的路徑錯誤偵測 19
2.3.5 動態位址重新配置(Dynamic Address Reconfiguration, DAR) 20
2.4 相關文獻研究 23
2.4.1 SCTP同步多路徑傳輸(Concurrent Multipath Transfer, CMT) 23
2.4.2 SCTP故障轉移機制相關研究 26
第三章 機制設計 28
3.1 情境假設 29
3.2 問題描述 30
3.3 同步多路徑傳輸協助之故障轉移評估機制運行流程 32
3.4 同步多路徑傳輸協助之故障轉移評估機制運作 34
3.4.1 同步多路徑傳輸協助之故障轉移評估階段的起始條件 34
3.4.2 同步多路徑傳輸協助之故障轉移評估機制的限制與終止 35
3.4.3 故障轉移評估階段終止的路徑選擇決策 44
第四章 模擬實驗與結果分析 45
4.1 模擬工具介紹 45
4.2 模擬環境與參數設定 46
4.3 模擬結果與分析 48
4.3.1 評測對象 48
4.3.2 數據分析 48
第五章 結論 59
參考文獻 60

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