隨著行動裝置與行動應用程式的增加，使用者對行動流量的需求暴增，如何疏 通行動網路的壅塞已成為目前極為廣泛討論的議題。 由於大部分的行動資料並不需 要即時為使用者使用，因此許多研究探討了在異質網路間分流資料來傳輸這些允許 延遲的檔案，例如: Wiffler、On-the-spot(OTS)。 而這些檔案只須在被允許延遲的時 間內傳完，但是這些方法貪婪地將資料分流到Wi-Fi，並沒有考慮Wi-Fi的分布密度 與Wi-Fi目前被使用的狀況， 因此在不穩定的網路環境中，這些方法無法保證檔案 都能在允許延遲的時間內傳完。
本論文提出一種在行動裝置上，基於檔案傳輸剩餘大小之行動資料分流。 我們的方法固定時間去檢查剩餘檔案大小，根據剩餘檔案大小與允許延遲時間決定如何 使用行動網路與Wi-Fi來傳輸檔案。 另外，本文也提出一種以使用者角度計算資料 分流成本的公式，並將我們的方法與Wiffler及OTS比較，研究結果顯示，在不穩定 的網路環境中，本論文提出的方法較能保證在允許延遲的時間傳完，並且將資料從 行動網路分流到較適合的Wi-Fi網路。

As mobile devices and mobile apps largely grow, mobile data traffic increases at an unprecedented rate. How to alleviate mobile traffic congestion becomes a widely dis- cussed issue. Because that most mobile data is not necessarily used immediately, some research discusses mobile data offloading among heterogeneous network for these delay- tolerant files, for example, Wiffler and On-the-spot(OTS.) These files are allowed to complete transmission before delay-tolerant deadline. However, these methods greedily offload data from cellular network to Wi-Fi network. The density of Wi-Fi deployment and current Wi-Fi situation are not considered. Therefore, under network environment with several factors, these methods cannot guarantee file transmission completion be- fore delay-tolerant deadline.

In this thesis, we propose residual size-based mobile data offloading for file trans- mission on mobile devices. Our method periodically checks the residual size of the file. According to the residual size and delay-tolerant deadline, our method decides how to use cellular and Wi-Fi networks for file transmission.

Besides, we also propose a cost function to investigate trade-off between deadline and the fraction of the transferred size using available Wi-Fi. We compare our method with Wiffler and OTS. The results show that under network environment with several factors, the cost of our method is the lowest one. Our method is more likely to guarantee file transmission completion before delay-tolerant deadline.

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