隨著行動通訊網路技術的發展，台灣近年也開始對第四代行動通訊系統(4G)進行部署。越來越多設備能透過行動網路連接至基地台上網，為因應行動網路數據資料量的暴增，電信業者往往整合所部署的WiFi AP (Access Point)，一旦其所屬使用者UE (User Equipment)進入其WiFi AP的涵蓋範圍，就會將該使用者UE直接從行動網路切換到WiFi網路，來達到行動資料分流卸載(mobile data offloading)的目的。
然而，若過多基地台使用者UE進入廣佈的WiFi AP訊號範圍內，將會導致過多使用者UE換手至WiFi AP，反而造成使用WiFi AP的資料傳送速度較行動網路速度慢的情況。此種強制切換到WiFi AP的方法，可能導致服務品質不佳的問題(QoS)。
軟體定義網路(Software Defined Network，SDN)的主要概念為透過交換器(switch)將傳統網路的控制權分離出來，統一交由連接的控制器(controller)做控管。Controller再將不同的封包傳送規則傳遞給switch，以達到對網路可程式化及控管的目的。
目前，雖有文獻探討如何利用SDN讓使用者UE在不同WiFi AP下換手(handover)，但尚未有文獻提出如何透過SDN將LTE的mobile data 有效卸載(offload)到WiFi AP的決策機制。本論文提出一個FMSDN (Flow Management on Mobile Data Using SDN)機制，利用SDN技術對WiFi AP、基地台、UE做控管，我們並提出實作決策機制，讓使用者UE在使用行動網路時，若移動到自己電信業者所認證的WiFi AP範圍內，可透過controller判斷該使用者UE當下或是使用基地台或是使用WiFi AP何者可獲得較高頻寬，據此決定是否需要換手，以確保在符合使用者QoS需求的前提下提高系統整體服務的data rate。

With the development of mobile network communication technology, Taiwan has begun developing fourth-generation (4G) mobile communication systems in recent years.
More and more devices are capable of connecting to the Internet through base stations, such as mobile phones, tablets, etc. In response to the increase of mobile data, telecom operators usually direct the data traffic to the WiFi AP (Access Point). Once their subscribers enter into the WiFi AP's coverage, they will be switched to WiFi APs from BSs in order to offload mobile data.
However, it may lead to excessive handover to WiFi AP if too many UEs (User Equipment) of BSs enter WiFi AP's coverage. Instead, the data rate of WiFi AP will be slower than the data rate of BS. This solution of enforced handover may result in problems of quality of service (QoS).
The main concept of Software Defined Network (SDN) is to separate the control part out of each switch, and all the control is managed by the controller. Controller assigns the rule of packet delivery to each switch such that the network is programmable and under control.
Currently, some literature discusses how to use SDN allowing users to do handover among different WiFi APs, but none has been proposed on the decision-making criterion in how to offload mobile data effectively from LTE BSs to WiFi APs through SDN. This thesis presents a FMSDN (Flow Management on Mobile Data Using SDN) mechanism, which uses SDN technology to manage the handover among WiFi AP, base station, and UE. The controller is able to make decision on handover according to the network access (WiFi or LTE) which is able to provide higher service bandwidth to UE. The proposed method is proved to be able to enhance service data rate with QoS guaranteed.

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