基於軟體定義的網路在OpenFlow協定標準下已漸趨成熟，軟體定義網路因控制平面與資料流平面分離的架構，而具備高度彈性與擴充性，控制平面統一交由SDN controller決定一切資料流向，路由，甚至防火牆或入侵偵測，使得網絡控制指令不再受限於各家網路廠商所綁定的專屬設備系統。

負載平衡機制傳統以來被綁定在專屬的系統之上，例如F5，A10等網路公司所產設備，導致負載平衡機制不具備全局的網絡視野，也受限於設備廠商專屬的控制指令，本論文中，選擇開源的Ryu軟體定義網路控制器，在其上開發出負載平衡應用，藉由軟體網路全局的縱觀視野，有效地分配網絡的鏈路負載。

The network based on software definition has gradually matured under the OpenFlow protocol standard. The software definition network is highly flexible and expandable due to the separation of the control plane and the data flow plane. The control plane is unified by the SDN controller to determine the flow of all data, routing, and even firewall or intrusion detection, making network control commands no longer restricted to proprietary device systems bundled by various network vendors.

The load balancing mechanism has traditionally been bound to proprietary systems, such as those produced by network companies such as F5 and A10. As a result, the load balancing mechanism does not have a global network view, and is limited by the device manufacturer's proprietary control commands. In the paper, the open source Ryu software is defined to define the network controller, and the load balancing application is developed on it. The network link load is effectively allocated through the global view of the software network.

Chapter 1. Introduction 1
Chapter 2. Background and Motivation 4
2.1 Background 4
2.2 Motivation 11
Chapter 3. Multiple path loadbalance 14
Chapter 4. Performance Evaluation 22
Chapter 5. Conclusion 27
References 28

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https://www.opennetworking.org/sdn-definition/
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https://osrg.github.io/ryu-book/zh_tw/Ryubook.pdf
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https://www.opennetworking.org/wp-content/uploads/2014/10/openflow-spec-v1.4.0.pdf
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https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html#t6
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http://eddmann.com/posts/depth-first-search-and-breadth-first-search-in-python/
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http://mininet.org/overview/
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[18]OpenFlow group table
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[19] OSPF Metric cost Calculation Formula Explained
https://www.computernetworkingnotes.com/ccna-study-guide/ospf-metric-cost-calculation-formula-explained.html