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https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/111451
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| 題名: | 軟體定義網路中負載平衡策略之探討 |
| 其他題名: | Research on load balancing strategies for Software Defined Networks |
| 作者: | 陳相儒;Chen, Hsiang-Ju |
| 貢獻者: | 淡江大學電機工程學系碩士班
莊博任;Chuang, Po-Jen |
| 關鍵詞: | 負載平衡;軟體定義網路;OpenFlow協定;Dijkstra最短路徑演算法;Load Balancing;Software Defined Networks(SDNs);OpenFlow protocols;Dijkstra's shortest path algorithm |
| 日期: | 2016 |
| 上傳時間: | 2017-08-24 23:53:11 (UTC+8) |
| 摘要: | 軟體定義網路(Software Defined Networks, SDN )概念是將網路設備上的控制層與網路層分開並將控制層抽離出來，透過控制層的策略管理來做到可程式化網路，可快速、輕易地決定與執行於資料層的底層系統，達成流量控制、負載平衡、網路安全以及創新的網路應用服務。OpenFlow為實現SDN概念的協定之一，OpenFlow定義了控制層裝置與資料層裝置的協定。網路路由規劃中，傳統上大多使用最短路徑搜尋法，來尋找兩端點之間最少跳點的路徑做為路由規劃的依據。在負載平衡方面會使用最短路徑演算法並將鏈結使用率作為邊權重，找出最佳負載的路由作為負載平衡的路由規劃。
實務上流量具有動態性，路由路徑初始規劃無法保障傳輸過程能維持負載平衡。當負載失衡時，需要對路由路徑調整進而恢復平衡。目前大部分在調整路由路徑的研究，會個別對每條路由使用最佳路徑演算法，尋找替代路徑並更新達成平衡。現階段調整路由路徑的方法，我們發現個別調整路徑因為路徑調整後，網路拓樸的邊權重改變，使得其他路由需要調整路徑才能達到的最佳路徑，達到平衡前需多次調整與花費較多調整週期才能到達穩定。
在達到負載平衡費時較長的問題上，我們提出新策略透過全局調整的方式，一次性的將全部路由重新安排最佳路徑，並統一更改路徑而達成平衡，可以確保單次調整就達到平衡。在全局調整策略因為會將全部的路由重新分配路徑，所以使得大量的路徑需要做變更，因此造成大量封包錯序的情況發生，導致短暫時間的網路品質不佳。
針對全局調整的策略，進一步提出改進策略-局部調整。局部調整是取部分路由做調整，並評估是否負載平衡，如未平衡則取更多的路由做調整，直到負載平衡，才會統一變更路徑。局部調整中，有機會透過部分路由的調整達到平衡，因此更動路徑較少，所以可以降低封包錯序的數量。
實驗結果證實，全局調整與局部調整可在單一週期達到平衡，而個別調整達成平衡會花較多週期，因此全局與局部調整在UDP封包的掉包率、封包錯序數、延遲抖動與吞吐量皆可在較短時間獲得改善。此外局部調整在部分情況只需調整部分路徑，因此造成封包錯序的數量較低。最後也利用TCP封包在長時間的平均延遲，證明提出策略都能達到預期的負載平衡。
Software Defined Network(SDN) concept decouples the control plane and the data plane of network devices. SDN can implement programmable network through the strategy management of the control layer. It can be quickly and easily implemented in the data layer of the underlying system. SDN can implement flow control, load balancing, network security and innovative web applications. OpenFlow protocol is used to realize SDN concept. OpenFlow protocol defines the communication between the control plane device and the data plane device. The shortest path algorithm was used to find minimum hop counts between two endpoints in the traditional routing planning. In load-balancing, we find optimal routings by using the shortest path algorithm and adding the link utilization rate as the edge weight.
Network traffics are dynamic in the practical application. The initial path can’t be guaranteed load balancing during transmission. When the network is load imbalancing, routing paths need to be adjusted in order to achieve load balancing. In the current studies, the optimal path algorithm is used to find the optimal path in each routing so that the network can achieve load balancing. However, we found the shortage in the current individual adjustment strategy. The link load is changed after the paths are adjusted. Therefore, other routing paths need to be changed in order to become optimal paths. The individual adjustment strategy will spend more time to achieve balancing and become stable.
We propose the global adjustment strategy which solve the problem about spending too much time to achieve load balancing. Our strategy reschedules the optimal path just one time. Next, all the paths will be changed to achieve load balancing in the same time. All the routings are rearranged, therefore a lot of paths need to be changed so that a large number of packets become out of order.
We also propose the partial adjustment strategy which is improved from the global adjustment strategy. The partial adjustment adjusts part of routings, and then we determine whether the networks are load balancing. If the networks are not load balancing, more routings would be adjusted until the networks achieve load balancing. Then all paths will be changed in the same time. In partial adjustment strategy, the networks may achieve load balancing by using part of routings. Therefore, fewer paths are changed and the number of packets which are out of order decreases.
The experimental results confirm that the global adjustment and the partial adjustment can achieve load balancing in single period. But the individual adjustment spends more periods to achieve load balancing. Therefore, the global adjustment and the partial adjustment in the UDP packets can improve packets loss rate, out of order, delay jitter and throughput in shorter time. In addition, the partial adjustment just adjusts part of paths to achieve load balancing in some cases. Number of packets which are out of order caused by routing adjustment decrease. Finally, we compare average delay of TCP packets in these three strategies in a long time. Our strategies achieve load balancing efficiently. |
| 顯示於類別: | [電機工程學系暨研究所] 學位論文
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