軟體定義網路將網路的控制層與數據層分離，在進行網路流更新，也就是當網路流的終點發生改變需要給網路流分配新的路徑，控制器只需要更改交換機上的轉發規則就可以完成更新，所以網路流更新的損耗與變更的轉發規則的數目成正比。但是不同的路徑分配方案會帶來不同的數目的轉發規則變更，因此需要提出一種路徑分配的規劃使得變更轉發規則的數目最小，同時由於擁塞的問題，路徑的規劃還需要考慮網路流的拒絕率。除此之外，網路流的優先權也需考慮。我們提出一種基於禁忌搜尋(Tabu Search)的啟發式(Heuristic)演算法，尋找最少的轉發規則改變的路徑分配規劃。模擬結果顯示，我們提出的演算法，比貪婪演算法有更少的轉發規則變更數目，和更低的網路流拒絕率。

Software-Defined Networking (SDN) decouples the networks as data plane and control plane. When the destination of network flows have changed, we need to assign new paths for the flows. We call this process network update. The controller only needs to update forwarding rules to accomplish the network update. The cost of the network update is in proportion to the number of changing rules. However, different path assignment plans have different numbers of changing rules and flow rejection rate. It is an important issue to generate a plan with the least number of changing rules. In addition, if the flows have different priorities, we need to satisfy the high priority flows first. In this paper, we propose a heuristic algorithm to find the path assignment plan with small number of changing rules and low flow rejection rate. Simulation results show that the performance of our algorithm is better than greedy algorithms in terms of number of changing rules and rejection rate.

List of Contents
Section I Introduction 1
Section II Related Work 4
Section III Algorithms 7
3.1 Problem Formulation 7
3.2 Hardness Analysis 10
3.3 Minimum Changing Ruls Path Assignment Algorithm 12
Section IV Simulation 23
4.1 Simulation Environment 23
4.2 Simulation Results 23
Section V Conclusion 30
References 31

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