近年來提出了一種新興的軟體定義網路(Software Defined Networking)架構，在此架構底下，網路分為控制層（Control Plane）與傳輸層（Data Plane），控制層的控制器（Controller）利用其中央集中式的控制模式，能使網絡運營商能夠通過更細粒度的網絡策略大大改善流量控制。但是，實現細粒度控制的成本是更多的轉發規則。 從而增加了性能和資源的稀缺性。
為了解決硬體的局限性，使用不同的移除策略進行流表管理。 其中，限制流規則存活時間可以大幅節省流表空間。此類方法目的為優化規則的持續時間以提高規則命中效率。在這項工作中，我們描述了基於時間的策略的關鍵屬性，並討論了它們對現有SDN網絡的影響。我們調查了目前對規則管理的工作缺少了同時使用流表命中率、流表使用率與重新安裝數量當作評量標準。在考量交換機效能時忽略流的服務。特別是，目前的策略只考慮單一交換機的最佳超時時間安排。此舉造成流路徑規則安插不同步衍生出一些問題且浪費流表空間。此文獻提出同步的解決方式並使用在超時時間上。此外，為了完全避免流表溢出的發生而提出了主動規則移除策略。
用具有代表性的流量數據和現實的拓撲，然後使用各種指標進行全面分析。 實驗結果表明，我們可以有效避免溢出事件，並將平均流表利用率降低約30％。 在多點拓樸的壓力測試中，我們可保證更多的流量通過，並且傳輸品質提高了約5％。 我們的方法有助於了解當前管理方法缺乏服務質量。

To solve the limitations of hardware, different removal strategies are used for flow table management. Among them, limiting the rule survival time can save the flow table space. The purpose of such methods is to optimize the duration of the rules to improve the efficiency of rule hits. In this work, we describe the key attributes of time-based policies and discuss the impact on networks. Current strategies only consider the rule scheduled for a single switch, this causes the flow path rules to evicted out of sync waste the flow table space. This paper proposes a solution and on timeout and a proactive rule eviction strategy to minimize flow table overflow events. Experiment with representative traffic data and realistic topologies, then analyze comprehensively with various metrics. The experimental results show that we can effectively avoid overflow events and reduce the average flow table utilization by about 30%. In the multi-point pressure test, we guarantee more flows to pass and the transmission quality improves by about 5%. Our approach helps to understand the current management method's lack of service quality.

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