弹性分组环网中拥塞控制算法的研究与改进-计算机科学与技术专业论文.docxVIP

南京航空航天大学硕士学位论文 南京航空航天大学硕士学位论文 弹性分组环网中拥塞控制算法的研究与改进 弹性分组环网中拥塞控制算法的研究与改进 I I II II 摘 要 弹性分组环(Resilient Packet Ring)是一种应用于高速城域网的环形网络架构，并且拥有故障 容忍与带宽使用率高等特性。在弹性分组环的拥塞控制中，公平性、稳定性、和收敛时间等是 很重要的研究课题。在本篇论文中，我们提出一种高效的模糊拥塞控制算法(FCC)，基于模糊 逻辑计算出一个准确的本地公平速率来减轻拥塞、达到全局公平。该算法由两个部份组成：平 滑公平速率计算(SFC)和模糊公平速率计算(FFC)。平滑公平速率计算模块结合 DBA 算法和移动 平均思想计算出一个初步的公平速率；模糊公平速率计算模块首先根据传输缓冲区(STQ)的占 有量与到达 STQ 的上游流量的大小推理出拥塞度，然后 FFC 以 SFC 计算出的公平速率为基准， 运用模糊控制的方法，根据模糊拥塞度进行调整，生成最终的反映真实流量状况的本地公平速 率。由于 SFC 与模糊控制思想的使用，FCC 算法与其它算法相比可以达到较小的收敛时间，并 且在不同规模的场景中都能获得很好的效果。仿真结果显示 FCC 算法不论在公平性、稳定性、 与收敛时间上都能获得很平衡的表现。因此可以看出，FCC 算法在 RPR 拥塞控制中是一个可行 且高效的方案。 关键词：弹性分组环，拥塞控制，公平算法，模糊控制，NS-2 网络仿真 ABSTRACT Resilient Packet Ring (RPR) is a ring based network for high-speed metropolitan area networks which has properties of fault tolerance and high bandwidth utilization. In congestion control of RPR, the issues of fairness, stability, and convergence time are important. In this thesis, we propose an effective Fuzzy Congestion Control (FCC) algorithm to achieve above considerations. FCC generates a precise local fair rate by fuzzy logic to suppress upstream traffic to mitigate congestion and achieve global fairness. FCC is composed of two components: Smooth Fair rate Calculator (SFC) and Fuzzy Fair rate Calculator (FFC). SFC uses the key idea in DBA and applies moving average technique to produces a primary fair rate; FFC first use STQ occupancy and arrival traffic rate to STQ as input to inference fuzzy congestion degree which are some grades of membership for linguistic terms of fuzzy sets, then it adopts the fair rate caculated by SFC as a basis, adjust it according to the fuzzy congestion degree using fuzzy control method to generate a local fair rate which reflects the real traffic condition. Since SFC and fuzzy control method are applied, the smaller convergence time than other fairness algorithms is obtained. Furthermore, even in different scales of congestion domain, FCC still has an excellent performance as compared with other fai