【作者】 吕建斌；

【导师】 廖晓峰；

【作者基本信息】 重庆大学 ， 计算机系统结构， 2005， 硕士

【摘要】 网络自身的特性以及不断增加的网络应用决定了网络拥塞的出现是无法避免的,而在拥塞没有更加恶化以前采取有效的拥塞避免机制是目前所知的保证网络不至于崩溃的唯一的方法——网络资源的增加或者应用的减少不足以保证网络的通畅,而且这不是一种积极的方法。拥塞控制按照不同的标准可以分为不同的控制机制,相应的有不同的拥塞控制策略。主动队列管理算法是一种运行于网络内部节点的积极的闭环控制的链路算法。该算法主要在网络的内部节点产生拥塞指示的信息,然后通过一定的方式将该信息传送到端系统,端系统据此调节发送速率来缓解网络拥塞。本文在对当前几种流行的主动队列管理算法——RED,REM,RED/ECN 以及RED/BECN 进行详细的分析基础上,总结出当前拥塞控制算法的优势和不足,并提出了一种更优化的解决方案。本文的主要工作如下: 1、在分析了当前拥塞控制算法的基础上,提出了一个新的算法——基于TTL 的主动队列管理(TRED: A TTL Based Active Queue Management),该算法是在主动队列管理算法RED 的基础上,将ECN 与BECN 结合作为拥塞指示的方式,同时借鉴了ECN 与BECN 的优点,又弥补了双方的缺点,可以更好地进行拥塞指示。2、对本文提出的算法建立了一个数学模型,对模型的分析结果表明该算法对控制拥塞、提高网络吞吐量等有更好的效果。3、在NS 环境下对算法进行了仿真,仿真结果支持了理论分析。更多还原

【Abstract】 The network congestion cannot be avoided since the network’s nature is dynamic and decentralized. Neither increasing network resources nor decreasing applications is sufficient to guarantee the stability of the network behaviors and, after all, they are not active ways. So an effective congestion avoidance mechanism is the only way to prevent the congestion collapse from a relative light congestion. The mechanisms of congestion control can be classified into many groups based on different rules. The algorithm of active queue management (AQM) that is applied in the inter node of the network is an active close-loop link algorithm to control congestion. This algorithm generates indicating congestion information in the link node of the network and transmits it to the end system, which is used by the end system to adjust the input rate to alleviate the network congestion. In this thesis, the advantages and disadvantages of the current prevalent congestion control algorithms are discussed in detail. Based on some general AQM algorithms such as RED, REM, RED/ECN and RED/BECN, an improved congestion control scheme is proposed. The main contributions in this thesis are as follows: 1. Proposes a new algorithm—TRED: A TTL Based Active Queue Management algorithm. The algorithm establishes on the famous AQM algorithm-RED and combines ECN and BECN to serve as a congestion notification. By exploiting the advantages of the ECN and BECN and diminishing the disadvantages of them, the algorithm can notify the congestion condition more effectively than previous algorithms. 2. The mathematical model of TRED is constructed in this thesis. Based on this model, the feasibility and the effectiveness of this algorithm are carefully discussed. The analysis results show that it does better than previous algorithm in controlling the congestion and improving the throughput in a congested network. 3. The simulation of the algorithm in the NS (Network Simulator) presents a strengthen support to the results of the theoretical analysis.更多还原