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题名:
基于Multihoming技术的传输层容错协议及其性能研究
作者: 乔元松
答辩日期: 2007-06-05
授予单位: 中国科学院软件研究所
授予地点: 软件研究所
学位: 博士
关键词: Multihoming ; SCTP ; 虚假切换 ; 重传策略 ; 路径故障检测
其他题名: Research on Multihomed Fault Tolerant Transmission Protocols and their Performance Improvements
摘要: Multihoming是指一个主机具有多个IP地址。随着网络接入技术的发展,带有多个网络接口的设备越来越普遍。本文研究在传输层利用Multihoming技术提供端到端容错能力的协议及其性能的改进。当前对支持Multihoming的传输层协议的研究还处于早期的阶段,协议中使用的算法基本上是从传统的单路径传输层协议继承而来。本文以流控传输协议SCTP(Stream Control Transmission Protocol)作为试验的基础,深入分析了在多路径条件下重传策略、路径故障检测机制对传输性能以及协议稳定性的影响。本文的主要贡献和创新点如下: (1)提出了一种基于时间戳选项来消除虚假切换的算法,用于避免本文所发现的两种导致SCTP停机的场景。在某些特殊的路径条件或者协议设置情况下,发送端无法获得准确的路径双向延迟的测量,从而引起虚假传输超时,并导致路径切换,进而使协议进入不稳定状态。第一种场景由接收端使用延迟确认而触发;第二种场景由发送端传输不同长度的数据包而触发。 (2)提出了一种判断接收缓冲区阻塞的数学模型,以确定快速重传时的路径选择。本文发现对于使用备份路径进行快速重传的策略,当备份路径带宽低于主路径带宽,并超过某个门限值时,数据包乱序会引起接收端缓冲区阻塞,从而降低传输性能。 (3)对多路径条件下的快速恢复算法进行了改进,使得各个路径的拥塞控制窗口在快速恢复阶段可以独立增长,以避免本文所发现的由选择确认SACK(Selective Acknowledgement)乱序所导致的传输性能下降;评估了两种数据突发控制算法,指出减小拥塞控制窗口的算法要优于限制最大发送包数的算法。 (4)研究了在多条路径共享拥塞点的情况下,快速重传算法在备份路径上的性能。结果表明在这种情况下,快速重传会导致更严重的拥塞。 (5)提出了一个SCTP协议参数配置决策树。评估了快速重传策略、超时重传策略、路径故障检测门限值设置,三者配合时在多种路径条件下的性能,并综合以上各种发现提出了在不同的路径条件下应该采取的重传路径选择策略以及路径故障检测门限值设置方案。 最后,本文强调指出,当前SCTP设计上的主要问题是把单路径的算法直接应用于多路径环境,因此单路径算法应该经过重新评估后才能在多路径环境下应用。
英文摘要: Multihoming technologies, where a host can be addressed by multiple IP addresses, are increasingly receiving attention from the network community. This paper studies transport layer protocols with end-to-end fault tolerance through multihoming technologies and their performance improvements. Currently, the research on multihomed transport layer protocols is in the early stages. Most of the algorithms in the protocols are inherited from traditional single-path oriented transmission protocols. This paper analyzes in-depth the effects of retransmission polices and path failure detection mechanisms on the protocol performance and stability in multi-path environments through SCTP (Stream Control Transmission Protocol) simulations. The contributions and innovations are as follows. (1) An algorithm for removing spurious failover is proposed to avoid two SCTP stall scenarios found by this paper. In some special path conditions or protocol setting situations, the sender can not obtain precise path delay measurements, which results in spurious transmission timeout, path failover and finally causes the protocol to enter an unstable state. The first stall scenario is triggered when the receiver is using the delayed acknowledgement algorithm. The second scenario occurs when the sender is transmitting packets with different lengths. (2) A mathematic model for estimating receiver buffer blocking is put forward to determine path selection during the fast retransmission phase. This paper illustrates that retransmission on an alternate path will degrade performance significantly when the secondary path bandwidth is lower than the primary path bandwidth at a certain level because of receiver buffer blocking due to disordered data chunks. (3) The fast recovery algorithm in SCTP is improved for multi-path environments through decoupling the Congestion Control Windows of alternate paths from the primary path Congestion Control Window in the fast recovery phase to prevent the performance degradation caused by disordered SACKs (Selective Acknowledgement). Two data burst control algorithms are evaluated. The test results indicate that burst control by adjusting the Congestion Control Window is better than burst control by limiting the maximum number of transmitted packets. (4) Fast retransmission on an alternate path is studied in the case of multiple paths sharing a congestion point. The results show that fast retransmission on an alternate path will increase congestion of the bottleneck link in this situation. (5) A decision tree for SCTP parameter configuration is proposed. This paper evaluates the performance of fast retransmission policies, timeout retransmission policies and path failure detection thresholds in multi-path contexts. It integrates the above findings and presents the policies for retransmission path selection and path failure detection threshold setting in different path conditions. Finally, this paper emphasizes that the main problem in the current SCTP design is that it employs TCP single-path algorithms in multi-path environments without significant modifications. Therefore, single-path algorithms should be re-evaluated before being applied to multi-path environments.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.iscas.ac.cn/handle/311060/6120
Appears in Collections:中科院软件所

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Recommended Citation:
乔元松. 基于Multihoming技术的传输层容错协议及其性能研究[D]. 软件研究所. 中国科学院软件研究所. 2007-06-05.
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