Self-Similar Network Traffic and It's Control

项目主页：www.example.com 摘要： 最近对局域和广域流量的测量表明， 网络业务是自相似的或分形的，即，测量的时间序列在几个时间尺度上是突发的。 这种现象已经被证明是普遍存在的，由于突发性的尺度不变性质，对网络性能具有潜在的可怕后果。 该项目调查 有效的流量控制算法、体系结构和机制，在提供服务质量的同时促进有效的资源利用 自相似业务下的实时和尽力而为业务流 条件 该项目建立在最近的工作特点的因果方面 的流量自相似性，并表明，规模不变的突发性，可以 对网络性能非常不利。 简而言之，它表明， 交通流的自相似性是网络的一个固有特性， 客户端/服务器系统，以不可忽略的频率传输非常大的文件或对象。 后者在技术上被称为文件或对象大小分布的重尾属性，这在包括UNIX文件系统在内的实际分布式系统中得到了证明。 上 性能方面，它表明，联合提供低延迟和高 吞吐量受到自相似性的不利影响。 我们遵循三管齐下的攻击方法来管理自相似 交通，前两个基于交通流量的动态控制， 第三种是结构性的，资源是在直接控制下设计和分配的。 第一种方法，预测反馈控制，是面向开发 自相似业务中存在的长程相关结构， 拥塞控制的目的。 我们确定集中期的开始 或高或低的交通活动-一个显着的特点， 规模不变的突发性-并调整拥塞控制模式 从保守到激进。 能够从精细的时间尺度观察中预测持续拥塞或空闲的开始 和有效利用这些信息是两个关键问题。 第二种方法，自适应前向纠错，是针对 支持具有实时约束的多媒体业务，而不涉及昂贵的资源预留。 重新传输丢失的信息是 由于往返时间过长， 在广域网环境中遇到的延迟使得重传的信息对于时间受限的应用无用。 我们制定和 分析自适应分组级前向纠错机制， AFEC，其中冗余度作为网络的函数进行控制 状态，在网络状况不佳时增加冗余级别，在网络状况良好时降低冗余级别。 控制问题是 非平凡的，因为增加冗余级别太多， 可能适得其反，进一步加剧拥堵， 在接收器处的及时信息恢复减少。 我们调查的条件下，自适应前向纠错是有效的流量自相似。 我们确定了两个制度-丢包为主的连接和延迟为主的连接-前者是最有利于AFEC为基础的流量控制，而后者是更微妙的，承认只有一个有限的范围内有用的冗余。 第三种方法是结构性资源分配， 两种主要网络资源类型的相对效用-带宽和 缓冲容量-相对于它们对自相似性的缩减效果。 我们推测带宽和缓冲区容量之间的高度偏斜的权衡关系有利于带宽，其定量形式为 在计算流量流的预留量时， 严格的服务质量要求。 带宽超过缓冲区容量的政策也影响了前两种方法的可预测性和分组丢失占主导地位/延迟占主导地位。 预计这三种方法将相互补充，每种方法都侧重于 自相似条件下服务质量提供的一种不同模式 交通状况。

Project Homepage: http://www.cs.purdue.edu/homes/park/nsf-ncr-9714707.html Abstract: Recent measurements of local area and wide area traffic have shown that network traffic is self-similar or fractal, i.e., the measured time series is bursty across several time scales. This phenomenon has been shown to be ubiquitous with potentially dire consequences to network performance due to the scale-invariant nature of burstiness. This project investigates effective traffic control algorithms, architectures, and mechanisms for facilitating efficient resource utilization while providing quality of service to real-time and best-effort traffic streams under self-similar traffic conditions. The project builds on recent work which characterizes the causal aspects of traffic self-similarity and shows that scale-invariant burstiness can be highly detrimental to network performance. In a nutshell, it is shown that self-similarity of traffic flow is an intrinsic property of networked client/server systems which communicate files or objects of very large size with nonnegligible frequency. The latter is known, technically, as the heavy-tailed property of file or object size distributions which is evidenced in actual distributed systems including UNIX file systems. On the performance side, it is shown that conjoint provision of low delay and high throughput is adversely affected by self-similarity. We follow a three-pronged method of attack for managing self-similar traffic, the first two based on dynamic control of traffic flow, and the third being of a structural nature where resources are architected and apportioned under direct control. The first method, predictive feedback control, is geared toward exploiting the long-range correlation structure present in self-similar traffic for congestion control purposes. We identify the on-set of concentrated periods of either high or low traffic activity - a distinguishing characteristic of scale-invaria nt burstiness - and adjust the mode of congestion control appropriately from conservative to aggressive. Being able to predict the onset of persistent congestion or idleness from fine time scale observations and utilizing this information effectively are two key issues. The second method, adaptive forward error correction, is directed at supporting multimedia traffic with real-time constraints without engaging in expensive resource reservations. Retransmission of lost information is not a viable strategy for such traffic classes since lengthy round-trip latencies encountered in wide area network environments render retransmitted information useless to time-constrained applications. We formulate and analyze an adaptive packet-level forward error correction mechanism called AFEC where the degree of redundancy is controlled as a function of network state, increasing the level of redundancy when the network is bad and decreasing it when the network is well-behaved. The control problem is nontrivial due to the fact that increasing the level of redundancy too much can backfire, further aggrevating congestion and causing the probability of timely information recovery at the receiver to decrease. We investigate the conditions under which adaptive forward error correction is effective when traffic is self-similar. We identify two regimes - packet loss dominated connections and delay-dominated connections - the former being most conducive to AFEC-based traffic control whereas the latter is more subtle, admitting only a limited range of useful redundancy. The third method, structural resource allocation, seeks to identify the relative utility of the two principal network resource types - bandwidth and buffer capacity - with respect to their curtailing effects on self-similarity. We conjecture a highly skewed trade-off relationship between bandwidth and buffer capacity in favor of bandwidth whose quantitative form becomes important when computing res ource reservations for traffic streams with stringent quality of service requirements. A bandwidth-over-buffer capacity policy also impacts the first two methods in terms of predictability and packet loss dominatedness/delay dominatedness. The three methods are expected to complement each other, each focusing on a different mode for quality of service provision under self-similar traffic conditions.