LatLong: Diagnosing Wide-Area Latency Changes for CDNs
LatLong: Diagnosing Wide-Area Latency Changes for CDNs
复制标题
LatLong：诊断 CDN 的广域延迟变化
DOI：
--
复制
发表时间：
2012
影响因子：
5.3
通讯作者：
Sridhar Srinivasan
中科院分区：
文献类型：
--
作者：
Yaping Zhu;Benjamin Helsley;J. Rexford;Aspi Siganporia;Sridhar Srinivasan
最大限度地减少用户感知的延迟对于托管交互式服务的内容分发网络(CDN)至关重要。延迟增加的原因有很多，比如域间路由变化、CDN自身的负载均衡策略等。CDN需要更好地了解延迟增加的原因，以便它们可以通过将流量定向到不同的服务器或路径来适应。在本文中，我们提出了一个用于CDN的工具，用于基于对性能、流量和路由的被动测量来诊断较大的延迟增加。将多种原因与后果分开是一件具有挑战性的事情。我们提出了一种用于对延迟变化进行分类的决策树，并确定如何将流量变化与现有服务器、路由器和路径的延迟增加区分开来。另一个挑战是网络运营商对相关客户端进行分组以减少测量和控制开销，但一个区域中的客户端可能在测量间隔期间使用多个服务器和路径。我们提出了量化服务器和路由器集合之间的延迟贡献的指标。在此基础上，我们实现了诊断CDN大延迟增加的LatLong工具。我们使用LatLong分析了Google CDN一个月的数据，发现近1%的日常延迟变化会使延迟增加超过100毫秒。请注意，100毫秒的延迟增加非常显著，因为这是客户端组的日平均值，而且我们在研究中只关注延迟敏感型流量。其中超过40%的增长与域间路由更改同时发生，超过三分之一涉及流量转移到不同的服务器。这是从纯被动测量中诊断大型运营CDN中的延迟问题的第一项工作。通过对个别事件的案例研究，我们确定了CDN管理广域延迟的研究挑战。
Minimizing user-perceived latency is crucial for Content Distribution Networks (CDNs) hosting interactive services. Latency may increase for many reasons, such as interdomain routing changes and the CDN's own load-balancing policies. CDNs need greater visibility into the causes of latency increases, so they can adapt by directing traffic to different servers or paths. In this paper, we propose a tool for CDNs to diagnose large latency increases, based on passive measurements of performance, traffic, and routing. Separating the many causes from the effects is challenging. We propose a decision tree for classifying latency changes, and determine how to distinguish traffic shifts from increases in latency for existing servers, routers, and paths. Another challenge is that network operators group related clients to reduce measurement and control overhead, but the clients in a region may use multiple servers and paths during a measurement interval. We propose metrics that quantify the latency contributions across sets of servers and routers. Based on the design, we implement the LatLong tool for diagnosing large latency increases for CDN. We use LatLong to analyze a month of data from Google's CDN, and find that nearly 1% of the daily latency changes increase delay by more than 100 msec. Note that the latency increase of 100 msec is significant, since these are daily averages over groups of clients, and we only focus on latency-sensitive traffic for our study. More than 40% of these increases coincide with interdomain routing changes, and more than one-third involve a shift in traffic to different servers. This is the first work to diagnose latency problems in a large, operational CDN from purely passive measurements. Through case studies of individual events, we identify research challenges for managing wide-area latency for CDNs.