Proxy Services in Wide-Area Networks

近年来，由于互联网的空前普及以及骨干网和接入带宽的增加，对流媒体服务的兴趣急剧增长。随着客户端接入带宽的进一步增加，对高质量音频/视频流的需求将会增长。新兴的应用程序包括编排的媒体应用程序，例如远程学习，它将来自一个或多个源的音频、视频、图像和文本组合在一起。其他具有挑战性的多媒体应用也即将出现，包括虚拟现实和分布式交互仿真。这些应用程序涉及不同流行程度的恒定比特率和可变比特率流，以及对用户交互性的不同程度的支持，例如VCR或分支操作。这些新兴的高质量多媒体应用将对网络基础设施提出严峻的挑战。这些应用程序之间的一个共同点是其数据的所谓“连续”性质。在连续媒体（CM）中，存在严格的时序关系，它定义了CM数据必须被渲染的时间表（例如，视频显示或音频播放）。在网络设置中，播放时间限制、特定CM（如可变比特率（VBR）视频）的速率可变性、网络中丢包和延迟的可能性以及有效使用网络资源的需求，使CM数据的交付成为一个非常具有挑战性的问题。由于单个网络服务提供商通常无法控制从源到终端客户端的整个路径，因此交付高质量音频和视频的挑战变得更加复杂。解决这些挑战的一个有希望的方法是在网络中部署代理服务。代理可以隐藏异构性，减少用户启动延迟，降低网络资源使用，并适应网络性能属性的波动。在这个建议中，项目主管概述了研究，其目标是开发和评估代理服务，以提高客户端看到的CM流的感知质量，同时提供低启动延迟。获奖者将重点关注服务本身的开发、代理所需的底层资源管理机制、使这些服务访问资源管理机制所需的编程接口，以及此类代理通常遇到的工作负载和访问模式的特征。评估这些服务和机制的方法是折衷的，依赖于基于linux的代理PRONTO的分析、模拟和实验的组合，PRONTO将在整个项目中得到进一步增强

Interest in streaming media services has grown dramatically in recent years due to the unparalleled popularity of the Internet and the increase in backbone and access bandwidth. As client access bandwidth further increases, the demand for high-quality audio/video streaming will grow. Emerging applications include orchestrated media applications, such as distance learning, that combine audio, video, images, and text from one or more sources. Other challenging multimedia applications are on the horizon, including virtual reality and distributed interactive simulation. These applications involve both constant-bit-rate and variable-bit-rate streams of varying popularity, and different degrees of support for user interactivity, such as VCR or branching operations. These emerging high-quality multimedia applications will pose serious challenges to the network infrastructure. A common thread among these applications is the so-called " continuous" nature of their data. In continuous media (CM), strict timing relationships exist that define the schedule by which CM data must berendered (e.g., a video displayed or audio played out). In a network setting, the playout timing constraints, the rate variability of specific CM such as variable bit rate (VBR) video, the possibility of packet loss and delay within the network, and the desire to use network resources efficiently combine to make the delivery of CM data an exceptionally challenging problem. The challenge of delivering high-quality audio and video is further complicated by the fact that a single network service provider typically does not control the entire path from the source to the end client(s). One promising approach to addressing these challenges is to deploy proxy services within the network. Proxies can hide heterogeneity, reduce user start-up latency, lower the network resource usage, and adapt to fluctuations in network performance properties. In this proposal,the project director outlines research whose goal is to develop and evaluate proxy services that improve the perceived quality of CM streams seen by clients while providing low startup latencies. The awardee will focus on the development of the services themselves, the underlying resource management mechanisms required at the proxy, the programming interface required so that these services access the resource management mechanisms, and characterizations of the workloads and access patterns typically encountered by such proxies.The approach to evaluating these services and mechanisms is eclectic, relying on a combination of analysis, simulation, and experimentation with a Linux-based proxy, PRONTO, which will be further enhanced throughout the project.1