CAREER: Streaming Prerecorded Continuous Media in Wireless Environments

网络的两个关键发展是：(1)互联网越来越多地用于连续媒体的流传输，其中很大一部分是预先录制的，以及(2)越来越多的无线(可能还有移动)客户端访问。视频等连续媒体对服务质量的严格要求，再加上无线链路的不可靠性，使得无线链路上的实时流媒体传输成为一个非常具有挑战性的问题。为了应对无线流媒体的趋势，研究人员提出了一种全面的理论和实用协议和机制的框架，用于将预先录制的连续媒体实时流传送到无线客户端。为了克服无线链路上的连续媒体的实时流传输的挑战，所提出的协议和机制将依赖于以下关键见解：1.对于预先记录的连续媒体，(I)在流传输开始之前确切的业务特征是已知的，以及(Ii)当流被播放时，流的段可以被预取到客户端的预取缓冲器中。在位置相关、时变和突发的无线链路错误面前，信道探测技术能够识别出传输状况良好的无线链路。现代无线系统(如第三代和第四代无线系统)的速率自适应技术允许动态地为各个正在进行的流分配传输容量。流协议的新颖思想是通过将连续媒体流的分段预取到客户端缓冲区来克服无线链路的可变性。预取是通过根据(1)客户端中的预取缓冲器内容和(2)无线链路条件(通过信道探测确定)来动态地向正在进行的流分配传输容量来完成的。通过预取(即，提前工作)，在客户端中建立预取预留，以允许客户端在无线链路上的不利传输条件期间继续回放。将加入最短队列(JSQ)策略与简单的信道探测机制相结合进行预取的初步仿真结果表明，预取带来了显著的性能提升，研究人员建议开发一个全面的框架来向无线客户端实时传输连续媒体。所提出的项目的具体目标是开发：1.单个无线小区的最佳预取机制，例如，对于给定的客户端缓冲器最小化客户端饥饿概率同时最大化所支持的流的数量的机制。研究人员将分析无线链路预取的基本权衡，并制定通话准入规则。支持异质多媒体流服务的可伸缩编码媒体的预取机制。无缝端到端流机制，用于通过有线和无线链路组成的网络将连续媒体实时传送到移动客户端。在拟议的项目的前期工作中，研究人员开发了一种预取协议，用于在基站和无线小区中的多个无线客户端之间实时传送连续媒体。这些是(1)推广和延伸教育，以及(2)基于802.11无线局域网的无线多媒体流试验床的开发。推广和扩大教育倡议的目标是吸引传统上代表性不足的少数群体进入工程学，并向代表性不足的学生，例如在职成年人提供高质量的网络教学。这将通过以下方式实现：(I)在亚利桑那州台地和NSF资助的WISE计划中为K-12学生和教师开发在线网络实验室，(Ii)利用基于网络的教具增强亚利桑那州大学扩展教育计划中的网络课程，以及(Iii)将网络课程整合到亚利桑那州专门基于网络的三所大学工程硕士课程中。流媒体试验台将作为整合研究、产业合作和学生教育的平台。无线服务质量协议，例如建议的预取协议，将在本科生(大学四年级)设计项目中实施，以补充和深化课堂知识。

Two key developments in networking are that the Internet is (1) increasingly used for the streaming of continuous media, a large portion of which is prerecorded, and (2) increasingly accessed by wireless (and possibly mobile) clients. The stringent Quality of Service requirements of continuous media, such as video, combined with the unreliability of wireless links make the real-time streaming over wireless links a very challenging problem. To address the trend towards wireless streaming, the researcher proposes to develop a comprehensive theory and a framework of practical protocols and mechanisms for the real-time streaming of prerecorded continuous media to wireless clients. To overcome the challenges of real-time streaming of continuous media over wireless links the proposed protocols and mechanisms will rely on the following key insights:1. For prerecorded continuous media (i) the exact traffic characteristics are known before the streaming commences, and (ii) while the stream is being played out, segments of the stream can be prefetched into a prefetch buffer in the client.2. Channel probing techniques can identify the wireless links with good transmission conditions in the face of location-dependent, time-varying, and bursty wireless link errors.3. Rate adaptation techniques of modern wireless systems (e.g., third and fourth generation wireless systems) allow to dynamically allocate transmission capacities to the individual ongoing flows.The novel idea of the streaming protocols is to overcome the variability of the wireless links by prefetching segments of the continuous media stream into the client buffer. The prefetching is done by dynamically allocating transmission capacities to the ongoing streams according to (1) the prefetch buffer contents in the clients, and (2) the wireless link conditions (determined through channel probing). Through prefetching (i.e.,work-ahead) prefetched reserves are built up in the clients that allow the clients to continue playback during adverse transmission conditions on the wireless links. The preliminary simulation results for prefetching using a Join-the-Shortest-Queue (JSQ) policy in conjunction with a simple channel probing scheme indicate that prefetching brings dramatic performance improvements.The researcher proposes to develop a comprehensive framework for the real-time streaming of continuous media to wireless clients. The specific objectives of the proposed project are to develop:1. optimal prefetching mechanisms for a single wireless cell, e.g., mechanisms that for given client buffers minimize the client starvation probability while maximizing the number of supported streams. The researcher will analyze the fundamental trade-offs in prefetching over wireless links and develop call admission rules.2. prefetching mechanisms for scalable encoded media that enable heterogeneous multimedia streaming services.3. seamless end-to-end streaming mechanism, for the real-time delivery of continuous media over networks consisting of wired and wireless links to mobile clients.In the preliminary work for the proposed project, the researcher has developed a prefetching protocol for the real-time streaming of continuous media between the base station and multiple wireless clients in a wireless cell.The proposed research is closely integrated with two educational initiatives. These are (1) outreach and extended education, and (2) the development of a wireless multimedia streaming testbed based on a 802.11 wireless LAN. The goals of the outreach and extended education initiative are to attract traditionally underrepresented minorities to engineering, and to provide high-quality networking instruction to underrepresented students, e.g., working adults. This will be achieved by (i) developing on-line networking labs for K-12 students and teachers in the Arizona MESA and the NSF funded WISE programs, (ii) enhancing the networking courses in ASU's Extended Education program with web-based teaching aids, and (iii) integrating networking courses into the exclusively web-based tri-university Master of Engineering program in Arizona. The streaming testbed will serve as a platform for integrating research, industrial collaborations, and students' education. Protocols for wireless QoS, such as the proposed prefetch protocol will be implemented in undergraduate (senior) design projects to complement and deepen the classroom knowledge.