A Scaleable Multicast Protocol to Enable Future-Generation Large Scale Multimedia Applications

一幅画胜过千言万语，加上声音和动作，就能使一幅画充满生气。因此，在各种多媒体应用中使用视频已成为20世纪90年代的一个重要发展。特别是视频点播（VOD）是许多重要应用的核心技术，如数字图书馆、远程教育、电子商务、娱乐、公共信息系统等。最简单的视频传输技术为每个服务请求使用专用流。显然，这种方案太昂贵了，而且已被证明几乎没有可伸缩性。为了大大降低这种成本，可以利用多播技术来允许多个客户端共享视频流。不幸的是，今天的多播技术是在80年代发展起来的，并没有针对这样的应用进行优化。错过组播可能意味着要等待很长时间才能收到下一个组播。这一限制最近导致了大量的研究在应用层面寻找补救措施。然而，应用程序级解决方案不能解决所有的缺点，特别是由太多的组播引起的流量拥塞。事实上，这个提议的动机是由研究者在他的最后一个NSF项目（1998年至2000年）中所做的应用级工作。该项目虽然取得了显著的成果，但也受到了标准组播的限制。最小化多播频率对于任何基于多播的应用程序都是至关重要的，特别是那些运行在公共网络（如internet）上的应用程序。实现这一目标需要对多播概念进行根本性的改变。研究人员提出了使组播树能够将整个视频发送给所有可能在不同时间订阅组播的接收者。这种新功能将显著减少必要的多播数量，从而降低网络资源需求。乍一看，这似乎是一个不可能完成的任务。但相反，这可以通过允许组播树上的路由器拦截和缓存通过的视频流来实现。数据可以转发给后续订户，进一步扩展组播树。在这个项目中，研究者建议开发一套技术，使这样一个环境在未来一代大规模多媒体应用中实用。为了评估提议的想法的潜力，研究者设计了一个初始版本的缓存多播协议（CMP）。初步研究表明，这种方法有可能彻底改变多媒体信息的传播方式。与应用程序级解决方案相比，该方案具有更高的可伸缩性和更低的成本。然而，新的通信范式要求在网络层面进行新的研究。在本计画中，研究者建议研究诸如高速缓存组织、高速缓存替换策略、组播路由算法、拥塞控制、客户端和服务器协议等问题。此外，他将实现一个原型，包括支持cmp的路由器，符合cmp标准的服务器（源）和符合cmp标准的客户端（目的地），以检查所提出技术的实用性。这个项目的意义在于推进多播技术，使多媒体应用能够大规模部署。尽管在信息技术领域取得了许多巨大的进步，但没有一个像多信息系统那样对普通公民的日常生活产生如此巨大和直接的影响。因此，这项研究的好处将惠及社会上的许多人。在教育方面，该项目将资助3名博士生。研究者在利用国家科学基金项目培训学生从事教学工作方面有良好的记录。在这些学生毕业后，他们可以帮助传播从这个项目中获得的CMP专业知识到他们的新机构。其他参加我们的高级数据库课程的研究生也可以通过在CMP测试台上试验各种新的组播应用程序来受益于这项工作。为了接触到社区成员，本研究的材料将在研究者的研究小组网站上发布。

A picture is worth a thousand words, and the addition of sound and motion can breathe life into a picture.As a result, the use of video in all kinds of multimedia applications has become an important developmentin the 1990s. In particular, Video on demand (VOD) is a core technology for many important applicationssuch as digital libraries, distance learning, electronic commerce, entertainment, public informationsystems, etc.The simplest video delivery technique employs a dedicated stream for each service request. Obviously,this scheme is too expensive and has been shown to have little scalability. To vastly reduce this cost, onecan leverage multicast technology to allow multiple clients to share a video stream. Unfortunately, today'smulticast technology was developed in the 80's, and was not optimized for such applications. Missing amulticast could mean a long wait until the next multicast. This limitation has recently led to a large bodyof research looking for remedies at the application level.Application-level solutions, however, cannot address all the drawbacks, particularly traffic congestioncaused by too many multicasts. In fact, this proposal is motivated by application-level work done bythe investigator in his last NSF project (from 1998 to 2000). The achievements of that project, thoughsignificant, were constrained by the limitation of standard multicast. Minimizing the multicast frequencyis crucial for any multicast-based applications, particularly those running on a public network such as theInternet. Attaining this goal requires a fundamental change in the multicast concept. The investigatorproposes enabling the multicast tree to deliver the entire video to all the receivers who may subscribe tothe multicast at different times. This new capability would significantly reduce the number of multicastsnecessary, and therefore lower the network resource requirements. At first sight, this seems like a missionimpossible. But on the contrary, this can be achieved by allowing the routers on the multicast tree tointercept and cache a video stream passing through. The data can be relayed to subsequent subscribers tofurther extend the multicast tree. In this project, the investigator proposes to develop a suite of techniquesto make such an environment practical for future-generation large-scale multimedia applications.To assess the potential of the proposed idea, the investigator has designed an initial version of hisCaching Multicast Protocol (CMP). The preliminary study indicates that this approach has the potentialto revolutionize the way in which multimedia information is disseminated. This scheme is much morescalable and less expensive than application-level solutions. The new communication paradigm, however,demands new research at the network level. In this project, the investigator proposes to study issues suchas cache organization, cache replacement policies, multicast routing algorithms, congestion control, clientand server protocols, etc. In addition, he will implement a prototype, consisting of CMP-capable routers,CMP-compliant servers (sources) and CMP-compliant clients (destinations) to examine the practicality ofthe proposed techniques.The significance of this project is in advancing multicast technology to enable large-scale deploymentof multimedia applications. Although many great advances have been made in the field of informationtechnology, none have had as great and direct an impact on the daily lives of ordinary citizens as multime-diainformation systems. As such, the benefits of this research will reach many people in society. In termsof education, this project will help to support three doctoral students. The investigator has a good recordof using NSF projects to train students for teaching careers. After these students graduate, they can helpto spread the CMP expertise developed from this project to their new institutions. Other graduate studentstaking our advanced databases course can also benefit from this work by experimenting with various newmulticast applications on the CMP testbed. To reach out to members of communities, materials resultingfrom this research will be disseminated on the investigator's research group website.