Architictures for Digital Multimedia On-Demand Services in Integrated Networks

网络化的进一步发展， 存储技术将使建立多媒体 按需服务器能够提供类似于 一个大都市地区的录像带出租店 网络 在这项研究中，我们调查的架构， 多媒体服务器可以允许多个订户 交互式地记录和回放多媒体对象 集成计算机网络。 我们解决了两个主要要求， 这种多用户多媒体服务器的开发：（1） 构成多媒体的每个媒体的连续回放 对象，以及（2）不同媒体的回放的相互同步 构成多媒体对象。 为了解决 连续性的要求，我们开发的接纳控制算法 多媒体服务器可以满足最大数量的 同时不破坏重放连续性的用户 对他们中的任何一个。 一种这样的算法是质量比例算法。 该方案以与媒体单元的速率成比例的速率来检索媒体单元。 平均到各自的播放速率，但使用交错 切换技术，通过该切换技术， 检索到的是微调个别承认和服务， 最佳用户数同时。 初始性能 估计表明，质量比例策略是一个命令， 与直接接纳相比， 控制策略，例如为每个磁盘头服务一个用户， 用户的循环服务。 在检索 多媒体对象，播放不同媒体的多媒体电话 对象的组件可以具有记录和回放速率 不匹配 此外，新兴的综合网络，如ATM 预期会引入抖动， 在媒体单元从服务器到媒体电话的传输中。 在 为了确保多媒体对象的同步播放， 研究多媒体服务器使用的反馈技术， 媒体电话生成的轻量级消息，称为反馈单元 并被传输回服务器以在 播放. 我们研究了各种不同的政策， 积极的，保守的，概率的，并比较他们的 视频/音频播放的性能。 初始性能 估计显示，虽然积极的政策预计将 仅在较低的播放速率下性能最佳， 预期仅在较高回放速率下表现最佳。 在 相比之下，概率政策有潜力执行 在所有回放速率下均匀良好。 策略和算法 在这个项目中开发的多媒体原型的基础上， UCSD多媒体实验室正在开发的服务器。

Further advances in networking coupled with rapid advances in storage technologies will make it feasible to build multimedia on-demand servers capable of providing services similar to those of a neighborhood videotape rental store on a metropolitan-area network. In this research we investigate architectures for multimedia servers that can permit multiple subscribers to interactively record and playback multimedia objects over integrated computer networks. We address two main requirements in the development of such a multi-subscriber multimedia server: (1) Continuity of playback of each media constituting a multimedia object, and (2) mutual synchrony of playback of the different media constituting a multimedia object. In order to address the continuity requirement, we develop admission control algorithms with which a multimedia server can satisfy the maximum number of subscribers simultaneously without violating continuity of playback for any of them. One such algorithm is a quality proportional scheme that retrieves media units at a rate proportional on an average to their respective playback rates, but uses a staggered toggling technique by which successive numbers of media blocks retrieved are fine tuned individually to admit and service an optimal number of subscribers simultaneously. Initial performance estimation shows that the quality proportional policy is an order of magnitude more scalable compared to straightforward admission control policies such as servicing one subscriber per disk head and round robin servicing of subscribers. During retrieval of a multimedia object, mediaphones that playback the different media components of the object may have recording and playback rate mismatches. Furthermore, emerging integrated networks such as ATM are expected to introduce jitter that can nevertheless be bounded in the transport of media units from servers to mediaphones. In order to ensure synchronous playback of multimedia objects, we study a feedback technique in which a multimedia server uses lightweight messages called feedback units generated by mediaphones and transmitted back to the server to detect asynchronies during playback. We study various resynchronization policies such as aggressive, conservative, and probabilistic and compare their performance for video/audio playback. Initial performance estimation shows that whereas aggressive policies are expected to perform best only at lower playback rates, conservative policies are expected to perform best only at higher playback rates. In contrast, probabilistic policies have the potential to perform uniformly well at all playback rates. The policies and algorithms developed in this project form the basis for a prototype multimedia server being developed at the UCSD Multimedia Laboratory.