【作者】 罗治国；

【导师】 王行刚；

【作者基本信息】 中国科学院研究生院（计算技术研究所） ， 计算机系统结构， 2004， 博士

【摘要】 流媒体内容分发网络是保障流媒体QoS的有效方法。流媒体传输和流媒体分发是流媒体内容分发网络的两部分功能,它们从不同的角度提高流媒体的QoS。流媒体传输是指采用特定的机制使流媒体服务器能够根据网络状态调节发送速率,保证用户观看的媒体质量尽可能高而且稳定;利用流媒体分发可以降低网络负载、避免主干网的拥塞,使用户的启动延迟更短、流媒体的质量更加稳定。本文从这两方面展开了研究,其主要贡献包括:(1)为了平滑连续帧的质量,提出了基于最高位平面的帧质量平滑机制(HBPFS)。(2)为了使连续GOP的质量保持稳定,在分析和研究MPEG-4 FGS流媒体位平面编码特征的基础上,根据FGS位平面R-D模型和HBPFS帧质量平滑机制得到GOP的位平面R-D模型,进而提出了GOP常质量带宽分配机制,实现了常质量GOP带宽分配的静态算法和动态算法。(3)为了在有丢包的Internet环境下获得平滑的质量,提出了GOP质量平滑、帧质量平滑的两阶段质量平滑机制以及FEC差错控制机制,进而提出了流媒体自适应传输系统。(4)针对GOP质量平滑,提出了三种GOP平滑机制,分别为基于总带宽的GOP平滑机制(BWGS)、基于增强层的GOP平滑机制(ELGS)和基于最高位平面的GOP平滑机制(HBPGS)。(5)针对分层编码的流媒体,结合流媒体预取提出了一种前缀优先的分层缓存策略。它能有效地降低用户的启动延迟,同时对系统的字节命中率和网络传输成本的影响较小。通过预取算法,代理服务器主动地从原始服务器预取内容,保证用户能够持续地获得服务,当条件不能满足时可以与用户进行QoS协商。(6)针对非分层编码的流媒体,提出了一种基于传输成本的流媒体缓存替换算法——基于传输成本的最小缓存效用(TCBSCU)算法,并将其统一到前缀优先的分层缓存策略中。TCBSCU能够针对各种传输调度方法对系统的传输成本进行优化,同时也降低了对原始服务器带宽的消耗。(7)为了提高流媒体缓存机制的有效性,在多代理服务器协作方面,提出了基于传输成本的流媒体代理服务器组(TCBSPG)的系统组织,并对系统的传输成本进行了性能优化,提出了基于缓存效用的缓存替换算法、基于联合缓存效用的缓存空间优化分配算法以及确定缓存内容分布的方法。更多还原

【Abstract】 Streaming by content distribution network (CDN) is an effective way to guarantee quality of service (QoS) of streaming media. Streaming media transmission and streaming media distribution are two functional modules of streaming media CDN, which improve QoS of streaming media from different aspects. Streaming media can adapt to the variety of network by certain streaming media transmission mechanisms, assuring QoS perceived by users as high and stable as possible. Streaming media can be distributed to edge network by distribution schemes so as to reduce network payload, avoid backbone network congestion, shorten users’startup latency, and steady the QoS of streaming media. The paper covers these two aspects, and main contributions are:1. To smooth the quality of continuous frames, highest bit plane based frame quality smoothing (HBPFS) scheme is proposed.2. Based on analysis and study of the characteristics of MPEG-4 FGS bit plane encoding, a GOP bit plane rate-distortion (R-D) model is deduced according to the FGS bit plane R-D model and the HBPFS scheme. A constant GOP quality bandwidth allocation scheme is presented. Offline and online algorithms are provided to make the quality of continuous GOP constant.3. An adaptive transmission system for MPEG-4 FGS streaming media is put forward based on the combination of two-phase quality smoothing scheme proposed and error control scheme. The system adjusts the sending bandwidth of every frame using GOP quality smoothing scheme, frame quality smoothing scheme and FEC error control scheme, in order to guarantee stable quality of continuous GOPs and successive frames in a GOP in the unstable and lossy Internet.4. With regard to the GOP quality smoothing scheme, three GOP quality smoothing strategies are brought forward, which are bandwidth based GOP quality smoothing (BWGS), enhancement layer based GOP quality smoothing (ELGS) and the highest bit plane based GOP quality smoothing (HBPGS) respectively.5. A prefix preferential layered caching strategy with prefetching algorithm is proposed for layered scalable coded streaming media. It can reduce users’startup lantency effectively with little effect on the byte hit ratio and network transmission cost of the whole system.更多还原