导　　师： 顾君忠

学科专业： G1102

授予学位： 博士

作　　者： ;

机构地区： 华东师范大学

摘　　要： 随着宽带ip网络和视频编解码技术的发展，网络视频服务正在成为影响人们生活和工作的一种重要信息服务。基于ip网络的视频服务主要分为两类：视频直播和视频点播。网络视频直播提供类似传统广播电视服务的单源、多接收者服务，能有效覆盖在ip网中广泛分布的用户群；而网络视频点播则突破了传统广播电视服务中用户只能被动接收视频节目的服务模式，为用户提供可自主选择视频节目和访问时间的服务。ip网络包括各种基于ip协议簇构建的网络，在数据传输方式上主要有单播和组播两种。单播是ip网络提供的基本数据传输方式。当采用ip单播传输技术来实现单源、多接收者服务时，存在着相同数据包在同一网络链路中多次重复传输的问题，传输效率较低。组播则能有效的解决这一问题。其利用网络传输设备——路由器来实现数据包的分发，使同一数据包在每条物理链路上都只传输一次，从而大量节省网络带宽。为了讨论的方便并不失一般性，本文分别以当前只支持单播的internet和能支持组播的ip网为背景来进行网络视频服务实现技术研究。本文研究内容包括2部分：1)在现有只支持单播的internet中实现高性能视频直播服务的技术研究；2)在支持ip组播的网络中实现高性能视频点播服务的流调度算法研究。 网络视频直播服务是典型的单源、多接收者服务，因此，ip组播传输技术是实现网络视频直播服务的理想方案。但对于现有的internet网，需要升级正在运行的路由设备才能支持ip组播。这种升级目前还难以大范围实现。为了能在现有只支持单播的internet中实现高效率的视频直播服务，研究人员提出了应用层组播传输技术。应用层组播系统基于单播传输技术，利用参与组播组的用户节点代替ip组播路由器来实现数据包的分发，能获得类似ip组播数据传输的高效率。并且由于这种技术对服务资源需求较少、易于部署，成为当前internet视频直播服务实现技术的研究热点。但现有的大多数应用层组播算法在构建应用层组播覆盖网时，都没有充分利用物理网络拓扑信息，导致构建出来的应用层组播覆盖网性能不高。另外，为了解决ip地址不足而大量应用的nat设备和为了安全而部署的防火墙，可能阻断用户间的直接连接，这也是应用层组播实现时需要解决的一个重要问题。本文对上述问题进行了深入研究，提出了基于物理拓扑导向的高性能应用层组播方案hham和新的对称nat穿透算法ps-stun。 网络视频点播服务与网络视频直播服务的主要区别在于：视频点播服务中，不同用户对同一视频的访问时间不同。因此，在支持ip组播的网络中实现视频点播服务时，不能像实现视频直播服务那样直接利用ip组播传输信道。静态流调度算法通过将视频分段并将这些视频段在多个组播信道中进行合理调度，从而有效利用组播信道来减少大量用户点播热门视频时的网络带宽消耗。这类算法的性能主要体现在传输某视频使用的组播信道数(带宽)与用户访问该视频所需等待的时间之间的关系：使用相同的组播信道数(带宽)，能获得越小的用户等待时间的算法性能越高。但对于特定的静态流调度算法，传输视频使用的组播信道数(带宽)越多，用户访问该视频的等待时间必然会越短。现有的静态流调度算法为了在使用固定的组播信道数(带宽)时获得最小的用户等待时间，都会静态最优地使用为视频分配的组播信道。因此，一旦开始进行视频传输，就难以动态增加或者减少该视频使用的组播信道数(或网络带宽)。对于视频点播服务系统来说，为了减小整个系统总的用户访问视频等待时间，通常期望给最热门的视频节目分配最多的组播信道数。但视频热门度是动态变化的，现有的静态流调度算法不具有根据热门度变化来动态改变所使用的信道数的能力，从而降低了整个服务系统的性能。另外，这类算法获取高性能时通常都采用具有贪婪特征的用户端视频数据下载策略，对用户端接入带宽和缓存资源要求都较高。为了解决这些问题，本文提出了分别用于cbr编码视频和vbr编码视频的高性能自适应流调度算法，以及能满足用户资源限制的流调度算法改进方法。通过理论分析和性能仿真测试得出：本文提出的算法不但能有效满足需求，且在性能方面优于现有同类算法，对于在ip组播网中实现高性能的视频点播服务具有较大的实用价值。 本文对在ip网中实现高性能视频服务的一些关键性技术进行了深入研究，并对现存的一些问题提出了有效的解决方案。具体的各项研究内容如下： 1．在实现网络视频直播方面，本文提出了新的基于物理拓扑导向的应用层组播方案hham。该方案有效利用物理拓扑信息来构造高性能的应用层组播覆盖网，能在现有的internet中实现用户对直播视频数据连续稳定的接收和播放，并具有如下特征：较小的数据源到每个用户节点的传输延迟；节省网络主干带宽；用户端稳定的视频流接收；满足分布广泛的大规模用户的访问需求。 2．针对nat设备对用户间直接连接的阻断问题，本文分析了现有nat穿透算法在处理对称nat时的不足，并提出新的对称nat穿透算法ps-stun。ps-stun算法根据对称nat在运行中的统计特征，使用基于测量的预测技术和合理的扫描方法来实现对这类nat的穿透。经过在实际网络环境中的测试证明，该算法能有效的提高位于不同私有网络内的用户间建立直接连接的成功率。 3．在实现高性能视频点播服务方面，本文全面分析和总结了适用于固定位率(cbr)编码视频的静态流调度算法，提出了具有自适应能力的流调度算法。通过形式化理论分析和性能测试，该算法能有效满足根据视频热门度变化来动态调整带宽消耗的需求，且在性能上优于现有同类算法。为适应客户端设备的多样化发展，本文还提出了能应用于资源受限客户端的流调度算法改进方法，该方法能在有效满足用户资源限制的情况下尽量节省网络带宽。 4．针对’vbr．编码视频与cbr编码视频的不同特征，本文提出了一种用于 vbr 编码视频的具有带宽可伸缩能力的流调度算法。基于广泛被用于网络传输测试的视频，本文进行了性能仿真试验。这些试验结果证明了本文提出的流调度算法能具有高性能，对于实现高性能的视频点播服务具有较大的实用价值。 通过对本文提出的多种算法进行形式化计算和仿真测试，结果都显示出它们能有效的解决相关问题，并具有较高的性能。因此，本文的研究成果对于在ip网中实现高性能的视频服务具有较大的实用价值。 With the development of Broad Band and video coding//decoding technology, /(IP/)Network-based video service is becoming a more and more important service effecting on people's life and work. /(IP/)Network-based video services mainly include video live broadcast and video on demand. Like the traditional radio or television broadcast service,/(IP/)Network-based video live broadcast provides single-source multi-receivers service, which can effectively overlay network users distributing extensively, while /(IP/)Network-based video on demand provides the video service that allows users to choose the video program and access time on their own initiative, which breaks through the service model that users can only receive passively as in the traditional way. IP networks contain the networks constructed with TCP//IP protocols, and whose data transmission method can be unicast or multicast . Unicast is the basic data transmission method on IP networks. When using unicast to realize the single-source multi-receivers service, each data packet may traverse the same link multiple times, and this decreases the data transferring efficiency. On the other hand, the multicast router can distribute the data packets and keep each data packet traverses the same link only one times on multicast networks. So using multicast can reduce a great deal of consumption of bandwidth for the type service. For the sake of discussion without losing its generality, our researches on realization technologies for video services are based on the Internet that only supports unicast and any IP networks that can support multicast. These researches contain two parts: 1/)To realize highly efficient video live broadcast service on the Internet; 2/)To realize high-performance video on demand service on IP multicast networks. Since video live broadcast service is a typical single-source multi-receivers service, IP multicast transmission technology provides an ideal solution for it. But multicast network is difficult to be deployed all over the Internet at present. In order to realize highly efficient video live broadcast service on the current Internet, application level multicast technology with similar high efficiency that provided by multicast technology is proposed. This technology utilizes user nodes that join multicast groups to realize the data transmission instead of multicast routers on multicast networks. It can reduce a great deal of consumption of concurrent streams from severs and trunk bandwidth of video live broadcast service on the Internet. Therefore it becomes a research hotspot. But without utilizing topology information of physical network effectively, most existed application level multicast algorithms can't build high-performance logic application level multicast networks. In addition, both a large amount of application of NAT equipments using to solve the problem of IP address shortage and deployment of firewalls for network security might interdict the direct connection between users, which is also an important problem that needs to be solved in application level multicast. Aiming at these problems, this paper has done a lot of researches and proposes a new physical topology oriented application level multicast solution of HHAM and a symmetric NAT traversal algorithm of PS-STUN. The characters of users accessing in Network-based video on demand service are different from those in video live broadcast: Different users may access to the same video at different time in Network-based video on demand service. So, the multicast channels can't be used in video on demand service like to do it in video live broadcast. With the segmenting video and scheduling these segmentations in multi-multicast channels, Static stream scheduling algorithms can make use of multicast channels to realize highly efficient transmission for hot videos. The main performance in these algorithms is demonstrated by the relationship between the number of channels /(network bandwidth/) assigned to broadcast a video and the client waiting time. It's higher performance of the algorithm that can bring fewer client wait time with the given number of channels /(network bandwidth/) for a video. However, to a given algorithm, the more channels /(network bandwidth/) assigned to broadcast a video can bring fewer client waiting time. For improving the performance, most of the existing static broadcasting algorithms use the channels assigned to each individual video statically. It would be impossible to increase or decrease the number of channels if it has being broadcasted. In order to meet most clients' requirement for minimal waiting time in whole system, VOD service system usually assigns more bandwidth to hotter video. But with the hot degree on a video changing dynamically, the static number of assigned channels is not optimal, and the performance of the whole system will be degraded. And there is another problem with this kind of algorithms that they are exigent with user resources. To solve these problems, this paper proposes some high-performance stream scheduling algorithms including improving stream scheduling algorithms that meet limit of users' resources and adaptive stream scheduling algorithms for CBR coding video and VBR coding video respectively. Through theoretical analysis and performance simulation testing, algorithms proposed in this paper is of high performance prior to current algorithms, which can effectively economize consumption of network bandwidth and concurrent streams from servers in Network-based video on demand service system. In total, this paper has done researches on some key technologies of high-performance Network-based video service and proposes some practical solutions on existing problems. These achievements are described as follows: 1. This paper proposes a new physical topology oriented application level multicast solution -HHAM. By effectively utilizing physical topology information to build a high-performance application level overlay network, HHAM aims at making users receive and play live broadcast video continuously and steadily on the Internet. It is characterized by following: less transmission delay between data source and every user node; economizing bandwidth of trunk network; steadily receiving video flows at user terminals; meeting large-scale access demands of users distributing extensively. 2.To solve the problem of NAT, this paper analyzes shortages of STUN algorithm deal with symmetric NAT and proposes a new symmetric NAT traversal algorithm PS-STUN. According to the dynamic and statistical characteristics of symmetric NAT, PS-STUN do symmetric NAT traversal by using forecasting technology based on measurement and scanning methods. Proved by testing in real network environment, this algorithm can improve effectively success rate of connecting directly between users in different private networks and increase transmission efficiency of the whole system consequently. 3.As to realizing high-performance video on demand service, this paper completely analyzes and summarizes static stream scheduling algorithms proper for CBR coding video and proposes an adaptive stream-scheduling algorithm. The algorithm proposed in this paper excels existing algorithms of this kind in performance via formal theory analysis and contrast in performance test. In addition, an improved stream scheduling algorithm was proposed, which can apply to clients with different limited resource. 4.Aiming at different characters between VBR and CBR coding video, this paper proposes a new scalable stream scheduling algorithm applying to VBR coding video. Based on videos used in simulation testing on network transmission, we do simulation testing on performance. These experimental results prove that the stream-scheduling algorithm proposed in this paper is high-performance. It has highly practical value for realization of video on demand service. Via formal calculation and simulation testing of these algorithms proposed in this paper, the results show their validity of solving related problems. These achievements are practically valued in realizing high-performance Network-based video service.

关 键 词： 网络视频直播 网络视频点播 组播 应用层组播 流调度算法 周期广播算法 视频编码

分 类 号： [TN948.64]

领　　域： [电子电信] [电子电信]