异构环境下层次编码多视频源多共享信道分层组播

视频组播是许多当前和将来网络服务的重要组成部分，如视频会议，远程学习、远地展示及视频点播，随着网络传送基础设施的改善和端系统处理能力的增强，组播视频应用日益变得可行，组播视频传输中存在的主要问题是网络送资源的异构性和动态性，其使得视频流的多个接收方都达到可接受的流量特性变得异常困难，目前该问题的一个有效解决方式就是利用自适应的分层视频传输机制，在该机制中，各源产生层次媒体流，并在多个网络信道中传输。对视频会议类的多点到多点视频组播应用，信道往往被所有潜在的发送方共享，任何发送方都可在任何一个共享信道中发送其视频层次。在该多点到多点、共享信道、分层视频组播模型下，一个关键问题就是如何动态确定各视频源层次到各共享组播信道的映射，映射策略直接影响到会话整体视频接收质量和网络带宽利用率。典型的方式是顺序映射，该映射方式同等对待各发送方，但利用该方式，随源数目的增加，在各共享网络信度上会出现带宽可伸缩性问题，而且顺序映射方式无法适应网络传送资源和会话状态的动态变化。为此，该文设计了一种基于接收方反馈信息的自适应的层次映射算法，接收方周期性地将其当前感兴趣的发送方及接收速率的信息反馈给某控制节点，而控制节点就利用当前反馈信息动态地调整映射策略。经证实，该算法始终能比顺序层次映射算法获得更高的整体视频接收质量，并具有高的带宽利用率和很小的复杂度。

Layered Multicast with Multiple Multi Layered Video Sources and Multiple Shared Channels in Heterogeneous Environments

Multicast distribution of video is an important component of many existing and future networked services, such as video conferencing, distance learning, remote presentation and media on demand, and improvements in network delivery infrastructure and increases in end system processing power have made these applications feasible. The main problem complicating multicast video transport is heterogeneity and variation of network transmission resources, which make it extremely difficult to agree on acceptable traffic characteristics among multiple receivers of the video stream. An attractive solution to this problem is to use an adaptive, multi layered video transmission scheme, in which each source generates a layered media stream that is striped across multiple network channels. In multipoint to multipoint video multicast applications such as video conferencing, channels are always shared by all potential senders, any sender can send its video layers in any shared channels. In this multipoint to multipoint, shared channels, and layered video multicast model, one key problem is how to determine the mappings from video source layers onto shared multicast channels dynamically, which affects directly the whole video receiving quality of the session and the bandwidth utilization of the network. Classic approach is sequential mapping. It treats each sender equally, but introduces a bandwidth scaling problem at each shared network channel as the number of sources increases. Moreover, it can not adapt to the variation of network transmission resources and session status. In this paper, we design an adaptive layer mapping algorithm that relies on feedback from the receivers. The receivers feed back information about their current interested sender and receiving rate to one control node periodically, and the control node adjusts mapping strategy according to current feedback information dynamically. It is proved that our algorithm always achieves higher total video receiving quality than the sequential layer mapping algorithm with high bandwidth utilization and little complexity.