Abstract: It has been proved that network coding technology can improve the overall performance of P2P streaming systems. However, the existing systems all use fixed segment granularity coding scheme for data dissemination. To overcome the limitations of fixed segment granularity coding scheme, and fit for the stochastic characteristic of real networks, this paper proposes the new concept of dynamic segment granularity, with which the peers can tune the segment granularity dynamically while encoding. Then this paper answers three questions about how to implement dynamic segment granularity, which are the coding modes, segment granularity range and output performance. Finally this paper designs a new coding scheme with dynamic segment granularity. According to the playing buffer states and the service capabilities of source peers, this scheme can tune the segment granularity of coded blocks dynamically. The experiments illustrate that this scheme can offer better QoS with network jitters or peer churns. It is believed that dynamic segment granularity shares a new idea of further improving the QoS of coding-based P2P streaming systems.

Key words: network coding, P2P streaming, dynamic segment granularity

摘要： 网络编码技术已证明能够提高P2P流媒体系统的整体性能，但是现有系统采用固定段粒度编码方式存在诸多局限性，为了克服固定段粒度的缺点，且适应实际网络的随机特性，提出了动态段粒度的新概念，即源节点在编码时能够动态调节编码块的段粒度。从编码方式、取值范围及输出能力三方面回答了升阶和降阶编码实现动态段粒度所面临的问题。最后设计了一种动态段粒度调节策略，该策略中源节点能够根据播放缓冲量和源节点服务能力来动态调节编码块的段粒度。实验表明该策略能够有效提高网络抖动和节点搅动时的服务质量。

关键词: 网络编码, P2P流媒体, 动态段粒度