在成功的同儕式媒體串流(peer-to-peer media streaming)系統中，節點間的合作已經成為一個重要的因素。然而，實際的觀察證實，現有同儕式系統中”自由騎士”( free-rider)的盛行嚴重地降低系統效能。在本篇論文中，我們研究現有的同儕式媒體串流誘因機制並且提出基於以物易物(barter-based)的誘因機制。透過讓節點以對稱式能力服務對方，我們所提出的機制允許在節點間直接互惠，因此得以降低鼓勵節點去貢獻資源的複雜度以及預防節點成為自由騎士。再者，惡質節點的欺騙行為可以用有效率而且輕量的方式被偵測並且加以阻隔。實驗結果顯示，我們提出的誘因機制可以大幅提升節點的合作層次和系統擴充性。

The cooperation among peers has been a key factor in the success of peer-to-peer (P2P) media streaming systems. However, practical observations corroborate the prevalence of free riders in existing P2P systems, which significantly degrade the performance of the systems. In this paper, we investigate the design of an incentive mechanism for P2P media streaming and propose a barter-based incentive mechanism. By making peers possess
symmetrical ability to serve each other, our proposed mechanism allows for direct reciprocity between peers, thereby greatly reducing the complexity of encouraging peers to contribute and preventing peers from free riding. Moreover, cheating behavior of malicious peers can be detected and thwarted in an effective and lightweight manner. The
experimental results show that our proposed incentive mechanism can boost the cooperation level among peers and thus the scalability of the system.