點對點視訊串流系統在近幾年來快速崛起，然而點對點系統中卻有一些問題有待解決，例如：免費享用、公平性、網路非預期變化，尤其在沒有免費享用控制的點對點自願性分享系統裡，太多的使用者拒絕貢獻，只希望接收資料。為了避免上述各項問題，本文提出了點數記錄的鼓勵機制，並使用打報告、公開金鑰密碼技術以及多重來源技術，使得在系統中的使用者不得不去分享資料。在提出來的方法中，使用者願意分享越多資源，就可在建立系統拓樸時越接近伺服端，並得到更多點數、擁有較少的封包遺失風險，進而得到較好的串流品質。免費享用者為拒絕分享或是謊報分享資源能力的使用者，藉由每個使用者所擁有的點數來做是否為免費享用者的判斷。為了防止使用者有不法行為，此機制也使用了公開金鑰密碼技術來保護分辨真假點數，並且可用以追蹤點數經過的路徑。使用本文所提出的機制，可讓百分之九十無上傳使用者的系統中減少百分之八十五無上傳使用者。而在百分之九十的謊騙使用者中可減少百分之九十四的謊騙者，且系統實際所得串流分支比率幾乎為百分之百，而距離伺服端最遠的節點數約為五到六，遠小於沒使用機制的節點數四十。並且系統拓樸的管理以及傳送串流分支的工作量可減少，系統資源也可有效利用。

Peer-to-Peer (P2P) technology is a kind of decentralized framework which is applied to file sharing and video streaming in Internet predominantly. However, there are some problems, like free-riding, fairness, unexpected fluctuation, in P2P systems. Especially, without free riding controlling, many users stop contributing data and only want to receive data. To avoid these problems, a credit-based incentive mechanism using sneak, public-key cryptography and multi-source technique is proposed to make peers in system have no choice but to share data. In the proposed incentive mechanism, the concept of credit is employed. If a peer can contribute more bandwidth for sharing stream, it is arranged closer to video server, to get more credit in return, have less packet loss risk and receive better stream quality. Free-rider is a peer who denies contributing or contributes less resource than it registers to the system. In the proposed mechanism, free-riders are judged by the credits of each peer. In order to prevent illegal behaviors, the public-key cryptography is used for differentiating real and fake credit, also used for tracing credits. Experimental results show that when 90% peers are zero uploading peers, using the proposed mechanism can reduce 85% of zero uploading peers. When 90% peers are cheating peers, adopting the proposed mechanism can reduce 94% of cheating peers. System utility is usually about 100%. Maximum number of hops to video server is about five to six which is much smaller than without using the proposed mechanism, about 40 hops. The loads in managing system topology and delivering sub-streams are reduced. Besides, the resource of the system is used effectively.

Chapter 1 Introduction 1
Chapter 2 Related Work 3
2.1 Multi-source Structure 5
2.2 Sub-stream Quota and System Load 6
2.3 Free-rider 7
Chapter 3 The Proposed Incentive Mechanism 8
3.1 Tit for Tat 8
3.1.1 Punishment on Zero Uploading Peer 9
3.2 Credit 10
3.3 Sneak 15
3.3.1 Parent Cheats Child in Sub-stream 18
3.3.2 Child Cheats Parent in Credit 19
3.4 Credit Recognition 20
3.5 Peer Position Placement 28
3.6 Peer List and Recovering 32
Chapter 4 Simulation 36
4.1 Simulation Parameters 36
4.2 Evaluation 37
4.2.1 Zero Uploading Peers 38
4.2.1.1 Terminated Zero Uploading Peers 39
4.2.1.2 Number of Peers Being Rejected 40
4.2.1.3 Number of Legal Peers in the System 41
4.2.1.4 Number of Child Peers of Video Server 43
4.2.1.5 Number of Terminated Legal Peers 45
4.2.1.6 Maximum Hops to Video Server 46
4.2.2 Cheating Peers 47
4.2.2.1 Terminated Cheating Peers 47
4.2.2.2 Number of Legal Peers in the System 48
4.2.2.3 Number of Child Peers of Video Server 50
4.2.2.4 System Utility 51
4.2.2.5 Number of Terminated Legal Peers 53
4.2.2.6 Maximum Hops to Video Server 54
4.2.3 Two Types of Free-riders 55
4.2.3.1 Terminated Free-riders 55
4.2.3.2 Number of Legal Peers in the System 56
4.2.3.3 Number of Child Peers of Video Server 57
4.2.3.4 System Utility 58
4.2.3.5 Number of Terminated Legal Peers 58
4.2.3.6 Maximum Hops to Video Server 59
Chapter 5 Conclusion 61
References 62

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