Peer-to-Peer(P2P)架構讓社群內的使用者收集分散在網路各處之資源，其中最為風行的P2P系統當屬P2P檔案分享系統。P2P檔案分享系統之架構可分為集中式及分散式，而分散式架構又可細分為結構化及非結構化兩種。採用分散式且非結構化之BitTorrent-like架構，因其可擴張性較佳而廣為風行。在經驗中發現，BitTorrent-like架構在非對稱網路之下雖擁有寬裕的下行頻寬，但是其頻寬使用率卻不高，我們分析其成因如下：(1) Fractional Upward Bandwidth (FUB) 、 (2)Blockage of Acknowledgement (BoA) 與 (3)Long Physical Paths 等。而其中的Blockage of ACK問題，現今尚未有研究學者提出完整解決方案。本研究之目的，即要針對此Blockage of ACK的問題，改良網路協定中的傳輸層 (Transport Layer) 協定以提昇P2P檔案分享系統之效能。我們改用UDP作為傳輸層協定，並在應用層加入自動重建遺失之封包、決定基本傳輸單位大小及決定資料傳送速率等機制，以彌補UDP之缺陷。文中並提供了傳輸協定運作時所需參數的估計法，並且也與其它傳輸協定做效能之比較。實驗結果發現，我們設計的傳輸協定確可改善P2P檔案共享系統的運作效能。

Peer-to-Peer (P2P) architectures let participants gather resources form network and make participants acquire more computation resources than they could offer. One of the most prominent P2P systems is P2P file sharing system. P2P file sharing system could be classified into to 2 categories: centralized and decentralized model. BitTorrent-like (BT-like) model can be classified as decentralized and unstructured model. BT-like model is quit popular nowadays due to its scalability. Unfortunately, BT-like model has several shortcomings on performance over asymmetric networks, because of some problems, such as Fractional Upward Bandwidth (FUB), Blockage of Acknowledgement (BoA) and long physical paths. No complete solution is available yet to solve the BoA problem. We propose a new UDP-based protocol to alleviate this problem. Since UDP protocol is not able to guarantee the data-integrity nor to determine the proper transmission rate by itself. To offer a complete solution, we have to enhance UDP, to add extra capabilities such as packet loss recovery, segment size determination and data rate determination mechanisms. Experiments show that our proposed protocol has good improvement on performance.

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