在傳統的無結構式點對點(peer-to-peer)網路中，系統必須透過訊息的廣播(flooding)或其類似方式來做資源的搜尋。Gnutella是目前最廣泛被討論的無結構式點對點網路系統，因為它使用盲目訊息廣播會產生許多重複的訊息，因此浪費了很大的網路流量。最近有研究顯示，在有50000個節點的Gnutella網路中，估計每秒總共會產生1 Gbit的網路流量。因此，有許多的研究工作在改進無結構式點對點網路中搜尋的效率，包括減少搜尋所使用的網路流量。然而，之前的研究並沒有考慮到搜尋結果的品質。
在本篇論文中，我們提出了一個利用多重樹狀結構(multiple tree-like overlay structure)來建造的無結構點對點式網路。我們利用了每個機器不同的效能，將效能越強大的機器放在每個樹狀結構越靠近根部的位置。依照我們所建出來的結構，網路流量的浪費可以大量地被減少。此外，我們也考慮到在外罩式(overlay)網路中，系統需滿足各個不同應用程式之需求的議題。我們使用Java v1.4.2來實作我們的系統，並設計數個實驗來驗證系統的穩定與效能評估。實驗的結果顯示機器可以快速且正確的加入我們的系統。即使面對大量機器的加入或離開，系統還是趨於穩定且正常運作。

Unstructured P2P systems rely on a certain kind of flooding to discover resources. A popular unstructured P2P system, Gnutella, uses the blind flooding which causes a large amount of network traffic due to redundant messages. The recent statistics results concluded that the total traffic introduced by a 50,000-node Gnutella network is roughly 1 Gbit per second. There are thus several research works on improving search efficiency (including the reduction of search network traffic) for unstructured P2P systems. However, previous studies do not address issues such as quality of search results.
In this thesis, we propose a multiple tree-like overlay structure for resource discovery in unstructured P2P systems. We exploit the heterogeneity of peers in each tree-like cluster by connecting peers with more capacity closer to the root of the tree. Based on our structure, the traffic overhead caused by pure flooding can be reduced considerably. We also address the application-specific issue in our system by tailoring each cluster according to users’ needs. We implement our system with Java v1.4.2 and validate the correctness of our implementation using prototype experiments. The experimental results show that peers can rapidly join our system; the system is robust even if peers arbitrarily join or leave.

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