Envoy: 利用自我組織機制的混合式點對點網路系統

Abstract

近年來點對點網路系統已然在網際網路上廣為使用，也影響我們分享資訊與收集資源的方法。而基本上我們可以將現存的點對點網路系統分成四大類—非結構式、結構式、半集中式以及混合式。前三種點對點網路系統都存在其優點與缺點，因此混合式點對點網路系統透過結合不同種類的點對點網路以達到截長補短的功用。特別是結合非結構式與結構式的混合式點對點網路系統，能夠兼有兩者的彈性、穩固性、搜尋效率和較低的維護成本並且避免兩者的缺點。然而現有的混合式系統仍需要一些集中化的機制或者是事先選出一些網路結點來架構結構式的點對點網路。 因此為了解決以上的問題本研究提出了Envoy，Envoy可以緊密地結合非結構式與結構式點對點網路成為一個泛用的網路平臺，更重要的是Envoy是全分散式的並不需要任何集中化的機制。為了強化結構式點對點網路的穩固性，只有穩定且高頻寬的網路結點(稱作超結點)才有資格成為結構式點對點網路的一部份。超結點從非結構式點對點網路層中自動互選出來，並且將自我組成構結構式點對點網路層。Envoy的自我組成機制確保足夠以及合適的超結點被鄰選出來。在最後我們將透過數學分析以及模擬實驗來證明Envoy的延展性和低維護成本。

In recent years, P2P (Peer-to-Peer) systems have drastically changed the way we share resources and gather information. Existing P2P systems can be roughly classified into four families-decentralized unstructured, decentralized structured systems, partial-centralized, and hybrid systems. The first three families have their own strengths and weaknesses. Therefore, hybrid systems tends to simultaneously adopt various approaches in other families to complement drawbacks of others. Some hybrid systems tend to concord features of unstructured and structured ones, such as flexibility, robustness, low maintenance and efficiency. However, existing hybrid systems adopt centralized mechanisms or pre-select powerful peers. In this paper we proposed Envoy, which organizes unstructured and structured P2P networks into a general-purpose hybrid P2P network without any kinds of centralized mechanism. To reinforce the structured overlay, only peers that meet several measures such as stability and bandwidth are eligible for serving on the overlay. Super-peers are automatically elected from the unstructured overlay and self-organized into the DHT overlay. Our self-organization mechanism ensures that elected peers are sufficient in number, stable and powerful enough. Through analysis and simulations, we prove that Envoy is scalable and low overhead even in the worst case.