建立快取策略合作之位置知覺P2P系統

Building a Locality-aware P2P System Based on Cache Collaboration

柯佳宏(Chia-Hung Ko)

指導教授 ： 曾黎明

國立中央大學/資訊電機學院/資訊工程學系/碩士(2006年)

摘要

傳統的用戶端-伺服器架構讓使用者能夠下載所需資料，但因伺服器頻寬固定，限制住所能服務的使用者數量以及傳輸速度。雖然以分散式伺服器架構可再提升其效能，但效果有限，伺服器頻寬不足仍是這個架構的主要瓶頸。同儕網路 (Peer-to-Peer；P2P) 技術對於伺服器服務的頻寬限制，提供了一個解決方法。P2P技術讓所有下載中的使用者同時擔任伺服器角色，互相分享已經下載的資料，使用者在進行下載任務時，等同建置相同數量的伺服器。
BitTorrent (BT) 為目前同儕網路中，熱門且有效的分散式檔案傳輸技術。BT以優秀的下載策略，如稀有片段先取（Rarest First），是否阻塞演算法（Choke Algorithm）等，來達到順利分享的目標。但是因為BT使用綜觀全局的方法來考量下載，使用者不具位置知覺 (Locality Aware) 能力，無法區分其它使用者所屬網域，造成大量的跨網域流量。使得網路服務提供者必須採取管制的策略以維護其它服務。
因此本論文提出如何修改 BT 建立一個「快取策略合作之位置知覺P2P系統」。系統中有兩個主要的角色：進階跟蹤伺服器 (Enhanced Tracker) 會分配使用者所屬網域的Super Peer Cache (SPC) 及適當的使用者清單；Super Peer Cache 能協同所屬網域內部使用者分工合作地將檔案從外部取一份回網域內，進而進行內部交換分享，達到節省跨網域流量之目的。此外Super Peer Cache 亦作為內部使用者之檔案備援快取，並採用有效率的以編碼為基礎的快取替代演算法，避免下載完成之使用者離開，造成網域內部檔案部份內容消失。在相容性方面，原始 BT 軟體使用所提出的進階追蹤伺服器，亦能達到節省跨網域流量的效果。

關鍵字

位置知覺 ； 同儕網路 ； 快取策略合作

並列摘要

Client-server structure is widely applied in variety of services today. Though the cost for deploying this structure is relatively inexpensive, limited bandwidth is the main problem. Peer-to-Peer (P2P) technology gives us a hand for solving this shortcoming described above. Clients in P2P network are not just clients but also act as servers.
Recently, BitTorrent (BT, P2P system) has become popular because of its efficiency. The reason why BT works so well is due to its content-exchange policy inclusive of “choke algorithm”, ” peer selection”, and ” piece selection”. There’s no doubt BT achieves the goal for file content delivery, however, lack of locality-aware causes huge cross-domain traffic. In Internet Service Provider’s opinion, since P2P traffic is so huge that to be out of control, the best way to maintain other service is to take restrictive policy. Hence we propose a new method named “Locality-aware P2P system based on cache collaboration” to solve this problem. In this system,“Enhanced Tracker” appropriately dispatches peer list while “Super Peer Cache (SPC)” makes peers become locality-aware and work collaboratively. In this way, goal for saving cross-domain traffic is achieved. Further, the SPC provides a backup support and applies encoding-based replacement scheme to avoid specific file blocks disappear due to peer leaving.

並列關鍵字

Peer to Peer ； Cache collaboration ； Locality-aware ； BitTorrent

參考文獻

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