針對在不同種類的同儕之中增強資料散播的一種BitTorrent修改方法

Abstract

我們的目的是想要解決在BitTorrent協議內並未被重視但卻有可能發生的兩個問題：第一，過於稀有的檔案資訊的散播在BitTorrent協議內是非常重要的問題，若是沒有將這些過於稀有的資訊散發出去會使得檔案片段分布狀態並不是非常平均，因此可能會使得整體的下載速度變慢；另外，過於集中的檔案資訊的散播也是擁有相同的問題。第二，無法禁止同儕在完成檔案下載時就離開分享的行列，這樣一來上傳頻寬高的同儕如果擁有那些過於稀有的檔案資訊或是過於集中的檔案資訊的同儕在下載完所有檔案片段就不再分享，則剩下的那些同儕就有可能無法下載完整的檔案。 我們提出兩種方法來解決上述的問題。首先，我們將下載階段分成三階段，每一個階段使用不同的上傳同儕選擇演算法，如此可以有效針對過於集中的資訊的散播，且要求大家必須多分享一些時間才能離開。接著，若是BT客戶端發現有過於稀有的資訊，則會盡全力去向擁有這些資訊的同儕要求拿取。 從實驗中我們觀察到幾項結果並得到兩個結論：一、資料的散播速度的確比原本的BitTorrent快；二、整體下載速度大幅增快。這些結果符合我們原本的期望，證明我們的方法表現的比原本的BitTorrent好。

Our purpose is to resolve two problems which are important but always ignored in BitTorrent. First, it is urgent to distribute extremely scarce pieces. If these pieces do not be broadcasted, these pieces will not be spread very well and decrease download speed of peers in the swarm. Otherwise, the seriousness of dispersing concentrated pieces is the same as scarce pieces. Second, BitTorrent client cannot request peers who download completed to stay in the swarm and share with other peers. Peers with high upload rates always download completed quicker than slow ones. If they have scarce pieces or concentrated pieces and close BitTorrent client after finishing download, the other peers in downloading group will not download completed file. We provide two methods to settle previous problems. First, we divide three stages when the BitTorrent client is downloading. Our revised BitTorrent client use different unchoke algorithm in each stage. It will help owner of concentrated pieces distribute those pieces and prolong on-line duration of peers. If revised BitTorrent client find the scarce pieces, it will do its utmost to request the scarce pieces. We observe several results from the experiments and get 2 conclusions. (1) the speed of spreading data of revised BitTorrent is faster than the original one; (2) overall average download speed of revised BitTorrent is far quicker than the original one. The results fulfill our expectations. The performance of revised BitTorrent is really better than the original one.