Improving ISP Locality in BitTorrent Traffic via Biased Neighbor Selection.ppt
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1、Improving ISP Locality in BitTorrent Traffic via Biased Neighbor Selection,P2P and ISPs: Not Friends,P2P applications are notoriously difficult to “traffic engineer” ISPs: different links have different monetary costs P2P applications: Peers are all equal Choices made based on measured performance N
2、o regards for underlying ISP topology or preferences,P2P and ISPs: Cant Be Foes,ISPs: need P2P for customers P2P: need ISPs for bandwidth Current state of affairs: a clumsy co-existence ISPs “throttle” P2P traffic along high-cost links Users suffer,Can They Be Partners?,ISPs inform P2P applications
3、of its preferences P2P applications schedule traffic in ways that benefit both Users and ISPs This paper gives an example for BitTorrent,Outline,Review of BitTorrent Biased Neighbor Selection: Design and Implementations Evaluations Comparison with Alternatives,BitTorrent File Sharing Network,Goal: r
4、eplicate K chunks of data among N nodes Form neighbor connection graph Neighbors exchange data,BitTorrent: Neighbor Selection,Tracker file.torrent,1,Seed,Whole file,A,5,2,3,4,BitTorrent: Piece Replication,Tracker file.torrent,1,Seed,Whole file,A,3,2,BitTorrent: Piece Replication Algorithms,“Tit-for-
5、tat” (choking/unchoking): Each peer only uploads to 7 other peers at a time 6 of these are chosen based on amount of data received from the neighbor in the last 20 seconds The last one is chosen randomly, with a 75% bias toward new comers (Local) Rarest-first replication: When peer 3 unchokes peer A
6、, A selects which piece to download,Performance of BitTorrent,Conclusion from modeling studies: BitTorrent is nearly optimal in idealized, homogeneous networks Demonstrated by simulation studies Confirmed by theoretical modeling studies Intuition: in a random graph, Prob(Peer As content is a subset
7、of Peer Bs) 50%,Random Neighbor Selection,Existing studies all assume random neighbor selection BitTorrent no longer optimal if nodes in the same ISP only connect to each other Random neighbor selection high cross-ISP traffic Q: Can we modify the neighbor selection scheme without affecting performan
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