Introduction Lack of cooperation is one of the key problems that confront today's P2P systems. –Free riding –Starvation This proposal intends to –analyze various incentive mechanisms/dishonest manipulation –extract the common pro-incentive parameters, and –propose to incorporate these pro-incentive parameters in information exchanges in the P2P streaming protocols. NOT intend to specify a particular incentive mechanism in the P2P streaming protocol. 2
Reward based on Peer Contribution A typical metric for peer contribution: –The amount of upload a peer has contributed. –E.g., BitTorrent uses a bilateral mechanism: tit-for-tat. Contribution-based approach is vulnerable to strategic manipulation by peers. –E.g., the Discount Parameter (DP) attack is an incentive threat that exploits the tit-for-tat based unchoking. –DP: Determines the degree to which the payoff of each move is discounted relative to the previous move –If the DP is small, players might defect and not worry about future consequences –In p2p systems, Piece Rarity is a DP 3
Alice Bob Connects to Bob, Request for download piece X Determines whether Alice is a good uploader ?? Ok send X.. Request for rarest piece Alice has: Y Bob loses a round of download Alice starts looking for other peers Alice : Y is a rare piece. None of the pieces Bob has is rare enough compared to X ALICE UNCHOKED BOB CHOKED 4
Starvation All peers have all pieces, except a few. Origins: –Choices made by peers in piece and peer selection –Positive Discrimination Use of rarest first approach Can positive discrimination guarantee safe state? –Peers benefit from under-reporting, increasing demand for pieces they have and faster completion. Why do we have Under Reporting Peers (URPs): –The orthogonal treatment of Piece Rarity and Peer Selection 5
DP/Starvation Remedy Peer selection not only depends on the uploading bandwidth of the candidate peers, but also how valuable the pieces they have uploaded are. Piece Rarity parameter –local availability (in the target swarm) of a piece: a rarer downloaded piece has more value to the swarm –# of upload slots a candidate peer has: long term benefit can be expected from peer with more uploading potential –completion factor (i.e., ratio of # of pieces that a peer has to total #of pieces of that file) of the candidate peer: peer with high completion factor is a good one to maintain a good upload/download relation with. –the contention in the swarm (i.e., the ratio of total # of peers to total # of seeds): high contention implies more strategic value of a piece. 6
Pro-incentive Protocol Parameters Important for peers to collect pro-incentive parameters to support incentive mechanisms and propose to include the parameters in Tracker and Peer Protocols. –no_upload_slots: a peer's upload bandwidth (i.e., number of upload slots a peer has). –bytes_uploaded: total amount of data that a peer has uploaded –bytes_downloaded: total amount of data that has been downloaded from a peer –chunk_nos: total # of chunks of a file that a peer has. –seed_nos: total # of seeds. –peer_nos: total # of peers. –chunk_copies_swarm: chunk availability, i.e., total # of copies of a chunk available in the swarm. 7
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