.torrent url of the tracker Pieces Piece length Name Length Files –Path –length
Tracker Peer cache –IP, port, peer id State information –Completed –Downloading Returns random list
Peer Operation File space allocated Connect to peers Bitfield –have(1) and not have(0) Have –Advertise pieces Interest /Not_interested –Expressing interest in the pieces published by the peer Requesting for a chunk –Request
Peer Operation Choking algorithm –Choke/Unchoke –Preferred peers –Optimistic unchoke –Snubbing behavior Prevented by Anti-snubbing. Upload to interested peers who are not choking.
Strengths Better bandwidth utilization –Never before speeds. Up to 7 MB/s from the Internet. Limit free riding – tit-for-tat Limit leech attack – coupling upload & download Spurious files not propagated Ability to resume a download
Drawbacks Small files – latency, overhead Random list of peers - naive Scalability –Millions of peers – Tracker behavior (uses 1/1000 of bandwidth) –Single point of failure Robustness –System progress dependent on altruistic nature of seeds (and peers) –Malicious attacks and leeches.
MNL’s Interest Robustness –Devise possible attacks and find loopholes –Secure against attacks Scalability –Sharing across files –Millions of users Possible extensions –Peer optimization Upload just enough to maximize your download. –Intelligent tracker Peer selection policy –Dead sites Share html content
Optimism - hack Connect to as many peers as possible Benefit –Optimistic unchoking –Probability of free download increases
Peer upload optimization Upload enough to stay within the preferred list of as many peers as possible Get the best download deal with minimum required upload download upload
Smarter tracker Classify peers Pick at random from each of these subsets No compromise on random choice Will lead to a more progressive peer network. Peers FastSlowCompleted
Interesting links Official site: BitTorrent FAQ: Torrent sites –http://f.scarywater.nethttp://f.scarywater.net –http://www.suprnova.orghttp://www.suprnova.org –http://tvtorrents.comhttp://tvtorrents.com Remember –leave your download windows open –Big brother is watching!