N6Lookup( title ) Client

Transcription

1 CS 640: Introduction Networks AdityaAkella Peer-to-Peer Lecture 24 -to Computer p2p Uses Downloading: Searching Centralized Flooding Smarter Routing file of sharing p2p The (Freenet, (Gnutella, flooding -what Whole-file index techniques (KaZaA, Road etc.) (Napster, works vs. ) well, chunks etc.) Ahead Challenges servers Hard Fairness, state vs. freeloading, arbitrary (backups!) nodes vssoft-state security, what (caches) doesn t? Quickly Dozens 35 Audio/Video 29% Internet million of grown all or P2p American hundreds Internet transfer in file-sharing popularity users adults of now dominates use US! P2P networks applications traffic --the 1

2 Chunk Based Whole FileWhat s BitTorrent Napster CentralGnutella Flood out there? KaZaA (bytes, chunks) Super-node floodnot DHTs edonkey 2000 Freenet Route Key= title Value=MP3 Publisher Publishing/Searching data N4 N1N2N3 Internet N5? N6Lookup( title ) Client Search Needles Searching Whole track names? vs. for Haystacks Searching (e.g., from expressiveness word? p2p Attributes? gnutellaor 1981 Regular top that 40, p2p Whole-text nobody s or expressions? google?) an obscure heard search? File punk of? 2

3 Common Join: Publish: Search: Fetch: how how Primitives: to Framework to do I to I begin I retrieve find advertise participating? a file? a file? my file? HistoryNapster: Centralized 1999: Peaked Jul Join: Publish: Search: 2001: Sean at 1.5 Database: Fanning million shuts launches simultaneous Overview Fetch: stores on the get reports startup, query the requested the file list client server directly of file files contacts down => from to return Napster central peer users someone server that Napster: Publish I have X, Y, and Publishinsert(X, Z! ) 3

4 Napster: Search Where is Fetch file QueryReply A? search(a) --> Pros: Cons: Simple Search Controllable Server Napster: maintains scope (pro is O(1) or lot Discussion Single point does of all failure processing con?) of state History: Query Soon In Join: Publish: Search: Gnutella 2000, 2001, many Gnutella: many J. other Frankel protocol clients: and enhancements T. Bearshare, Pepper Overview Fetch: become when/if Ping-Pong TTL Flooding: get limits its no startup, ask found, the need neighbors neighbors, protocol propagation file reply directly to who contacts sender. ask from their a peer from few Morpheus, neighbors, including other Nullsoftreleased nodes; ultrapeers LimeWire and these on... 4

5 I have file A.Gnutella: Search Where Reply Query is file A? I have file A. Pros: Fully Processing de-centralized Gnutella: distributed each node permits Discussion TTL-limited Cons: Search Nodes For re-issue scalability, leave time scope query search often, later O(???) does O(N) network works NOT search well unstable powerful every for haystacks. node. search May semantics have to Gnutella Smart Query No But.. Join: Publish: Search: Fetch: point amongst simultaneously didicatedserver not become get X startup, send themselves. KaZaA: all Napster peers list one query from file Flooding: client of itself are directly to files multiple equal! supernode, contacts to Overview from supernode peers a peer(s); supernodesflood supernode... can fetch may query at some 5

6 KaZaA: Network Super Nodes Design KaZaA: File Insert I have insert(x, ) Publish X! KaZaA: File Search Where is file search(a) --> Replies A?Query search(a) -->

7 More Use than KaZaA: one node may have Fetching How Must Same KaZaAuses Alternatives: same Hash be tell? filename of able file UUHash: to MD5, not identify necessarily SHA-1 fast, similar but same not files requested secure file... with not file... Get Alternative: to bytes fetch? [ ] Erasure from Codes A, [ ] from necessarily B Why Superpeerselection Query Caching Many Stability superpeers? consolidation connected nodes and may Superpeers How long Propagating Requires than you ll long answering effect you ve be network a around. query it been yourself stability to is on a sub-node time-based is have a good only would predictor a few take files more of b/w how Cons: Pros: Tries Rumored Bandwidth Host Why to KaZaA: Computational Availability take to this take into important? into account (?) Resources account Discussion node network heterogeneity: Similar Mechanisms Still Can no behavior freeload real guarantees easy easily to Gnutella, circumvent on search but scope better. locality or search time 7

8 Key Focused Popularity Motivation: BitTorrent: exhibits temporal History Has E.g., Distribute Single Crowds) movie/game some Slashdot publisher, on real publishers Efficient the release effect, samefile multiple CNN Fetching, to downloaders on all locality 9/11, peers not new (Flash Searching: Swarming: Big Publish: Search: Join: Fetch: Chunk BitTorrent: Run Out-of-band. a tracker E.g., server. use Overview few Anti-freeloading the peers. chunks differences file large contact based Download you files focus have want. downloading centralized from to chunks mechanisms them. Napster: of tracker server, the Google file from to your find get a peers. a tracker list Upload of for BitTorrent: Publish/Join Tracker 8

9 BitTorrent: Fetch Employ BitTorrent: A Be Otherwise Also him download optimistic: will downloading Tit-for-tat sharing allows let the from no you fastest occasionally one when Sharing to from would discover they N some of ever reciprocate those better let start! other Strategy freeloaders download strategy peers people to from Pros: Cons: Works Gives Pareto Central (Tracker freeloaders BitTorrent: peers reasonably incentive well to in share Discussion you with know other Efficiency tracker is from approaches.) a design your server relatively projects. choice, needed practice not weak Could resources; to a requirement, condition bootstrap easily avoids combine swarm as 9

10 Many Lessons each centralized, Single Flooding Underlying Not Need different P2P: flooding, styles; swarming, Summary Privacy Structure routing all incentives points learned: nodes and messages can network security of are provide failure to equal to discourage topology are everyone theoretical are remember important is freeloading important is unstructured bad bounds pros and and and guarantees cons structured of 10