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Peer-to-PeerTechnologies

Seminar by:

Kunal Goswami

(05IT6006)

School of Information Technology

Guided by:

Prof. C.R.Mandal,

School of Information Technology

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Outline

• Introduction • P2P Architecture • Types of P2P

– Centralized– Decentralized

• Unstructured• Structured

• Conclusion• References

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Client/Server Architecture

• Client requests data from server

• Server is the only data source

• Very successful model– WWW, FTP etc.

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Limitations of Client/Server

• Single point of failure

• Requires administration

• Unused resources.

P2P tries to address some of these limitations

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Introduction

• What is Peer-to-Peer System ?

– Sharing of resources and services by direct exchange between systems

– Peer can decide what data on their computer will be shared in the network

– Parties have same capabilities

– Peer is also known as Servent (Server+ Client)

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P2P Architecture

• All nodes are both clients and servers

– Provide and consume data

– Any node can initiate the session

• No centralized data source

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Types of Peer-to-Peer Systems

• Centralized– Napster

• Decentralized– Unstructured

• Gnutella

• Kazaa

– Structured• Freenet

• Chord

• Pastry

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Napster

• A way to share music files with peers

• Peer uploads the list of shared files onto the Napster server

• User sends search request to the server

• Server replies with the information of nodes containing the file

• User connects directly to remote peer and start download

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Napster

• Central Napster server

– Single point of failure– Prone to denial of service – Ensure correct results

• Search is centralized

• File transfer is direct (Peer to Peer)

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GNutella

• Share any type of files• Decentralized search• Request send to

neighbours• Neighbour forwards it to

its neighbours.– If TTL is over request is

finished.

• Users with matching file replies

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GNutella

• Decentralized system

– No Single point of failure

– Less Prone to denial of service

– Cannot ensure correct results

• Flooding queries– Increase network congestion

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Kazaa• Hybrid of centralized Napsters

and decentralized Gnutella.• Super Nodes acts as local search

server– Each super node act as a Napster server

for a small network– Super nodes are chosen according to

their capacity and availability

• User upload the list of shared files to a super-peer

• Super nodes exchange the list periodically

• Peer send the query to super node

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Freenet

• Napster, Gnutella and Kazaa don’t provide anonymity i.e.Peers know about each other

• Freenet provide anonymity– Impossible to know if user is initiating or forwarding

query

– Impossible to know is user is consuming or forwarding data

• Smart Query– Data flows in reverse path of query to the originator peer

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Freenet

• Loosely Structured– File placements based on hints

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Structured P2P

• Based on Distributed Hash Tables (DHT).

• DHT stores (key, value) pairs

• Nodes maintain the list of neighbors in routing table

• Core operation: Find node responsible for a key– Key mapped to node

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DHT Interface

• Node ID (similar to IP address)• Key (similar to filename)• Value (contents of file)

• Put(key, value)– Store (key, value) at specified node responsible for the

key

• Value=get(key)– Retrieve value associated with key from the node

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DHT Applications

• Distributed File Storage

• Distributed databases

• Service discovery

• Implementations of DHT interface– Chord– Pastry– Etc.

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Chord

• Nodes organized in an identifier circle based on node identifiers.

• Hash functions ensures even distribution of nodes and keys on the circle

• Lookup in table the farthest node that precedes the key

• Nodes have poor network locality

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Pastry

• Similar to Chord

• Considers network locality to minimize hops message travel

• New node needs to know a nearby node to achieve locality

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Conclusion

• P2P is thought as the distribution model of the future

• Enormous effort are being addressed to P2P

• Still many issues are to be resolved.

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References

• http://www.eecg.toronto.edu/~jacobsen/mie456/slides/p2p-mie.pdf• http://tisu.mit.jyu.fi/embedded/TIE370/oldlectureslides/

P2PIntroduction.pdf• http://www.cs.sfu.ca/~mhefeeda/Papers/p2pSurvey.pdf• http://ntrg.cs.tcd.ie/undergrad/4ba2.02-03/p4.html• http://momo.lcs.mit.edu/regions/qlrn/node1.html• http://plum.sfsu.edu/csc835/presentations/topic7/• http://www.webopedia.com/DidYouKnow/Internet/2005/

peer_to_peer.asp• http://www.oreilly.com/catalog/peertopeer/chapter/ch01.html• http://www.cs.princeton.edu/~qlv/download/searchp2p_sigm02.pdf• www.stanford.edu/class/cs347/notes/Notes11.ppt

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Thank You