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Transcript
Innovations in P2P Communications David A. Bryan College of William and Mary April 11, 2006 Advisor: Bruce B. Lowekamp P2P Communications • VoIP – Voice over IP (Internet Protocol) • IM – Instant Messaging (such as AOL) • Communications systems running over a network – not always the public Internet – Private networks (corporation, research lab) – Remote/ephemeral networks (sensor networks, meetings, battlefields, etc.) – Next generation (3G and later) cellular phones run over IP networks Client/Server Session In a Client/Server session, two nodes must use a central server to communicate Peer-to-Peer (P2P) • Instead of a central server providing services, the members of the network collaborate to provide them as peers • Each node in addition to be a client is responsible for some portion of server work • Classic example is file sharing (Napster and the like) P2P Session Innovations in P2P Communications • What has been happening in this space? – Several issues have emerged as problems – Work on many fronts to solve “hard” problems • • • • • Security Offline Message Storage Standardization NAT Traversal Improving Routing Mechanisms A Example of the Problems… • Can insert nodes with nearer values, and censor/intercept data or split a node from the overlay. Can’t let user choose location. Sybil Attack • Even if you can’t pick your Node ID, if you can occupy bulk of namespace, attack is possible Efforts to Prevent This Attack • Chord limits attack by locking ID to IP address – Bad for multiple nodes on one IP -- NATs • Our solution: Replace last 5 digits with port number: – IP is fixed, assume for example this hashes to abcdef – Client on port 5000 becomes abcdef05000 – Client on port 5001 becomes abcdef05001 • Client can have multiple nodes, but all are “near” each other -- harder to attack a particular machine. Using Limited Central Servers • Still hard to limit number of nodes, and hard to know who is authorized – A bit of a “cheat” -- use a central server, but only to get onto network – Issues a certificate when a user wants to join the network, certificate “chain” is stored in the overlay, so only need to contact to join – Small cost can be used to rate limit – Also solves the identity problem -- who gets to be “David”? – These certificates can be used for many things, including encrypting messages for offline storage Standardization and NATs • Standardization is essential for VoIP and IM • Image two phones not being able to talk to each other… • Main groups for telephony are IETF and ITU – IETF defines VoIP standard SIP – We have been chairing IETF efforts to standardized P2PSIP – Looks liklely to become a standard in the next 1-2 years • Some open questions -- use SIP for P2P messages too? What DHT? • Helps solve some problems with NAT traversal Which DHT? / Routing • Most P2P routing research is for file sharing – Only need to find an instance of a file – May give up after searching part of network if not there • For communications, can’t have false positive or negative • Anonymity is different in communication – Almost always desirable for file sharing – Sometimes good, sometimes not for communications • Using buddies or phone book can improve performance Acknowledgements • This work is supported by: – VSGC: David Bryan is supported by a VSGC graduate student research grant – Cisco Systems through a grant from the University Research Program (URP) • Thanks to others involved in this work: – Bruce B. Lowekamp, W&M – Cullen Jennings and Feng Cao, Cisco Contact Information • Email : [email protected] • Web : – http://www.cs.wm.edu/~bryan – http://www.p2psip.org