Università degli Studi di Pisa
Dipartimento di Informatica
MASTER DEGREE
COMPUTER SCIENCE
COMPUTER SCIENCE AND NETWORKING
Peer to Peer Systems
LAURA RICCI
2/5/2011
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
1
WHY A P2P SYSTEMS COURSE?
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P2P applications have become extremely popular and currently contribute to
a vast amount of Internet traffic
The present: lots of P2P applications, developed in the last decade:
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File Sharing, the killer Application:
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Gnutella, Kazaa, E-Mule, Bittorrent
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P2P Telephony
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Skype
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P2P TV
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Sopcast
The future: several accademic research projects
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Massively Multiplayer Online Games
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P2P Social Network (SafeBook)
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
2
CLIENT SERVER VERSUS PEER TO PEER
Client Server
Peer to Peer
Asymmetric: client / server
Symmetric: no distinction among
nodes
Global knowledge of the network
Limited Local Knowledge
Single Point of Failure
Robustness
Limited Scalability
High Scalability
Detectability
Anonimity
Expensive
Low Cost
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
3
P2P SYSTEMS: THE CHALLENGES
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even if P2P systems offer interesting features, a set of challenging problems
need to be solved
what are the challenges?
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distributed models/algorithms developed in the past cannot be exploited
because of their limitations
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investigation of
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mathematical models
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distributed algorithms (routing, resource detection,...)
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linguistic constructs
taking into account
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massive amount of nodes
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high dinamicity of the system
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untrusted nodes
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
4
P2P SYSTEMS: THE CHALLENGES
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Application level P2P Overlays
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unstructured overlays:
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Gnutella, Kazaa, Bitorrent
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structured overlays:
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Distributed Hash Tables: Chord, Kademlia....
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Delaunay Overlays,...
Statistical analysis of overlays: investigation of the properties of the overlay
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Random Graphs
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Small Worlds
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Scale Free Networks
Probabilistic algorithms
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Random walks (Markov processes,...)
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Probabilistic data structures (Bloom filters,.....)
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
5
P2P SYSTEMS: THE CHALLENGES
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Startegies to cope with the high churn. P2P systems are highly dynamic,
peer can join /leave the overlay at each time. This requires mechanisms for
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statistical modelling of user behaviour
overlay reconfiguration
avoiding data loss: replication strategies
Cooperation Incentives: detection of free riders
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credit systems
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chocking algorithms
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game theory
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
6
EXAMINATION RULES
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Exam Rules:
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a written exam or a project
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oral exam can be replaced by the solution of a set of mid term
assignments
Project development is strongly recommended
Examples of projects proposed in the last years:
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analysis of the topology of unstructured overlays
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extension of existing Distributed Hash Tables
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analysis of a well known P2P client
Programming Environments for the development of the project:
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Overlay Weaver
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Peersim
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
7
THESIS PROPOSALS
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Several bachelor and master thesis completed in the last years
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XtreemOS European Project: definition of a P2P distributed directory
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P2P support for distributed virtual environments
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see subjects of past thesis at
http://www.di.unipi.it/~ricci/masterbachelorthesis.htm
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download thesis reports from
http://etd.adm.unipi.it/
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Some proposal available on the Computer Science and Networking page
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Further proposals will be available on the course page
http://www.di.unipi.it/~ricci/
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
8