Università degli Studi di Pisa
Dipartimento di Informatica
MASTER DEGREE
COMPUTER SCIENCE AND NETWORKING
P2P SYSTEMS: COURSE OUTLINE
LAURA RICCI
20/9/2010
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
1
WHY A COURSE ON PEER TO PEER SYSTEMS?


Peer-to-Peer applications have become extremely popular and currently
contribute to a vast amount of Internet traffic
Popular applications, developed in the last decade:

Sharing of Content:

File Sharing, Content Delivery Networks

Napster, Gnutella, Kazaa, E-Mule, Bittorrent, Akamai

Sharing of storage

Distributed File Systems

Thaoe, XtreemOS distributed filesystem

P2P Telephony

Skype

Massively Multiplayer Online Games

OutBack Online

Several academic projects
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
2
CLIENT SERVER VS.PEER TO PEER
Client Server
Peer to Peer
Asymmetric: client / server
Symmetric: no distinction among
nodes
Global knowledge of the network
Limited Local Knowledge
Centralization
Decentralization of Control
Single Point of Failure
Robustness
Limited Scalability
High scalability
Expensive
Low Cost
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
3
WHY A COURSE ON P2P SYSTEMS?

Even if P2P systems offer a set of interesting features, a set of
challenging problems have still to be solved

The course presents these problems, discusses the existing
solutions, presents the current research efforts for the design of
a P2P system

Which are the challenges?
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
4
P2P SYSTEMS: THE CHALLENGES



Overlay Network: logical network between the peers. Each peer has a
limited knowledge of the whole network

unstructured overlays:

Gnutella, Kazaa, Bitorrent

structured overlays:

Distributed Hash Tables,Chord, Kademlia....

Delaunay Overlays,...
Routing algorithms

Flooding, Random Walks

O(log n) routing over DHT
Statistical analysis of overlays:

Node degree

Average path length

Clustering coefficient
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
5
P2P SYSTEMS: THE CHALLENGES



High Churn Rate: P2P systems are highly dynamic, peer can join /leave the
overlay at each time:

replication strategies to avoid data loss

strategies to dinamically preserve the properties of strucured overlays
Lack of a central autorithy

security issues

distributed consistency algorithms for updating on replicated data
Cooperation Incentives:

detection of free riders

credit systems

chocking algorithms

game theory
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
6
FINAL EXAM



Exam conditions

a written exam or a project

oral exam is mandatory

project is strongly recommended
Past projects examples:

analysis of unstructured overlays

extension of existing Distributed Hash Tables
Programming Environments

P2P network simulators

Overlay Weaver

Peersim

P2P programming environments

JXTA
Dipartimento di Informatica
Università degli Studi di Pisa
Laura Ricci
7
THESIS PROPOSALS

Several bachelor and master thesis completed in the last years

XtreemOS European Project: definition of a P2P distributed directory

P2P support for distributed virtual environments

see subjects of past thesis at
http://www.di.unipi.it/~ricci/masterbachelorthesis.htm

download thesis reports from
http://etd.adm.unipi.it/

Some proposal available on the Computer Science and Networking page

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