A short overview of
p2p technologies
Marcelo Dias de Amorim
Laboratoire LIP6
Université Pierre et Marie Curie
http://www.lip6.fr/
Caen – Le 11 Juin 2003
Plan

Introduction
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Models
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Example of applications
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Some systems
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References
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Definitions
P2P is a class of applications that take advantage of
resources – storage, cycles, content, human presence –
available at the edges of the Internet.
Clay Shirky (www.shirky.com)
P2P refers to a class of systems and applications that
employ distributed resources to perform a critical
function in a decentralized manner.
Milojicic et al. (HP)
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Some controversy

Is p2p a new approach?
Problems is peer-to-peer systems are neither new nor
unique; they make us look for solutions to old problems
that we all worked around or tried to ignore before.
Andy Oram (O'Reilly & associates)
speech at Free and Open Source
Software Developers's Meeting
Brussels, BE, Feb. 2002
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Curiosity (traffic)
One year ago…
… and today!
Others
31%
41%
Unidentified
P2P
18%
48%
51%
11%
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source netflow.internet2.edu
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Properties
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No central control, no central database
No hierarchy
 Every node is both a client and a server
 The communication between peers is symmetric
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No global view of the system
 Scalablity
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Availability for any peer
Peers are autonomous
System globally unreliable
 Robustness and security issues
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Examples of p2p usage
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File-sharing applications
Distributed databases
Distributed computing (grid?)
Collaboration
Distributed games
Instant messaging
Ad hoc networks
Application-level multicast
Etc.
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Overlay networks
Overlay
IP
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Overlay networks
Overlay
IP
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Centralized model (Napster)
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File-sharing system
Almost distributed system
 The location of a document is centralized
 The "transfer" is peer-to-peer

Problems
 Robustness
 Scalability (?)
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Centralized model (Napster)
location
server
register
INTERNET
 Document x!
OK:
Document
Peer Z x?
IP = a.b.c.d
x
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Non-structured system (Gnutella-like)
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Two phases (like Napster)
 Localization + exchange
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No server
Open source
 gnutella.wego.com
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Distributed search
 The query is flooded
 Loop avoidance
 Limited TTL (not all nodes are visited)
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Gnutella
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Structured systems (DHTs)
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Based on distributed hash tables (DHTs)
No flooding
 Exact matches
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Overhead
 Gnutella-like  O(n)
 DHT  O(log n)

Examples
 CAN, Pastry, Chord, Kademlia, Tapestry, etc.
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Content-Addressable Networks (CAN)
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Provides a large scale distributed hash table
 Keys are mapped into values
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CAN defines a d-dimensional virtual space
 No relationship with the physical space
 Query  O(n1/d)
 Neighbors  O(d)
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The virtual space is completely distributed among
the peers
 Each peer is responsible for one share of the space
 The peer that is responsible for region R is also responsible
for the values inside R

Documents must be uniquely identified
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Example
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Example
1
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Example
1
2
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Example
1
2
3
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Example
4
1
2
3
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Example
4
4
1
5
2
3
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Example
1
4
6
5
2
3
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Example
1
7
4
6
5
2
3
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Association ID  node
1
7
4
6
5
2
Ex: Node 3
holds this
document
3
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Association ID  node
1
7
4
6
5
2
3
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Application-layer multicast

Native multicast  not yet completely deployed

ALM  easier/faster to implement
 Scalability  states at end-systems
 High-level support
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Application-layer multicast
source
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Taxonomy
P2P Applications
Parallel
Content and
file mngt
Compute Compo- Content
Intensive nentized exchange
File
system
Collaboration
Filtering, Instant
mining
message
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Shared
apps
Games
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Many works and projects

Gnutella and Napster @sourceforge.net
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JXTA (Sun)
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Open platform for p2p cooperation
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Interoperability
 Any system/peer/application
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Platform independency
 Languages (C, Java, etc)
 Systems platforms (Unix, Windows, etc)
 Networking platforms (802.11, Bluetooth, TCP/IP, etc)
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Ubiquity
 Sensors, PDAs, routers, desktops, laptops, storage systems
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JXTA (Sun)
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Objectives
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Find peers and resources
Share files with anyone across the network
Create a particular group of peers across different networks
Communicate securely with peers across public networks
Projects
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Applications (24 projects)
Core (13 projects)
Demos (3 projects)
Forge (15 projects)
Other (12 projects)
Services (24 projects)
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JXTA (Sun)  Protocols
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Peer discovery protocol
Peer resolver protocol
Peer information protocol
Rendezvous protocol
Pipe binding protocol
Endpoint routing protocol
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JXTA (Sun)
JXTA Community Applications
JXTA Community Services
Peer Groups
JXTA
Shell
Sun JXTA
Services
Peer Pipes
Peer
Commands
Peer Monitoring
Security
J
X
T
A
Peer (Desktop, cell phone, PDA, etc.)
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C
O
R
E
JXTA applications
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Final remarks
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P2P implies a very large spectrum of areas
High interest in both academicals/industrials
Much has already been done, but no conclusions are
definitive
IPv6 and P2P
 NAT, firewalls, IPv6 as an overlay

Many open issues
 Trust, security, scalability, QoS, etc.
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Working groups et al.
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A generic site on p2p from O'Reilly
 www.openp2p.com
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P2P working group
 www.peer-to-peerwg.org/
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Internet2 p2p working group
 p2p.internet2.edu
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Peer-to-peer development (p2p-hackers)
 zgp.org/mailman/listinfo/p2p-hackers
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Interesting meeting
 www.codecon.org
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References
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Distributed Computing
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Distributed (www.distributed.net)
SETI@home (www.seti.org)
Genome@home (gah.stanford.edu)
Folding@home (www.stanford.edu/group/pandegroup/folding)
Global Grid Forum (www.globalgridforum.org)
Globus Project (www.globus.org)
File sharing
 Napster (www.napster.com)
 Gnutella (gnutella.wego.com)
 Kazaa (www.kazaa.com)
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References

Distributed hash tables
 CAN (www.acm.org/sigs/sigcomm/sigcomm2001/p13ratnasamy.pdf)
 Pastry (research.microsoft.com/~antr/Pastry)
 Chord (www.pdos.lcs.mit.edu/chord)
 Tapestry (www.cs.berkeley.edu/~ravenben/tapestry)
 Freenet (freenet.sourceforge.net)
 Kademlia (kademlia.scs.cs.nyu.edu)
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Ad hoc networking
 AODV (www.ietf.org/internet-drafts/draft-ietf-manetaodv-13.txt)
 OLSR (www.ietf.org/internet-drafts/draft-ietf-manet-olsr10.txt)
 Tribe (rp.lip6.fr/site_rp/_publications/350-79Viana.ps.gz)
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References
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Platforms
 JXTA (www.jxta.org)
 .NET (www.microsoft.com/net)
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Collaboration
 Groove (www.groove.net)
 Endeavors (www.endeavors.com)
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IPv6 as a p2p overlay
Working Groups
 p2p.internet2.edu
 www.openp2p.com
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