1. Peer-to-Peer Computing
Objectives
What Does Peer-to-Peer Mean?
Taxonomy
Characteristics of P2P Systems
P2P Systems
Distributed Computing, File Sharing, Collaboration, and Platforms
Strength and Weaknesses of P2P systems
Non-Technical Challenges

2. What Does Peer-to-Peer Mean?
Characterization from CFP of IPTPS 2004:
decentralized
self-organizing
distributed systems
in which all or most communication is symmetric

3. Benefits of P2P Systems Improving scalability
There is no dependency on centralized points
Eliminating the need for costly infrastructure
Direct communication is enabled
Enabling public resource aggregation

4. Introduction characteristics peer-to-peer client-server manageability
self-organized
managed
configurability
ad-hoc
configured
organization
mesh
hierarchy
functionality
discovery
lookup
nature
mobile
static
dependency
independent lifetime
server dependencies
components
custom naming
DNS-based

5. Computer Systems Taxonomy
Centralized systems
Distributed systems
(e.g. mainframes,SMPs,workstations)
Client-Server
Peer-to-Peer
Flat
Hierarchical
Pure
Hybrid

6. distributed computing
P2P Systems Taxonomy
P2P Systems
file sharing
distributed computing
collaborations
platforms
(e.g. Napster)
(e.g.
(e.g. Jabber,Groove)
(e.g. JXTA,.Net)

7. Characteristics of P2P Systems
Decentralization
emphasis on user’s ownership and control of data and resources
makes implementation of P2P model a challenge
hybrid P2P (e.g. Napster) versus pure P2P (e.g. Gnutella)
Scalability
peers directly interact with other
Napster was able to scale up to 6 million users at the peak of its time
focusing on a task that is parallel
has over 3.5 million users so far

8. Characteristics of P2P Systems
Anonymity
multicasting can be used as a technique for Publisher anonymity
identity spoofing can also be used for Publisher anonymity
encryption, splitting files into shares, and splitting keys are techniques used for document anonymity
Self-Organization
it is essential for P2P systems to have self-organization since P2P systems are fluctuating environments

9. Characteristics of P2P Systems
multicast
group
multicast group concept: use of indirection
hosts addresses IP datagram to multicast group
routers forward multicast datagrams to hosts that have “joined” that multicast group

10. Characteristics of P2P Systems
Cost of Ownership
shared ownership reduces the cost of owning the systems, the content, and the cost of maintenance
is faster than the fastest supercomputer in the world, but only at a fraction of its cost: 1%
Ad-Hoc Connectivity
variable-size pool of resources
ad-hoc nature of content sharing
ad-hoc nature of connectivity

11. Characteristics of P2P Systems
Performance
replication
reduces the distance between requester and provider
copes with the disappearance of peers
caching
reduces the path length required to fetch a file/object
caching replicas can be used for load balancing
intelligent routing and network organization
sending requests to closely located peers
group peers based on common interest
improve performance by proactively moving data

12. Characteristics of P2P Systems
Security
P2P share most of their security needs with common distributed systems
session key exchange, encryption, digital signatures, etc.
sandboxing
safety properties such that the external code will not crash the host box
enforcing security properties to prevent sensitive data from leakage to malicious peers
digital rights management
protecting the authors from having their intellectual property stolen
watermarking

13. P2P Systems Strengths P2P has more decentralized control and data
P2P supports systems whose parts come and go
cost of ownership is distributed among the peers
peers can be anonymous
due to the higher decentralization nature of P2P systems
scalability, performance, and self-organization can be better satisfied

14. P2P Systems Weakness Security Interoperability
sufficient guarantees of additional trust has to be established among the peers
Need to model trust
Interoperability
is a matter of investment
as development proceeds, more interoperability may evolve
getting P2P applications to interoperate with each other is possible
For example, implementing common protocols or using standardized messaging formats based on XML
while P2P applications may be closer to talking with one another, they are still separate applications with their own baggage, consuming their own share of resources

15. P2P Systems Weakness Non-altruism in Gnutella
70% of all users do not share files
50% of all requests are satisfied by the top 1% sharing hosts
incentive mechanisms are needed
reputation-based incentives
economic-based incentives
Service-quality-based incentives
The success of P2P systems depends on altruism

16. Non-Technical Challenges
Acceptance and Use
peers rely on one another
freeloaders
peers are not alike
Fragmentation of user base
the overall utility of P2P systems is limited because of fragmentation
interoperability seems to be the only solution
Release of control
Recording Industry Association of America’s (RIAA) lawsuit against Napster