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

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

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

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

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

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

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 SETI@home has over 3.5 million users so far

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

Characteristics of P2P Systems 128.59.16.12 128.119.40.186 multicast group 226.17.30.197 128.34.108.63 128.34.108.60 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

Characteristics of P2P Systems Cost of Ownership shared ownership reduces the cost of owning the systems, the content, and the cost of maintenance SETI@home 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

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

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

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

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

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

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