Peer-to-Peer Systems



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Peer-to-Peer



An alternative to the client/server model of distributed computing is the peer-to-peer model.
Client/server is inherently hierarchical, with resources centralized on a limited number of servers.
In peer-to-peer networks, both resources and control are widely distributed among nodes that are theoretically equals. (A node with more information, better information, or more power may be “more equal,” but that is a function of the node, not the network controllers.)


Decentralization


A key feature of peer-to-peer networks is decentralization. This has many implications. Robustness, availability of information and fault-tolerance tends to come from redundancy and shared responsibility instead of planning, organization and the investment of a controlling authority.
On the Web both content providers and gateways try to profit by controlling information access. Access control is more difficult in peer-to-peer, although Napster depended on a central index.


Applications outside Computer Science


Bioinformatics
Education and academic
Military
Business
Television
Telecommunication


Why Peer-to-Peer Networking?


The Internet has three valuable fundamental assets- information, bandwidth, and computing resources - all of which are vastly under utilized, partly due to the traditional client-server computing model.
Information - Hard to find, impossible to catalog and index
Bandwidth - Hot links get hotter, cold ones stay cold
Computing resources - Heavily loaded nodes get overloaded, idle nodes remain idle


Bandwidth Utilization


A single fiber’s bandwidth has increased by a factor of 106, doubling every 16 months, since 1975
Traffic is still congested
More devices and people on the net
More volume of data to move around same destinations ( eBay, Yahoo, etc.)


Benefits from P2P


Theory
Dynamic discovery of information
Better utilization of bandwidth, processor, storage, and other resources
Each user contributes resources to network
Practice examples
Sharing browser cache over 100Mbps lines
Disk mirroring using spare capacity
Deep search beyond the web