Peer-to-Peer Modeling: Expanding and Specifying the Model Mike Kissinger and Jeremy Tout

Characteristics of P2P Networks Decentralized Decentralized Dynamic Dynamic Ad-hoc Ad-hoc Mostly egalitarian Mostly egalitarian Powerful Powerful Resistant to control Resistant to control

Nature of the P2P Market(s) P2P market (internal economy) vs. market for P2P services P2P market (internal economy) vs. market for P2P services Different market terms depending on type of P2P (p2p development, distributed computing are other types). We are assuming P2P filesharing. Different market terms depending on type of P2P (p2p development, distributed computing are other types). We are assuming P2P filesharing. Participants are users of the software, as well as developers and owners of any infrastructure Participants are users of the software, as well as developers and owners of any infrastructure Publicity is key Publicity is key

P2P Modeling Approach P2P is extremely complex with many multi- causal interactions P2P is extremely complex with many multi- causal interactions Thus, System Dynamics is used Thus, System Dynamics is used SD Archetype: Limits to Growth SD Archetype: Limits to Growth Resource-based model Resource-based model Key ideas: growth rate and limiting factors Key ideas: growth rate and limiting factors Checks out historically Checks out historically

Model Characteristics and Assumptions for P2P SDR Network is “pure” p2p Network is “pure” p2p Users contribute content Users contribute content Users contribute network resources Users contribute network resources Performance based on ratio of traffic per bandwidth availability Performance based on ratio of traffic per bandwidth availability User population changes determined by actual and perceived attractiveness User population changes determined by actual and perceived attractiveness

Challenges to the Assumptions Some networks use servers (Napster) Some networks use servers (Napster) Some networks use “super-peers” (Gnutella) Some networks use “super-peers” (Gnutella) Different network activities can be the responsibility of different users. Different network activities can be the responsibility of different users. (Example: file searches and indexing versus content hosting and transfer) (Example: file searches and indexing versus content hosting and transfer)

Model-fications Indexing and searching (tied to content availability) resources separate from file transfer traffic resources Indexing and searching (tied to content availability) resources separate from file transfer traffic resources Stock of super-peers tied to indexing and searching Stock of super-peers tied to indexing and searching Super-peer serves up to ~100 peers well Super-peer serves up to ~100 peers well

Free-rider Problem Arises when users do not contribute to network resources and content Arises when users do not contribute to network resources and content Types: fishing, non-sharing, sharing undesirable content Types: fishing, non-sharing, sharing undesirable content Solution: impose an economy! Solution: impose an economy! Users earn credits for contributions to the network and spend them to use it. Users earn credits for contributions to the network and spend them to use it. Creates incentive to contribute. Creates incentive to contribute.

Legal-Economic Nexus (Oh yeah!) P2P, legally, is vastly complicated P2P, legally, is vastly complicated Furor over Napster / Grokster is pemitted? Furor over Napster / Grokster is pemitted? Policy changes, both internal to and external of the P2P network, will have profound effects on P2P Policy changes, both internal to and external of the P2P network, will have profound effects on P2P External policy: regulation/discouragement? External policy: regulation/discouragement? Internal policy: to promote network growth/efficacy Internal policy: to promote network growth/efficacy

Adding Policy to the Model This will allow us to see long-term ramifications of suggested policies This will allow us to see long-term ramifications of suggested policies External policy affects peer network attractiveness, therefore user arrivals and departures, i.e. profound effect on network users stock External policy affects peer network attractiveness, therefore user arrivals and departures, i.e. profound effect on network users stock Internal policy affects the other free sectors: content, bandwidth, network performance Internal policy affects the other free sectors: content, bandwidth, network performance

Possible Addition: Better Tech? The advancing state of the art is clearly an accelerating factor in the growth of P2P networks The advancing state of the art is clearly an accelerating factor in the growth of P2P networks Software improvements would affect: added content (easier encoding, etc.), traffic (load balancing & overhead reduction) Software improvements would affect: added content (easier encoding, etc.), traffic (load balancing & overhead reduction) Hardware improvements would affect: average private collections size (more HDD space), bandwidth Hardware improvements would affect: average private collections size (more HDD space), bandwidth