Peer-to-Peer Peer-to-Peer Modeling: Modeling:

Expanding and Expanding and Specifying the Specifying the

ModelModel Mike Kissinger and Jeremy Mike Kissinger and Jeremy

ToutTout

Characteristics of P2P Characteristics of P2P NetworksNetworks

DecentralizedDecentralized DynamicDynamic Ad-hocAd-hoc Mostly egalitarianMostly egalitarian PowerfulPowerful Resistant to controlResistant to control

Nature of the P2P Nature of the P2P Market(s)Market(s)

P2P market (internal economy) vs. P2P market (internal economy) vs. market for P2P servicesmarket for P2P services

Different market terms depending on Different market terms depending on type of P2P (p2p development, type of P2P (p2p development, distributed computing are other types). distributed computing are other types). We are assuming P2P filesharing. We are assuming P2P filesharing.

Participants are users of the software, Participants are users of the software, as well as developers and owners of as well as developers and owners of any infrastructureany infrastructure

Publicity is keyPublicity is key

P2P Modeling ApproachP2P Modeling Approach

P2P is extremely complex with many P2P is extremely complex with many multi-causal interactionsmulti-causal interactions

Thus, System Dynamics is usedThus, System Dynamics is used SD Archetype: Limits to GrowthSD Archetype: Limits to Growth Resource-based modelResource-based model Key ideas: growth rate and limiting Key ideas: growth rate and limiting

factorsfactors Checks out historicallyChecks out historically

Model Characteristics Model Characteristics and Assumptions for P2P and Assumptions for P2P

SDRSDR Network is “pure” p2pNetwork is “pure” p2p Users contribute contentUsers contribute content Users contribute network resourcesUsers contribute network resources Performance based on ratio of traffic Performance based on ratio of traffic

per bandwidth availabilityper bandwidth availability User population changes determined User population changes determined

by actual and perceived by actual and perceived attractivenessattractiveness

Challenges to the Challenges to the AssumptionsAssumptions

Some networks use servers Some networks use servers (Napster)(Napster)

Some networks use “super-peers” Some networks use “super-peers” (Gnutella)(Gnutella)

Different network activities can be Different network activities can be the responsibility of different users. the responsibility of different users.

(Example: file searches and indexing (Example: file searches and indexing versus content hosting and transfer)versus content hosting and transfer)

Model-ficationsModel-fications

Indexing and searching (tied to Indexing and searching (tied to content availability) resources content availability) resources separate from file transfer traffic separate from file transfer traffic resourcesresources

Stock of super-peers tied to indexing Stock of super-peers tied to indexing and searchingand searching

Super-peer serves up to ~100 peers Super-peer serves up to ~100 peers wellwell

Free-rider ProblemFree-rider Problem

Arises when users do not contribute to Arises when users do not contribute to network resources and contentnetwork resources and content

Types: fishing, non-sharing, sharing Types: fishing, non-sharing, sharing undesirable contentundesirable content

Solution: impose an economy!Solution: impose an economy! Users earn credits for contributions to Users earn credits for contributions to

the network and spend them to use it.the network and spend them to use it. Creates incentive to contribute.Creates incentive to contribute.

Legal-Economic Nexus (Oh Legal-Economic Nexus (Oh yeah!)yeah!)

P2P, legally, is vastly complicatedP2P, legally, is vastly complicated Furor over Napster / Grokster is pemitted?Furor over Napster / Grokster is pemitted? Policy changes, both internal to and Policy changes, both internal to and

external of the P2P network, will have external of the P2P network, will have profound effects on P2Pprofound effects on P2P

External policy: External policy: regulation/discouragement?regulation/discouragement?

Internal policy: to promote network Internal policy: to promote network growth/efficacygrowth/efficacy

Adding Policy to the Adding Policy to the ModelModel

This will allow us to see long-term This will allow us to see long-term ramifications of suggested policiesramifications of suggested policies

External policy affects peer network External policy affects peer network attractiveness, therefore user arrivals attractiveness, therefore user arrivals and departures, i.e. profound effect on and departures, i.e. profound effect on network users stocknetwork users stock

Internal policy affects the other free Internal policy affects the other free sectors: content, bandwidth, network sectors: content, bandwidth, network performanceperformance

Possible Addition: Better Possible Addition: Better Tech?Tech?

The advancing state of the art is The advancing state of the art is clearly an accelerating factor in the clearly an accelerating factor in the growth of P2P networksgrowth of P2P networks

Software improvements would affect: Software improvements would affect: added content (easier encoding, etc.), added content (easier encoding, etc.), traffic (load balancing & overhead traffic (load balancing & overhead reduction)reduction)

Hardware improvements would affect: Hardware improvements would affect: average private collections size (more average private collections size (more HDD space), bandwidthHDD space), bandwidth