Free Riders: Fact or Fiction?

Free Riders: Fact or Fiction? Presented by Floriaan in ‘t Groen 18/06/2003

Agenda • Problem statements • Free riding on Gnutella • Incentives for Sharing in Peer-to-Peer Networks • Conclusion • Discussion The Economics of Peer-to-Peer Architectures

Problem Statements • What exactly is the free riding problem? Does it exists? • What are the effects on p2p systems? • Can the problem be solved? • How to create incentives? The Economics of Peer-to-Peer Architectures

Free riding on Gnutella • By Eytan Adar and Bernardo A. Huberman The Economics of Peer-to-Peer Architectures

Free riding on Gnutella • Users are not monitored • No statisitics are maintained • user community gets large • social dilemma users are confronted with even if they are not aware of it The Economics of Peer-to-Peer Architectures

Social dilemma • group of people attempts to utilize a commongood in the absence of central authority • common good • provision of a large library of filesto the user community • shared bandwidth • The dilemma for each individual • contribute to thecommon good • shirk and free ride on the work of others The Economics of Peer-to-Peer Architectures

Social Dilemma • Rational to max utility • Only download No upload • every individual can reason this way • system's performance can degrade considerably • everyone worse off  the tragedy of the digital commons The Economics of Peer-to-Peer Architectures

Hypotheses • Hypothesis 1: A significant portionof Gnutella peers are free riders. • Hypothesis 2: Free riders are distributed evenly across differentdomains (and by speed of their network connections) • Hypothesis 3: Peers that provide files for download are not necessarilythose from which files are downloaded The Economics of Peer-to-Peer Architectures

Experiment 1 • Extensive analysis of user traffic • sampling messages on the Gnutella network over a24-hour period • collected both pong and query response messages • PONG and QUERY HIT messages contain an IP address and useful data related to sharing • In the 24-hour period 33,335 hosts issuing pingmessages, which shared a total of 3,100,464 files were observed The Economics of Peer-to-Peer Architectures

Results 66% share no files The Economics of Peer-to-Peer Architectures

Results The Economics of Peer-to-Peer Architectures

Results 63% never responded The Economics of Peer-to-Peer Architectures

Results • which hosts provide files and which hosts provide files that are actually downloaded? • 7,349 peers, or approximately 63%, neverprovided a query response • hosts had files to share butnever responded to queries • Files are probably not desirable The Economics of Peer-to-Peer Architectures

Results • very few peers do thebulk of the work • Of the 11,585 sharing hosts the top 1 percent of sites providesnearly 47% of all answers, and the top 25 percent provide 98% The Economics of Peer-to-Peer Architectures

Discussion point • Authors claim that sharing undesirable files (no query response) is also a form of free riding. • Do you agree? Why or why not? The Economics of Peer-to-Peer Architectures

Experiment 2 • hosts based in domain a do not contribute more thanhosts in domain b • free riders are distributed equally • Domains can serve as a proxy for bandwith The Economics of Peer-to-Peer Architectures

Experiment 2 • Filtered the set to 26,014 peers which were hosts with IP addresses that were readily converted to host names. • Number of hosts in each domain were counted (mit.edu, home.com) • Number of hosts in each top-level domain were counted (.edu, .com, .net) The Economics of Peer-to-Peer Architectures

Results • 2538 unique domains • The range of peers ineach ranged from 1 to a maximum of 2,951 • Each of the points in the figure represents a domain in terms of thenumber of peers and the total number of files shared • The dashed line is the trend line for this data The Economics of Peer-to-Peer Architectures

Results The Economics of Peer-to-Peer Architectures

Experiment 3 • Quantity vs Quality • number of queriesanswered is not necessarily proportional to thenumber of files offered • Intuition: queries that are issued by the bulk of users are veryoncentrated on particular topics • popular musical artists, adult material, file extensions (*.mp3) The Economics of Peer-to-Peer Architectures

Results • files returned for these queries aretherefore more desirable, which defines their quality • only a smallnumber of peers will actually share anything that is considered to be high“quality” • The top 1percent of those queries accounted for 37% of the total queries and the top 25 percent account for over 75% of the total queries The Economics of Peer-to-Peer Architectures

Results • the topresponding host only hosted 695 files, but responded to 3,436 queries. The nextmost responsive peer hosted 956 files and responded to 1,474 queries. The Economics of Peer-to-Peer Architectures

Results • little evidence of a relationship between quantity and quality The Economics of Peer-to-Peer Architectures

Threats • Difficulty of generating spontaneous cooperation in large anonymous groups • Rampantfree riding may eventually render systems useless, as few individuals willcontribute anything that is new and high quality The Economics of Peer-to-Peer Architectures

Threats • peers that provide files are set to only handle some limited number ofconnections for file download • connections to these peers is limited • peers will rapidly becomesaturated and remain so • impact ofadditional hosts on the search horizon (ex ttl of 6) The Economics of Peer-to-Peer Architectures

Threat • Vulnerability • When everything is functioning  there is a diminished risk of the system being shut downby either lawsuit or attack • Small amount of peers that provide bulk • Top-providing peers act as centralized servers The Economics of Peer-to-Peer Architectures

Solutions • forcing caching of downloaded files invarious hosts • download all files into a shared upload directory • market based architecture • Micropayments? • reduce the cost • Offloading bandwith • “Participation Level” rating to give better performance to peers that share more files (Kazaa) The Economics of Peer-to-Peer Architectures

Discussion point • According to your opinion is one of these solutions feasible? Why, or why not? • Could you think of others? The Economics of Peer-to-Peer Architectures

Incentives for sharing in p2p networks Philippe Golle, Kevin Leyton-Brown, Ilya Mironov Stanford University The Economics of Peer-to-Peer Architectures

Model • model assumes the following mechanism • Centralized database server • Keeps track of who’s logged into the network • Keeps track of what files a user is sharing • Performs searches and returns results The Economics of Peer-to-Peer Architectures

Game setup • Divided into time periods of equal duration • n agents • Pure strategies • Sharing: s0 (no sharing), s1 (moderate), s2 (sharing all) • Downloading: d0(no d/l), d1 (moderate), d2(heavy) • Mixed strategies also allowed The Economics of Peer-to-Peer Architectures

Game setup • Utility • Ui=[fiAD(AD)+fiNV(NV)+fiAL(AL)]-[fiDS(DS)+fiBW(BW)]+FT • AD (amount to download) • NV (network variety) • DS (disk space used) • BW (bandwidth used) • AL (altruism) • FT (financial transfer) • f-functions describe agent's preference for different values of the variable, in money The Economics of Peer-to-Peer Architectures

Game setup • Initial analysis • Disregard AL, FT • S={(s0,d2),…,(s0,d2)} is a weak equilibrium • All agents will have 0 utility in this case  Nothing to download The Economics of Peer-to-Peer Architectures

Game setup • AL must be included to activate P2P file sharing networks • Sources of altruism (AL) • Sense of community • Chat rooms, newsletter, and messaging • Low cost to share • Share by default (opt-out system) The Economics of Peer-to-Peer Architectures

Game setup • Two types of users • AL outweighs DS and BW • (s2,d2) is dominant strategy • DS and BW outweigh AL • (s0,d2) is dominant strategy The Economics of Peer-to-Peer Architectures

Discussion Point • Is Altruism enough to keep motivating peers? The Economics of Peer-to-Peer Architectures

Game setup • AL is the only motivator in P2P • Difficult to quantify AL • AL is not enough for motivation • Proposal: • Drop AL variable from utility equation and find other motivations to share The Economics of Peer-to-Peer Architectures

Other motivators • Micro payments • charge users with downloading and reward for uploading • fAD(1) > a • Utility gained from downloading one file exceeds the payment • Utility from downloading is decreased, but still exists • fiDS(1) + fiBW(1) < a • Disutility incurred from sharing one file and uploading it is less than the payment they get for uploading it • Gains utility by sharing The Economics of Peer-to-Peer Architectures

Micro Payments • Results in strong and unique equilibria • S=((s2,d2),…,(s2,d2)) • Micro payments may be distasteful  flat pricing • Users pay for block of files The Economics of Peer-to-Peer Architectures

Discussion point • What will happen when one of the p2p systems will charge money for downloading files? • What would you do? The Economics of Peer-to-Peer Architectures

Point-Based Mechanisms • Agents allowed to buy points with money or contribution • Points not redeemable for money • Same equilibrium as pure MP The Economics of Peer-to-Peer Architectures

Rewards for sharing • Reward for amount available for sharing • Downloading a file costs cm points • m is size in megabytes • c is a system constant • How long a new file must be shared to waive its download cost The Economics of Peer-to-Peer Architectures

Rewards for sharing • Agents still get negative utility for bandwidth used for uploads • May share unpopular files • May share at low-usage times • Solution • a(t) is scaling factor proportional to demand The Economics of Peer-to-Peer Architectures

Conclusions • Free riding problem exists • But p2p is still alive • A lot of challenges for the future • Creating incentives • Get companies involved The Economics of Peer-to-Peer Architectures

Questions? ? The Economics of Peer-to-Peer Architectures

The Economics of Peer-to-Peer Architectures

Free Riders: Fact or Fiction?