Incentives

Problem

File-sharing networks like KaZaA and Gnutella have popularized the peer-to-peer (P2P) resource sharing model. Based on the altruistic behaviour of its users, principles of P2P systems sometimes conflict user's rational individuality. The individual's utility function is also influenced by negative factors like e.g. upload costs, limited upload bandwidth, enviousness or egoism. Hence some users use P2P networks without sharing own resources (free-riding).

Incentive systems

Point incentive system

Simple point incentive mechanisms as in e.g. the Maze-network don't prevent users from cheating. Two kinds of user collusion are observed.

• Pair-wise collusion

Two users mutually exchange large amounts of data to increase their points. This kind of collusion profits from the rule that uploading earns more points that downloading consumes.

• Spam account collusion

A user registers a number of spam-accounts to download from his main-account. Thus he transfers initial points given to new accounts to his main-account.

EigenTrust

EigenTrust is an incentive system based on the traffic history of each peer. Uploading data to peer A increases the reputation of peer B from peer A's perspective. The reputation between all peers can be pictured using a trustmatrix $M$ with elements $c_{i,j}$. $c_{i,j}$ is peer j 's rank from i 's perspective related to normalized download volumes that i has received from j during a certain time period.

Networktraffic mapped to a Trustmatrix

Tit-for-Tat

coming soon