Incentivizing peer-assisted services: a fluid shapley value approach
A new generation of content delivery networks for live streaming, video on demand, and software updates takes advantage of a peer-to-peer architecture to reduce their operating cost. In contrast with previous uncoordinated peer-to-peer schemes, users opt-in to dedicate part of the resources they own to help the content delivery, in exchange for receiving the same service at a reduced price. Such incentive mechanisms are appealing, as they simplify coordination and accounting. However, they also increase a user's expectation that she will receive a fair price for the resources she provides. Addressing this issue carefully is critical in ensuring that all interested parties--including the provider--are willing to participate in such a system, thereby guaranteeing its stability. In this paper, we take a cooperative game theory approach to identify the ideal incentive structure that follows the axioms formulated by Lloyd Shapley. This ensures that each player, be it the provider or a peer, receives an amount proportional to its contribution and bargaining power when entering the game. In general, the drawback of this ideal incentive structure is its computational complexity. However, we prove that as the number of peers receiving the service becomes large, the Shapley value received by each player approaches a fluid limit. This limit follows a simple closed form expression and can be computed in several scenarios of interest: by applying our technique, we show that several peer-assisted services, deployed on both wired and wireless networks, can benefit from important cost and energy savings with a proper incentive structure that follows simple compensation rules.