1. ISP Friendly. Most residential ISPs (including DSL and cable ISPs) have been dimensioned for “asymmetrical” bandwidth usage, that is, for much more downstream than upstream traffic. But P2P video streaming and file distribution applications shift upstream traffic from servers to residential ISPs, thereby putting significant stress on the ISPs. Future P2P applications need to be designed so that they are friendly to ISPs [Xie 2008].
2. Security. Because of their highly distributed and open nature, P2P application scan be a challenge to secure [Doucer 2002; Yu 2006; Liang 2006; Naoumov 2006; Dhungel 2008; LeBlond 2011].
3. Incentives. The success of future P2P applications also depends on convincing users to volunteer bandwidth, storage, and computation resources to the applications, which is the challenge of incentive design [Feldman 2005; Piatek 2008; Aperjis 2008; Liu 2010].