No more crash or crunch: Sustainable credit dynamics in a P2P community

Abstract

Many peer-to-peer file sharing communities implement credit policies to incentivise users to contribute upload resources. Such policies implicitly assume a user model -how the user controlling each peer behaves. We show using an agent-based model that credit policies, based on bandwidth contribution, and a selfish user model, can lead to both "crunches" and "crashes" where the system seizes completely due to too little credit or too much credit. We explore the conditions that lead to these system pathologies and present a theoretical analysis that allows us to determine if a community is sustainable or will eventually crunch or crash. Finally we apply the analysis to produce a novel adaptive credit system that automatically adjusts credit policies to maintain sustainability.

On the sustainability of credit-based P2P communities

“…For a given community set up, the size of all the files are equal (F) and the size of a piece is 1. As it was shown in [19], a community crunches if F = 10 and 0.1 ≤ R ≤ 0.2, while with F = 10 and R ≥ 0.9 it crashes.…”

“…Our current paper is complementing the work done in [19]. In [9,10] another kinds of extended considerations have been done, different from ours, mainly focusing on remedy schemes avoiding crashes or crunches.…”

“…All the other cases lead to sustainable community. As it was also shown in [19], F = 10 and 80% initial rich proportion leads to an unstable system in which the Up until now, we have discussed the consequences of changing parameters regarding the whole system. It is also interesting to see what is the effect of these parameter changing on the individual user's performance.…”

“…Basically, the system model we use in this paper is very similar to the one used in [19]. Here we give a short overview, detailing the modifications we applied.…”

“…Note that sustained status is usually temporary, which could be held for both short term or longer term. On the other hand, crash and crunch are both definitive, they can only be fixed with external interventions [9,19].…”