This is one of my favourite papers from OSDI ’08 (yes, still doing a few reviews, trying to get to five or so before SOSP…). FlightPath is a system developed by some folks mainly at UT Austin for peer-to-peer streaming in dynamic networks. This is a reasonably challenging problem in itself, although one that’s seen a good deal of work before. However, the really cool thing about this paper is that they treat participants in the network as potentially rational agents. Since Lamport’s seminal work on the Byzantine generals problem, it’s been standard practice to assign one of two behaviour modes to members of distributed systems: either you’re alturistic, which means that you do exactly what the protocol tells you to do, no matter what the cost to yourself, or Byzantine, which means that you do whatever you like, again no matter what the cost to yourself.
It was realised recently that this is a false dichotomy: there’s a whole class of behaviour that’s not captured by these two extremes. Rational agents participate in a protocol as long as it is worth their while to do so. At its most simple, this means that rational agents will not incur a cost unless they expect to recoup a benefit that is worth equal to or more than the original cost to them. This gave rise to the Byzantine-Alturistic-Rational (BAR) model, due to the same UTA group, which can be used to more realistically model the performance of peer-to-peer protocols.