Role of incentives in networks CS 653, Fall 2010
Selfish behavior in networks Game theory in networks an area in itself Today: Three case studies BitTorrent Selfish routing Overlay routing Interdomain routing
BitTorrent
BitTyrant: Optimizing return-on-investment
BitTorrent is an auction [LLSB08]
BitTyrant as a Sybil attack c_1 >= c_2 >= … >= c_(s-1) are the rates required to make it to the i’th slot in the auction.
BitTorrent Does the BitTorrent game reach a desirable equilibrium state?
Nash equilibrium A state where no player has an incentive to unilaterally change their strategy Classic example: Prisoner’s dilemma
Does BT reach a NE? BitTorrent has not been shown to reach NE under a reasonable game model Example from 4.2 in [QS04] What about PropShare? Best-response not prop-share, so not guaranteed to reach NE
Selfish routing
If users choose routes (eg, overlay routing), is there an efficiency loss?
Braess’s paradox Q: What is the price of selfish routing here?
Price of selfish routing [RT02] Assuming one unit of flow, what is the “price of anarchy” here? With linear cost functions, this is about as bad as it gets
Selfish routing in Internet-like environments [QYZS06] Underlay: OSPF or MPLS Overlay Independent source routing Cooperative routing in each overlay Link latency functions: M/M/1 and others Summary: Selfish routing Achieves near-optimal average latency while overloading some links Interacts poorly with traffic engineering
Selfish interdomain routing [MWA07] Example of price of anarchy