1. Role of incentives in networks CS 653, Fall 2010

2. Selfish behavior in networks  Game theory in networks an area in itself  Today: Three case studies  BitTorrent  Selfish routing Overlay routing Interdomain routing

3. BitTorrent

4. BitTyrant: Optimizing return-on-investment

5. BitTorrent is an auction [LLSB08]

6. 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.

7. BitTorrent  Does the BitTorrent game reach a desirable equilibrium state?

8. Nash equilibrium  A state where no player has an incentive to unilaterally change their strategy  Classic example: Prisoner’s dilemma

9. 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

10. Selfish routing

11.  If users choose routes (eg, overlay routing), is there an efficiency loss?

12. Braess’s paradox Q: What is the price of selfish routing here?

13. 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

14. 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

15. Selfish interdomain routing [MWA07]  Example of price of anarchy