Role of incentives in networks CS 653, Fall 2010.

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 makeit 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

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