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