Download Designing Incentive-Compatible Routing and Forwarding Protocols

Designing Incentive-Compatible
Routing and Forwarding Protocols
in Wireless Ad-Hoc Networks
By,
Arun Venkat Ramachandran
Challenges
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Routing and Forwarding incentives
required.
Nash equilibrium not always
desirable
Wireless and Ad-hoc properties
make classic game theory tools not
applicable
Individual nodes cannot determine
Ad-hoc Games Model
Ad hoc network N = { 1,2,...,N} N is finite
Utility consists of 2 parts
ui= -ci+pi
Where ci is the nodes cost ,
pi is the payment.
Assumptions
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Nodes transmit at only discrete power levels.
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Binary link model (for now)
Definitions
Uncooperative Behavior
Non-existence of ForwardingDominant Protocol
For the above definition of ad-hoc games
Non-existence of ForwardingDominant Protocol
i is not going to get paid for the 1st packet
If j is going to drop a packet then i has no
incentive to forward the packet to j !
Solution: Enforce tamper-proof hardware
But this is an ad-hoc network
Not everybody will have same hardware
Cooperation Optimal Protocol
Divide the ad hoc game into 2 stages
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Routing
Determination of optimal path to be taken based
on maximum utility.
Joint decision made by all the nodes in the
network.
Forwarding
What a node is supposed to do when it gets a
packet
For both these stages incentives are required
Routing
Routing
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It is good enough if we can say that with high
probability following the protocol is a dominant
sub action
Since there is no central node/authority to do the
computation the computation is done by the
destination
If the destination is untrustworthy you can have
random computation checks to verify.
Extensive game tree
For example. Every node has 3 options
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Drop
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Tamper
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Forward
Forwarding
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Subgame perfect equilibrium means a Nash
equilibrium for every subgame
For the specific routing decision the path is a
subgame perfect equilibrium
Cooperation Optimal Protocol
Vickrey Clarke Groves (VCG)
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Family of payment schemes based on added
value
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D be the declared cost of a link e.
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g1 be the cost of routing on the graph
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g2 be the cost of routing on the graph minus
the link e.
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Payment = D + g2 -g1
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Strategyproof mechanism
VCG failure
Actual Power Ratio = 5, Power emitted = 5.
A claims power emitted = 30
B claims power ratio = 15
Fails because transmission requires receivers
feedback to estimate power level.
Prevent Cheating using Crypto
2 possibilities of cheating
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node j cheats by making P(i,j) larger
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node i cheats by making P(i,j) smaller
➔
➔
The first case avoided because we choose the
cheapest path and node j will make itself less
likely to be chosen
How to avoid the second case??
Answer: Crypto
Routing Protocol
Routing Protocol
Routing Protocol
Properties of the protocol
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You can verify that the cost doesnt change for
each link from different reports
Computation runs in polynomial (cubic) time
Blocks are computed using cryptographic hash
chains
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Mutual decisions to avoid conflict
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Digital signature verification
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Optimal protocol
Lossy Links
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How to determine transmission success rate?
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S=Nr/Ns
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How to choose power level?
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L= argmax (Si/l)
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How do we adapt the protocols?
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Changing the weighing system to weigh the
links with probability as well
Results
Conclusion
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Forwarding incentives alone are not sufficient
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Need an optimal protocol
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VCG is not strategyproof in wireless
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Crypto techniques can be used to gain incentive