Eunyoung Chang 1 CS 6204 Mobile Computing

 Problem  Proposed Approaches  COMMIT Approaches  THE SYSTEM MODEL  The COMMIT Protocol  Protocol Analysis  The Cost of Cooperation 2

 Problem - In ad hoc network, establish a route for sending packets between a Sender and Destination - rational selfish Nodes, maximize their own utility. 3

 Proposed Approaches 1. Ad Hoc-VCG : based on momentary transfer - energy-efficient, truthful 2. CORSAC : route discovery and packet forward cooperation-optimal - utility maximizing - Problem The source cannot act strategically The number of messages must be exchanged 4

 COMMIT Routing Protocol Goal 1. individual rationality 2. Truthfulness 3. The most energy-efficient(least Cost) path. 4. The message complexity is low.  COMMIT Protocol - COMMIT : Sender-centric, incentive-compatible routing protocols 5

6 ProtocolTruth. RoutersTruth. ForwardStrategic senderMessage Complex Ad Hoc-VCGYesPartiallyNo O(n 3 ) CORSAC Yes NoO(n 3 ) COMMIT Yes Partially Yes O(|M| 2 d) The major difference - The costs of routing are relative with nodes, not links. - periodic topology control protocol - Game theory simple - Message complexity low

Network Model - n nodes - Links in the communication graph G. - Symmetric wireless link - 2-connected - topology control protocol - K-Neigh, CBTC, CTR Modeling routing as a Game : D, S, Relay nodes, - D : “neural referee” - S : private information (type), u s = m - c s (D) (u: utility of S, m: maximum per-packet price, c s (D):actual per-packet price ) - R : C v = l(v), u s = pay(v) – l(v) (l(v) : power level, C v : cost to relay a packet, pay(v) : per-packet payment) 7

Strategy Game – truth telling 1. A node can declare any type. 2. Drop control messages 3. Modify messages 4. Create bogus messages The Goal - Route message with the most efficient paths The features - truthful, incentive compatible, strategy proof 8

1.The mechanism 1. Winner determination by D 2. Payment computation by D 3. Billing. 2. The pricing scheme 3. Protocol Specification 9

2. The Pricing Scheme : Determine c s (D) ? c(P) : The energy cost of a path P between S/D c(P) = ∑ vЄP, v Є {S,D} l(v) MP : The wining path = {v 1, v 2, v 3 } P -v : the path that does not include v c(P -v ) : the cost of the minimum energy (S,D) path P -v `pay(v) : Payment for a node v in the wining path MP pay(v) = c(P -v ) – c(MP) +l(v) pay(v) = 0 ( for the nodes, that are not on the wining path) (S,D,20) SD v1v1 v2v2 v3v3 v5v5 v4v4 5 1 m = 65 l

2. The Pricing Scheme : Determine c s (D) (Q. Would the communication take place in the nodes?) 11 m = 65 (A. If truthfully, The communication would NOT take place) (S,D,20) SD v1v1 v3v3 v4v4 v5v5 v2v2

2. The Pricing Scheme : Determine c s (D) (Q. Would the communication take place in the nodes?) 12 v2v2 MP (The wining path) = {v 1, v 2, v 3 } = 26 c(P -v1 ) (Replacement path ) = {v 4 v 5 } = 40 = c(P -v2 ) = c(P -v3 ) pay(v 1 ) = c(P -v1 ) – c (MP) +l(v 1 ) = 40 – = 19, pay(v 2 )= 34, pay(v 3 ) = 15 pay(v 1 ) + pay(v 2 ) + pay(v 3 ) = 68 > (S,D,20) SD v1v1 v3v3 v4v4 v5v5 m = 65 Utility for all the players = 0 (A. The communication would not take place)

2. The Pricing Scheme : Determine c s (D) (Q. Would the communication take place in the nodes?) 13 v2v2 But assume that node V 2 falsely declares power level 30 ? pay(v 1 ) + pay(v 2 ) + pay(v 3 ) = 48 < 65 Utility of v 2 : 34 – 20 = (S,D,20) SD v1v1 v3v3 v4v4 v5v5 m = 65 (The communication would take place) (V 2 would increase its utility) Therefore, cs(D) = ∑ vЄP, v Є {S,D} pay(v) would result in a nontruthful mechanism l

2. The Pricing Scheme : Determine c s (D) (Q. Would the communication take place in the nodes?) 14 v2v2 But assume that node V 2 falsely declares power level 30 ? pay(v 1 ) + pay(v 2 ) + pay(v 3 ) = 48 < (S,D,20) SD v1v1 v3v3 v4v4 v5v5 m = 65 In order to circumvent this problem : c s (D) = c(P -mp ) = 40 c(P -mp ) : global replacement path c s (D) < m : feasible

2. The Pricing Scheme : Determine c s (D) - feasible : protecting the condition individual rationality. c(P -mp ) ≠ ∑ pay(v) : budget is imbalanced c(P -mp ) > ∑ pay(v) : getting additional money by D c(P -mp ) < ∑ pay(v) : Contributing to the payment by D 15 vЄP, v Є {S,D} l l l

3. Protocol Specification 1. Route discovery S : RD (S, D, m) using l(S) R : RD (S, D, m, v 1,l(v 1 ),…, v k-1,l(v k-1 )), V k build up local view D : RD (S, v 1, v 2,…, v k-1, v k, D) from S to D, P -vi, P -mp MP feasible(c s (D) = c(P -mp ) < m) 2. Data transition: (only if MP is feasible) start : along the winning path MP from S to D end : last packet of S, changes topology control protocol 16

- Truthful route discovery imply truthful data forwarding? 1. forward only new edges : reduces the message complexity phase. 2. V k compute whether a newly received path is feasible - 17

1. Energy Efficiency : If truthfully, COMMIT computes MP 2. Message Complexity 18 SD M n1n1 n 1 d d d d Each node forwards to |M| n 1 forwards to |M| * degree d n 1 has complete |M|d Each node |M| repeats ‘same’ Thus, |M|(|M|d) 3. Truthfulness and Individual Rationality : S, R, D (The subset of all relay node s) (the maximum node degree ) d

3. Truthfulness and Individual Rationality - prove : for the sender Sender : S will never pay a price that exceeds m. 1. m f < m : a. C(P -mp ) < m f < m : the utility remains the same. b. m f < C(P -mp ) < m : the communication would not takes place. c. C(P -mp ) < m f < m : declaring utility unchanged at zero. 2. m f > m : along the same line of case 1 above. 19

3. Truthfulness and Individual Rationality : S, R, D - prove : the Relay nodes A relay node : will never get a negative utility when acting truthfully. - Analyze the different cheating behaviors of the rely node : An relay node v could 1. lie about its type (power level l(v)) 2. Propagate a path with false information 3. internationally fail to propagate a path with new information 4. combine the above possibilities 20

3. Truthfulness and Individual Rationality : S, R, D 1. lie about its type (power level l(v)) : Utility unchanged - Cheating option 1 : l(v), l f (v) a. l(v) l f (v) : (S,D,20) SD v1v1 v2v2 v3v3 v5v5 v4v4 5 1 m = 65 if vЄMP No effect on the decision rule (S,D,20) SD v1v1 v2v2 v3v3 v5v5 v4v4 5 1 m = 65 if vЄMP v’s utility would not be changed

3. Truthfulness and Individual Rationality : S, R, D 2. Propagate a path with false information : case - Creating a false neighbor take : RD(S,D, m, v 1,, l(v 1 ),…, v i-1, l(v i-1 ) ) forward: RD(S,D, m, v 1,, l(v 1 ),…, v i-h, l(v i-h ), v, l(v) ) 1. v is in the MP, feasible 2. v is in the MP, Not feasible 3. v is not in the MP, but it is in the (false) minimum-energy MP - Creating a false overhop path forward: RD(S,D, m, v 1,, l(v 1 ),…, v i-h, l(v i-h ), v, l(v) ) 1. v is in the MP, feasible 2. v is in the MP, Not feasible 3. v is not in the MP. 22

3. Truthfulness and Individual Rationality : S, R, D 2. Propagation with false info – 1) creating a false neighbor Case: 1. v is in the MP, which is feasible : e’ = (v i-h, v ) 23 u v = c(P -v ) – c(MP) utility cost ↑, the cost of false MP f ↓ by e’ e’ ∈ MP f But e’ does not exist in G Payments during data session : zero SD v1v1 v v3v3 v5v5 v4v4 e’ reduce utility

3. Truthfulness and Individual Rationality : S, R, D 2. Propagation with false info – 1) creating a false neighbor Case: 2. v is in the MP, which is NOT feasible : e’ = (v i-h, v ) 24 utility zero 2 SD v1v1 v v3v3 v5v5 v4v4 e’ utility cost ↑, the cost of P -mp ↓ by e’ Not belong to P -mp

3. Truthfulness and Individual Rationality : S, R, D 2. Propagation with false info – 1) creating a false neighbor Case: 3. v is not in the MP, but it is in the (false) minimum-energy MP : e’ = (v i-h, v ) 25 SD v1v1 v2v2 v3v3 v v4v4 utility zero e’ ∈ MP f e’ does not exist in G Payments during data session : zero e’

3. Truthfulness and Individual Rationality : S, R, D 2. Propagation with false info – 2) Creating a false overhop Path Case: 1. v is in the MP, which is feasible : e’ = (v i-h, v i+1 ) 26 SD v1v1 v2v2 v3v3 v5v5 v4v4 e’ reduce utility u v = c(P -v ) – c(MP) The c(P -v ) ↓ while cost of MP unchanged by e’

3. Truthfulness and Individual Rationality : S, R, D 2. Propagation with false info – 2) Creating a false overhop Path Case: 2. v is in the MP, which is NOT feasible : e’ = (v i-h, v i+1 ) 27 Data session would be aborted SD v1v1 v2v2 v3v3 v5v5 v4v4 utility cost ↑, the cost of false MP f ↓ by e’ However, test Msg along global replacement path e’ does not exist in G e’

3. Truthfulness and Individual Rationality : S, R, D 2. Propagation with false info – 2) Creating a false overhop Path Case: 3. v is not in the MP : e’ = (v i-h, v i+1 ) 28 SD v1v1 v2v2 v3v3 v5v5 v4v4 e’ utility zero Not on the end point of e’ Leave v out of MP by e’

3. Truthfulness and Individual Rationality : S, R, D 3. Intentionally fail to propagate with new info Case: 1. v is in the MP, which is feasible 29 SD v1v1 v2v2 v3v3 v5v5 v4v4 no incentive in not reporting edge info u v = c(P -v ) – c(MP) utility cost ↓, the cost of MP ↑ by no reporting

3. Truthfulness and Individual Rationality : S, R, D 3. Intentionally fail to propagate with new info Case: 2. v is in the MP, which is NOT feasible 30 no incentive in not reporting SD v1v1 v2v2 v3v3 v5v5 v4v4 No way utility cost ↑

3. Truthfulness and Individual Rationality : S, R, D 3. Intentionally fail to propagate with new info Case: 3. v is not in the MP and try to join the MP by not reporting one of the edges e 31 SD v1v1 v2v2 v3v3 v5v5 v4v4 utility zero c(MP) > c(MP v ) c(MP v ) ↑ by no reporting no way for v to turn MP v into the MP

3. Truthfulness and Individual Rationality 4. combine the above possibilities 32 SD v1v1 v2v2 v3v3 v5v5 v4v4 utility zero No way utility cost ↑

3. Truthfulness and Individual Rationality : S, R, D 3. D acts truthfully - Interest : receive data, new connection, customers happy - No interest : Sender pay less, R’s overpayment Thus If COMMIT executes in ad hoc, truthfulness is strategy 33

 The cost of cooperation : The Difference between premium and MP cost : The measure of inefficiency (C(MP) < m) but c(P -mp ) > m ; communication aborted - COMMIT Approach : changing the topology of the new network. 34