1. On Designing Incentive-Compatible Routing and Forwarding Protocols in Wireless Ad-Hoc Networks ---- An Integrated Approach Using Game Theoretical and Cryptographic Techniques Authors: Sheng Zhong, Li(Erran) Li, Yanbin Grace Liu, Yang Richard Yang Published on MobiCom 2005, Aug. 28 - Sep.2 2005 Presenter: Xia Wang for CS610jw

2. Outline Introduction Main contributions of this paper Ad-hoc VCG routing protocol (MobiCom03) Cooperation-optimal protocol design Evaluations Conclusion and future work

3. Introduction Cooperation between nodes in wireless ad-hoc network can not be assumed in an environment with selfish nodes. Routing protocol has to address incentive issue to stimulate intermediate nodes to forward data. Classic game theory VCG (Vickrey-Clark- Groves) mechanism has been applied in network routing protocols. But a direct application (Ad-hoc VCG) has flaws. Ad-hoc VCG is not applicable on a lossy links.

4. VCG Mechanism Assume each user has a private type. A user declares its private type to a social planner The social planner decides the outcome to optimize a social objective and a payment to each user. The outcome and the payment are determined in such a way that reporting the type truthfully is a dominant action and the outcome is socially optimal. Example: The second-price auction

5. Main contributions Show that no forwarding-dominant protocol exists. Design a cooperation-optimal protocol called Corsac, a Cooperation-optimal routing-and- forwarding protocol in wireless ad-hoc networks using cryptographic techniques. The protocol can be extended to a practical radio propagation model where packet reception is probabilistic.

6. Ad-hoc VCG Routing Protocol(1) Source S = V 0 wants to communicate with a destination D=V n. S → * : (REQUEST, s 0,n, 0, n,,c0) Every node V j (not S and D) receives the ROUTE REQUEST from a node V i do the following: –Check whether it is a new ROUTE REQUEST –Determine the received power: –Estimate the minimum power for V i to reach V j Replace with in the ROUTE REQUEST packet; append its own identification j and the emission power. v j → *: (REQUEST, s 0,n, 0, n,,c 0, 1,, c 1, …, j, P emit j,c j )

7. Ad-hoc VCG Routing Protocol (2) Destination D: –Compute the SP and |SP| –Calculate the VCG-payment for each intermediate node Where is the shortest path from S to D that doesn’t contain node, is the cost.

8. Ad-hoc VCG Routing Protocol (3) –Send ROUTE REPLY with route sequence and the corresponding minimal required transmission power as well as the VCG- payment for each intermediate node. vσ(j) → vσ(j−1) : (REPLY, s k, 0, σ(1),…, σ(k),...,,…,, Mσ(1),..., Mσ(k) )

9. Ad-hoc VCG Routing Protocol(4) An example network with edge-weight

10. Ad-hoc VCG Routing Protocol(5) Ad-hoc VCG is claimed to be cost- efficient and truthful against one node cheating. What if more than one nodes cheat?

11. Notations and definitions a i : action of node i a -i : action of all nodes except node i a = (a i, a -i ) action profile for all nodes A node i’s utility: u i = -c i + p i (c i is the cost, pi is the payment) In a non-cooperative strategic game, a dominant action of a player is one that maximizes its utility no matter what actions other players choose. Specifically, a i is node i’s dominant action if, for any a i ’!= a i and any a −i, u i (a i, a −i ) ≥ u i (a i ’, a −i ).

12. Example of ad-hoc VCG fails P emit = 5 R = 5 B doesn’t cheat, B gets utility 0; If B cheats by claim R = 15, B gets payment 12-6 = 6, its utility of 2 Ad-hoc VCG Fail! Fail with more nodes cheating because of mutually- dependent types.

13. A cooperation-optimal Protocol Def: A routing protocol is a routing- dominant protocol to the routing stage if following the protocol is a dominant subaction of each potential forwarding node in the routing stage.

14. A cooperation-optimal Protocol Extensive game model Each vertex – node Edge – possible decision Each subtree – subgame Each path from root to a leaf – a possible set of decision by the wireless nodes. In classic game theory, such a path is said to be a subgame perfect equilibrium if it is a Nash equilibrium for every subgame An example game tree

15. A cooperation-optimal Protocol Def: A forwarding protocol is a forwarding- optimal protocol to the forwarding stage under routing decision R if all packets are forwarded to their destinations in this protocol and following the protocol is a subgame perfect equilibrium under routing decision R in the forwarding stage.

16. A cooperation-optimal Protocol This routing protocol addresses two components: –routing stage: determines a packet forwarding path from a source to a destination; –Forwarding stage is to verify that forwarding does happen.

17. Routing Stage Source node’s test signals –Source S starts a session of M packets. –divides the packets into blocks, where b is the number of packets in a block. –S picks a random number r 0. –Let H be a cryptographic hash function. S computes r =

18. Routing Stage –For each power level l ∈ P (in increasing order), S sends out (TESTSIGNAL, [S, D, r], [S, hl]) at power level l, where r is a random number used to distinguish different session with source S and destination D. hl contains an encryption of [S,D, r, l, α S ] using key k S,D and a MAC of the encryption using the same key. k S,D is a shared key between S and D using Diffie-Hellman key exchange in cryptography. α S is a cost-of-energy parameter representing the cost of unit energy at node i. (In ad-hoc VCG, it is c i )

19. Routing Stage Upon receiving (TESTSIGNAL, [S, D, r], [P, h]) from an upstream neighbor P, an intermediate node i does the following : –Node i sends out (ROUTEINFO, [S, D, r], [P, i, h]) at power level P ctr (where P ctr is a power level for control messages such that the communication graph is connected when all links use power level P ctr for transmission). h is computed by encrypting h using key k i,D. For integrity, this message is protected by a MAC using key ki,D. –If the TESTSIGNAL is the first one i receives for session (S, D, r), then for each l ∈ P (in increasing order), node i sends out (TESTSIGNAL, [S, D, r], [i, hl]) at power level l, where hl contains an encryption of [S,D, r, l, αi] using the key k i,D and a MAC of the encryption using the same key.

20. Routing Stage Upon receiving (ROUTEINFO, [S, D, r], [P, i, h]), an intermediate node j does the following: – If this ROUTEINFO is new to node j, then node j sends out (ROUTEINFO, [S, D, r], [P, i, h]) at power level P ctr

21. Routing Stage Destination D maintains cost matrix for each session (S, D, r). –Upon receiving (TESTSIGNAL, [S, D, r], h) from neighbor P, D decrypts h, verifies the MAC using the key k P,D, and “translates” h to the corresponding power level l and cost-of-energy parameter α P. D records (l, α P ) in the cost matrix’s entry for link (P,D). –Upon receiving (ROUTEINFO, [S, D, r], [P, i, h]), D decrypts h, verifies the packet’s MAC using key k i,D, and “translates” h to the corresponding power level l and cost-of-energy parameter α P. D records (l, α P ) in the cost matrix’s entry for link (P, i).

22. Routing Stage After collection all link cost information, D check, for each link, that the cost-of-energy parameter does not change. Computes LCP(S, D) and the unit payment for each intermediate node i.

23. Packet forwarding stage After the routing discovery phase, the destination D sends the routing decision ([S,D, r], LCP(S,D), P S,{(Pi, pi) | i is an intermediate node on LCP(S,D)}) with digital signature along the reverse path of LCP. P i is the power level for node i p i is the payment for node i

24. Packet forwarding stage The source node sends out packets in block. Together with the last data packet in the m- th block, the source sends out = For each block, the intermediate node waits for a confirmation after it forwards the block and before it start sending the next block. The destination decrypts all packets in a block, it decrypts, and sends it back along LCP(S, D) as a confirmation. Each intermediate node verifies that r =

25. Evaluations Simulation using GloMoSim Simulation package. The scenario consists of 30 nodes that are randomly distributed in an area of 2000 by 2000 meters. Each node has transmission power level at 7 and 14dBm. is set to 1 for every node

26. Topology of simulation setup A network with 30 nodes. The ID’s of the nodes are labeled. A link between two nodes indicates that they are neighbors. The credit balance and forwarding energy cost at the end of 15 minutes are represented by the sizes of the circles.

27. Evaluation Results the credit balance of the nodes (the total credit received by forwarding others’ traffic minus the total credit paid in order to send one’s own traffic)

28. Evaluation Results (2) forwarding energy cost

29. Effects of Cheating Credit balance for node 3 with four different settings After 30 minutes’ simulation

30. Effects of Cheating(2)

31. Conclusion and Future work Conclusion –Design the first incentive-compatible, integrated routing and forwarding protocol in wireless ad-hoc networks. –Combine incentive mechanisms and security techniques to address link cost issue. Future work –This method can be extended to congestion price in network with limited capacity. –A general model to integrate incentive issue in different layers: MAC layer and application layer.

32. Question?