1. Stimulation for Cooperation in Ad Hoc Networks: Beyond Nuglets Levente Buttyán, Jean-Pierre Hubaux, and Naouel Ben Salem Swiss Federal Institute of Technology – Lausanne Laboratory of Computer Communications and Applications EPFL-I&C-LCA, CH-1015 Lausanne, Switzerland {Levente.Buttyan, Naouel.BenSalem, Jean-Pierre.Hubaux}@epfl.ch

2. 2 Motivation and goal Ad hoc networks no infrastructure all networking services are provided by the nodes themselves cooperation is essential Problem assume that nodes don’t belong to a single authority there’s no good reason to cooperate nodes tend to be selfish Example if the average number of hops from source to destination is ~5  ~80 % of the energy is devoted to packet forwarding  temptation to deny packet forwarding is strong Our goal: to design a mechanism that stimulates cooperation (packet forwarding)

3. 3 Related work  Mitigating Routing Misbehavior in Mobile Ad Hoc Networks, by Marti, Giuli, Lai, and Baker (Stanford), Mobicom 2000  Performance Analysis of the CONFIDANT Protocol: Cooperation Of Nodes - Fairness In Distributed Ad-hoc NeTworks, by Buchegger and Le Boudec. MobiHOC 2002  CORE: A Collaborative Reputation Mechanism to enforce node cooperation in Mobile Ad hoc Networks, by Michiardi and Molva  Sprite: A Simple, Cheat-Proof, Credit-Based System for Mobile Ad-hoc Networks, by Zhong, Yang and Chen

4. 4 Related work  Enforcing Service Availability in Mobile Ad Hoc WANs, by Buttyán and Hubaux (EPFL), MobiHOC 2000  nuglets (virtual currency)  Packet Purse Model: source pays by loading nuglets in the packet before sending it forwarding nodes acquire nuglets from the packet when forwarding it +intuitive, imitates real life –it is difficult to estimate the amount of nuglets to be loaded in the packet purse, and... –to control the amount of nuglets that forwarding nodes can take from it

5. 5 Proposed stimulation mechanism Each node has a credit counter c, and 1.when sending an own packet –the number n of needed intermediate forwarding nodes is estimated –if c < n, then the packet cannot be sent –otherwise, the packet can be sent, in which case c is decreased by n 2.when forwarding a packet –c is increased by 1 + Protection that ensures that –the user cannot manipulate the credit counter –the user cannot tamper with the above mechanism (but she can decide to drop a packet before the mechanism is called !) –c is increased only if the packet has indeed been forwarded We propose a protection mechanism that is based on a tamper resistant hardware module in each node

6. 6 Single node model (basic) B, C, N IN o IN f OUT = OUT o + OUT f DRP = DRP o + DRP f B – initial battery level C – initial credit level N – constant charge b – battery c – credit counter out o – own packets sent (during whole lifetime) out f – forwarding packets sent (during whole lifetime) Selfishness: maximize out o subject to (1) out o, out f  0 (2) N out o – out f  C (3) out o + out f = B b,cb,c

7. 7 Single node model (extended) - own packets are generated at rate r o - forwarding packets arrive at rate r f - no buffering (if an own packet cannot be sent due to the low level of the credit counter, then it is dropped) t end – time when the battery is drained out (not a constant! ) Selfishness: maximize out o and z o subject to z o = out o / r o t end – fraction of own packets sent (1) out o, out f  0 (2) out o  r o t end (3) out f  r f t end (4) N out o – out f  C (5) out o + out f = B

8. 8 Forwarding rules If f = (NB – C)/(N + 1) then drop else –rule 1: always forward –rule 2: if c  C then forward else forward with prob C /c –rule 3: if c  C then forward else drop –rule 4: if c  C then forward with prob c /C else drop where f is the number of packets forwarded so far and c is the current credit level Pr fwd (c) 1 C c rule 1 Pr fwd (c) 1 C c rule 2 Pr fwd (c) 1 C c rule 3 Pr fwd (c) 1 C c rule 4

9. 9 Comparison of forwarding rules (1) Simulation parameters B = 100000 r o = 0.2 pkt/s C = 100 r f = 0.6 … 1.6 pkt/s N = 5 Simulation results out o = 16683 = (B + C )/(N + 1)

10. 10 Comparison of forwarding rules (2) Simulation parameters space500 m x 500 mpkt generation rate0.2 (0.5, 0.8) pkt/s number of nodes100choice of pkt. dest.random power range120 mroutinggeodesic pkt fwding mobility modelrandom waypointinitial credits100 speed1 m/s – 3 m/scredit sync interval 5 (10, 15, 20) s avg. pause time60 ssimulation time7200 s Simulation results

11. 11 Throughput The effect of less cooperative nodes (rule 3) on the total cumulative throughput

12. 12 Conclusion We proposed a mechanism to stimulate the nodes of an ad hoc network for packet forwarding Our approach is based on a credit counter and enforcement of some simple rules in each node (tamper resistant hardware) We showed that the mechanism is effective assuming the following: –each node generates packets continuously –own packets are not buffered (they must be sent immediately or dropped) –selfishness is represented by the goal of dropping as few own packets as possible Future work Weakening the above assumptions Application to other network functions (not only packet fwding) Application in higher layers (e.g., peer-to-peer systems) Application in hybrid (multi hop cellular) networks