Stimulation for Cooperation in Ad Hoc Networks: Beyond Nuglets

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. 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. 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. MobiHOC2002 • 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. 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. 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. B, C, N INo OUT = OUTo + OUTf INf DRP = DRPo + DRPf Single node model (basic) B – initial battery level C – initial credit level N – constant charge b – battery c – credit counter b,c outo – own packets sent (during whole lifetime) outf – forwarding packets sent (during whole lifetime) Selfishness: maximize outo subject to (1) outo, outf³ 0 (2) N outo – outf£ C (3) outo + outf = B

7. Single node model (extended) - own packets are generated at rate ro - forwarding packets arrive at rate rf - no buffering (if an own packet cannot be sent due to the low level of the credit counter, then it is dropped) tend – time when the battery is drained out (not a constant! ) zo = outo / ro tend – fraction of own packets sent Selfishness: maximize outo and zo subject to (1) outo, outf³ 0 (2) outo£ro tend (3) outf£rf tend (4) N outo – outf£ C (5) outo + outf = B

8. Prfwd(c) Prfwd(c) rule 2 rule 1 1 1 C c c C Prfwd(c) rule 3 1 c C rule 4 Prfwd(c) 1 c C 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 /Celse drop where f is the number of packets forwarded so far and c is the current credit level

9. Comparison of forwarding rules (1) Simulation parameters B = 100000 ro = 0.2 pkt/s C = 100 rf = 0.6 … 1.6 pkt/s N = 5 Simulation resultsouto = 16683 = (B + C )/(N + 1)

10. Comparison of forwarding rules (2) Simulation parameters space 500 m x 500 m pkt generation rate 0.2 (0.5, 0.8) pkt/s number of nodes 100 choice of pkt. dest. random power range 120 m routing geodesic pkt fwding mobility model random waypoint initial credits 100 speed 1 m/s – 3 m/s credit sync interval 5 (10, 15, 20) s avg. pause time 60 s simulation time 7200 s Simulation results

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

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