1/18 Philipp Obreiter 1, Birgitta König-Ries 2, Georgios Papadopoulos 1 Engineering Incentive Schemes for Ad Hoc Networks A Case Study for the Lanes Overlay 1 Universität Karlsruhe Institute for Program Structures and Data Organization Universität Karlsruhe GERMANY The First International Workshop on Pervasive Information Management March 18, 2004 – Heraklion, Crete, Greece 2 Technische Universität München Faculty of Computer Science

2/18 Motivation and Case Study: Lanes Service Announcement Service Search any cast any cast Why should you store and forward service advertisements? Why should you forward service requests? Why should you match service requests and advertisements? Why should you refrain from lavishly searching services?

3/18 General Approach: Incentive Schemes Incentive Scheme: A distributed scheme that offers incentives for cooperation How to develop an incentive scheme?  The size of the design space is large  Existing incentive schemes for ad hoc networks  have been developed in an art-like manner  are virtually not reusable since they are  bound to specific cooperation protocols  monolithic  not evaluated according to comparable criteria  A systematic procedure is needed (Development of incentive schemes as an engineering discipline)

4/18 Overview Engineering Steps (exemplified for Lanes) 1.The Cooperation Protocol a.Analysis b.Adjustment 2.Choice of Appropriate Incentives a.Definition of Commitments b.Incentives for Entering into Them c.Incentives for Adhering to Them 3.Evaluation of the Incentive Scheme a.Objective and Key Quantities b.Simulation Parameters

5/ The Cooperation Protocol: Analysis (1) Evaluation Choice of Incentives Cooperation Protocol Cooperation Protocol 1. Kinds of Cooperation: What kinds of inter-entity cooperation exist? any cast any cast (a) Service Advertisement Protocol (c) Intra-lane Maintenance Protocol (d) Inter-lane Maintenance Protocol (b) Service Search Protocol

6/18 The Cooperation Protocol: Analysis (2) Evaluation Choice of Incentives Cooperation Protocol Cooperation Protocol 2. Non-beneficial Steps: Which steps of the cooperation protocol are not beneficial? (a) Service Announcement:  Storing and forwarding announcements (b) Service Search:  Matching and forwarding searches (d) Inter-lance Maintenance:  Participating in split/merge of lanes (c) Intra-lane Maintenance:  Admitting newcomers, sending status information

7/18 The Cooperation Protocol: Analysis (3) Evaluation Choice of Incentives Cooperation Protocol Cooperation Protocol 3. Perceptibility of Misbehavior: Is behavior perceptible? If yes, how reliable is such perceptibility? (a) Service Announcement:  Storing and forwarding announcements (b) Service Search:  Matching and forwarding searches (d) Inter-lance Maintenance:  Participating in split/merge of lanes (c) Intra-lane Maintenance:  Admitting newcomers, sending status information partially no partially no partially no partially

8/18 The Cooperation Protocol: Adjustment (1) Evaluation Choice of Incentives Cooperation Protocol Cooperation Protocol Omission of non-beneficial protocol steps  impossible in Lanes Application of perception mechanisms  digital signatures  assert non-repudiability  Lanes: appended to service advertisements/requests  redundancy  invasive adjustment of the protocol, e.g., receipts  Lanes: receipts for partially perceptible behavior  overhearing  probing

9/18 The Cooperation Protocol: Adjustment (2) Evaluation Choice of Incentives Cooperation Protocol Cooperation Protocol Lane 1Lane 2Lane 3 Searching Entity (SE)Matching Entity 1 (ME1) verifies signature matching unsuccessful verifies signature matching successful signs search message signs receipt signs response verifies signature Matching Entity 2 (ME2)

10/18 Choice of Appropriate Incentives (1) Evaluation Choice of Incentives Cooperation Protocol Choice of Incentives 1. Definition of Commitments: Is failure to execute a non-beneficial step punished?  requires perceptibility of such failure  Lanes: failure to forward is perceptible and should be punished  Incentives for Adhering to Commitments Is the execution of a non-beneficial step remunerated?  only requires perceptibility of successful execution  Lanes: successful matching should be remunerated since it implies  storage of the service advertisement  processing of the service search  Incentives for Entering into Commitments

11/18 Choice of Appropriate Incentives (2) Evaluation Choice of Incentives Cooperation Protocol Choice of Incentives 2. Incentives for Entering into Commitments Incentive Pattern Properties trust basedtrade based collective pattern community pattern barter trade bond based patterns (e.g., note pattern) Rolesasymmetricsymmetricasymmetric Remuneration type none reputation service in return note Enforcement of remuneration −+o Overheadsmallmediumsmallhigh Scalability− −+o Philipp Obreiter, Jens Nimis A Taxonomy of Incentive Patterns - The Design Space of Incentives for Cooperation 2nd Workshop on Agents and Peer-to-Peer Computing (AP2PC'03), Melbourne most appropriate for matching

12/18 Choice of Appropriate Incentives (3) Evaluation Choice of Incentives Cooperation Protocol Choice of Incentives 3. Adhering to Commitments: Exchange Protocols  couple degree of adherence of mutual commitments  Lanes: number of outstanding notes (note credit) is limited Distributed Reputation Systems  provide a means for punishment by keeping track of the trustworthiness of an entity  Lanes: application of the Buddy System

13/18 Choice of Appropriate Incentives (4): Example Evaluation Choice of Incentives Cooperation Protocol Choice of Incentives checks SE‘s note credit Lane 1Lane 2Lane 3 Searching Entity (SE)Matching Entity 1 (ME1) verifies signature queries SE‘s reputation matching unsuccessful verifies signature queries SE‘s reputation matching successful signs search message signs receipt signs response adjusts trust in ME2 verifies signature issues note adjusts trust in SE adjusts trust in ME1 adjust trust in ME1/2 Matching Entity 2 (ME2) checks SE‘s note credit

14/18 Evaluation of the Incentive Scheme (1) Evaluation Choice of Incentives Cooperation Protocol Evaluation Objective of the Evaluation  fairness: high correlation of individual costs/utility  an entity must cooperate if it wants to profit Modelling of the Entities’ Behavior  altruists always cooperate, uncooperative entities never cooperate  cooperative entities: cooperate if peer trustworthy  definition of the note credit Simulation Parameters  cooperation protocol  the original Lanes protocol versus the engineered S-Lanes protocol  simulation environment  composition of the population and number of cooperations Key Quantities  coefficient of correlation between individual costs/utility  slope b of the regression line

15/18 Evaluation of the Incentive Scheme (2) Evaluation Choice of Incentives Cooperation Protocol Evaluation 10 notes credit 4400 searches 15 cooperative entities 5 uncooperative entities Key Quantities  coefficient of correlation: 0.69  slope b of the regression line: 0.54 Key Quantities  coefficient of correlation: -0.21

16/18 Evaluation of the Incentive Scheme (3) Evaluation Choice of Incentives Cooperation Protocol Evaluation 4400 searches 10 coop. 10 uncoop. 10 note credit 4400 searches 10 note credit 10 coop. 10 uncoop.  S-Lanes guarantees fairness for different parameterizations

17/18 Related Work Incentive Engineering:  A systematic procedure for the engineering of appropriate incentives in economics  Inappropriate for the development of incentive schemes in ad hoc networks 1.Adjustment of the cooperation protocol is not considered 2.The choice of incentives  assumes adherence to commitments  assumes “perfect” incentive pattern  is exogenous (which contradicts autonomy) 3.Analytical approach, hence evaluation unsupported

18/18 Summary and Future Work Summary  autonomous entities require incentives in order to stick to the cooperation protocol,  incentive schemes are difficult to develop,  we propose a systematic procedure for their engineering:  analysis and adjustment of the cooperation protocol,  choice of incentives for  entering into commitments: incentive patterns  adherence: exchange protocols, reputation systems  evaluation with multi-variant simulation Future Work  engineering of incentive schemes for other cooperation protocols,  better guidance for the choice of exchange protocols and reputation systems