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Chapter 14: Incentive-aware opportunistic

network routing

Greg Bigwood and Tristan Henderson

University of St Andrews

Routing in Opportunistic Networks

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Problem:

Opportunistic networking relies on cooperation between nodes to perform efficiently Opportunistic routing protocols depend on nodes

forwarding messages Otherwise nodes must delivery directly to

recipient

Cooperative forwarding incurs a cost to forwarding nodes Energy Storage

Self-interested nodes avoid forwarding cost: Refuse to pass messages on for other nodes

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Outline

We discuss attack on opportunistic routing With a focus on selfishness

We discuss incentive mechanisms for opportunistic routing

Conclude with discussions of outstanding challenges in the area

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Opportunistic Network Routing

Frequent disconnections Mobile nodes coming into and out of range

Non-static forwarding paths A varied set of nodes in range over time

No predictable interaction schedule Nodes are most likely carried by users with diverse

and variable mobility patterns

Nodes must opportunistically use any available nodes for forwarding

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Cooperation

Opportunistic networking necessarily relies on cooperation to perform efficiently If all nodes participate, we find the shortest paths

If nodes do not participate in forwarding, we must pass message directly to destination High latency Low delivery ratio

Cooperative forwarding involves cost to intermediaries: Storage of ferried messages Energy cost of forwarding

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Selfishness

Selfishness: refusing to forward other nodes messages Reduces cost for intermediary Still expect their own messages to be forwarded by

others

Harms performance of network

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Reality Mining Selfishness Simulation

As proportion of selfishness nodes increases, Delivery ratio decreases. Selfishness harms the network.

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Attacks on Opportunistic Routing

Manipulation of routes Nodes may alter the delivery path

Selective maliciousness Nodes may be malicious only under certain

circumstances

Selfishness Nodes messages may not reach destination Users’ economically rational desire to preserve

battery affects their selfishness

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Selfishness

Opportunistic routing protocols, in particular Epidemic routing and Spray-and-wait routing are vulnerable to selfishness (Panagakis et al).

Once 30% of the nodes in the network are selfish, performance degrades (Keränen et al).

Is there an acceptable amount of selfishness? What if selfish nodes only forward to the destination,

but not other intermediaries? Is this acceptable?

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Incentivising Routing Participation

Many approaches in traditional networks Bartering

Swap messages 1-for-1

Currency Purchase credits to give to other nodes in return for

their forwarding service

Asynchronous bilateral trading Nodes perform actions that benefit each other, but

not necessarily simultaneously

Watchdog mechanisms Nodes monitor each others communication to ensure

compliance

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Which are appropriate for Opp Nets?

Bartering Not all nodes have equal number of messages to

exchange

Currency No out of band oracle to administer currency

Watchdog mechanisms Not many encounters will be observed by a third

party

Asynchronous bilateral trading Nodes perform actions that benefit each other, but

not necessarily simultaneously

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What information do we have?

We must rely only on encounters between nodes

Nodes can collect opinion data based on their interactions

Nodes can use collated opinion data to make decisions about the trustworthiness of individual nodes

Encounter tickets Use PKI to generate provable encounter tickets Used to prove messages were exchanges and

encounters took place

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How to bootstrap the mechanism?

The incentive mechanism must throughout the entire lifetime of the network

We need a mechanism to generate initial trust opinion data

We can use Self-Reported Social Networks (SRSNs) Use online social network data or similar out of band

data to provide information available before network startup

These SRSN data may correlate with trustworthyness

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Attack against incentive mechanisms

Exploiting friendship mechansisms Do not incentivise nodes to add as many other nodes

as “friends”.

Increasing trust through epidemic behaviour Malicious nodes may ignore routing protocols to gain

credits/currency/inflated ranking

Tailgating Generating large numbers of encounter tickets by

following nodes

Manipulation of control traffic Withholding ranking information Offer non-existent routes

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Attack against incentive mechanisms 2

Defamation Creating false reputation claims to damage other

nods

Exploiting detection algorithms Exploiting grace periods or allowances made for

genuine device limitations such as battery failure Do not encourage nodes to drop old messages (this

may be acceptable)

CollusionSybil attacks

How do we know a user cannot easily create a new identity

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IRONMAN: Addressing these concerns

IRONMAN Incentives and Reputation for Opportunistic routiNg in Mobile and Ad hoc Networks (Bigwood et al)

Use SRSN information to bootstrap network Increase personal ranking of nodes considered

friends Use encounter histories to detect selfishness

No oracles, watchdogs, infrastructure networks nor flooded delivery receipts required

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IRONMAN Detection Mechanism

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Incentive Mechanism Performance

Detection Time The time it takes a mechanism to correctly detect

selfish behaviour

Detection Accuracy The proportion of selfish nodes that were correctly

detected as selfish by a mechanism

Selfishness Cost The proportion of forwarded messages that were

generated as a result of a node creating a message while selfish

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Performance Comparison

Simulation of several popular incentive mechanisms

Epidemic routing over the Reality Mining Trace

We compare the selfishness cost when two proportions of nodes behave selfishly

Nodes have finite buffer, energy and message TTL

IRONMAN greatly outperforms other mechanisms

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Incentive Summary

By bootstrapping the trust mechanism using SRSNS, and using Encounter histories IRONMAN outperforms existing mechanisms

IRONMAN suited to particular networking constraints in Opportunistic Networks

This demonstrates that Incentive mechanisms designed for opportunistic routing and useful, and motivates future work in this area

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Challenges For Incentive Aware Routing

User behaviour Some nodes may behave altruistically except under

specific circumstances. Is this acceptable? How can nodes corroborate information? Exact

timings difficult in opportunistic network

Using social-network information SRSN information has shown to be useful. Can we

perhaps classify users based on social network information?

Are opportunistic routing patterns similar to social network communication patterns?

May lead to cross disciplinary research

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Challenges For Incentive Aware Routing

Cross-layer information use Many Opportunistic Routing applications might

themselves involve social networks. E.g. crowdsourcing and mobile social networks.

Can we use information from the application at the routing layer or (vice versa)? E.g., spammers have their messages dropped?

Modeling social network behaviour Advanced simulation Allows for comparison of social networks and

network communication networks Predictive user location may improve routing

performance

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Challenges For Incentive Aware Routing

Academic challenges Collecting datasets is costly A lack of datasets is harming research Datasets are not shared among researches

effectively

Metrics for analysing incentive mechanism No consensus on how best to compare and analyse

the incentive mechanisms for opportunistic networks.

What constitutes a fair distribution of forwarding?

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Conclusions

Incentive mechanisms will be vital for any opportunistic networking deployment

Existing incentive mechanisms from MANETs and DTNs are innapropriate for opportunistic networks

Using SRSN information provides incentive mechanisms with a method of bootstrapping their protocols

There a many challenges left for opportimostic routing, many of which are cross-discipline problems