New Approach for Selfish Nodes Detection in Mobile Ad hoc Networks
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New Approach for Selfish Nodes Detection in Mobile Ad hoc
Networks
Djamel Djenouri: Basic Software Laboratory, CERIST Center of Research, Algiers, Algeria.E mail: [email protected] Nadjib Badache: Computer Science Department, USTHB University, Algiers, Algeria.E mail: [email protected]
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Outline
1 Overview on Mobile Ad hoc Networks (MANETs) 2 Selfish behavior on packet forwarding problem 3 Watchdog4 Watchdog’s limitation5 New Solution6 Simulation results7 Perspectives8 Conclusion
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A MANET is a collection of Wireless mobile hosts making on the fly a temporary network, without relying on any fixed infrastructure. No central administration exists Mobile hosts cooperate to ensure roles ensured by the fixed infrastructure in traditional networks
MANET Overview (Definition)
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MANET Overview (Multi-Hop)
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• Dynamic Topology• Limited bandwidth• Limited physical Security• Infrastructurless• Limited energy resources
MANET’s features
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Selfish behavior
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Watchdog
• Proposed by Marti et al. In MobiCom 2000
• Many recent sophisticated solutions rely on it in their monitoring component
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Watchdog’s principles
• Based on the promiscuous mode monitoring and implemented with a source routing protocol.
• When a node Na sends a packet to Nb to forward to Nc, it monitors it by simply overhearing the channel, it validates the forwarding iff it overhears the packet retransmitted by Nb.
• This process is generated for each couple of hops in the route
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WatchdogIf packet heard OK
Else increase Nc’s failure Tally
failure Tally > threshold the node misbehave
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Watchdog’s detection drawbacks
• Does not detect correctly and could cause false detections when the power control technique is employed
• Does not detect selfish nodes in many cases (collisions, partial dropping, collusions)
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New solution (Two-hop ACK)
• We propose a new monitoring solution based on two-hop ACK.
• Assume A monitors B’s forwarding to C, this latter acknowledges each packet by sending a two hop ACK back to A via B.
• An efficient asymmetric encryption strategy is used to ensure authenticity of ACKs and to prevent the following vulnerability:
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New solution (hop ACK)
• B misbehaves and drops packets, to circumvent A it sends it a falsified ACK on behalf of C.
• The encryption strategy we used gets over this vulnerability and,
• it is relatively of low cost, since it merely encrypts short random numbers, instead of compute digital signature on the packets.
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New solution (hop ACK)
- Generates r- Encrypts it with C’s PK- Adds it to the packet
- Decrypts r- Encrypts it with A’s PK- Adds it to a 2 hop ACK packet
- Decrypts r- - Checks whether it matches the one it generates - If so, it validates the forwarding
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Simulation results
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Two-hop ACKs Problem
• The obvious problem of our first solution is the important overhead it engenders, even if the nodes well behave. It requires a two-hop ACK for each data packet, which is costly.
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Perspectives
We plan to complete the proposal by • Reduce the overhead• Defining efficiently the threshold of
accusasion• Defining actions that have to be taken
when a node is accused as a selfish• and particulary by proposing a mechanism
allowing nodes to exchange their knowledge regarding nodes that behave selfishly.
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Random two-hop ACK
• To overcome the two-hop cost, we suggest that A would not continuously ask an ACK, but randomly decides whether to do so with a probability p, and maps the decision in the packet.
• This randomization and mapping prevent B from deducing which packet includes an ACK request, and let it motivated to forward all packets
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Random two-hop ACK
• P is updated according to B’s behavior, it is decreased each time B forward a packet until reaching its minimum value, and set to 1 upon a dropping detection.
• This way, more trust is accorded to well-behaving nodes and ACK ask is enforced after a dropping, which ensure the efficiency and decreases the cost especially when selfish nodes rate is low, as shown in the simulation results
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Conclusion
• Our solution is operational regardless the power control employment
• It reduces the false detection rate with low cost (energy and delay)
• The random two-hop ACK reduces dramatically the overhead
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