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System Model

This section presents the network model, the node model, and the bundle model. The design goal is also illustrated.

Network Model

In the MSN, the routing is carried out in an opportunistic way as the end-to-end connections can not always exist. In the MSN, a source node Src sends bundles to a destination node Dst depending on relays of intermediate nodes {N1, N2,..., Nn}.

To enable the nodes to pay, there is a Credit Clearance Center (CCC), which is employed to manage the virtual currency for each node [15, 30]. Therefore, before joining the system, every node can register itself to the CCC and obtain its account. Each node should hold a digitally signed receipt for each transaction of relay service and submit the receipt to the CCC. The CCC is a server connected to the Internet, so that the node in the MSN can access the CCC when it connects to the Internet. When the destination receives a bundle and submits ACK to the CCC, the node can get paid after the CCC verifies the receipt. Virtual currency can be used in bundle forwarding to pay for bundle relay service provided by other nodes. If a node does not participate in bundle delivery, it will not get the virtual currency. This means that it will not be able to afford the services from other nodes for its own bundles in the future.

According to the number of message copies in routing, the routing mechanisms can be divided into single-copy and multiple-copy routing. Single-copy routing means that there is only one node having the message copy in the network anytime. Multiple-copy routing is that the message is duplicated to generate multiple copies, and each copy makes routing decisions independently to reduce transmission delay. However, multiple copy routing often consumes and occupies a large amount of network resources. Therefore, the single-copy mechanism is adopted to study the incentive scheme in this chapter.

In this chapter, we focus on the cooperation problem and the incentive scheme to stimulate selfish nodes to participate in data forwarding. Based on related work [15, 31, 32], the mechanism of CCC has already been used by a lot of works, where the overheads for connection and access to the CCC could be controlled and reduced. The reason is that mobile nodes connect to the CCC intermittently and only transfer control messages (receipt and registration) to reduce both the load and overhead, which does not need much power of each node. In addition, in this chapter, as the single-copy mechanism is adopted, it does not need to consume too much energy from the network. There is only one node that has a message, and it needs few connections.

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