**3.3. System assumptions**

260 Wireless Sensor Networks – Technology and Protocols

**Figure 1.** SNARE Reputation system framework

rating component.

The monitoring component, EMPIRE(Efficient Monitoring Procedure In REputation system)[84], observes packet forwarding events. A monitoring node will not be in a continuous monitoring mode of operation, rather, it will monitor the neighborhood periodically and probabilistically to save resources. When a misbehaving event is detected, it is counted and stored until an update time, Tupdate or TON is due, then a report is sent to the

The rating component, CRATER(Cautious Rating for Trust Enabled Routing)[85], evaluates the amount of risk an observed node would provide for routing operation. The risk value is a quantity that represents the previous misbehaving activities that a malicious node (a node that drops packet) obtained. This value is used as an expectation for how much risk would be suffered by selecting that malicious node as a router. It is calculated based on the first hand information and the second hand information. The first hand information is achieved by the direct observation done by the node of concern. Risk values are updated based on the first hand information every time a new misbehavior report is received from the monitoring component. Moreover, if an observed node shows an idle behavior during a certain period, its risk value is reduced. A monitor also updates the risk values of its neighbors by second

hand information received periodically from some announcers.

In order to understand how our system works and how simulations have been carried out, it is essential to formally identify the general assumptions on system requirements and boundaries. We will look at system assumptions from different perspectives.
