**5.1. Routing approach**

We provided a simulation based performance analysis for the efficiency of our proposed GETAR routing protocol. Simulation results proved the following points : GETAR improves the delivery ratio, decreases the drop and retransmission ratio and saves the retransmission power when compared with the previous work. The improvement in a performance metric can be achieved at different values of β parameter starting at a minimum value of β at a knee point in the curve. This value can be an optimum choice that guarantees best delivery ratio and better energy balancing. Energy balancing is negatively impacted by an increase in trust awareness. Thus, trade off considerations should be taken carefully in order to design an appropriate value of β. This will be subjected to the application preference between security and energy.

In SAR[70], The routing operation needs to encounter a trusted route setup phase, which contributes some initial delay, especially with the crypto-based authentication required at the route setup. The trust metric used in SAR does not reflect nodes' behavior; rather, they represent a "rank" that a node exhibits based on its identity and various security service provision. Thus, a trusted node in SAR is a node that has the appropriate rank that meets the routing requirements. To rank a node is a problem by itself and requires crypto mechanisms. Our protocol, GETAR, is much simpler in that it assigns trust values to nodes based on nodes behavior. The routing decision rules in SAR are governed by the source, which makes the protocol less flexible. The routing decision is not to select the next hop but to decide to participate in the trusted route. As a result, selfish behavior is not addressed well in SAR. WSN constraints of power consumption are not treated. In fact, SAR targets ad hoc networks with an assumption of more relaxed conditions as compared to WSN.

In TRANS[72], the trust, in fact, is associated with locations rather than nodes. The problem is that a location can be infected by a single node. The detour, then, will be around a larger area rather than a single node. "Innocent" nodes located in proximity of an infected location might be also isolated. If not, they are also exposed to heavy routing duties that may induce selfish behavior. TRANS is limited by single or multiple sink communication models. This assumption is necessary for the efficient operation of the protocol. Our proposed protocol, however, is more generic and can be applied to TRANS model or even for peer-to-peer model. TRANS discusses approaches to decrease energy consumption due to the security provision overhead. However, the protocol does not provide energy efficient techniques in the routing operation itself since it relies on GPSR.

The RGR[73] protocol has no provision for energy efficiency as it relies on GPSR. The protocol totally relies on trust-based forwarding. If a node is completely surrounded by misbehaving nodes, there is no other mechanism proposed to select a next hop since all nodes will be eliminated from the node's forwarding list. RGR is a multi-path trust-based routing. Although multi-path is important for reliable services, we believe that it can be energy consuming which we try to conserve in our work using GETAR.

In RFSN[2], the monitoring mechanism uses a normal watchdog mechanism that assumes a promiscuous mode operation for every node. This is not suitable for the WSN conditions in terms of energy scarcity as discussed earlier. The system does not show a practical solution implementation of monitoring and rating phases. From an implementation point of view, the study should provide an example of how monitoring and rating will be done under some application assumptions. The work does not propose a response methodology, for example, a routing algorithm. Instead, it leaves it as an open issue. Therefore, the work lacks performance figures that can show the efficiency and security gain and benefits in routing operation that can be obtained in adopting this solution.

Main Contributions of our work are the following :

