**4.1. The original protocol: GEAR**

## *4.1.1. GEAR description*

Geographic and Energy Aware Routing [9] (GEAR) is a geographic routing protocol in which the routing decision accounts for the geographic location of a selected node with respect to the destination. It is also considered as a location based routing protocol because nodes are assumed to be interested in communicating with other nodes that reside in certain geographic locations regardless of their identities. The protocol implements greedy forwarding approach based on distance to destination and energy consumption considerations. In fact, the protocol tries to fairly consider energy balancing among the neighbors of a packet forwarder node.

In GEAR, the routing mechanism involves two phases:

268 Wireless Sensor Networks – Technology and Protocols

by the rating component, CRATER in our case.

node to forward its packets.

any further actions against them is adopted.

**4.1. The original protocol: GEAR** 

neighbors of a packet forwarder node.

*4.1.1. GEAR description* 

**(GETAR) protocol** 

**4. Response component : Geographic, energy and trust aware routing** 

In this section, an enhanced routing protocol that aims to provide a secure packet delivery service guarantee by incorporating the trust awareness concept into the routing decision is presented. Our proposed protocol is called Geographic, Energy and Trust Aware Routing (GETAR) which is an enhanced version of the Geographic and Energy Aware Routing (GEAR) protocol [9]. GEAR is basically a geographic routing protocol in which the next hop is selected based on two metrics: the distance between the next hop and the destination and the remaining energy level the next hop owns. The new contribution in GETAR is to add a third metric in the next-hop selection process, i.e. the risk value of a node that is computed

After a node monitors its neighborhood using EMPIRE and rate them based on CRATER, the node should make the proper response that leads to a proper routing decision. Assume that node A computed a risk value for a malicious neighboring node, B. Then, node A may or may not respond to B's behavior. Since our system treats the secure routing purpose, A should respond in a proper manner. Among different possible reactions provided in many

 *Defensive approach*: Here, node A just avoids using node B as a router. This avoidance can be gradual as the risk value of node B increases. However, B can still use A or any

 *Offensive approach*: In this approach, node A avoids B as in the previous approach. In addition to that, A takes further actions by punishing node B. However, node B still has the right to defend itself and to be treated normally if it can prove a good behavior. *Dismissal approach*: In this approach, node A totally ignores node B as if it is not in the network. So, A does not receive any packet coming through B and does not forward to

In this work, the defensive approach where malicious nodes are simply avoided without

Geographic and Energy Aware Routing [9] (GEAR) is a geographic routing protocol in which the routing decision accounts for the geographic location of a selected node with respect to the destination. It is also considered as a location based routing protocol because nodes are assumed to be interested in communicating with other nodes that reside in certain geographic locations regardless of their identities. The protocol implements greedy forwarding approach based on distance to destination and energy consumption considerations. In fact, the protocol tries to fairly consider energy balancing among the

reputation systems [3, 5, 72], we can identify three main response approaches:

it. Moreover, B will never rejoin the network as seen by node A.


**Forwarding:** Forwarding operation in GEAR can be summarized by the following steps:


$$\text{h(N,R)} \approx \text{c(N, R)} = a \text{ d (N, R)} + (1 \text{ -} a) \text{ e (N)}\tag{3}$$

where d(Ni, R) is the distance from Ni to the center of R normalized (divided) by the largest such distances among all other candidates. e(Ni) is the so far consumed energy at node Ni normalized by the largest consumed energy among all candidates. α is a tunable weight parameter that varies from 0 to 1 and indicates the routing decision preference. So, if α is close to one, the decision will be biased by the distance. If α is close to zero, the decision will be biased by the consumed energy levels.

 After selecting the Nmin for routing, N updates its learned cost value to the destination region R as follows:

$$\text{In(N}\_{\prime}\text{ R)} = \text{h (N}\_{\text{min}\_{\prime}}\text{ R)} + \text{c(N}\_{\prime}\text{ N}\_{\text{min}}) \tag{4}$$

where the latter term is the cost of transmitting a packet from N to Nmin considering the same approach in equation (3).

As we can see, from equation (3), when all nodes are equal in energy, the routing decision will be simply the greedy approach as in GPSR [8]. In case all nodes are equidistance from the destination, the selected node will be the one that consumed the least energy among others. This guarantees a fair selection of the node in terms of energy balancing.

**Dissemination:** Once a packet reaches the center node Ci of the destination region R, the protocol switches to the dessimination phase as follows:


In our proposed protocol, this phase is avoided and we restrict the operation to forwarding with the cost functions since there is actually no routing decision to be made in the dissemination phase as suggested by GEAR.

**Void Regions Problem :** If a node wants to forward a packet and it finds out that the learned costs of all its neighbors are greater than its own learned cost, the node should select itself. However, the node's transmission range does not cover the destination. In this case the node is said to be in a void region. GEAR escapes this void region as follows:


**Figure 3.** Escaping void regions in GEAR
