## 4 Proposed Metrics
### Results and Discussion of the Proposed Metrics
#### 4.2.2 Network Layer Metrics  
The metrics of the network layer are very important, because they show the performance and usefulness of a routing protocol. Each routing protocol is designed for specific applications and certain scenarios. These metrics indicate how the use of bandwidth is affected by the overhead of the routing protocol in use. In addition, the availability of effective routes and the ability of the network for self-configuration show the capacity of the protocol to recover from topology changes. Recovery times have an impact on the latency in the network. Figure 11: Average retransmissions and CSMA/CA retries _vs._ time (s). Overhead  
Overhead is an important metric that influences the amount of network collisions and the channel occupancy, and this is why we compare this metric for each of the protocols under study. Overhead depends on the number of routing packets that the routing protocol needs to connect to nodes and to route packet traffic. Thus, it is calculated taking into account the number of control packets that are needed to route a traffic packet. Ideally, a routing protocol should need the least amount of control packets. Overhead as a function of time is presented for each of the protocols in Figure 12. Overhead represents the fraction of the total transmitted packets that are control packets. At the beginning of the simulation, the nodes know the network through their neighbors, so as a part of the routing protocol, the nodes send discovery and response packets. For this reason, there is a more pronounced peak at the beginning of the plot. Subsequently, AODV and DSR protocols send route discovery packets periodically when a node does not have a route to a desired destination, because this has expired or is broken. The AODV protocol has expiration timers for routes, so it has more overhead than the others. DSR does not have timers, and it only sends error messages for invalid routes. ZTR is the protocol with the least overhead, since it does not keep routing tables in the nodes, as routing is assigned by the coordinator at the beginning. The MPH protocol presents a behavior similar to ZTR, even though MPH has neighbor discovery packets to form the neighbor tables, response neighbor discovery packets and a verification reply ACK packet. This shows that MPH does not congest the network with overhead packets and can be similar in behavior to the simple protocol, ZTR. We can see that MPH protocol shows a reduction of 26.9% on overhead with respect to AODV and 17% with respect to DSR. Besides, MPH presents only a 11% increment on overhead with respect to ZTR. Figure 12: The percent of overhead _vs._ time. The discovered routes percentage is a metric that measures how quick a routing protocol is at finding the routes needed to reach the coordinator node (because for this scenario, the coordinator node is the final destination). These routes may be direct links to the coordinator node or indirect links requiring intermediate nodes. This percentage is calculated considering the maximum number of possible routes that each node can reach in each of the evaluated protocols. This amount of routes is based basically on the average number of neighbors of each node, according to the information on the neighbor or routing tables. This metric reflects the time taken to find these routes: the faster the nodes find these routes, the sooner they will start sending information packets to the destination. This metric is also affected by the amount of maintenance routes that each of the routing protocols has. Discovered routes analysis is shown in Figure 13. MPH has already-defined routes when a node has a packet to send. This is why in Figure 13 we observe that MPH quickly reaches almost 100% of the routes to the destination node, whereas the AODV and DSR protocols take a little longer to find the routes due to the discovery mechanism and, if these routes have expired, to complete the whole discovery process.