## 4 Partition Aware-RPL Protocol Overview
### Parent Selection Algorithm
In addition, Figure 12(d) illustrating the duty cycle per node per second as a function of the elapsed time, shows that both protocols consume almost the same amount of energy and that this energy consumption is almost independent of the number of parcels in the farmland (i.e., 1 to 9). Figure 5:2 PA-RPL performance as a function of elapsed time

Finally, Figure 13c depicts the evolution of the ratio of received packets over time. Similar to the previous metrics, we observe two operation regimes. During the first (transient) regime, the ratio of received messages is very low, however during the permanent regime, this ratio substantially increases around 90%, hence reaching standard RPL performance. This is obviously despite the important intrinsic difference between both resulting DODAGs. In conclusion, we can say that PA-RPL, behaves similarly to the standard RPL even when pushed to its limits and where we are not really making use of the key advantage of reflecting the spatial partitioning of the farmland. The advantage of PA-RPL over the standard RPL will be presented in the next section. #### 6.2.2 Case 2: Few Parcels Simultaneously Monitored

For the second case, we consider a more realistic scenario. Given that each type of crop grows during a particular season and observes a number of evolution phases, a good monitoring application shall take such variability into account. In fact, along the evolution phases, crop monitoring requirements vary in terms of type of information to gather, and periodicity of data collection. As such, in the same multi-crop farm, it is common to have different data collection frequencies simultaneously; raised from different parcels. Each frequency reflects the crop evolution phase and season. When the collection frequency of a given parcel is very low, nodes belonging to this parcel will be in a sleep mode for quite long periods (i.e., further saving precious energy). However, when high frequencies of data gathering are applied, nodes will wake up for more time and thus consume more energy. Moreover, even during these \"requiring-high-frequency\" phases, it is possible to turn nodes into sleep mode for longer periods of time with no risks. For example, after the irrigation of a parcel, it is reasonable that the soil moisture collecting frequency gets extremely reduced. With such realistic scenarios, the superiority of PA-RPL over RPL becomes more tangible. Indeed, the standard RPL clearly forces the nodes of one culture (or one parcel) to wake up and function during the season of another culture (or another parcel), in order to route the information. This may clearly cause an important loss of energy. In fact, based on the radio duty cycle mechanism [39], a node sleeps most of the time and periodically wakes-up to check if a radio transmission activity is detected. In this case, the node stays awake to listen to the communications. With RPL, a communication message arising from one parcel will take several paths before reaching the sink node. Obviously, all the nodes belonging to the routing trajectory, in addition to their neighbors, will detect this communication activity. Therefore, an important number of nodes remain uselessly awake. In contrast, the PA-RPL will choose a unique trajectory linking the Parcel Head (PH) to the sink, hence avoiding the messages to be dispatched to a large zone of the farm LLN. This saves considerable amounts of energy because large number of non-concerned nodes will not need to listen to non-pertinent communications, i.e., they do not disturb their sleeping. In order to compare the performance of PA-RPL and RPL we consider periods of time, or scenarios, where only some of the parcels have crops that need monitoring. For instance, let us consider the case where only nodes located in parcel VI need to transmit data to the sink node. We then vary the applied data load and measure the duty cycle per node per second in permanent regime (i.e., after the 1500 s transient time).