## 4 Evaluation
### Fairness-Oblivious Routing  
While the same movement conditions apply across the simulations for each routing protocol, the resulting fairness varies depending on the routing approach. This is because different types of forwarding utilities and algorithms have different levels of aggressiveness in utilizing popular nodes. SnF shows the highest fairness among the selected (fairness-oblivious) routing protocols. Due to binary spraying, a less popular node with more copies of a message may end up doing more sending than a more popular node carrying the same message, thereby allowing for more fairness. dLife's fairness is similar to that of PRoPHET. This is because forwarders are not limited to nodes with high level of popularity. By including a utility function that determines better relays based on the social engagement with the destination, dLife is able to distribute the burden among a larger set of nodes.  
The encounter-based strategy of PRoPHET selects relay nodes based on their encounter frequency with the destination. Since popular nodes experience more encounters and may also encounter neighbours more frequently, they often present higher delivery predictabilities. Furthermore, PRoPHET's transitive property allows this knowledge to be perceived over multiple hops, which increases the chances of selecting popular nodes as relays. That being the case, less popular nodes have less chance of being selected as relays, since the number of nodes they often encounter is relatively less. Consequently, PRoPHET's fairness is reduced as more messages are pushed towards popular nodes.  
Bubble Rap is designed to utilize central nodes to disseminate messages within and between communities. Messages are thereby directed towards nodes with higher centrality. Unfortunately, nodes with high centrality are relatively few in the network. Consequently, the same set of few highly central nodes receive a significantly high number of messages in the network, which decreases fairness. As for HERO, a potential relay node is either a node from the same region as the destination  
Figure 14: The number of central nodes in the network when running under PRoPHET, CCAF and FLARoute.  
Figure 13: The impact of CCAF and FLARoute on PRoPHET in terms of transmission overhead and average energy consumption.  
or a node that visits the destination's region more frequently than the custodian of the message. Under higher degrees of spatial locality, there are less chances of encountering a node from the same region as the destination. Hence, only nodes that often travel longer distances are able to present a better forwarding utility. Since only relatively few nodes visit many different regions in the network, fairness is significantly degraded.  
From the results in Figure 10, it is noticeable that energy distribution has a significant impact on fairness (cf., Figure 9). Among the routing protocols oblivious to fairness, SnF shows the highest fairness as well as the highest energy distribution. This is followed by PRoPHET and dLife, which correspond to the next set of protocols in terms of fairness. Finally, Bubble Rap and HERO record the lowest energy distribution, and correspond to the routing protocols with the lowest fairness.