## 4 Evaluation
### Routing with Variable-Quota Replication Using ADS and LARep  
A noticeable trend is the relationship between message transmission overhead and energy consumption, such that incurring more of the former results in more of the latter. For instance, routing without a replication technique incurs the highest transmission overhead and also records the highest energy consumption as compared with utilizing a replication technique. With fixed-quota replication, more quota incurs more message transmission overhead and consumes more energy as well. It is also noticeable that more quota increases delivery guarantees, thereby resulting in more throughput. The flexibility lacking in fixed-quota replication can be achieved with variable-quota replication. The challenge however, is achieving this with realistic assumptions that comply with the characteristics of OppNets for sensed data collection. By terminating replication even before the quota is exhausted, ADS achieves a balance between fixed-quota's message transmission overhead and throughput (i.e., both metrics are neither maximum nor minimum as compared with utilizing fixed replication quotas). While this relaxes the need for an optimal quota, the mechanism is based on a switch value that is derived from network area. Unfortunately, obtaining the area of a highly dynamic network on demand is impractical, especially without knowledge about global network parameters. Furthermore, the number of generated copies is still limited by the selected quota.  
LARep records the lowest transmission overhead and highest throughput--incorporating it into PRoPHET reduces transmission overhead by 99.7% and increases throughput by 49.4%. LARep takes a different approach by replicating messages at different rates depending on their likelihood of delivery and progress towards the destination. Unlike existing variable-quota replication techniques, LARep is designed to cope with the characteristics of OppNets for sensed data collection, and replicates messages without the need for global knowledge about network parameters. As compared with replicating every message at the same rate, reducing the replication rate of some messages reduces transmission overhead as well as the number of failed transmissions. As shown in Figure 19, the number of failed transmissions corresponds with the energy expenditure of the proposals. This is because each failed transmission accounts for energy. Furthermore, more failed transmissions results in more re-transmission attempts, hence, more energy consumption. LARep records the lowest number of failed transmissions, thereby consuming the least energy in this aspect.  
Reducing the replication of messages that have more chances of delivery also accounts for reduced transmission overhead due to less redundant transmissions. This can be observed from LARep's ability to reduce the transmission overhead that LAMeD incurs mainly due to retaining messages with more chances of being delivered for longer periods. Our proposed replication mechanisms also introduce more copies of messages with less chances of delivery, thereby improving throughput significantly. Retaining some messages for longer periods also has an impact on the time taken to deliver messages as LARep records the highest average delivery delay at 10.6 hours. However, delivering messages within a half-day period is acceptable considering the delay-tolerant nature of the data involved.