# On the Potential of Enhancing Delay-Tolerant Routing Protocols via Age of Information
## 4 Protocol Evaluation
### Cumulative Comparison
Possibly, the value of 100 is a balance point (for a number of time slots equal to 5000). Therefore, it can be concluded that the reduction of the upper bound of the AoI up to the value of 100 (for the number of time slots equal to 5000) does not significantly change the throughput; therefore, it is considered a profitable option, as it achieves a very sharp reduction in the average age of the packets. The throughput is almost unchanged of the AoI Bound up to the value 100, which is justified by the fact that for large barrier values (800, 600) we have fewer packet drops but much more remaining packets in the system, while for smaller barrier values (200, 100) we have more drops but much less remaining packets, with the result that the final throughput of the system remains almost unchanged, as the number of successfully transmitted packets remains almost constant. Figure 8: Dependence of AoI versus number of DTN nodes for Modified-near-v1, Modified-near-v2, FRESH-near-v1 and FRESH-near-v2 protocols. Finally, an undoubtedly important metric in any kind of simulation is the time performance (execution time). More specifically, Figure 11 shows the time required to complete  
Figure 10: Dependence of AoI versus Bound of AoI for Modified-neigh, Modified-near-v1 and Modified-near-v2 protocols. Figure 9: Dependence of throughput versus Bound of AoI for Modified-neigh, Modified-near-v1 and Modified-near-v2 protocols. the simulations for the protocols Modified-near-v1, Modified-near-v2, FRESH-near-v1 and FRESH-near-v2 for various values of the system parameters. Understandably, in the majority of cases, the near-v2 version requires less execution time compared to the near-v1 version in the respective protocol, since there each node only searches for one best \"neighbor\" and not the best \"neighbor\". In addition, it is observed that the increase in the number of time slots brings about a much smoother increase in the execution time than the corresponding increase brought about by the doubling of the number of nodes in the network, which could be characterized as almost exponential. Furthermore, Figure 11 shows that the simulation time in the instance (100, 10,000) is reduced compared to the previous simulation (500, 5000), despite ostensibly being a more complex problem. Regarding this, we should note that we have taken a discrete-event simulation approach for the evaluation of the systems under investigation, which means that in each time slot considered, we account for all events taking place among nodes in the system. The two main parameters of the technique that significantly affect the execution time of the simulation are the size of the DTN network (i.e., practically the number of network nodes) and the number of time slots that will be selected for each simulation. Each simulation produces events between nodes at random, for the duration of the simulation, i.e., the number of slots simulated. Between the above two scenarios, one parameter of the problem increases in value (the number of time slots), while on the contrary the other parameter of the problem decreases in value (the density of the DTN network). Indeed, it is clear that the latter is significantly reduced (sub-fivefold), while the number of time slots is doubled. Furthermore, the number of events taking place in each time slot depends on the number of nodes of the scenario, since the events essentially represent interactions between nodes (and the more the density of the network, the more interactions will emerge on average). Thus, the complexity in the simulation can be essentially attributed more to the developing events in each time slot that require proper handling in each time slot loop, and lesser to the time slot loops. Experimentation confirmed that the increase in the network density leads to a more rapid increase in the execution time than the corresponding increase  
Figure 11: Running time of simulations for various values of system parameters for Modified-near-v1, Modified-near-v2, FRESH-near-v1 and FRESH-near-v2 protocols.