# On the Potential of Enhancing Delay-Tolerant Routing Protocols via Age of Information
## 4 Protocol Evaluation
### Cumulative Comparison
Similarly, in Figure 6, we demonstrate the dependence of the average age of the packets with the change in the number of time slots for the four protocols. From this figure, the superiority of the two modified versions of the FRESH protocol over the original versions is evident. More specifically, especially for the large values of the number of time slots, the average age of the packets in the two FRESH-near protocols is almost 30-fold higher than the corresponding age of the packets in the two Modified-near protocols. Therefore, choosing the modified protocol over the original one is an effective option, since the difference in throughput is almost insignificant, while on the other hand, the benefit in packet age is considerable. Another outcome regards the effect of throughput with respect to how dense the DTN network is, i.e., with respect to the number of its nodes. This effect is depicted in Figure 7.  
Figure 6: Dependence of AoI versus number of time slots for Modified-near-v1, Modified-near-v2, FRESH-near-v1 and FRESH-near-v2 protocols. It can be observed that for all protocols the throughput decreases almost exponentially with the increase in the network density. This result is expected, as with the increase in the number of nodes, the available \"near\" nodes also increase, making it more difficult to transmit a packet to its destination. This observation is directly related to a well-known and general result of [PERSON] and [PERSON] [38] that the throughput is \(\Theta\Big{(}\frac{W}{\sqrt{n}}\Big{)}\) bits per second for each node for a destination that is not too far away, assuming that \(n\) nodes are optimally placed in a disk of unit area, traffic patterns are optimally assigned, the range of each transmission is optimally chosen, and each node is capable of transmitting at \(W\) bits per second. In addition, it is observed that the best performance is again achieved by the two protocols that choose their \"nearest anchor node\" as a relay node, while again there is a small superiority of the modified protocols over the original ones even in the throughput part. In Figure 8, the behavior of the average age of the packets compared to the network density is similarly shown. Again, the overwhelming superiority of the two modified protocols over the two original ones is evident in the part of the average age of the packets, while overall regarding the part of the network density, it is concluded that the use of the modified protocol FRESH on the one hand does not significantly affect the part of throughput, on the other hand it offers a significant gain in the AoI of the packets, which here are much fresher than the corresponding packets in the original FRESH protocol. Figure 7: Dependence of throughput versus number of DTN nodes for Modified-near-v1, Modified-near-v2, FRESH-near-v1 and FRESH-near-v2 protocols. At the same time, an interesting observation to be made is whether the two metrics considered (throughput and average packet age) are affected by the AoI Bound in the modified protocol. Intuitively, if the threshold value for the AoI is reduced enough, on the one hand the packets have a younger age, and on the other hand this leads to more drops, therefore possibly to a reduction in throughput. The figures below (Figures 9 and 10) show the effect of AoI Bound on throughput and average packet age for the three modified versions of the FRESH protocol. It is noted that in all cases, the number of time slots is equal to 5000. As expected, lowering the AoI Bound leads to a decrease in throughput and average packet age in all cases. It is observed that the reduction of the average age is steeper for the Modified-near-v1 and Modified-near-v2 protocols than for the Modified-neigh protocol. At the same time, it seems that in terms of throughput, for all protocols, reducing the AoI Bound up to the value of 100 does not cause serious reductions in throughput, while there is a noticeable reduction when the Bound is set equal to 50.