# Priority-Based Content Delivery in the Internet of Vehicles through Named Data Networking +
## 6 Evaluation Results  
**Single-face NDN vs. multi-face NDN schemes:** The first set of results, reported in Figure 7, is aimed at shedding light onto the performance of the multi-face forwarding strategy against the single-face solution, when no prioritization is enabled. The content retrieval time is reported in Figure 7a. Regardless of the considered scheme, it can be observed that as the number of consumers increases, the content retrieval time gets significantly shorter. Values get nearly halved when passing from 8 to 24 consumers. This is because consumers can benefit from cache hits for the requested content in neighbor vehicles, which previously requested or forwarded the content, with no need to reach the original content source. Such a trend is more evident for the SF-NDN scheme where Interest and Data packets are exchanged over the IEEE 802.11 OCB face only. As expected, the MF-NDN scheme exhibits lower content retrieval times w.r.t. the SF-NDN. This is especially visible in the case of a few consumers, when the benefits of the broadcast medium are less noticeable. Whenever consumers are multiple hops far from a content source (i.e., either the RSU or a caching vehicle), with MF-pNDN, they can benefit from the Data packets received over the LTE face, without straining in retransmitting Interest packets in broadcast over the error-prone 802.11 OCB face, which may delay the content retrieval. Such a trend is confirmed by the results reported in Figure 7b, which shows that the percentage of retransmitted Interests for MF-NDN is very low compared to SF-NDN. Indeed, the number of Interest retransmissions is always lower than 10% with MF-NDN, while it is always higher than 30% with SF-NDN, with a peak of nearly 53% for 12 consumers. As mentioned before, SF-NDN benefits from the presence of a higher number of vehicles requesting and, consequently, sharing contents. This is why the number of retransmitted Interests shrinks as the number of consumers increases. The best performance of MF-NDN compared to SF-NDN is achieved at the expenses of a higher Interest overhead due to the simultaneous transmission of Interests over the two faces; see Figure 7c. To gain more insight into the Data delivery performance over the two faces, let us refer to Table 2, which reports the percentage of Data received over the 802.11 OCB face for the MF-NDN solution (first row). The metrics increases with the number of consumers due to the higher content sharing over the short-range interface. Indeed, starting from 12 consumers, a slightly larger part of Data packets is received over the 802.11 OCB face rather than over the LTE connection. It is worth noticing that many vehicles/RSUs with a cached copy of the Data may answer to the same Interest. Indeed, there is no guarantee that the BF protocol can completely mitigate the Data redundancy. However, duplicated packets are simply discarded by the consumer, and they are not considered in the metrics computation, where only each first received Data packet is considered as valid. **Single-face NDN vs. multi-face prioritized NDN schemes:** The second set of results targets the assessment of the prioritization routines enabled in the SF and MF schemes (Figure 8). In the figures, we distinguish the performance of HP and LP contents. Similarly to the results achieved without prioritization in Figure 7a, the content retrieval time gets significantly shorter as the number of consumers increases (Figure 8a), thanks to the higher content sharing opportunities over the 802.11 OCB interface. Moreover, it can be clearly observed that both solutions are successful in prioritizing HP contents over LP ones: (i) HP contents are retrieved in a shorter time w.r.t. LP ones; (ii) content retrieval times for HP contents are significantly lower compared to the ones experienced without prioritization and reported in Figure 7a.