# Priority-Based Content Delivery in the Internet of Vehicles through Named Data Networking +
## 6 Evaluation Results
For instance, for 24 consumers, the retrieval time of HP contents is nearly 20 s and 35 s with MF-pNDN and SF-pNDN, respectively, while the counterparts MF-NDN and SF-NDN, without prioritization, exhibit an average retrieval delay of nearly 55 s and 70 s, respectively. Thanks to the parallel transmission of Interests over multiple faces, the content retrieval time for MF-pNDN is significantly reduced compared to the SF-pNDN scheme. Such a trend applies for both HP and LP contents; however, it is more noticeable for the former ones. With MF-pNDN, Interests are satisfied by the LTE face, whenever the 802.11 OCB face is too slow either because of harsh propagation conditions/interference or when consumers are multiple hops far from a content source (i.e., either the RSU or a caching vehicle). Such a behavior translates into a lower number of Interest retransmissions for MF-pNDN compared to SF-pNDN, as depicted in Figure 8b. In particular, Interest retransmissions of HP contents are very low for MF-pNDN because, for them, thanks to the usage of the parallel strategy, they are likely to receive a Data packet, with no need to issue a retransmission. Interestingly, the reduced load over the 802.11 OCB face (a lower number of Interest packets is exchanged over such a face since some of them may be served by the cellular network before the expiration of the corresponding RTO) has also the additional benefit of shortening the retrieval time for LP content. Thus, *-pNDN schemes are effective in dealing with HP contents and also reduce the retrieval time for LP ones. The significantly improved performance achieved by MF-pNDN in terms of retrieval time for both HP and LP contents is achieved at the expense of a higher overhead incurred w.r.t. SF-pNDN; see Figure 8c. However, unlike the previous results for the non-prioritized schemes, smaller differences are noticeable between the SF and the MF schemes, because only Interests for HP contents are transmitted simultaneously over the two faces. Interestingly, the incurred overhead is lower than the one achieved when prioritization is not enabled; see Figure 7c. Figure 7: Metrics vs. number of consumers for the non-prioritized NDN schemes. (**a**) Content retrieval time; (**b**) Interest retransmissions; (**c**) Interest overhead. Table 2 reports the percentage of Data received over the 802.11 OCB face for the MF-pNDN solution (second row). Similarly to the previous case, values increase as the number of consumers increases due to the higher content sharing over the 802.11 OCB interface. In absolute terms, we can observe that a large percentage of Data packets is received over the 802.11 OCB face. Instead, only a few HP Data packets are received through the LTE face, whenever retrieval over the 802.11 OCB face fails either because of lossy links or when consumers are multiple hops far from the providers of the desired content. Figure 8: Metrics vs. the number of consumers for the prioritized NDN schemes. (**a**) Content retrieval time; (**b**) Interest retransmissions; (**c**) Interest overhead.