# Priority-Based Content Delivery in the Internet of Vehicles through Named Data Networking +
## 5 Simulation Settings
With LTE, an OBU with an Interest to send must first obtain a resource in the uplink through a random access mechanism, then transmits the message in the uplink towards the eNodeB, in its turn connected to the remote content server through the Packet Data Gateway (PDG) in the core network. We assume that the access delay and the transmission delay over the uplink are almost negligible compared to the RTT towards the server set. RTT values typically considered in the literature are in the order of 100 to 200 ms [45,46], thus we set the overall RTT equal to 150 ms.  
**Benchmarking solutions:** The performances of the following NDN schemes are evaluated and compared:  
Figure 6: Map of the city center of Rome as from OpenStreetMap. * Single-Face NDN without prioritization (SF-NDN): All content is requested only over the 802.11 OCB face. The forwarding strategy is based on the BF protocol; Interest/Data packets of different contents are transmitted without differentiation. * Single-Face NDN with prioritization (SF-pNDN): Similarly to the previous case, all content is requested only over the 802.11 OCB face, and the forwarding strategy is based on the BF protocol. In addition, the timing algorithm for traffic prioritization mechanism is applied; two transmission windows, IDW and DDW, are identified for high/low priority data delivery, as described in Section 4.3. * Multi-Face NDN without prioritization (MF-NDN): Similarly to [12], content requests are transmitted over both faces, regardless of their performance and the priority of content. * Multi-Face NDN with prioritization (MF-pNDN): According to the pNDN face selection module, LP and HP contents are differently transmitted over the network faces. LP content is only requested over the 802.11 OCB interface by both consumers and forwarding vehicles; HP content is requested with the parallel strategy by consumers, while forwarding vehicles use the 802.11 OCB face only. Packets transmitted over the 802.11 OCB face follow the timing algorithm described in Section 4.3 for prioritization. For each implemented scheme, the timing algorithm applies the following settings. The window sizes for the defer timers are set by considering the IEEE 802.11 OCB parameters with \(DDW=IDW=(slotTime+2\cdot SIFS)\cdot CW\), where \(SIFS=36\)\(\upmu\)s, \(slotTime=13\)\(\upmu\)s and \(CW\) is the maximum contention window size for 802.11 OCB, set equal to 511 [3]. **Metrics:** The following performance metrics are computed to measure the effectiveness of data delivery and the efficiency in the usage of network resources, respectively:  
* Content retrieval time: the average time required for a consumer to retrieve all of the Data packets of the desired content. * Interest overhead: the total number of Interest packets transmitted and retransmitted (over both faces when MF-schemes are considered) during the simulation by all of the nodes involved in the content retrieval (i.e., consumers and intermediate nodes) over the total number of useful (non-duplicated) Data packets received by the consumers. * Interest retransmissions: the percentage of Interests retransmitted by the consumers (at the RTO expiration) over the number of Interest packets required to retrieve the desired content (excluding retransmissions). * Data retrieved over the 802.11 OCB face (defined for the MF-* schemes only): the percentage of useful Data packets received by the consumers via the 802.11 OCB face over the number of Interest packets required to retrieve the desired content (excluding retransmissions). The percentage of Data packets received from the LTE face can be inferred through the complementary value. Results are averaged over 15 independent runs and reported with 95% confidence intervals.