# Context-Aware Pending Interest Table Management Scheme for NDN-Based VANETs
## 5 Context-Aware Pending Information Table Entry Management (CPITEM) Scheme
### Non-Safety PITE Priority
#### 5.2.4. PITE Priority
In this experimental scenario, the producer and consumer vehicles and all other vehicles are mobile. Therefore, the PIT entries are satisfied in a short period of time. To create a load on the PIT, the PIT size is considered small (30 entries). The proposed CPITEM scheme is able to prioritise the PIT entries based on application type (safety, non-safety), time rested in PIT, size (in terms of InRecords), and application popularity. In Figure 1, it can be seen that the proposed scheme prioritises the safety content over the non-safety content. Moreover, CPITEM prioritises popular, non-safety content over non-popular, non-safety content. CPITEM results in a lower number of messages being dropped compared to HLLR. The reason is that a CPITEM drops the incoming Interest if its priority is lower than the lowest priority \(PITE\) in the PIT. To make the multimedia application popular, more Interests are transmitted related to the application compared to other safety and non-safety non-popular applications. Three consumers are sending Interests related to multimedia applications. The PIT size is considered small to create a load on the PIT as vehicles are mobile. In the event of a PIT size being above a certain threshold, CPITEM tries its best to replace the newly received safety content Interest message \(PITE\) with non-popular content PITE, as shown in Figure 1b. However, in the event that all entries in the PIT are related to popular non-safety content, the lowest priority popular \(PITE\) is replaced with a safety content \(PITE\). Moreover, the PIT size is very limited, and when it is full of popular content entries, the upcoming popular content Interest \(PITE\) cannot be placed in the PIT. Therefore, it will be dropped. In Figure 1d, it can be seen that for the CPITEM scheme, some of the PIT entries related to popular content are dropped (due to PIT size) when the load on the network in terms of Interest messages increases. HRRL, upon receiving each new valid Interest message, replaces one of the existing \(PITE\) with the new one, in case of PIT overflow. The HLLR scheme replaces the \(PITE\) for the upcoming Interest with the \(PITE\) in the PIT with a maximum lifespan and a minimum number of incoming faces. It does not take into account the time \(PITE\) spend in the PIT, waiting for the Data packet. This impacts PIT utilization. It is possible that the \(PITE\) in the PIT which is selected for removal might be closed to satisfaction, as it is waiting for a long time. Moreover, the newly received Interest \(PITE\) priority is not considered. It is always replaced with the existing lowest priority entry (with a maximum lifespan and a minimum number of incoming faces) in the PIT. It can be seen that due to these reasons, the HRRL results in more PIT entries being dropped compared to the CPITEM. Figure 1f illustrates the average interest satisfaction delay of HLLR and CPITEM schemes in a VANET highway scenario. It can be seen that CPITEM results in lower average ISD compared to HLLR. ### Experiment 2: Effect of PIT Size

The experiment is conducted to demonstrate the behaviour of CPITEM as a function of growth in PIT size. The network comprises 130 vehicles, 8 of which are consumers, and 7 are producers. Consumers are transmitting Interest messages at a rate of six messages per second. The number of messages transmitted is 2400, with 600 related to safety, 900 related to popular, non-safety and 900 related to non-popular, non-safety content. The PIT size, which represents the amount of available space in each vehicle in terms of PIT entries, varies from 20 to 60 entries. Upon receiving the valid Interest, each vehicle creates

Figure 1: Experiment 1: total number of drop Interest messages as a function of growth in interest messages.