# 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
#### 5.2.3 Application Popularity  
The application attribute in the CACN can be exploited to compute the application ID of content requested in the Interest message. The popularity of the non-safety application \(App_{i}\) indicates whether the content requested by the consumer vehicle is in demand in the geographic region. If the application \(App_{i}\) is popular, it indicates that the \(PITE\) associated with it is more valuable and relevant. Likewise, there is a greater likelihood of obtaining the content in the vicinity. Application popularity may be calculated based on the number of Interests received during a certain time period on the face(s). CACN with its coding scheme can represent a wide range of safety and non-safety applications. For this purpose, the AppID information component is exploited. Since vehicles in the VANETs are mobile, passing through different geographical areas, different applications contents can be in demand. Moreover, an application may be popular for a certain time and then may be disregarded in a spatial region. If the scheme assigns equal weightage to the Interest messages received over time, requests for popular content may not be addressed. It would be difficult to differentiate between the situation whether the application is high in demand currently or was in demand previously. Let us consider an example scenario, the application \(App_{i}\) is highly demanded (a large number of Interest messages received) at a certain time period while moving through some geographical area. After the passage of some time \(t_{2}\), let us consider that a large number of requests are received for application \(App_{i}\), but no additional Interests are received for \(App_{i}\). If the count of Interests received for \(App_{i}\) is greater than \(App_{j}\), it will still be considered as a highly demanded application. As a result, when calculating application priority, the time-sensitivity requirement must be taken into account. If the time-sensitivity requirement is not taken into account, it would be difficult to differentiate between whether the application is high in demand currently or was in demand previously.  
The time sliding window [28; 29] is used to address the time-sensitivity requirement when calculating application popularity. Let us consider that for an application \(App_{i}\) recent time window \(App_{i-}\)tr, the dimension is in the form [FROM Start, TO End]. Each record in the time window is kept for the duration \(t\) using time unit (SECOND (s), MINUTES (m)). When a vehicle receives an Interest, considering its arrival time, its expiry time is calculated and it will store a tuple in the \(App_{i-}\)tr. At the expiry of the timer associated with each entry in \(App_{i-}\)tr, the entry will be removed from the \(App_{i-}\)tr.  
Let us consider that the current PIT entries for non-safety content belongs to \(n\) applications. Application priority is represented with Utility of \(App_{i}\) at time t (\(Utility\_App_{i}^{\text{tr}}\)). The \(Utility\_App_{i}^{\text{tr}}\) is calculated using Equation (3). \(Utility\_App_{i}^{\text{tr}}\) represents the current demand of an application \(App_{i}\). \(Infreq\_App_{i}\) represents the number of valid Interests received for \(App_{i}\) in time window \(App_{i-}\)tr. \(\sum_{m=1}^{n=n}Infreq\_App_{m}\) represents the count of valid Interest messages received for each of the n applications in the recent time period t.  
\[Utility\_App_{i}^{\text{tr}}=\frac{Intfreq\_App_{i}^{\text{tr}}}{\sum_{m=1}^{m =n}Intfreq\_App_{m}^{\text{tr}}} \tag{3}\]  
\(Utility\_App_{i}^{\text{tr}}\) denotes the relationship or comparison between the Interest messages received for a specific application and the total number of Interest messages received for all applications. It compares the two quantities with respect to each other. Higher \(Utility\_App_{i}^{\text{tr}}\) is calculated for an application (\(App_{i}\)) for which a larger number of Interest messages are received compared to an application with a lower number of Interest messages.