# Context-Aware Pending Interest Table Management Scheme for NDN-Based VANETs
## 4 Current State-of-the-Art Schemes
### Static PIT Management  
There exists work [14; 15; 16; 17; 18; 19] which considers static PEL. In [14; 15; 16; 17; 18; 19], each forwarder vehicle stores the \(PITE\) for the fixed duration of time. If the Data message is received after \(PITE\) expiry, it will be considered as unsolicited. Source-based communication schemes [14; 15] involve communication overhead as they require vehicles to be aware of the topology and physical characteristics of nearby vehicles. Periodic Beacon messages are used to disseminate information. Each vehicle maintains tables and stores relevant information after receiving it from neighbours (such as speed, direction, and connectivity duration). The vehicle then uses the information in these tables to choose the best forwarder. In this way, the broadcast storm problem is addressed in source-based schemes. Moreover, receiver-based forwarding schemes are also presented in the literature to avoid congestion in the not-safety applications [16; 17; 18]. Such schemes consider static PEL. The receiver-based forwarding scheme considers assigning priorities to the vehicles in the neighbourhood. A small waiting time is assigned to high-priority vehicles. The vehicle's suitability to be selected as a forwarder is determined based on its probability in the least waiting time. The vehicle with the lowest deferred timer value is able to forward the Interest message first. All other neighbouring vehicles, upon overhearing the message with the same Nonce and Name (not present in the DeadNonceList), already scheduled for broadcast, stop their timer and back-off from broadcasting duplicate messages. This occurs,for example, in schemes where the forwarder is selected based on the distance to previous forwarder [16; 17; 18]. Compared to neighbouring vehicles, a lower deferred timer value is calculated for vehicles far from the previous forwarder vehicle. This deferred timer-based rebroadcast mechanism reduces message collision chances and lowers bandwidth usage. [PERSON] et al. [19] proposed a scheme for caching content near the consumer to reduce the content retrieval delay. This aims to reduce the overall number of PIT entries. The higher the ISR, the less time PIT will keep entries for. The scheme introduced three new fields in the Interest and Data packets: chunk-threshold, hop-count, and TTL. The content holder node inserts the number of pieces available with the content requested by the requester into the chunk threshold. The requester uses ChunkTHd as the priority for conducting Interest prefetching. In a VANET dynamic environment, a high number of Interests and a large PEL can exhaust the PIT, impacting the overall ISR. In the case of using constant PEL, the PIT must keep the \(PITE\) for its associated PEL duration. VANETs applications have varying latency requirements; exploiting similar PEL will not be feasible. With a static PEL, the size of the PIT may grow rapidly because all Interests may not be satisfied due to the unstable wireless environment. Moreover, considering parameters such as speed and direction, the vehicle with PITEs might not receive the Data message, resulting in an increase in the load on PIT. In V2V scenarios where the request is met by other vehicles, when the vehicle still holds the PITE, its performance will degrade due to the large PIT table. The large size of the PIT will exacerbate the search delay, making it unsuitable for the dissemination of safety content. This problem becomes worse in the case of \(PITE\) long lifetimes, which increases the number of stale entries in PIT. Stale PIT entries not only waste PIT storage but also increase search time. PIT is a key player in finding content in NDN. Due to the limited opportunities offered by current memory technologies, PIT size is a bottleneck. PIT overflow results in service disruptions as new Interest messages cannot be added to PIT.