# Enhancing the 3 GPP V2X Architecture with Information-Centric Networking
## 3 NDN for V2X Communications
### NDN-Based Content Delivery for V2X: An Overview  
Related work on vehicular NDN mainly focused on effective and low-overhead forwarding strategies for the IEEE 802.11 access technology, with only a few works [15; 16] analyzing hybrid cellular-IEEE 802.11 V2X deployments. When considering Interest/Data forwarding, the following main aspects have been explored thus far: (i) the design of content retrieval schemes over the shared IEEE 802.11 wireless medium; (ii) the design of reliable transport services; (iii) the design of prioritized transmission schemes that distinguish contents with different requirements, e.g., in terms of latency; and (iv) the definition of transmission schemes over hybrid network access (i.e., cellular/802.11). **Content retrieval schemes. ** After receiving an Interest and performing CS and PIT lookup without finding a matching, vehicles have to apply a forwarding logic to decide if they can further forward the packet or not, based on the FIB content. The forwarding schemes available in the literature can be distinguished into (i) _pure broadcast-based_ schemes, where only broadcast transmissions are enforced with a controlled-flooding mechanism used during Interest forwarding; and (ii) _unicast-based_ schemes, where after an initial content discovery phase based on broadcasting, Interests are forwarded in unicast mode from node to node (this type of forwarding is possible in NDN provided that the identifier of the next-hop, e.g., the IP address [17] or the MAC address [18], is tracked in the FIB). Unicast-based schemes reduce the adverse broadcast storm effect due to multi-hop Interest broadcasting (in multi-hop wireless networks, broadcast storm is defined as a condition in which, due to a high number of broadcasted packets, nodes may experiment a high level of contention and collisions at the link layer [19]), as demonstrated in [17; 18]. However, these schemes may suffer from connectivity breakages due to node mobility and harsh propagation conditions, and may limit the data sharing capability of the wireless medium, enabled by packets overhearing and distributed in-network caching. This is why, thus far, the majority of the works on vehicular NDN have preferred broadcast-based schemes enhanced with proper broadcast storm mitigation mechanisms and/or self-eligibility forwarding decisions that nodes can implement during the data retrieval. In particular, in [20], a vehicle is considered an eligible forwarder only if it is in the path towards the data source, which has been discovered during a preliminary flooding stage. In [21], the authors presented the Distributed Interest Forwarder Selection (DIFS) algorithm, where eligible forwarders are only the vehicles that have maximum connectivity time and good link quality with the consumer. In [22], instead, eligible forwarding vehicles are selected based on the neighbor distance, node density, and the closeness to the consumer. Forwarding metrics can be carried in the Interest and/or Data packets and can be considered to further improve the forwarding decision. For instance, in [23], to maximize the packet dissemination scope, Interests carry the geographical position of the sender, and the best forwarder is identified as the farthest away node from the sender. In [24], such position-based forwarding strategy is further extended with information about the vehicle trajectory, while, in [25], vehicles consider both their distance from the previous sender and from the target data source. The forwarding decision is usually coupled with a channel overhearing mechanism to further limit packet collisions and redundancy. A defer time is calculated before each Interest transmission: if the same packet or the related Data is overheard during the waiting time, the Interest packet is dropped. To further control the Interests propagation, time-to-live (TTL) information, such as the hop count, can be included in the packet [26]. **Reliable transport.