# Context-Aware Data Dissemination for ICN-Based Vehicular Ad Hoc Networks
## 3 Context-Aware Packet Forwarding
### Forwarding Suppression and Suppression Scope  
Distance-based forwarding and the modified PIT can reduce the number of forwarded packets considerably. However, it might also reduce the possibility of successful data delivery and/or increase the time taken to obtain data. As illustrated in Figure 7, suppose an Interest for content held by node D is sent by node A. Although node B, C, and E will receive the packet simultaneously (here the time difference for radio transmission can be neglected), only node B will forward the packet since the distance from B to A (\(d_{BA}\)) is the longest among the nodes receiving the Interest packet (i.e., \(d_{BA}\) is bigger than \(d_{CA}\) and \(d_{EA}\)). In other words, forwarding by nodes C and E is suppressed. Although, while waiting, C and E will receive the same Interest again, from B, they will discard it on account of the retransmission. However, in the case when there are few vehicles on road, as shown in Figure 7, it is only possible to reach the content holder D if node C forwards the Interest. To avoid the occurrence of such a case when the vehicles are sparsely distributed, we use a suppression angle \(\alpha_{SA}\), which demarcates a sector within which packet forwarding is suppressed since the nodes in this sector and node B are similarly situated with respect to the requested content holder. For instance, in the case described in Figure 7, node E is inside the sector in which forwarding will be suppressed; node C is outside the suppression sector and hence forwards the packet too, just like the furthest node, node B. We have introduced the concept of suppression angle in our previous work [26]. However, the density and distribution of the vehicles was not then considered.  
As shown in Figure 7, each node maintains a suppression angle \(\alpha_{SA}\), which varies with the density of the vehicles nearby and the priority of the content requested in the Interest packet. The greater the vehicle density \(\rho\) and the lower the content priority \(p\), the bigger the suppression angle \(\alpha_{SA}\) and the greater the number of nodes being suppressed. The relationship between \(\alpha_{SA}\) and \(p\) and \(p\) is defined as Equation (4), and thus \(\alpha_{SA}\) has a value between 0 and \(\pi/4\), i.e., \(\alpha_{SA}\in[0,\pi/4]\).  
\[\alpha_{\text{SA}}=\frac{\pi}{4}[1+e^{-\rho}]^{-1}+\frac{2}{p} \tag{4}\]  
When node C overhears the same Interest packet forwarded by B during the deferral time, the angle \(\alpha_{F}\) formed by line AB and AC, which denotes the direction similarity of B and C for A, can be calculated: \(\alpha_{F}=\arccos\frac{d_{BA}^{2}+d_{CA}^{2}-d_{CB}{}^{2}}{2d_{BA}+d_{CA}}\). Here, \(d_{BA}\), \(d_{CA}\), and \(d_{CB}\) are the distances between node B and A, node C and A, and node C and B, respectively, which can be calculated according to the geo-position information carried in the corresponding Interest packet and the node's own geo-position. If \(\alpha_{F}<\alpha_{SA}\), which means that C is in a direction sufficiently similar to B towards the requested content holder, C will discard the Interest received both from B and A, stop the deferral timer, and delete the corresponding entry from the deferral table DFT. In this way, redundant Interest packet forwarding  
Figure 7: Suppression angle and scope in the distance-based forwarding.  
will be suppressed. If multiple copies of requested content are cached in the network, the suppression of Interests will greatly reduce the number of the responded Data packets. However, if \(\alpha_{F}>\alpha_{SA}\), as for the case shown in Figure 7, which means that C is in a direction different from B, the forwarding of the Interest will not be restricted. This increases the possibility of reaching the requested content and/or in a short time.