## 5 CIDF-WSN
### CIDF-WSN Operation
#### 5.3.2 Interest Packet Processing  
When the interest packet arrives at the designated node, the following Interest packet processing mechanisms, such as Normal Mode Interest Packet processing and recovery mode Interest packet processing, can be executed. 1. **Normal Mode Interest Packet Processing:** The Normal Mode Interest Packet Processing occurs during stable network conditions. When the lower-layer node forwards the Interest packet to the designated upper-layer node, the packet is also received by the immediate neighbors of the designated node due to the shared medium. The immediate neighboring nodes temporarily store the Interest packet in their ICT (discussed in Section 5.3.4) and associated forwarder timer (the forwarder timer is computed based on the node's residual energy and distance from the boundary of the layer; the node closer to the boundary of its host layer and high residual energy reservoir has a low forwarder timer value ) with the received packet to avoid the packet losses, in case of designated node failure. Once the Interest reception is finalized, the further Interest processing involves (a) Normal Mode Downstream Interest packet processing and (b) Normal Mode Upstream Interest packet processing. 1. **Normal Mode Downstream Interest packet processing:** In the Normal Mode Downstream Interest packet processing, when the upper-layer designated forwarder forwards the Interest packet further, the forwarded Interest packet is also received by the downstream forwarder node (in the lower layer) due to the shared medium. When the downstream node receives the forwarded interest, it increases the number of successful transmission parameters of the upstream forwarder and updates the associated virtual face cost of the upstream forwarder node in the NFIB table by utilizing the cost updating mechanism. The updated NFIB table allows the node to select an upstream relay that has the highest associated cost for the future interest forwarding process. 2. **Normal Mode Upstream Interest packet processing:** In the Normal Mode Upstream Interest packet processing, upon the designated node Interest packet transmission, the immediate neighbors of the designated node (in the upper layer) also receive the Interest packet. Upon receipt, these immediate neighbor nodes stop their forwarder timer and purge their ICT to avoid cache pollution and to vacate the ICT to accommodate future Interest requests. The complete procedure of Normal Mode Downstream Interest packet processing and Normal Mode Upstream Interest packet processing is shown in Figure 4.  
Figure 4: Downstream Interest packet processing. Consider a scenario where the node N1 of layer 1 (\(N1_{L1}\)) requests some Data from the producer by forwarding an Interest (\(I_{1-N1-L1}\)), as shown in Figure 4.  
The \(N1_{L1}\) forwards the Interest packet toward the selected virtual face, i.e., N2 of layer 2 (\(N2_{L2}\)). The neighboring nodes of \(N2_{L2}\) (\(N1_{L2}\), and \(N3_{L2}\)) also receive the Interest packet as they fall in the transmission radius of \(N1_{L1}\). These neighboring nodes temporarily store the received Interest packet in their ICT and associate the forwarder timer with the Interest packet. The \(N2_{L2}\) verifies its node Id against the designated Id presented in the Interest packet and forwards the Interest towards the designated virtual face, i.e., N4 of layer 3 (\(N4_{L3}\)), by consulting its NFIB. Due to the shared wireless medium, the Interest packet forwarded by the \(N2_{L2}\) towards the \(N4_{L3}\) is also received by the downstream \(N1_{L1}\); therefore, upon receiving the Interest packet, the \(N1_{L1}\) (executes the Normal Mode Downstream Interest packet processing) increments the number of successful transmissions of \(N2_{L2}\) and updates the associated cost of the face (\(N2_{L2}\)) in its NFIB (e.g., \(C1^{*}\) in the Figure 4 denotes the updated cost of face \(N2_{L2}\)).