## 5 CIDF-WSN
### CIDF-WSN Operation
#### 5.3.2 Interest Packet Processing
Whereas, the neighboring nodes of \(N2_{L2}\) (e.g., \(N1_{L2}\), and \(N3_{L2}\)) execute the Normal Mode Upstream Interest packet processing to purge their ICT and stops the forwarder timer. 2. **Recovery Mode Interest packet mechanism:** The wireless channel may never remain consistently reliable and it confronts severe fluctuations due to path losses, capture effect, and fading. As a result, the forwarded Interest may fail to reach the potential provider. The consumer node may resend the Interest packet as it has not received any response against the transmitted Interest. The frequent Interest packet re-transmissions may induce congestion and collisions in the network. To this end, we devise an efficient mechanism referred to as recovery mode. The recovery mode involves two types of processing and is described as follows. (a) **Recovery Mode Downstream Interest packet processing:** In Recovery Mode Sownstream Interest packet processing, if the designated node fails to further transmit the Interest packet, the immediate neighbors of the designated node continue the transmissions. As the Interest packet is also received by the immediate neighbors of the forwarder node, these nodes store the Interest packet in ICT and associate the forwarder timer to the received Interest packet. Therefore, on nominated forwarder failure, the immediate neighbor facing the destined provider forwards the Interest packet upon the expiration of the forwarder timer in order to avoid the Interest packet loss. When the neighbor node of the designated node forwards the Interest packet, the downstream forwarder node located in the lower layer overhears the packet, updates the number of successful Interest transmission parameter, and computes the costs of virtual faces in NFIB accordingly. (b) **Recovery Mode Upstream Interest packet processing:** As discussed earlier, the medium is shared and the forwarded Interest is also received by other immediate neighbors of the designated node. The nodes (which cache the forwarded Interest packet in the ICT), upon receiving the same forwarded Interest packet, purge their ICT entry and stop their forwarder timer to avoid the ICT redundancy and allocate the space for the future Interest packets. The example scenario for both aforementioned mechanisms is depicted in Figure 5 and described as follows. As shown in Figure 5, the Interest packet is received successfully at the designated node \(N_{2-L2}\) in the upper layer. Due to the shared medium, the Interest packet is also received by the immediate neighboring nodes of the designated node (e.g., \(N_{1-L2}\), \(N_{3-L2}\)). The consumer downstream node (\(N_{1-L1}\)) overhears the transmission of \(N_{2-L2}\) to update the associated cost of \(N_{2-L2}\) in the NFIB table. If for certain reasons (e.g., lack of currently available resources, congestion, hardware failure, etc.) the \(N_{2-L2}\) fails to forward the request, the forwarder timer of the immediate neighbor expires. To avoid the broadcast storm and ensure the directive forwarding, since the \(N_{3-L2}\) is also facing towards the provider, it forwards the Interest packet towards the upstream node, i.e., \(N_{2-L3}\). The \(N_{1-L1}\) also receives the Interest packet and upon reception, the \(N_{1-L1}\) perform the cost computation and update the NFIB table (as shown in the Figure 5) to ensure the improved performance for future transmissions.This process continues until the Interest packet successfully reaches the provider node.