## 5 CIDF-WSN
### CIDF-WSN Operation
#### 5.3.3 Data Packet Transfer  
Once the Interest packet reaches the producer node, the producer node verifies the Interest packet authenticity, assembles the Data packet of the requested content, and forwards it towards the consumer. In the conventional NDN, the Data packet follows the reverse path of PIT entries maintained in the PIT table of downstream nodes. This means that the Data are forwarded back to the consumer node by following the breadcrumb path of the received Interest packet. Following the breadcrumb path, the Data delivery at the consumer end may fail due to poor channel conditions. To cope with these constraints, CIDF-WSN offers a robust Data packet forwarding mechanism to avoid Data packet loss. The Data packet forwarding includes (1) Normal Mode Data Forwarding and (2) Recovery Mode Data Forwarding. The detailed operational description of the above mentioned Data Forwarding modes assisted by the illustrative example depicted in Figure 6 is as follows. Figure 5: Upstream Interest packet processing. 1. **Normal Mode Data packet forwarding:** The Normal Mode Data packet forwarding refers to the Data packet forwarding towards the lower-layer downstream virtual face (node) from where the Interest request arrives. Upon the arrival of the Data packet, the designated downstream node verifies the received Data packet and forwards it towards its designated lower-layer Forwarder. The immediate neighboring nodes of the designated node in the same layer also store the Data packet in their TCT (discussed in Section 5.3.4) and associate the forwarder timer with the received Data packet to avoid the data packet losses when the designated node fails to forward the Data packet towards the consumer. Upon designated node Data forwarding, the immediate neighboring nodes also receive the Data packet. These immediate neighbors stop their forwarder timer and purge the Data packet from their respective TCT to avoid redundancy. This process continues until the Data packet arrives at the provider node. 2. **Recovery Mode Data forwarding:** Recovery Mode Data forwarding corresponds to the immediate neighbors of the downstream node which may take part in Data forwarding during disastrous conditions. If the designated forwarder does not receive or fails to retransmit the Data packet in the reverse path towards the consumer, the immediate neighboring nodes of the designated node directing towards the consumer act as the backup nodes and forward the Data packet incorporating their TCT. The information of the next forwarder downstream node--in the breadcrumph--is maintained in the PIT table of the failed designated node while the immediate neighbors of the failed node do not have that entry in their PIT table. In this case, the potential immediate neighboring node upon expiration of forwarder timer utilizes TCT and broadcasts the Data packet towards the lower-layer nodes. Upon receipt of the Data packet, the nodes in the lower layer compare the name of received Data with their outgoing requests record in the PIT. The node with a matching PIT entry with the incoming Data name immediately forwards the Data packet towards its designated downstream layer node. The remaining neighboring nodes which have the same entry of forwarded Data packet in their TCT stop their forwarder timer and purge their cache upon further retransmission by the lower-layer designated node. This process significantly improves the interest satisfaction ratio, circumvents redundant transmissions, and avoids long transmission delays. Figure 6: Data packet transfer. The complete Data packet forwarding process is presented in Figure 6. The figure elucidates that once the Interest arrives, the Producer node verifies the Interest, assembles the requested content in the Data packet, and forwards it in the reverse path. In transmission phase \(T_{0}\) (as shown in Figure 6), the producer forwards the Data packet towards the \(N_{3-L3}\).