# Packet-Forwarding Algorithm in DTN Based on the Pheromone of Destination Node
###### Abstract  
The pheromone can be used for target tracking and, consequently, for packet forwarding to the destination node in delay-tolerant networking. In this study, an initiative community model is proposed by simulating pheromone production and diffusion, which contains all of the nodes that can receive the core node pheromone. We can set the distance of the edge node to the core to be less than five hops by establishing the appropriate spread coefficient \(\omega\). Packet forwarding is then converted into the process of tracing the pheromone of the destination node. A set of simulation results shows that the proposed initiative community model can effectively increase the delivery ratio and reduce delay when the community structure is relatively stable. delay-tolerant networking (DTN); pheromone; initiative community; packet forwarding 0.000.0  
nodes whose distance is over two hops; hence, it cannot represent the betweenness centrality of a node. [PERSON] et al. [4] constructed frequent movement patterns of nodes by analyzing the hotspots that nodes visited, and computed the centrality of nodes based on the movement patterns. Then, they utilized the inverse symmetrized entropy of the personal hotspots between two nodes to compute the similarity between them. Even so, this may be of low efficiency when the hotspots change. Ref [5] compared the number of same neighbors among nodes to determine whether the nodes belong to the same community. In this manner, nodes can be classified into different communities that contain nodes with a tight connection. However, nodes in such a community cannot obtain the relative location of others, and the current node cannot indicate the direction when forwarding packets to the destination node. Therefore, the path for packet forwarding may not be the best. The packet-forwarding path in a community without a core node is illustrated in Figure 1.  
In Figure 1, we suppose that \(\
u_{1}\) is required to forward the packet to \(\
u_{8}\) and packet forwarding to node \(\
u_{4}\) occurs at present. When \(\
u_{4}\) is forwarding the packet to the destination node, it must select a relay node from \(\
u_{5}\) and \(\
u_{7}\), and if \(\
u_{5}\) was chosen, it would increase the total forwarding hops, and the cost of packet forwarding will increase. To address this problem, we study and analyze the role of pheromones in the process of moth mating and attempt to use it in the packet-forwarding process in DTN. First, we can compute the communication capability between the neighbor and core nodes according to the analysis of the connections and disconnections between them, which can be the analog pheromone of the core node. Second, we apply the six degrees of separation theory [6] to spread the analog pheromone to nearby nodes within a four-hop distance. The community can then be constructed based on the analog pheromone of the core node. We propose a simple and efficient packet forwarding algorithm (Packet Forwarding Algorithm Based on Pheromone, FABP) based on this special community structure. In the proposed algorithm (FABP), the pheromone of the core node is calculated periodically and then spread to the surrounding neighboring nodes via the attenuation model. Every node that receives the pheromone will update itself and spread it via the attenuation model. If a node cannot receive the pheromone within a certain period, then it will decrease the pheromone of the destination node until it reaches zero. If the pheromone of the node becomes zero, then the current node detaches from the community. Taking advantage of the pheromone, if a packet is forwarded to nodes that hold the pheromone of the destination node, and then the packet will be delivered to the destination node along the direction where the pheromone is stronger. A high delivery rate and a low forwarding delay can then be obtained.