# Multi-Decision Dynamic Intelligent Routing Protocol for Delay-Tolerant Networks
## 3 Proposed Routing Protocol
### Dynamic Decision Based on Node Relationships  
In the design of community-based routing schemes, the primary challenge lies in defining the social relationships between nodes and determining the mechanism for message propagation. Due to intermittent connections between nodes, there is a need for opportunistic message routing. In other words, message exchange occurs only when two nodes are within each other's range, and one node has a lower probability of delivery than the other. Node features can serve as metrics for quantifying node social relationships. Previous research has mainly relied on historical encounter information to derive social relationship attributes. However, depending solely on social relationships can lead to an uneven distribution of loads on nodes with higher degrees of connectivity. Moreover, most have primarily focused on node attributes and have not comprehensively considered message attributes and interaction quality. In this paper, when defining network node relationships, we take into account both the global knowledge of nodes and the comprehensive node interaction information. The network node relationships are defined as the following three types:  
**Friendship Relationship:** A friend node, compared with other nodes in the network, interacts with the local node more frequently, and the quality of interaction is higher. **Colleague Relationship:** A colleague node, compared with other nodes in the network, has occasional contact with the local node within a certain timeframe, but the quality of interaction is generally lower, indicating a less intimate connection. **Stranger Relationship:** A stranger node, compared with other nodes in the network, has minimal or almost no social interaction with the local node. Figure 2 illustrates that when nodes \(a\) and \(d\) established a connection at time t0, they also connected at moments t1, t2, t3, and t4 within the past time interval \(T\). When they are in the process of connecting, both nodes update their historical interaction information,  
including the average number of encounters within a period \(T\), the average encounter duration, and the average number of forwarded messages. Next, let's take nodes \(a\), \(b\), and \(m_{d}^{i}\) as an example, suppose we now need to decide whether to forward \(m_{d}^{i}\) from node \(a\) to node \(b\) or not. First, the historical encounter information between node \(a\) and node \(b\) is computed. Node-to-node relationships are determined by historical encounter information and interaction data. Nodes \(a\) and \(b\) have encounters within the time interval \(T\), and each encounter lasts for a duration of \(ET_{a}^{b}\). The number of encounters is \(CT_{a}^{b}\). The average encounter duration is as in (6)  
\[\overline{ET_{a}^{b}}=\frac{\sum_{i=1}^{CT_{a}^{b}}ET_{a}^{b}}{CT_{a}^{b}} \tag{6}\]  
The quality of interaction between node \(a\) and node \(b\) is evaluated based on the number of messages successfully forwarded to each other. The number of messages forwarded at a time is \(M\Sigma_{a}^{b}\). The average message forwarding quantity between nodes \(a\) and \(b\) within the time interval \(T\) is calculated by (7). \[\overline{MS_{a}^{b}}=\frac{\sum_{i=1}^{CT_{a}^{b}}MS_{a}^{b}}{CT_{a}^{b}} \tag{7}\]  
Within the time interval \(t\), the total sum of historical encounters between node \(a\) and other nodes it has come into contact with, the total sum of historical average encounter times, and the total sum of historical average forwarded message quantities are calculated by (8), (9), and (10), respectively. \[allCT_{a}=\sum_{j\in N_{a}}CT_{a}^{j} \tag{8}\]  
\[all\overline{ET_{a}}=\sum_{j\in N_{a}}\overline{ET_{a}^{j}} \tag{9}\]  
\[all\overline{MS_{a}}=\sum_{j\in N_{a}}\overline{MS_{a}^{j}} \tag{10}\]  
Figure 2: The encounter history between node \(a\) and node \(d\) within the time interval \(T\). Substitute (8)-(10) into the (11) to calculate the contact value \(C(a,b)\).