# An Adaptive Routing Algorithm Based on Relation Tree in DTN
## 1 Introduction  
Traditional Internet networks are based on the TCP/IP protocol and rely on physical links that need to meet the characteristics of bidirectional, end-to-end continuous stability. However, as the research field continues to expand, more diverse and complex network environments have emerged, such as the interstellar Internet [1], social networks [2], vehicle-mounted networks [3, 4], wireless sensor networks [5], and so on. In these networks, even if end-to-end transmission paths exist, they are relatively susceptible to interruptions, small data transfer rates, and long transmission delays. In these application scenarios, many serious challenges are encountered when using the traditional TCP/IP protocol for network communication.  
To solve the data transmission problem in these networks, [PERSON] first proposed the Delay Tolerant Network (DTN) model in 2003 [6]. When a message arrives at a node, that node will first store the message and carry it through the network. When the node carrying the message needs to pass the message to other nodes, the message will be moved from a storage location on that node to a storage location on another node. In this way, the message is transmitted until the delivery of the message is completed or the message lifecycle is exhausted and discarded. The \"carry-store-forward\" model overcomes the problems associated with intermittent connections, long delays, variable network topologies, and high bit error rates, improving the quality of network communications [7]. The research of DTN provides strong scientific theory and technical support for message interaction in military warfare, aerospace communication, disaster recovery, emergency rescue, and other fields.  
In DTN, nodes may be in constant motion, the network does not have a fixed topology, and there is usually no end-to-end network connection between nodes, so a series of routing algorithms based on stable topology in traditional Internet are not applicable to DTN, whichmakes routing algorithms one of the most important research areas in DTN [8; 9]. Nodes in opportunistic networks often refer to vehicles or users carrying wireless short-range communication devices, and these nodes participating in social scenarios also have unique social attributes [10], so applying social attributes in DTN routing algorithms has attracted a great deal of attention from researchers in recent years.  
In this paper, we propose an adaptive routing algorithm based on Relation Tree (AR-RT) to address the above issues, and the main contributions are summarized as follows:  
* We propose a new method for constructing the Relation Trees, which is based on the fact that in most application scenarios of DTN, nodes exhibit social attributes.
* We propose a sub-policy forwarding method based on the Relation Tree, which is capable of more targeted forwarding based on the social attributes of each node.
* We propose an adaptive replication method based on node cache occupancy that can adapt to the dynamically changing network environment.  
The rest of the paper is organized as follows. We discuss related work in Section 2, Section 3 provides a brief overview of the AR-RT algorithm, Section 4 describes how to construct the Relation Tree, Section 5 describes the adaptive sub-policy replication forwarding approach of the AR-RT algorithm, and in Section 6, we demonstrate the performance of the AR-RT algorithm based on four key parameters by comparing it with existing algorithms. In Section 7, we conclude the whole paper.