A Review of Delay-Tolerant Networks for IoT: Multidimensional Taxonomy and Deployment Perspectives

Abstract

Delay-tolerant networks (DTNs), originally developed for interplanetary communication, have emerged as a key enabler for reliable data delivery in resource-constrained and intermittently connected Internet of Things (IoT) environments, including disaster-affected regions, infrastructure-limited rural deployments, and massive machine-type communication (mMTC) systems for beyond-5G networks. This review provides a comprehensive and structured examination of DTN integration within IoT systems through three major contributions. First, this article presents the fundamental concepts of DTNs, including node architectures, protocol layers, routing protocol classifications, and security requirements relevant to IoT-DTN environments. It further discusses IoT adaptation features, mobile DTN nodes, and real-world deployment case studies. Second, this article proposes a 4-D taxonomy for IoT-DTN systems based on the protocol classification, routing strategies, application domains, technology integration (X-DTN), and mobility-model distribution. The taxonomy is constructed from insights derived from representative operational deployments and existing literature. Third, this article analyses current deployment challenges, including latency, scalability, security, and energy efficiency, while identifying future research directions for resilient large-scale IoT connectivity. In addition, the review highlights emerging developments in machine-learning (ML)-assisted routing, graph neural network (GNN)-based forwarding, and hybrid LoRa/BLE-DTN architectures as promising approaches for adaptive and intelligent DTN-enabled IoT systems. Overall, this article serves as a reference framework for researchers and practitioners developing next-generation resilient IoT communication infrastructures.