# All about Delay-Tolerant Networking (DTN) Contributions to Future Internet
## 1 Introduction  
The Delayed/Disruptive Tolerance Network (DTN) has experienced significant growth in usage and applicability throughout the years since its inception. Hence, although the original focus of DTN was space communications [1, 2], its utility has rapidly extended to encompass a growing number of diverse applications [3, 4]. These applications span various domains including, but not limited to, space communications, the Internet of Things (IoT), smart cities, and underground or underwater environments. To this end, we discuss how the DTN suite of protocols and mechanisms work, its underlying philosophy, and the technological gaps it addresses in order to identify DTN's utility across a broad spectrum of applications.  
Therefore, this work explores the contribution of DTN towards a Future Internet, including a Space Internet: what new concepts it brings, what possibilities it creates, and consequently, how internet users gradually change the way they think. Practically, DTN is a technology that allows for connectivity with disruptions and/or delays, even when disruptions or delays dominate. This changes the notion of \"connected\" devices in its own right, since it turns all devices into potentially connected or temporarily disconnected. In turn, this changes the volume of data that can be gathered in a search if the search results can be returned at a later time; the number of devices that share their relevant information can be much larger if the response time can be extended in order to accommodate information from currently disconnected devices. Therefore, requests need not necessarily be satisfied immediately if they prioritize content optimization over response time. Another interesting aspect is the varying impact of disconnections on applications. In space, for instance, where the line of site is typically a communication requirement, a minute of disruption may result in days of data-delivery delay. In space, occasionally time \"stops\". Hence, the ability to interconnect devices and reroute the data, using contact graph routing for example, allows for time to restart or otherwise allows for transmission scheduling based on well-known apriori, deterministic events. Clearly, the traditional conception of communication changes, and disconnection impact is restrained.  
While several comprehensive surveys on DTN exist in the literature, with each emphasizing specific aspects such as routing protocols [5; 6] or IoT integration [7], our approach in this work is to highlight the major novelties of DTN applications across certain research areas. Therefore, we focus on describing the innovative aspects of DTN rather than attempting an exhaustive survey covering every possible dimension. Based on this approach, we filtered out these publications based primarily on their relevance to the selected topics, along with their impact, in our opinion, on the applications of the Future Internet. Along these lines, we gather related works in specific domains where DTN introduces some conceptual or technological novelty; in particular, we examined the following domains as illustrated in Figure 1:  
* Space.
* Information-Centric and Named Data Networking.
* Internet of Things and Smart Cities.
* Underwater.  
The remainder of the paper is organized as follows: In Section 2, we provide an overview of the general concept of the DTN approach and discuss the major challenges it encounters. In Section 3, we present the taxonomy of major research areas where the DTN suite is applied, while we also detail the relevant works and proposed solutions within each category. Finally, in Section 4, we highlight our concluding remarks and future work emphasizing the utilization of DTN in shaping the future internet landscape.