## 8 Conclusions and Future Work  
As it was described at the beginning, the aim of this work is to offer an overview of the evolution of DTN technology as a support for terrestrial applications or if it is meant to die. The SLR performed demonstrates that there is much research interest in DTN technology, which varies in depth and mostly in four topics, architecture, performance, routing, and applications. Most of the papers related to applications are supported by experimental testbeds and simulations to prove the feasibility of the concept and to measure the performance of this protocol. There is a tendency to combine DTN with new telecommunication technologies, such as 5G, 6G, and sensors. Still, there are many unsolved issues related to performance and routing, mainly linked to mobility, energy consumption, and the computing capabilities of nodes. Very few experiments focus on TCP itself but rather on the overall performance of applications. Nonetheless, this SLR does answer the main inquiry we had about whether DTN can be considered a support for TCP/IP applications or terrestrial applications. DTNs for terrestrial applications, especially in areas where infrastructure is lacking, represent a feasible alternative. This is demonstrated by the many use cases collected in this SLR, which varies from communication in rural areas and agriculture, applications for the environment, including tracking animals and studies in the sea; smart cities, including transportation and natural disaster scenarios; and implementations in the architecture level or software. This SLR offers a broad compendium of work on DTN, which has been classified using key and valid elements to study and evaluate a communication protocol and its architecture, performance, routing, and applications. The matrix developed in this SLR is a reference tool for researchers to easily find papers that have more content of their interest. Not only does it show the level of content classified based on the four main aspects of DTN, such as architecture, performance, routing, and applications, but it also shows more specific aspects related to these categories, which can be very valuable for researchers to speed up their experiments. In the performance category, computing and processing capabilities, storage and buffer, energy, and mobility are included. In the routing category the contact type, route determination, number of copies, and design were included. Even though routing also affects performance, it was organized this way to facilitate identifying works focused on any of these subcategories, and these were the more recurrent topics found in the revision. The colors that represent, green, high focus; yellow, medium; and red, low help to easily and quickly identify specific works. Through this SLR, the main identified limitations of DTN include the scarcity of storage capabilities of nodes, energy constraints, and mobility. These three aspects affect finding routes to the destination and thus performance. As stated in the IPNSIG-SW's plan, still, there is space for research finding synergies between MANET and DTNs; therefore, this is a topic of interest as future work, more specifically testing it in different scenarios with TCP/IP [49]. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/network4030012/s1](https://www.mdpi.com/article/10.3390/network4030012/s1)]([https://www.mdpi.com/article/10.3390/network4030012/s1](https://www.mdpi.com/article/10.3390/network4030012/s1)) (references [50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 7  
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