## 6 Results
### DTN Performance  
A total of 55 papers focus on performance. This topic is quite large and involves different issues, including the computing and processing capabilities of nodes to receive and process packets and the storage and buffer capabilities of the node to be able to store packets until there is another node to forward them. This also involves the content dissemination capabilities of the nodes. An issue that is considered a great deal is energy consumption and capabilities in the nodes as this is vital for a route to be established from source to destination, especially when dealing with mobile devices. Mobility is another key aspect of performance, which also might involve node localization. Mobility. An essential characteristic of multi-hop wireless networks (MWNs) is mobility as it makes path breakages in multi-hop and can produce more delay [10]. Moreover, the way DTN is implemented on an application does impact the achievable throughput. Elements that impact throughput are the duration and frequency of contacts, as well as the mobility of nodes. Longer contact and less mobility mean more data exchanged and higher network throughput [20]. The constant mobility of nodes can create the instability of network topology, long-term segmentation, asymmetrical and unstable node channels, or connection between nodes. This results in high packet loss, errors, and network delay uncertainty, among other issues [21]. From our perspective, mobility is an essential feature for nodes, and if DTN is based on the supposition of intermittent connectivity, then it does not make sense to consider this as a main concern for performance. The system must be able to perform in the presence of mobile nodes. Storage capability. Storage is another issue that impacts performance. The disconnection due to dynamic mobility patterns and long queuing delays increase the need for the store to forward, no matter the node's limited resources (memory, processing, power) [23]. Content dissemination goes together with the storage capability of nodes, as information might have to be stored for long periods on each hop. Therefore, the performance of I/O and storage is a key component in the overall performance of DTN. Unlike the TCP/IP stack where end-to-end retransmissions of higher-level protocols prevent data loss, DTN requires data to be stored persistently (HDD, flash) to avoid data loss on node restarts, even before custody is accepted. Copying affects performance dramatically [20; 21]. Mauldin found that link layer overhead and control messages overhead affect the protocol throughput, but message replication overhead is the largest impacting element [24]. For us, this should be the main concern for any DTN application due to the fact that the essence of DTN is \"store\" and forward; therefore, if nodes are not able to store packets, they are not doing any good in this kind of system. Computing and processing capability. Performance metrics in DTN include the hop-to-hop throughput, end-to-end throughput, delivery delay, discovery latency, contact utilization, and bundle rate. Throughput is largely determined by the available computing or network resources and the quality of the protocol implementation. Node connection creates a delay and depends on the capacity to process it. The delay is also influenced by the path choices of a routing algorithm, as well as by congestion control, which increases with low contact utilization. A high discovery latency affects contact utilization. This last is also affected by the bundle rate that includes processing to parse, generate, and forward bundles, which also depends on I/O and storage performance [25; 4; 20]. Computing and processing are, from our point of view, not only a feature solely based on the node but also on the lightness of the implementation. We found several implementations, such as IBR-DTN, DTN7, and ION-DTN. In consequence, here, there is room for research. Energy constraints. Energy consumption is another element linked to DTN performance [25; 4].