## 5 Conclusions and Future Works  
A study of the existing protocols capable of offering compelling enough features, while at the same time being used in the environment that has been described (underwater autonomous maritime vehicles, low bandwidth availability, unreliability for transmissions at the data level), has been included in Section 2. The open issues and challenges that have been found are dealt with by the protocol that  
Figure 15: Appearance of the PDU used as an answer for periodic mission status data.  
has been thoroughly described in Section 3. Since the protocol is expected to be more than just a mere design, implementation works have been carried out, as described in Section 4. As far as the authors are concerned, a protocol tailored for the needs of transmissions at the data level among distributed elements of a collection of maritime vehicles is not presented in any piece of literature. Furthermore, its usefulness is guaranteed, as it is expected from it that will transfer information in a level of detail and accuracy that is hardly matched by any other current proposal.  
There are several future works to be undertaken, as part of the activities to be done in the SWARMs project. The protocol will be tested with the plethora of vehicles expected to be used in the project, which range from AUVs to ASVs or ROVs. Their differences in performance and computational capabilities should not be significant for the protocol, as it is lightweight enough to guarantee that it can be used in a transparent way by them. Furthermore, any partial modification that has to be done on the protocol will be tackled, even though after collecting all the information that is required for the application domain where it is used, changes or further extensions of MDTP seem unlikely. Finally, even though there is inter-compatibility among the different versions of DDS, the usage of a single one at both ends of the communication will be taken into account in order to optimize the procedure used for automatic discovery of elements during data transfer. This could provide an important advantage due to the fact that using a single DDS distribution will minimize the amount of time required for automatic discovery, as it has been defined in the standard.  
The research and development activities that have been included in this manuscript have been performed as part of the SWARMs (Smart and Networking Underwater Robots in Cooperation Meshes) 1034 European research project. It is under Grant Agreement 1035 n.662107-SWARMs-ECSEL-2014-1 and is being partially supported by the Spanish Ministry of Economy and Competitiveness (Ref: PCIN-2014-022-C02-02) and the ECSEL JU. We would also like to thank Evologios GmbH for the support given when using their tools for the testing activities.  
The contributions of the authors have been made like this: [PERSON] has made contributions in the introduction and has reviewed half of the related works that have been included in the manuscript. He has also provided information in the modelling considerations and description of the Maritime Data Transfer Protocol, its performance and the conclusions that can be extracted from the development works done. [PERSON] has provided extensive information about the PDU structure that has been defined in Section 3, as well as about the overall structure of the manuscript and the implementation works that have been included in the manuscript. [PERSON] has contributed with information regarding the serialized data and the information to be exchanged in the possible scenarios where the protocol is used. [PERSON] has delivered content for the introduction and the other half of the related works that have been reviewed in order to conceive the PDUs of the protocol.  
The authors declare no conflict of interest.