## 7 Concluding Remarks  
The ETSI MEC architecture was not conceived with multi-domain aspects in mind. This paper analyzes different potential alternatives of integrating MEC environments from distinct administrative domains. Such a multi-domain scenario is foreseen as commonplace in forthcoming 5G networks, as the costs for providing the performance expectations of low latency and high bandwidth of 5G will require huge investments for enabling the delivery of advance services in proximity to the end users. Situations of infrastructure sharing, the appearance of MVNOs with focus on edge services, or even micro 5G operators can change the business landscape fostering the deployment of edge computing capabilities. ETSI MEC is becoming the reference system for these future environments at the network edge.  
Even though the different alternatives considered here could be theoretically feasible, the difficulties of ensuring interoperability in some of the interfaces can make some of the options technically difficult to achieve. It has been shown that depending on the particular scenario, either the management, platform or external interfaces can be impacted by the multi-domain aspects. Furthermore, those interfaces have to be augmented by incorporating new functionality to address the business and technical implications of multi-domain as described in the paper.  
Future work will be focused on identifying what are the necessary extensions to the MEC interfaces and the suitability of each scenario, as well as promoting the multi-domain specification in ETSI MEC, where this paper can be a primary input for gap analysis. For instance, it is necessary to elaborate on the implications in terms of--to mention just a few--security, scalability, monitoring, accounting or discovery automation in the interactions between functional blocks belonging to different administrative domains. All of those interactions will differ depending on the specific integration scenario to be followed, since there could be implications at the infrastructure, platform, service or even system level, according to the selected scenario. All the interactions should be transparent to the applications running on top of the multi-domain MEC environment, in such a way that it can be perceived as a single infrastructure, hiding the complexity of the multi-provider operation. This should be accomplished ensuring backward compatibility with the existing ETSI MEC framework, which implies the augmentation of existing reference points, reusing them as far as possible. All these directions need to be further investigated to provide a complete and operational solution for multi-domain ETSI MEC scenarios.  
Conceptualization and writing--original draft preparation, L.M.C.; Supervision and writing--review, C.J.B. All authors have read and agreed to the published version of the manuscript.  
This work has been partly funded by the European Commission through the projects EU-TW 5G-DIVE (Grant Agreement no. 859881) and H2020 5 GROWTH (Grant Agreement no. 856709). This information reflects the consortia views, but neither the consortia nor the European Commission are liable for any use that may be done of the information contained therein.  
The authors declare no conflict of interest.