## 3 Integration of Multi-Domain MEC Environments
### MEC Architecture  
The MEC reference architecture is described in [27], and graphically represented in Figure 1. It is composed on functional components and the reference points between them. It also includes a number of mobile edge services that complement the overall solution. As seen in Figure 1, the MEC framework differentiates among mobile edge system and mobile edge hosts levels. The Multi-access Edge System (MES) consists of a number of multi-access edge hosts and the multi-access edge management entities necessary to execute multi-access edge applications within an operator network. The Multi-access Edge Host (MEH) is an entity that contains a Multi-access Edge Platform (MEP) and a virtualization infrastructure. The MEP provides a functional environment where applications can discover, advertise, consume and offer multi-access edge services. The MEP controls the data-plane in the virtualization infrastructure following a Software Defined Networking (SDN) approach, configures the DNS proxy/server in the MEH based on DNS records obtained from the multi-access edge platform manager, and provides access to persistent storage and time of day information. The virtualization infrastructure is, generally speaking, a Network Function Virtualization Infrastructure (NFVI) as the one described in [28], which provides compute, storage, and network resources, for running multi-access edge applications on top of it. The virtualization infrastructure includes a data plane that executes the traffic rules received by the MEP, routing the traffic among applications, services, DNS server/proxy, and both local networks and external networks. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Edge Computing** & **Edge Infrastructure** & **Main Scope of Use** & **Standardization** & **Integration Path** & **Specific** \\
**Alternatives** & **Ownership** & **Cases** & **S** & **with NFV and 3 GPP** & **Surveys** \\ \hline \hline \multirow{2}{*}{Multi-access Edge Computing (MEC)} & \multirow{2}{*}{Telecom operator} & Carrier services and & & & \\  & & performance & ETSI MEC & Yes & [21; 22] \\ \hline \multirow{2}{*}{Fog computing} & Private entities/industries & Smart cities and applications & - & - & [23; 24] \\ \hline \multirow{2}{*}{Cloudlet} & Private entities/industries & Application offloading & - & - & [25; 26] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technological computing alternatives at the network edge. Then, the multi-access edge applications, running as virtual machines, are instantiated on the virtualization infrastructure of the mobile edge host (forming an NFVI point of presence, or NFVI-PoP) based on configuration or requests validated by the mobile edge management. They can either consume or provide multi-access edge services present in the MEH. These applications could be even relocated to another multi-access edge host, if supported by the system and the application. Typically, they will have associated rules and requirements (e.g., traffic redirection, DNS re-configuration, maximum latency, etc. ), that will be enforced by the multi-access edge system level management. The Multi-access Edge Platform Manager (MEPM) will act as the element management of the MEP, performing the management of the application rules, including service authorization, traffic rules, DNS configuration, conflict resolution, etc., and also performing the lifecycle management of the multi-access edge applications, including the notifications towards the orchestrator of any application related lifecycle event. Finally, through the interaction with the VIM, it will receive virtual resource fault reports and performance measurements coming from events in the virtualization infrastructure. Already at system level, the MEO maintains an overall view of the system and multi-access edge hosts, including available resources, available services and topology. It selects the appropriate host for each application, satisfying its rules and requirements, then triggering the application instantiation, relocation and termination.