  Multi-access Edge Computing (MEC) is an essential technology for the fifth
generation (5G) of mobile networks. MEC enables low-latency services by
bringing computing resources close to the end-users. The integration of 5G and
MEC technologies provides a favorable platform for a wide range of
applications, including various mission-critical applications, such as smart
grids, industrial internet, and telemedicine, which require high dependability
and security. Ensuring both security and dependability is a complex and
critical task, and not achieving the necessary goals can lead to severe
consequences. Joint modeling can help to assess and achieve the necessary
requirements. Under these motivations, we propose an extension of a two-level
availability model for a 5G-MEC system. In comparison to the existing work, our
extended model (i) includes the failure of the connectivity between the 5G-MEC
elements and (ii) considers attacks against the 5G-MEC elements or their
interconnection. We implement and run the model in M\"{o}bius. The results show
that a three-element redundancy, especially of the management and core
elements, is needed and still enough to reach around 4-nines availability even
when connectivity and security are considered. Moreover, the evaluation shows
that slow detection of attacks, slow recovery from attacks, and bad
connectivity are the most significant factors that influence the overall system
availability.
