# 5G Cross-Border Operation for Connected and Automated Mobility: Challenges and Solutions
## 2 Challenges for Cross-Border Operation  
One of the challenges of CCAM services is that they should be provided along different countries when vehicles drive across national borders. Service continuity must be guaranteed, and the quality of services cannot be jeopardized when crossing borders. The situation is particularly challenging when considering the multi-country, multi-operator, multi-telco-vendor, and multi-car-manufacturer scenario that cross-border deployments imply, both from the technical cross-border connectivity perspective as well as business and legal challenges. While the specification of 5G technologies has progressed a lot in the last years, so far only a few actions have been taken to guarantee that a high QoS wireless connectivity, and indirectly, the support of the services on top of it, can be kept when a vehicle is moving across national borders. Therefore,there are some uncertainties associated with the deployment of 5G networks for the provision of CCAM services in cross-border settings that require dedicated innovation efforts. A first set of potential gaps and challenges has been identified already, and it is also expected that some further technical cross-border challenges will be identified along the deployment of a real network in the trials. Cross-border means, first of all, a handover from one operator to another. A first challenge concerns the radio handover. Indeed, the data connection has to be handed over from one operator to another. For now, data handovers do not consider any key performance indicators (KPIs). Even if basic QoS requirements can be done with current mobile networks, the challenge is to provide a more detailed service-level agreement (SLA) handover, guaranteeing that SLAs are maintained. SLAs are application specific. Thus, each application (or service) running on a mobile device has its own requirements. Generally speaking, each application has its own 5G slice, which must be handed over from one MNO to another in the way that the minimum requirements are fulfilled. The exact metrics (e.g., min throughput, max latency, etc.) have to be defined. These metrics have to be communicated in some way during the handover procedure, allowing the visited network operator to do a decision on the 5G slice to be established. This handover must work independently of the equipment used by the operator (i.e., cross-vendor). There should be also a network feedback on the success or failure to provide those minimum requirements, allowing the application to react if they cannot be provided (e.g., change from autonomous assisted driving to manual mode, etc.). The ultra-low latency and reliability requirements imposed by automotive services, which are a complex issue as explained in [16], could be met through an extensive usage of edge resources, deploying components of the end-to-end services closer to the network edges. This approach reduces the delay between the generation and the elaboration of the application data, enabling faster processing and timely reactions at the service level. Network slices and virtual services in 5 GcroCo are thus characterized by a strong presence of edge applications that, in cross-border scenarios, need to be deployed in multiple domains, characterized by different geographical positions, administrative operations and technological solutions. Moreover, each MNO will have a different 5G architecture in general, and specifically a different MEC architecture. Indeed, an MEC can be implemented at different hierarchical levels in an operator network: the highest level would be near or in the core network, being the most cost-effective solution but the worst from latency perspective. Alternatively, MEC may be at regional point-of-presence (POP) level, at local POP or at the radio cell level. Other intermediate levels are also possible. However, it is clear that a MEC at radio cell-level provides the lowest technical possible latency, but the highest amount of investment.