# Slicing on the Road: Enabling the Automotive Vertical through 5G Network Softwarization
## 5 Mobility Management  
In the context of V2X, mobility should be handled as a norm; it becomes a complicated issue in the case of roaming, requiring inter-operator interactions. We now focus on the capability of the proposed framework to manage inter-operator mobility, since intra-operator mobility can be seen as a simplified roaming case. Whenever a vehicle moves from the home network to a visited network, the same service quality must be seamlessly provided to it, if the federated network slicing concept is in place. This is possible thanks to the orchestration capabilities of the conceived network slicing framework, which allows tracking the vehicles and monitoring: _(i)_ the link and quality availability in the end-to-end chain of radio and core network elements; and _(ii)_ the processing capabilities of MEC servers, so to promptly trigger slices reconfiguration.  
The main proposed interactions during roaming are depicted in Figure 4. The SDN Controller continuously monitors the status (i.e., position, planned trajectory, and radio coverage options) of currently served vehicles. Status parameters are retrieved from the MEC server and used by the SDN Controller to predict the need for a vehicle to roam from a home to a visited network. Whenever the SDN Controller detects that such a condition is going to occur, it notifies the home network Slice Manager, which interacts with the Slicing orchestrator. The latter one contacts its peer in the visited network to exchange the SLAs of the roaming slice.  
The Slicing Orchestrator in the visited network checks, among the activated slices, the one that better matches the requirements of the slice to be hosted. If there is a slice that matches the indicated requirements, it is allocated to host the new customer. Otherwise, the slice that better suits the demands is adapted to accommodate the requirements of the visiting subscriber. In its turn, the Slicing orchestrator in the visited network may also resort to network resources from other operators (if slicing federation is in place) to ensure the desired service quality. In the worst case, a _default V2X slice_ is activated for it, which ensures the basic functionalities.  
The Slice Manager of the selected visited slice interacts, via the Slicing Orchestrator, with the Slice Manager of the home slice to agree about the overall slice configuration, e.g., whether and which UP/CP functionalities should be migrated, and triggers the release/activation of functionalities in the home/visited slice, respectively.  
If the accessed service is available at a MEC server, the Infrastructure Manager of the visited network triggers a migration request for the V2X AS into the targeted MEC server. The MEC application migration between edges of different MNOs, with service continuity guaranteed, is still an open issue [41]. According to the available processing capabilities at the edge and the service requirements, the Infrastructure Manager could either decide to trigger a scale-up operation in the edge server and/or enforce cooperation among nearby edge servers [42], if the closest MEC server is overloaded.  
The SDN Controller sets-up the paths to ensure a quick service migration and configures the RAN to guarantee a comparable quality (e.g., by instructing multi-RAT access). In the case of intra-operator mobility, the same procedures are triggered, with the main difference being that the Slicing Orchestrator is only required to interact with the Slice Managers of the slices activated by the same MNO to assure slice isolation in case of slice reconfiguration on the fly.