# Seamless 5G Multi-Hop Connectivity Architecture and Trials for Maritime Applications
## 3 Maritime Network Architecture and Solutions for Seamless Connectivity
### Network Splits for Coast-to-Vessel Communication  
The focus of this section is to provide different architectural alternatives of network splits to address the connectivity from the coast/shore to the vessel/onboard. A general depiction is provided in Figure 6.  
The first possibility, shown in Figure 7, corresponds to what is commonly known as wireless access backhaul. In this case, the base band unit (BBU) would be located onboard, and the N2 and N3 interfaces that connect it to the 5G core control plane and the data plane onshore would be realized via IP connectivity (as pointed out above, the discussion on the architecture is agnostic in terms of the underlying IP technology available, as long as it meets certain requirements) between ship and shore. In this case, access to further data networks (DNs) (e.g., the Internet) would be carried out onshore via the N6 interface. A loss of IP connectivity would almost instantly lead to a total network outage due to timeouts on the control plane on the N2 interface. Even before that, application services on the user plane would likely stop working as backend servers in the DN would not be reachable. In terms of infrastructure costs, this split would only require a BBU and onboard antennas.  
Figure 5: Main links to be studied for the seamless connectivity problem in maritime environments.  
Figure 6: Link from the shore to the sea—Link A.  
The second considered architectural split is depicted in Figure 8, where only the control plane functionalities of the 5G core remain onshore, and the data plane is moved to the vessel premises. This architecture enables the possibility of accessing an additional DN that physically resides in the vessel as well. The most straightforward application would be accessing MEC servers to provide services for users onboard. Application services running the backend on an MEC server might for a very short time, usually few seconds, survive an IP connectivity outage. After that, control plane timeouts would cause a total network outage where all the connected end-devices would go into a \"no service\" state. In terms of infrastructure costs, this split would require a BBU and onboard antennas together with servers that host the UPF and MEC functionalities.  
Finally, the third considered option is depicted in Figure 9 and consists of having the full 5G network (RAN and 5G core) onboard. Only connectivity to external DNs, such as the internet, would be achieved via IP connectivity. A loss of this connectivity would only cause internet services to fail, while all MEC-hosted services would remain operational. However, many modern systems use public cloud-based management and monitoring platforms that would also stop working upon a loss of IP connectivity. This would affect the network and end-devices such as routers in cases where they are cloud-managed,  
Figure 8: Control plane core onshore.  
Figure 7: Core onshore (also known as) wireless access backhaul.  
but usually this would not lead to a complete application service outage. In terms of infrastructure costs, this split would require a BBU and onboard antennas together with servers that host the whole core and MEC functionalities. Accordingly, when considering the cost scaling with the number of vessels, this last architectural split is the one that would require the highest infrastructure costs, and the wireless backhaul would be the one with the lowest infrastructure costs.  
Table 1 below summarizes the main differences among the three splits described above.