# Multi-Layered Satellite Communications Systems for Ultra-High Availability and Resilience
## 5 Results: Findings from Simulations and Testbed Activities
### Testbed Activities  
The MLSS testbed is illustrated in Figure 10. Two different locations, one in Fraunhofer FOKUS in Berlin and one in a controlled location in Spain, were deployed, emulating an end-to-end distributed system like previous testbeds for 5G with GEO backhaul [48]. To be able to control the end-to-end environment and to execute the measurements the Open5 Core benchmarking tool was installed on the Berlin premises emulating the UE and the gNB. This abstracts the local 5G access network, enabling us to concentrate on the impact of the backhaul connectivity. This local 5G radio emulation is specifically important as its delay is highly dependent on the UE and gNB used, ranging from 4-6 ms for high-quality base stations and UEs adapted for minimal delay and up to 100 ms for more prototype or initial products area, thus significantly influencing the measurements. In a final deployment, such delays should be considered, especially when deciding on an end-to-end service delay, as well as on the expected capacity from the specific gNBs deployed. Co-located in Berlin with the Open5 GCore Benchmarking Tool, a satellite emulation script was deployed. The satellite emulation script pushes the SCNE data as parameters every second to a Linux OS Traffic Control (TC) tool, adding to the data plane the respective delay as well as defining a random jitter on top of it for the specific link. To be able to have accurate measurements, the system was synchronized using the Network Time Protocol (NTP) across the best-effort internet. Although it has a worse accuracy compared to the Precision Time Protocol (PTP), it is considered enough for a backhaul with satellite network transport. Additionally, PTP is not expected to function significantly better due to the continuous variable jitter between the locations. The rest of the core network was deployed in the Spain testbed, emulating a central network location, such as the headquarters of a large enterprise network be it for public protection and disaster relief, maritime, aeronautical, or IoT data aggregation. On the Spain side of the testbed, the control plane components as well as the User Plane Function (UPF) and the gateway to the internet were deployed. The minimal control plane components were deployed. A two-location setup interconnected with a best-effort internet backhaul was chosen to be able to better emulate the effects of a backhaul. Specifically, we assume that the best-effort backhaul between the Berlin and the Spain location is equivalent to a best-effort backhaul between a satellite gateway and the remote central location of an enterprise network. As both the Berlin and the Spain locations are directly connected with dark fiber to the local operator backhauls, the delays and the jitter of these links are realistic for the selected scenario. As with these measurements, we were interested in the effects of the backhaul, even though an offloading at the Berlin premise is possible by deploying a local UPF with a specific local Access Point Name (APN) enabling the usage of the local services, this was not used, and it is not depicted. For the data plane, a set of four measurement points were established in the UE, the exit of the Berlin location, the entry of the Spain location, and on the internet GW, the last possible measurement point in the end-to-end connection. With these measurement points, we could assess the end-to-end delay as well as the dependency on the undependable backhaul interconnection between the two locations. Using the data from the SCNE simulator, the following end-to-end delays presented in Figures 11 and 12 were obtained for the GEO and the LEO-based data paths. Figure 10: The testbed setup. Gray boxes represent physical locations for parts of the system. Functional technical blocks are shown in white. Solid lines represent the measured data links and dotted lines are links between functional blocks.