by Marius Corici, Marc Emmelmann, Manfred Hauswirth, Thomas Magedanz (Fraunhofer FOKUS, TU Berlin)
Local 5G networks are a major area of 5G innovation and offer vital insights into practical 5G deployment. Local 5G networks can give us important information because in these environments 5G technologies must be tightly integrated with different access network technologies and with the end-to-end software stacks of different vertical application domains, such as manufacturing and energy. To achieve this in an efficient and economical way, the Open5GCore.net software toolkit of Fraunhofer FOKUS provides the first 3GPP Release 15 5G core network implementation facilitating the rapid deployment of local 5G use-case-oriented testbeds. We have also developed the FOKUS “5G Playground”, a reference live deployment, with multiple customised network slices based on the Open5GCore and use case applications. The “5G Playground” has served as a blueprint for many other 5G testbeds deployed across Europe and around the world in the context of 5GPPP.
After many years of international research and standardisation  the 5th Generation of Mobile Communications (5G) is on the verge of being deployed. The first 5G network deployments will start this year after the first 5G frequency auctions. Like previous generations of mobile communication systems, 5G will evolve functionally over time by means of new 3GPP releases and from practical experience obtained during the deployments of previous releases. However, the 5G system architecture is probably the most complex one so far, representing a radical change from previous generations due to its incorporation of various technology innovations, such as software-defined networks (SDN), network function virtualization (NFV), and edge computing, which make 5G a distributed, dynamically programmable software platform. Another reason for the complexity of 5G is its multi-access network support, including the novel 5G New Radio (NR) system, which adds a lot of flexibility, but also complexity to interworking in the migration to 5G. In addition, concepts like network slicing and local networking enable completely new levels of network customisation and new business models within different vertical domains. This means that the scope, the degree and the dimensions of flexibility are quite different from previous versions.
Thus, current 5G technology is still in its infancy and still requires a wide range of validation and optimisation by means of proof-of concepts and real-world trials in different application contexts in order to be fully applicable and gain acceptance in the different vertical domains. In this context the notions of campus networks and local/regional networks are gaining strong momentum. In contrast to public trials focussing on enhanced multimedia broadband use cases, requiring significant infrastructure investments with unpredictable returns, 5G deployments in a local context will be more affordable and can focus on very specific industrial requirements in the field of ultra-reliable, low-latency communication for complex business processes, such as automation in manufacturing. Also, business model exploration is going to happen in this area, as new deployment and operation models may evolve. In these local network environments, scalability and interoperability become key issues because local networks vary in size. Their access network and backhaul technologies, and their applications also vary, often demanding dedicated networks or different network slices. These emerging considerations have moved to the centre of discussions in the latest German plans for local/regional 5G spectrum assignments in the 3,7-3,8 GHz frequency range.
This is the environment for the Open5GCore, a scalable 5G core network; highly customisable to different application needs (mMTC vs. eMMB) for building 5G testbeds, developed by Fraunhofer FOKUS. Fraunhofer FOKUS has a long track record of building reference software toolkits for testbeds since 3G.
Open5GCore provides a solution for most of the requirements currently under discussion as it adequately reflects the 3GPP Release 15 for the core network functionality and its integration with 5G New Radio along with legacy off-the-shelf LTE-based access and non-3GPP accesses. As such, Open5GCore enables the immediate demonstration of different features and applications and supports the current requirement to support a genuine 5G Core Network in addition to an evolved EPC one.
Figure 1: Architecture of the Open5GCore.
Figure 1 depicts the current components of the Open5GCore implementation, in particular the integration with 5G New Radio, the implementation of the control-user-plane split, service-based architecture features, and data path diversity, supporting local offloading and backhaul control. Open5GCore runs on top of available hardware platforms and can be deployed with containers or virtual machines on top of a large number of virtualisation environments, ranging from Raspberry PI to a complete rack of servers. As such, Open5GCore – being a highly customisable and scalable 5G core adjustable to the needs of specific use cases – is a unparalleled candidate for building 5G testbeds on-premises and for deploying local campus and industrial networks.
In the current implementation version, the Open5GCore concentrates on three major innovation areas proving the feasibility of the 5G system: (1) It includes the functionality required for access and mobility control, session management and authentication and authorisation to enable the carrier-grade connectivity of the 5G devices in both standalone and non-standalone mode. (2) For the highest flexibility, the control plane is implemented using the 3GPP service-based architecture and it integrates dynamically with the data path using the 3GPP session and data path management. (3) With these features, Open5GCore represents the first available prototype implementation of the 5G core network, enabling the immediate demonstration of the use cases in a similar and vendor-independent environment to the real deployments.
For enabling customised deployments at the edge, the Open5GCore additionally includes the interoperability with the backhaul management for networks deployed for use cases at multiple locations interconnected with best-effort third-party internet connections. Additionally, Open5GCore can be deployed using a set of edge-central models which enable the appropriate interaction according to the use case requirements and the available computing, storage and networking resources at the edge location. Through this, the current implementation facilitates customisation of connectivity for the specific needs of local networks.
To address all of these requirements in an appropriate fashion, Open5GCore was implemented in the C programming language on Linux OS platforms, using our own software platform which is able to manage the different threads, inter-thread communication and memory requirements specifically tailored to systems in which delay and reliability are more important than the fine-granular management of resources. At the moment, Open5GCore represents a large software system with multiple components and interactions between the components as specified by 3GPP and extended with our own innovations in the area of data path and subscriber management. Table 1 provides an informal overview of the complexity of the overall Open5GCore system.
|Modules||112||The 112 Open5GCore modules span from protocol modules, interface modules and component modules.|
|Files||5860||Each of the modules includes a large number of files. From these, 2600 files are C code modules.|
|Commits||15000||A large team of developers are extending the software to address the latest requirements and standards.|
|Components||16||Components are considered independent network functions having a specific functionality. Multiple of these software components may be instantiated within the same testbed as to enable more complex scenarios.|
Table 1: Overview of the over all Open5GCore system.
Some interesting experiences and findings from the implementation of the Open5GCore are: The most complex part of the overall system is the interaction between the different components. The large number of interfaces and exchanged messages can result in a very large number of side effects. On the plus side, the independence of the subscriber-related state information on each of the network functions enables a very good parallelisation of the different operations. Thus a highly scalable system can be achieved with limited cost, enabling the local network to scale according to the requirements. Because of these properties, a 5G packet core can be installed on different types of hardware supporting different numbers of subscribers, making a software-only implementation combined with off-the-shelf hardware an ideal solution for initial deployments.
The Berlin 5G Playground hosted by Fraunhofer FOKUS is an instantiation of such a testbed designed to enable innovative product prototyping in a realistic, comprehensive 5G end-to-end environment, including calibration, benchmarking and interoperability testing among new prototypes and products. For that, the 5G Playground can be flexibly augmented by infrastructure, software network functions and service components from third parties.
Employing local and experimental spectrum licenses in conjunction with spectrum provided by telecommunication providers, the 5G Playground offers outdoor radio coverage of the Berlin city around the Fraunhofer FOKUS campus. By combining 5G, 4G and non-3GPP access technologies, the 5G Playground allows the user to perform and validate experiments in a diverse outdoor-indoor environment previously only feasible in laboratories (see Figure 2). As such, it also enables the creation of dedicated, specialised networks via “slicing” as required for general, highly-reliable networks, automotive verticals, as well as for networks for security and safety use cases.
Figure 2: Components of the Berlin 5G Playground.
In conjunction with the Open5GCore, the Berlin 5G Playground acts as a blueprint for planning and installing remote testbeds at the use case locations. Fraunhofer FOKUS contributes the 5G Playground to several European research projects, e.g., 5GENESIS and 5G-VINNI, providing the only German-based 5G testbed which is part of two of the three existing EU-funded 5G infrastructure initiatives. In addition, the Open5GCore provides the basis for the SATis5 testbed of the European Space Agency (ESA) to showcase the advantages of satellite-terrestrial convergence as part of the 5G environment, especially underpinning the benefits provided for a large number of multimedia delivery and dedicated IoT deployments. The participation in these projects allows Fraunhofer FOKUS to further advance its Open5GCore towards 3GPP Release 16 capabilities and to evaluate current 5G KPIs related to the network core via end-to-end, large-scale trials. Until now, the testbed has been replicated 12 times at customer premises, addressing the needs of various use cases.
The full availability of an integrated 5G testbed and its underlying software components with all services and functionalities currently under standardisation enables telecommunication companies, equipment manufacturers and companies from any vertical segment to test business models and functionalities in a realistic environment. On the research side, such environments and software are essential in finding new approaches and evaluating them according to highest scientific standards.
 M. Shafi et al., “5G: A Tutorial Overview of Standards, Trials, Challenges, Deployment, and Practice,” in IEEE Journal on Selected Areas in Communications, vol. 35, no. 6, pp. 1201-1221, 2017.
Fraunhofer FOKUS, Software-Defined Networks group, Berlin, Germany