Opportunities and Challenges in Multi-Vendor and Single-Vendor Open RAN Solutions

1. Introduction

With the increasing importance of radio access networks (RAN) and their moves on the agenda for the network operators and in the research communities, remote radio head deployments that handle the spectrum also come on the agenda. Network operators try to use their networks in the most efficient way as the desire to reduce operating expenses and capital expenditure is increasing. Network sharing and virtualization have gained importance in recent times due to the need to densify and reduce interference. This kind of infrastructure sharing between operators can be seen, especially in deployment scenarios in remote and rural areas. It also becomes more important to improve the efficiency of hardware usage such as Base Band Units and Radio Heads to meet the increasing capacity and quality of the network and to support the development of remote and rural regions.

Previously, buyers of network equipment were suppliers; still, suppliers sell network equipment directly to the operators. More flexible architectures are being developed to facilitate efficient use of network equipment. SDRAN is responsible for the development of technologies necessary to help supply these services in an effective and flexible manner. As for the services, there is a reduction in the cost of equipment in comparison with the previous hardware cost, and the supplier dependency is reduced. In contrast to the traditional RAN, there are several opportunities. When the Open RAN solutions are analyzed, it is seen that it is generally divided into two main parts. The results of the research were obtained by using them as the Multi-Vendor and Single-Vendor approaches. Therefore, these approaches are presented in more detail in the following subsections. Moreover, studies are also being carried out to support this approach.

1.1. Background of Open RAN Solutions

In the telecommunications sector, traditional solutions of mobile networks involving proprietary interfaces inherently lead to vendor lock-in, high costs, a lack of innovation, slow reactions from the market, and thus a need was felt for a more open and interoperable solution. The evolution of traditional radio access networks with proprietary hardware-based solutions constricted by vendor lock-in and a hybrid cloud-based solution to cloud-native virtualized networks with open interfaces and programmable RAN is detailed. As a reaction to the demand for more competition and innovation across the supply chain of the telecom industry, Open RAN is gaining currency in the roadmap of different studies. However, acceptance of Open RAN in different parts of the world and the establishment of several national entities and different memoranda of understanding have seen operators walk a narrow line between a few important large equipment manufacturers, and the move to an Open RAN market should be gradual.

1.2

The evolution of RAN networks following greater end-user traffic demand and new 5G service opportunities is changing RAN network and equipment design and characteristics. 5G RAN networks are different in multiple ways in both deployment characteristics and operational strategies, and the new FAN and RAN concepts, along with deploying new technologies for Virtual Network Functionality, Dynamic Spectrum Sharing, and Slicing, are major drivers of this change. In this chapter, we identify some of the key changes that are impacting RAN networks. Initially, a survey of radio access technology evolution for cellular networks motivates the broad set of potential Open RAN opportunities in the RAN ecosystem. It then briefly discusses the recent evolution of cellular networks to identify the challenges.

The past evolution of cellular networks has emphasized solutions restricted to the spectrum and RAN technologies designed and deployed by one key vendor. This single solution was selected, designed, and customarily developed to support a limited number of specific use case requirements. Many of the past RAN designs and deployments were designed in and supported segment-specific use cases as the major primary focus. Although mobile data services have evolved to be increasingly important as a potential revenue generator, the actual deployment of these services has been limited based on the anticipated, displayed, realized, and agreed upon need for this service in specific use case customer segments, the required technologies and network deployment, proposals and needs for the coverage area of these customers, and an anticipation of the average and peak traffic requirements.

To address these requirements and avoid associated bottlenecks, Open RAN can be considered a solution. As Open RAN technology is currently at the center of attention for various degrees of excitement and speculation among researchers, scientists, and industrialists in the field of communications, networking, and distributed computing systems, an in-depth look at this Open RAN technology is currently in high demand. This is due to different stakeholders being deeply involved in this telecommunications and networking business. Opportunities and challenges in Open RAN portray a comprehensive narrative on the role of different stakeholders, the huge potential for investment, and the possible impacts on privacy, security, and network layer players from different perspectives, such as academia, industries, and regulatory institutions.

2. Understanding Multi-Vendor and Single-Vendor Open RAN Solutions

Open RAN solutions can be deployed with different architectural approaches. Open RAN can be classified into these architecture groups: (a) Multi-Vendor Open RAN Solutions; and (b) Single-Vendor Open RAN Solutions. Each architecture is completely different from the other in terms of its design considerations and functional blocks. Multi-Vendor Open RAN Solutions are established systems incorporating radios from multiple vendors. Multi-Vendor Open RAN Solutions allow network operators to deploy diverse radio technologies, which may be better optimized for different environmental conditions. Moreover, it allows operators to exploit the best vendors in the market, avoiding vendor tie-up. These solutions rely on specific interfaces that can be used by different vendors to interconnect their radio units with an open centralized control unit. Radios can have stand-alone products and be directly connected to the standard or virtualized radio unit over the interface. Alternatively, radio elements can be collected via specific aggregation points in the field. The aggregated signals are interfaced via gateway devices working at the Fronthaul Interface. Besides, Multi-Vendor Open RAN Solutions have defined the arrangements of control layers and the abstract mechanism called the interface mechanism. Single-Vendor Open RAN is a close-to-box solution where, in most cases, the system known as a telco cloud system is either provided by the vendor providing radios or it is from another vendor's cloud system, but fully tested and integrated with Cloud RAN. These Open RAN Solutions are implemented in a compact way connecting radios from a single vendor, reducing the complexity of the management of the disaggregated system. In the implementation of these systems, both functions should work in a deeply coordinated fashion to achieve low-level functional cooperation. These solutions usually come in a pre-integrated solution where a given standard computing infrastructure, along with central and distributed data centers, is earmarked. In these systems, most flexibility is allowed in the selection of radio units. Regarding the separated distributed units, radio unit, and baseband, all architectures allow the use of preferred combinations of adjoined partner ecosystem products. As with other open initiatives, hardware and software components are based on industry standards for improved flexibility. Focusing on specific components in Multi-Vendor and Single-Vendor Open RAN solutions, radio units are split into two parts: one part that is radio front-end-specific and another part that is Open RAN-compliant. The split specification should have a set of normalization criteria to allow interworking between different vendors. This is where standardization should be able to enforce common and unique behavior so that any vendor's RUs can work in any vendor's disaggregated system. Centralized control functions are put in a virtualized instance, coordinating work over a centralized unit and distributed unit. The operations are coordinated by a standard or ad-hoc north-south interface. Orchestrators come with different interfaces but general roles for traffic balancing. The Flexible Management and Orchestration unit can work in all Open RAN nodes for automated functional management of the Radio-RAN functionalities. Similar to interface flexibility, Multi-Vendor Open RAN solutions have specifications for any management interfaces used. These specifications should contain a wide range of options for network operators. The single-vendor distributed unit contains orchestration tools to manage NFs within its RAN network, and there is a standard or custom API through which DevOps or network operators can manage and control the intra-RAN components. The interface must contain a single solution.

2.1. Definition and Key Components

Open RAN solutions are based on the vendor-neutral open architecture in which radio access network functionalities are built up by the integration of the hardware and software parts provided by different vendors. In this context, the Multi-Vendor Open RAN Solutions (MV-ORAN) is defined as the integration of hardware and/or software components from different suppliers across the following Open RAN specified interfaces: X2, E1, F1-U, A1, O1, and NDS. In contrast, in the Single-Vendor Open RAN Solution (SV-ORAN), the CU and DU functionalities are supplied by the same vendor. The hardware and software used to implement Radio Units remain vendor-neutral in both models for 5G New Radio (NR) Base Stations. This section discusses interfaces, management layer services, and orchestration frameworks in MV-ORAN and SV-ORAN. The SV-ORAN model includes COTS servers and operational software. The hardware parts of the Radio Units, such as antennas or power supply units, are not included in the ORAN architecture. This solution is called the Standalone System. MV-ORAN and SV-ORAN relate to different system deployments and reflect their roles in the network. The implementation and use of these solutions affect network performance, including efficiency, stability, scalability, software automation, and related operational costs. In order for the radio access network to work efficiently and effectively, internal functionalities should fit together well. In this case, interfaces, including management layer services, orchestration frameworks, and some development guidelines, are defined in the Open RAN model. The technical and operational principles of interfaces in the context of using the MV-ORAN and SV-ORAN solutions are presented. Additionally, the opportunities and constraints in this aspect of the ORAN network are also discussed. These solutions can be used together, and this is possible due to the readable and understandable standardized system architecture.

3. Opportunities in Multi-Vendor and Single-Vendor Open RAN Solutions

The disaggregation of radio hardware and software is a unique concept in the RAN market that was introduced in Open RAN networks. It took years to develop and standardize these challenging characteristics, mainly due to the tight coupling between vendor hardware and software. While fulfilling all the requirements to translate the market conditions to the Open RAN ecosystem, it is necessary to focus on Multi-Vendor and Single-Vendor Open RAN solutions. The growing complexity of consumer demands continually challenges the abilities of network operators. As traffic patterns, devices, data usage, market niches, and even acute external circumstances force rapid and sometimes dramatic changes, operators require networks that are flexible enough to adapt and meet these needs.

Innovation is ultimately necessary to provide this flexibility, and it thrives on competition. One area where this becomes apparent is in the dynamism of technology, and in turn, the resiliency of the available solutions on the market. In an ecosystem where there are multiple vendors pursuing new and novel technologies to gain market share and offer the best or newest solutions first, research and development cycles compress, pilot trials of cutting-edge techniques proliferate, and improvements on features happen at a faster pace. Price is always a concern with network investments, particularly those made in technology value chains. In the RAN ecosystem, operators have long expressed an interest in increasing supplier competition to reduce this barrier to novel technology adoption. In the spectrum space sold through competitive auction, multiple operators demand improvements in the flexibility of resources if they are to take part. Anachronistically, in the hardware space, the spectrum of desirable options was significantly more compressed.

3.1. Enhanced Flexibility and Innovation

3.1. Enhanced Flexibility and Innovation: Multi-vendor and single-vendor open RAN solutions allow operators to be more dynamic and adaptable in how they manage and grow their networks. Flexibility, in particular, allows for more rapid adjustments to changes in demand, expansion into new geographies, reactions to competitors’ moves, market accelerations, and opportunities. Longer term, innovations in technology will arise from this new level of competition. The major framework includes architectural tenets of reusability and extensibility produced by interfaces and their interaction mechanisms. These principles are provided by modular and functionally coherent designs that enable functions, updates, and enhancements to be swapped and deployed with little or no impact on the overall system. As a result, they enable operators to build networks that are more resilient, flexible, and scalable. Collaborations and partnerships are an essential facet of the innovation networks. This has helped link operators who have made investments in networks that include open and modular architectures with the communities of technology providers and other operators working to develop open and disaggregated interfaces. The community that has been involved in developing network slicing interfaces also serves as a discussion arena where many participants are exploring other use cases and thus new interfaces and requirements. This may lead to not-yet-precise visions of 6G. The interplay between the discussions is itself a source of enduring network capabilities. The benefit of any open and modular innovation network is that through time they can be looked back on as the crucible in which future visionary network capabilities were first conceived.

4. Challenges in Multi-Vendor and Single-Vendor Open RAN Solutions

In an increasingly complex technology landscape, one of the most practical challenges for implementing multi-vendor and single-vendor Open RAN solutions is ensuring interoperability among various vendors, equipment, and uplink technologies. Compatibility between different technological solutions to the same problem domain is essential. This raises the potential for effective network integration among the suppliers to ensure that services work properly in a mixed-vendor Open RAN environment. It starts with the successful integration of relevant software and hardware components. The network may comprise multiple sites, RAN using different processing engines, abnormal time-bounded protocols, 5G NR, MAC, RLC, scheduler, software-defined routing, and others which are implemented using different programming languages, where raw computational power and speed vary significantly.

An increase arises in a requirement for technical skills to manage multi-vendor and technology-diverse Open RAN in order to satisfactorily meet KPIs and customer requirements. However, coordination and vendor lock-in over the set of standards, enhancing platform extensibility and player agglomeration can cause single-vendor Open RAN deployment to face multi-vendor Open RAN-induced uncertainties. Single-vendor Open RAN poses the key challenge of selling network equipment and having strategic control of the network to a single vendor. Hence, the best option to counter the above arguments could involve the establishment of a mixed-vendor Open RAN network. Evidently, unlocking network protocol softwarization poses new security challenges with different vendors. Each vendor is expected to deploy its own comprehensive security mechanisms and standards. In addition, Open RAN endpoints in use by the different vendors have the advantage of the ability to implement new features and protocols quickly by generating software updates. However, by not following a full testing cycle, such implementations could potentially expose vulnerabilities while the network is in deployment or operation. Consequently, the subsequent unplanned security fixes will incur additional costs with a negative impact on the operational budget and service deployment. Exhaustive testing requirements will span across multiple communication domains in a multi-vendor mixed Open RAN.

4.1. Interoperability Issues

The interoperability challenge is one of the major challenges while integrating RAN components from different vendors. An operator may have their infrastructure from a single vendor or multiple vendors in different countries. In either case, interoperability is an issue as products in the network are from different vendors. There are very limited standards defined for the RAN interface among different telecom operators. One main result of this is that it is not simple to test and foresee interoperability and compatibility between products that are not from the same vendor. Operators in these countries with a different vendor who want to expand require testing of network elements with new vendors. Fearing network disruption, they need to be careful in introducing new network components. The converged atmosphere with new and old vendors further expands the testing and identification of various scenarios that would be challenging in complex network environments. Operators believe that new network vendors will be a stumbling block in enhancing performance and user experience.

A temporary suspension in the rollout of new products and software upgrades of its new RAN portfolio in different countries due to this interoperability and interface complication has been disclosed. Another prominent and fitting example is the specification of RIC components defined by authorities. While integrating RIC components developed by various vendors, they are struggling to shape it as a single solution that can work in different customer environments, although different deployments might have products from different vendors in the network. It is clear from these examples that we need to coordinate the vendors in physically developing an integrated single-vendor as a multi-vendor solution, obvious from various interfaces and protocols. The unique aspect of this area is that solutions will be defined through coordination between various vendors to develop interoperable single or multi-vendor open RAN solutions.

5. Case Studies and Real-World Implementations

Opportunities and Challenges in Multi-Vendor and Single-Vendor Open RAN Solutions - A Qualitative Investigation

Case Studies and Real-World Implementations

In the industry workshop held ahead of the 5G World event, in Part 1 of this series, multi-vendor and single-vendor RAN approaches were illustrated through a series of 12 real-world implementations. Each illustration was accompanied by a narrative that attempted to put the project in a useful context and to state some lessons learned. This paper develops further six of the illustrations presented in the previous workshop.

The first two case studies took us to collaborative R&D and operational challenges faced by mobile network operators that have pursued multi-vendor transformations. The first of these tells the story of their journey—supported by experts from the academic community—in developing the infrastructure automation that comes with full virtualization of the RAN, taking a particularly critical view of where operational efficiency could be achieved. In the second case, colleagues discovered that increased vendor variety in the RAN has amplified the strategic value of their collaborative research agenda and are currently using the arrival of new big vendors as a "land grab" to create competitive differentiation in multi-RAT management off the back of their deepened network automation capabilities.

5.1. Comparison of Multi-Vendor and Single-Vendor Deployments

The deployment and management of multi-vendor, multi-technology networks offer a lot of flexibility. The MNOs get to choose from a variety of vendors to build and supply the Radio Units, Distributed Units, and Centralized Units. A deployment like this is also referred to as a standalone O-RAN, where 5G New Radio is completely dependent on the O-RAN functionality. Secondly, such deployments can also help to bring the best-of-breed solutions for smaller islands and carrier segments. For example, 5G for many superfast areas from one vendor, 5GRAN for enterprise from another, and an OFDM-based solution to cover rural areas from the third. However, such a deployment will need a high level of integration and may face interoperability challenges.

In a single-vendor case, the virtualization and brownfield deployments are much easier, as one vendor is expected to provide services for a complete or partial stack. The access layer can be opened by an MNO, and the core can be offered as a third-party service. Such an integration can optimize OPEX and provide end-to-end service assurance. At the same time, such deployments are locked to a single vendor, which is suboptimal and makes an operator vulnerable to multiple risks. The very first risk would be to offer 5G services to consumers and enterprises without having a multi-vendor deployment. Without this architecture, the auto-scaling of 5G becomes a proprietary feature of a single vendor managing the radio, transport, and core network. In case the operator needs to migrate to another vendor, she again comes back to a similar problem of vertical lock-in, at least for the migration period. Hence, from an OPEX perspective, a single-vendor solution may appear to be simple, but it exposes the operator to many risks in terms of migration and security as well. We are likely to see a trend reversal in the upcoming years for a shift to multi-vendor deployment.

References:

Bonati, L., Polese, M., D'Oro, S., Basagni, S., & Melodia, T. (2020). Open, programmable, and virtualized 5G networks: State-of-the-art and the road ahead. Computer Networks. sciencedirect.com