There’s a lot to like about Open Radio Access Network (O-RAN). It frees mobile operators and private network operators to choose hardware and software from multiple vendors rather than being locked into a single supplier’s ecosystem. That can reduce capex and opex while providing operational flexibility and competitive advantages.
But there’s also a lot to fear, starting with complexity. As Figure 1 illustrates, O-RAN and 5G are both new architectures, so operators have two learning curves to climb. The multi-vendor environment adds another layer of complexity because now operators are solely responsible for integrating, managing and troubleshooting everything. In the hypercompetitive mobile market, operators want to be confident that their 5G O-RAN network delivers performance and reliability that exceeds both 4G and their competitors’ 5G networks.
Figure 1: The O-RAN Evolution Fundamentally Changes the Mobile Network Architecture
These concerns and challenges highlight why testing an O-RAN should start long before it’s installed. Interoperability testing is particularly important because there will likely be multiple vendors compared to just one or two with a traditional RAN. As a result, operators should make extensive testing in the lab the first step. Waiting until installation work begins to uncover interoperability issues runs the risk of delaying commercial launch.
In the lab, testing should cover the RAN Intelligent Controller (RIC), which is the "brains" of the operation. Testing the RIC helps ensure that all the network elements are operating correctly, both independently and in conjunction with other vendors’ platforms.
In the field, testing considerations are similar to those of traditional RANs. For example, testing should cover the individual O-RAN radio units (O-RUs), Distributed Units (O-DUs) and Centralized Units (O-CUs) and near-RT RIC network elements, as well as full end-to-end open network validation. O-RAN testing can be a long process, with the ultimate destination being a proactive network assurance system for ongoing maintenance, optimization and trouble-shooting. A comprehensive O-RAN testing strategy can be divided into three broad areas: validation, verification and visibility.
Validation
In a multi-vendor O-RAN environment, network vendors and service providers will face situations where they must support a varied set of O-RU configurations, potentially supporting O-RUs from multiple vendors simultaneously in the same network. Having different O-RU configurations can add complexity in terms of interoperability. This is compounded by the fact that compared to testing over RF of single vendor networks, the O-DU and standardized O-RAN Fronthaul interface are new entities, which introduces a new risk. O-DU focused testing is used to minimize this risk to the 3GPP features and interactions the network must support, which requires all disaggregated nodes to perform well. O-DU vendors therefore need to ensure that O-DUs can handle multi-vendor O-RUs without introducing performance compromises and avoid the addition of new risks from a 3GPP feature interaction point of view
The test platform for validation should be agnostic to network disaggregation so it can accommodate any combination of a vendor’s hardware with any other vendor’s software. It should include a broad, deep selection of realistic mobility models and mobility scenarios, and produce measurement logs, KPIs and protocol metrics during and after each test case.It also should support 4G because, with the exception of greenfield operators, most 5G smartphones and other devices will fall back to 4G in areas where 5G coverage hasn’t yet been built out.
UE validation should cover QoS aspects suchas whether the network is meeting latency and round-trip times for voice and other delay-sensitive applications. These performance KPIs are key for supporting IoT applications, so the ability to test them is critical for both public operators and enterprises with private 5G networks.
For example, the 5G NR Ultra-Reliable Low-Latency Communications (URLLC) feature set reduces latency to as little as 1 millisecond. So if the O-RAN will use URLLC to support Industry 4.0 factory automation use cases such as time-sensitive networking (TSN), then the test platform must be able to verify that the network is meeting those stringent benchmarks.
When it comes to testing the O-RU, look for capabilities such as real-time generation of the O-RAN Control/User/Synchronization/Management plane messaging for the IQ data stream. The platform also should be able to test multiple O-DUs and O-RAN profiles from different vendors. This flexibility reduces the cost and complexityof testing.
Verification
O-RAN health verification testing identifies high-level problems between the O-DU and O-RU during deployment. The test platform should use packet capture and filtering in this interface to support advanced troubleshooting and analysis.
The tool should support stateful M-plane because the O-DU cycles through typical M-plane procedures and establishes a link with the O-RU. The O-DU emulator’s C/U-plane engine should generate real-time eCPRI packets for the downlink . The Open Fronthaul interface carries the eCPRI packets to the O-RU, so another key feature is the ability to analyze the downlink signal going through the O-RU’s transceiver ports.
To verify radio performance, look for tools that can analyze beamforming performance, assess radio conformance, measure transmit power and evaluate downlink modulation quality. It also should include a portable component to enable drive and walk testing to help ferret out issues in specific areas, such as deep inside a factory where metal racks and equipment create multipath issues.
The functionality of the near-RT RIC is performed by a mix of xApps, which may be from multiple vendors. As a result, the verification process includes ensuring that these xApps always operate flawlessly —both individually and in concert with other vendors’ xApps —throughout every step of the lifecycle,from sandbox development to live operation. This process includes verifying that the heterogeneous xApps are correctly implementing the operator’s policies for any combination of subscribers, services and slices.
Visibility
There are profound benefits of disaggregation of the network into multiple discrete components with a decoupled control system in the form of the RIC. And with more components comes more complexity and an increased number of ways for the network to experience performance degradations. Performance issues in a more complex network can be harder to detect, diagnose and resolve than they would be in a simpler network with fewer components. Considering the many and varied potential ways that the operational network can experience degraded performance, the network may suffer from failure in the transport network (fronthaul, mid-haul, backhaul). This may range from congestion leading to latencies or packet loss out of acceptable ranges, to complete loss of a fiber link through breakage or physical disconnection.
The disaggregated RAN or core network functions may also become impaired, for example, through overload or software quality issues. The SMO system may experience impairment or the physical infrastructure on which the logical functions are hosted may degrade. Also, the nonRT RIC or near-RT RIC may experience conflict or confusion between rApps or xApps from different vendors respectively.
The 5G network is envisioned to support a large variety of use cases, and can sometimes be poorly tuned to the demands placed on it by specific subscribers. Concentrations of increasing demand for 5G services can lead to congestion on the radio resources. Poor coverage or interference can impact the accessibility of the network services. These phenomena will vary as the spatial dynamics of demand for services around the network changes. This is compounded by the fact that 5G will generally be deployed on top of a mix of legacy 4G, 3G and 2G systems so creation of a consolidated view of system performance and of fault-finding will also be critical to effective management of the operational network. And as the demand for different mixes of services with novel mobility profiles pushes the resource management capability to the limit, new edge failure cases beyond what was tested at the pre-deployment stage can be exposed and manifest as degraded performance.
All this means that an end-to-end view of the network is critical for identifying problems before they become noticeable to customers and performance-sensitive IoT devices such as those use in industrial automation. Look for a test tool that can capture, geolocate and analyze every type of event that occurs across the RF, RAN, xHaul transport and core components.
This is a tall order, considering the complexity. One example is the demand for different mixes of services, each with novel mobility profiles. This trend is pushing the resource management capability to the limit, resulting in new edge failure cases beyond what was tested at the pre-deployment stage. Hence the importance of a network monitoring and assurance that provides visibility into all the hardware and software components where the degraded performance is originating.
These insights give network management engineers the highly detailed information they need to quickly identify and resolve problems. These capabilities have always been important, but enterprise customers have even higher expectations with 5G. For example, enterprises are increasingly requiring SLAs for their 5G-powered mission-critical applications. Operators that can meet those SLAs —and provide test results to prove it —have a competitive advantage over those that don’t.
SLAs also will be key for success in the private 5G market. Many manufacturers and other businesses will choose a virtual slice of a public network for private 5G rather than bearing the cost of buying and operating their own core and RAN. So public operators will need end-to-end visibility to ensure that each slice is meeting each customer’s unique performance requirements.
It is long road from the lab to the field to assurance, but it is a road that operators around the world have decided is the right road – for good reason. O-RAN brings many benefits for operators such as an open ecosystem that removes vendor lock-in, lays down the foundation for virtualized network elements, and introduces white-box hardware that can be quickly scaled up through software-based nodes. At the same time, it also creates significant challenges in terms of test and integration. Having the right test and network management strategy and the right partner during the development, deployment and operation of an O-RAN network can help operators overcome those challenges.
