Open RAN Interoperability Between Multi-Vendor!
April 17, 2022

For the introduction of RAN functions disaggregation and open interfaces in 5G, 3GPP has in Release 15 specified a Higher Layer Split (HLS) option of the gNB, which is also known as the Option 2 NR-PDCP split option. In this option, the gNB may consist of a Central Unit (gNB-CU) and one or more gNB Distributed Units (gNB-DU) connected through the F1 interface. 3GPP has delivered a set of specifications for the F1 interface, however realizing multivendor interoperability over the F1 interface can be very challenging as these specifications have been defined with options that can be used in different manners depending on vendors’ implementations.

The Challenges of Multi-Vendor Interoperability

Imagine all the advanced coordination features, power control algorithms, and intra-technology interactions in a multi-vendor RAN. Today, having one vendor simplifies all that. And, when product-related network performance issues arise, which is unavoidable, MNOs work with only one vendor to resolve them.

Now imagine a network where RAN components such as central unit (CU), distributed unit (DU), and radio unit (RU) is supplied and supported by multiple vendors – operators and vendors will face greater challenges in both identifying and isolating issues as well as ensuring that performance/cost compares favorably to that of an optimized single vendor solution.

Another key challenge of an O-RAN-based multi-vendor network will be network management and resource management. Management of multi-vendor spares and training resources to maintain a multi-vendor network will be a learning curve for service providers’ operations teams. Not to forget, integrating new functions and orchestration of new services from various vendors in an O-RAN-based network will be another key challenge.

So the key challenges operators need to address when considering O-RAN is interoperability, ownership accountability, how to troubleshoot and isolate problems, and also how to actually manage and orchestrate all the multi-vendor virtual network functions and physical network functions on a common cloud infrastructure, which may
also, be multi-vendor.

Open RAN Has The Solution

O-RAN is delivering well-defined specifications to the industry to enable deployments of O-RAN-based programmable networks consisting of fully-disaggregated modular O-RAN network functions. These are designed to be multi-vendor interoperable over open interfaces running on cloud-based virtual systems.

So One of the main benefits of Open RAN is Enabling an open, multi-vendor interoperable ecosystem driving healthier competition, lowering costs for RAN equipment, and delivering a much larger pool of vendors.

WG5 (Open 3GPP Interface WG)

WG5 promotes activities with the aim of achieving multi-vendor interoperability and improving performance by targeting network equipment interfaces specified by 3GPP (F1 and E1 equipment in interfaces within base stations, X2 interface between eNB and gNB, Xn interface between gNBs, etc.).

These interfaces have been designed with a relatively high degree of freedom to cover every possible operation scenario and equipment implementation to the degree possible. This has enabled operators and vendors to achieve their original operations and implementations while resulting in degradation of connectivity and other performance issues (for example, temporary data interruptions and degraded user throughput) in multi-vendor deployment.

Example of Multi-vendor Issue

An example of such a problem in multivendor operation is shown in the below figure from NTT DOCOMO Technical Journal.

The problem in Multivendor Operation (Source: NTT DOCOMO)

Fig. 4 (a) shows the case in which vendor-A and vendor-B implement a 3GPP interface with different interpretations of the parameter (X) of the interface. As a result, the equipment behaves differently between vendors A and B, which can raise concerns that a problem may occur causing degradation of connectivity and other performance issues.

Fig. 4 (b), on the other hand, shows the case in which vendors A and B implement parameter X with the same interpretation. In this case, both units of equipment perform the same operation with respect to this parameter thereby enabling connectivity and performance to be maintained even in a multi-vendor scenario.

In this way, WG5 is working to clarify the interpretation of parameters specified by 3GPP and the expected behavior of equipment with the aim of achieving a multivendor environment with any combination of vendor equipment.

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