Realizing a Multi-Vendor Virtualized RAN

It’s now been over 6 months since Cisco announced that it had joined the Open Air Interface (OAI) software alliance, with the aim of accelerating open, multi-vendor, RAN splits and the first week of November marks a milestone in that co-operation.

If you recall, back in February, Cisco open-sourced a set of libraries and simulators that implement the Small Cell Forum’s (SCF) nFAPI MAC/PHY split base station architecture, and in May we went on to describe our intent to use our OAI membership to demonstrate how to integrate the open-nFAPI libraries into an existing LTE RAN stack. The rationale for this is clear, Cisco’s enterprise customers are increasingly expecting indoor cellular systems to provide multi-operator service. If the RAN is going to split, then the Physical Network Function, akin to 5G’s gNB-Distributed Unit, needs to support multi-operator sharing over a multi-vendor interface.

Now, 6 months later, we are pleased to announce that this week, during the OAI’s Fall Workshop in Paris, Cisco will be demonstrating an open-nFAPI enabled Software Defined Radio implementing the OAI PHY layers, communicating over the SCF’s multi-vendor defined nFAPI fronthaul interface to a Virtual Network Function implementing the OAI’s RRC/PDCP/RLC/MAC functionality. We have seen quite a number of vendors demonstrating their vendor proprietary approach to splits and virtualization, but we think this is the first time a split defined for multi-vendor operation has been realized.

Appreciating that in the same timeframe we have seen progress in terms of 5G split architectures. 3GPP has defined the F1 split between the gNB-Centralized Unit implementing RRC/PDCP and the gNB-Distrubuted Unit implementing RLC/MAC/PHY layers. This split, together with a separate OAM management approach for the gNB-DU “PNF”, are both aimed at supporting multi-vendor interoperability. Importantly, we can now see some top level architectural alignment between these different approaches, with both nFAPI and F1 splits looking able to support neutral host deployment.

We are convinced that 5G will need to focus on lowering the barriers for deploying active sharing in order to support multi-operator deployments. This naturally means addressing the thorny issue of multi-vendor interoperability of internal RAN interfaces. This week’s demonstration, showcasing the results of the co-operation between Cisco, the Open Air Interface and the open-nFAPI open-source project is a testament to that vision of 5G RAN realization. Irrespective of specific splits, we hope that being able to demonstrate how open source complements the standardization of RAN splits will improve market adoption and multi-vendor interoperability into the future.