The entire telecoms industry is going through a change that can be only compared to the change that data centers went through in the 2000s, both driven by Moore’s Law.
Evolution of HW/SW disaggregation
Source: Parallel Wireless
This allows the move from costly, proprietary solutions to COTS-based and open, software-based ones, and to create a broader vendor supply chain. How does this concept apply to the RAN?
Most of the CAPEX required to build a wireless network is related to the RAN segment, reaching as high as 80% of the total network cost. Any reduction in the RAN equipment cost will significantly help the bottom line of wireless operators as they struggle to cope with the challenges of ever-increasing mobile traffic and declining revenues.
Though the RAN interfaces are “supposed” to be open as they are 3GPP-standards based, in traditional RAN deployments, the software and interfaces remain either proprietary or “closed” by the individual vendor and are often tied to the underlying hardware by the same vendor. Meaning operators cannot put vendor B’s software on a BBU from vendor A or connect a radio from vendor A to a vBBU hardware and software from vendor B. Any software upgrades are tied into the installed base, and if an operator wants to do a vendor A swap, they need to rip out all of it: from the vendor A radio to the vendor A BBU hosting the vendor A software - they cannot replace just one component in the legacy RAN deployment. This creates a vendor lock-in.
Vodafone, the leading innovator in Open RAN, recently noted that “the global supply of telecom network equipment has become concentrated in a small handful of companies over the past few years. More choice of suppliers will safeguard the delivery of services to all mobile customers, increase flexibility and innovation and, crucially, can help address some of the cost challenges that are holding back the delivery of internet services to rural communities and remote places across the world.”
Vodafone added the move will improve “supply chain resilience,” introducing “a wave of new 2G, 3G, 4G and 5G technology vendors, in addition to the existing market leaders.”
It will be easier and cheaper to keep the radio from vendor A on the tower, installed, so no one has to climb up and replace it, and then keep the COTS-based BBU at the bottom of tower, and then just simply upgrade the software from vendor A to software from vendor B remotely without going to a site. This is what OpenRAN allows to do: mix and match software and hardware (radios and COTS servers) without rip and replace. Not to be confused with C-RAN or vRAN. Let us explain why.
C-RAN
About 10 years ago, virtualization of the RAN functions started with the C-RAN (cloud RAN or centralized RAN) initiative from IBM, Intel and China Mobile. C-RAN resulted in a deployment model where a baseband unit that was doing digital processing could be located in a data center and not on the site itself, under the radio where the processing was happening in legacy RANs. Instead radios were connected to the baseband in the data center unit via a dedicated high-bandwidth connection. This made C-RAN deployments only applicable to areas where there was access to fiber.
The C-RAN required a new fronthaul interface, and various industry standards such as the Common Public Radio Interface (CPRI) and the Next Generation Fronthaul Interface (NGFI) evolved to enable these new interfaces between the radios and baseband. C-RAN wasn’t necessarily open, but it did begin the movement toward disaggregating the RAN, but the use cases, because of pooling all digital processing in a centralized location, were limited to high density urban. And it still did not solve issue of vendor lock in.
vRAN
Next came Virtual RAN, or, vRAN. Does Virtual RAN equal Open RAN? Not exactly. Let us explain why. With vRAN, the proprietary radio hardware remains as it is, but the BBU gets replaced by a COTS server rather than being proprietary BBU hardware. The software that runs on the BBU is virtualized to run on any COTS server. But the proprietary interfaces between radios and COTS-based BBU remain as they are.
Virtualized RAN (vRAN) versus OpenRAN
Source: Parallel Wireless
So, though RAN functions are virtualized on a COTS server, the interface between the BBU and RRU/RRH is not an open interface, so any vendor’s software cannot work with the RRU/RRH unless the interfaces become open. So, to use the analogy from the way we described legacy RAN, vRAN consists of vendor A radio and vendor A software running on COTS BBU. An operator cannot put vendor B software on the same COTS BBU unless the interface to the vendor A radio is open. So, vRAN still allows for a vendor lock-in.
Open RAN
The key thing with Open RAN is that the interface between the BBU and RRU/RRH is an open interface, so, any vendor’s software can work on any open RRU/RRH. More open interfaces enable them to use one supplier's radios with another's processors - which is not possible with C-RAN or vRAN.
Open RAN is a movement to define and build 2G, 3G, 4G and 5G RAN solutions based on a general-purpose, vendor-neutral hardware and software-defined technology with open interfaces between all the components. Open RAN Is the disaggregation of hardware and software: the RRU/RRH hardware becomes a GPP-based or COTS hardware that can be purchased from any ODM, OEM or RAN hardware vendor (Vendor A). The BBU is the same as in the case of vRAN: COTS server + vendor’s (Vendor B) proprietary software with virtualized functions.
The OpenRAN makes the RAN open within all aspects and components, with the interfaces and operating software separating the RAN control plane from the user plane, building a modular base station software stack that operates on commercial-off-the-shelf (COTS) hardware, with open north- and south-bound interfaces. This software enabled Open RAN network architecture enables a “white box” RAN hardware - meaning that baseband units, radio units and remote radio heads can be assembled from any vendor and managed by Open RAN software to form a truly interoperable and open “best of breed” RAN. This way, the underlying hardware layer (radios form vendor A and COTS servers) can stay on site when a mobile operator decides to do a swap; the only thing that gets replaced is the software from vendor B to vendor C.
Source: Parallel Wireless
So, a mobile operator can virtualize and disaggregate their RAN, but unless the interfaces between the components are open, the RAN is not truly open.
Summary
Open RAN is about horizontal openness - with open interfaces enabling functions of the RAN to connect with other functions, from a radio unit (RU) to a baseband (DU-CU), to the controller to the NMS/orchestrator.
When RAN is opened up horizontally, it could bring in a new range of low-cost radio players, and it gives mobile operators a choice to optimize deployment options for specific performance requirements at a much better cost.
