5G FAPI specs updated with richer 3GPP feature set

5G FAPI suite with richer 3GPP feature set to underpin supply chain diversification

SCF has updated the suite of 5G FAPI specifications which underpin the high-performance low-cost components integral to 5G mobile base stations, whether small cell or macro. This update demonstrates the ongoing commitment of the ecosystem to continually improve the standard, adding new features and maintaining existing ones.

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SCF Plenary: A turning point for 5G standards, and wider industry cooperation

Small Cell Forum was engaged in driving open interfaces long before the macro network world became interested in multivendor interoperability. Now that the operators are insisting that this openness will be essential to their 5G business cases at every layer, SCF’s work is moving to the heart of the new mobile platform. That will drive new momentum behind its key standards, such as the FAPI and nFAPI interfaces, and its management models. And higher profile and applicability will mean that SCF has to work with a large number of partners – standards organizations, vendors and service providers – to develop its standards in future.

These issues will be central to the agenda at our upcoming Plenary meeting, to be held in London on September 16 and 17. We believe it is very important for as many members as possible to join the sessions devoted to SCF’s collaborations with partner organizations, so that your views and inputs can shape the shared agenda and accelerate progress.

This is becoming urgent on the eve of dense 5G roll-outs. Many studies show that the economics of dense, disaggregated 5G networks will not work without open interfaces. These will support the ability to mix and match different network elements (centralized units, distributed units and remote radio units) from different suppliers, allowing operators to achieve the best price points and the highest levels of innovation without technology dead ends.

SCF has a long history of driving open interfaces and multivendor networks. To amplify the impact of FAPI, nFAPI and the management model, among other specifications, it is working with two Linux Foundation open source organizations, the ORAN (Open RAN) Alliance and the ONAP (Open Network Automation Protocol) Alliance. Both of these were initially established around code supplied by AT&T and other operators, and are now highly influential in the evolution of an open 5G architecture. The Plenary will provide a critical opportunity to learn about the progress of the TECH group’s work on aligning our specs with those of these two other important Alliances.

Items for discussion in multiple sessions will include further development of (n)FAPI specs 4G and 5G small cells, including additions to support 3GPP’s P19 (RF front end) and P4 (network listen results) interfaces.

As well as aligning terminology and approach with that of ORAN, to ensure our efforts are coordinated and mutually supportive, there will be detailed consideration of the key issues of functional splits for disaggregated networks. The 3GPP provides a long list of potential splits between centralized and distributed functionality, and between virtualized and physical network functions. Operators are starting to work on key decisions about the splits they will adopt in different types of network and different environments, and it is a crucial point at which SCF must ensure its own priorities align with those of service providers. In the small cell world, the most relevant options in the near to medium term are 6 and 7.2.

At the Small Cells World Summit (SCWS) in London in May, there was intense discussion about the pros and cons of these two splits, and some operators are planning to use a combination of both. Many SCWS speakers and attendees took the view that Option 6, which aligns with nFAPI, is the strongest choice for affordable deployments in lower capacity scenarios, especially indoors. Others believe that Option 7.2 will be superior for high capacity and ultra-reliable requirements, because it has strong support for multi-point transmission.

A common concern was that there were still too many options and that MNOs either don’t know which to prioritise, or each will want a different combination – leading to fragmentation and lack of scale, with consequent risks for pricing and time to market. But some operators, like BT, are already driving the market towards a common hardware platform that could support all split options in software, to avoid the need to choose just one and to future-proof early deployments. In all cases, cost and availability of transport will be a key consideration.

Figure 1 shows how a base of 76 MNOs are currently prioritizing functional splits across their entire networks, although the market is so immature that these viewpoints may well change as they move to real world roll-out. In the early years of 5G, the focus is heavily on Option 6 as being a deployable architecture that can address near term use cases, especially indoors. As operators augment their 5G networks and move to emerging architectures, a wider variety of splits are seen coming into play, though in a far larger market, Options 6 and 7 will enjoy continuous growth as a percentage of deployments.

Figure 1. Selected 3GPP functional splits expected to be deployed (% of deployments)

These arguments and concerns will take center stage in the Plenary and you will have your chance to add to the debate and ensure your organization’s requirements and innovations get a full hearing.

Another important area of standardization and collaboration is work on the management of disaggregated small cells, especially when this uses NETCONF/YANG – the IETF-defined way to update the configuration of a network element in a software-defined environment (YANG is the modelling language to define the changes while NETCONF is the protocol to apply the changes). NETCONF/YANG helps to ease deployment of multivendor disaggregated networks and to support advanced operations like network slicing. SCF plans to update its current management model to support these interfaces, and to provide a common approach for disaggregated and 5G cells.

It will be important to align this work with the recommendations of ONAP in these areas, since ONAP is taking a leadership role in moving the industry forward from conventional operations support systems to a management and orchestration (MANO) layer that is optimized for disaggregated networks. In its first major code release, called Amsterdam, ONAP specified that virtual network function (VNF) providers must support a device YANG model and NETCONF APIs in order to comply with the ONAP standards. In its most recent release, Casablanca, it defined support for NETCONF/YANG southbound from the ONAP controller to both physical and virtual network functions, using OpenDaylight netconf-connector as the client.

With (n)FAPI and the updated management model, SCF is addressing requirements that are absolutely central to the economics of 5G, since these, for many operators, rest on the ability to disaggregate the RAN using equipment and VNFs from multiple vendors. SCF has already made considerable progress on this, in a small cell context, and is also addressing aspects of the interface which which are not a central focus for other initiatives, filling gaps in work by 3GPP or the open projects.

So far, the move towards open interfaces has been more advanced in the small cell layer than the macro network. Several suppliers already offer architectures in which a number of small cells are clustered around a centralized, virtualized controller. Once standard interfaces between the radio and the controller are supported, along with open baseband virtual network functions (VNFs), the economic argument for densification will be far stronger, and a key disadvantage vis-à-vis WiFi (its open ecosystem) will be removed.

5G, to be successful, needs to enable a far greater variety of services and network behaviors than 4G, and that will affect the deployment. A machine-to-machine service requiring ubiquitous coverage of a city, for instance, will require cells to be positioned and coordinated in a very different way from an enterprise application requiring a limited zone of very high capacity. The key will be uniform specifications for equipment and interfaces, which will enable limitless flexibility in how the cells are deployed and which form factors and suppliers are included.

All this highlights the important role projects like nFAPI can play in accelerating the progress towards a fully deployable, commercially viable dense 5G network. This will be critical to the small cell industry and help smooth the path to 5G densification. However, as small cells become a central element of all RANs, it will also be important for the influential new open RAN groups to get even closer to SCF, enriching their own work by tapping into SCF’s interfaces.

Pre-registration is essentials, so do sign up to attend these sessions at the SCF Plenary, to contribute to this rapidly evolving set of standards, and to understand the impact on your most critical technical and commercial decisions.