nFAPI (network FAPI) provides a transport wrapper around the established FAPI PHY APIs to create a fronthaul interface between an S-RU (Small cell Radio Unit) and S-DU (Small cell Distributed Unit). These specifications enable open small cell networks, ensuring multi-vendor interoperability between S-RU and S-DU.
5G nFAPI specifications
The 5G network functional application platform interface (5G nFAPI) is an initiative that extends for 5G the functional split between the MAC and PHY functions that enables virtualization of the MAC function. This document defines a transportable interface for MAC-PHY 5G function application platform interface (5G-FAPI) defined for 5G small cells [SCF222]. This RAN architecture virtualization MAC function [SCF159] is also known as the Option 6 [3GPP TR 38.816, v15.0.0] architecture split.
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S-RU and S-DU Test Support
5G nFAPI [SCF225] adds a network transport wrapper around the 5G FAPI PHY API [SCF222] to create the split 6 interface between S-RU and S-DU small cell network units which SCF describes as Open6. This paper is not a specification. It considers how to test the disaggregated units S-RU and S-DU of the RAN.
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About 5G nFAPI
SCF has released two iterations of its nFAPI specification that enable early implementations for evaluation by mobile operators and other small cell deployers. In this informative companion document to the normative specification we provide an overview of the specification’s application, a roadmap for ongoing feature implementation and ecosystem support, and an FAQ.
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Network FAPI provides a ‘wrapper’ for PHY FAPI and RF FAPI to make them transportable over network interfaces. The FAPI and network FAPI together define the split option 6 network interface between S-RUs and S-DUs.
The main changes to the latest version of the nFAPI specifications include:
- Support for the RF FAPI P19 interface, enabling rich configuration and analogue beam-forming over the network interface.
- nFAPI framework robustness enhancements to handle S-DU and S-RU deployment scenarios.
- P7 over Ethernet transport.
- Hardware optimized nFAPI headers.
- Maintenance updates and corrections.
SCF release papers
You might be interested in the following documents
5G FAPI: PHY API specification
PHY FAPI is the main API for FAPI, defining P5 and P7 interfaces for user and control plane into the PHY. Its typical application is between a PHY layer System on a Chip and the software stack for MAC and higher layer protocols. It can also be used to enable Embedded NIC Inline Accelerators for the High-PHY function in an O-RAN DU. This latest iteration includes support for 3GPP Rel-16 Remote Interference Management (RIM) and new high-resolution L1 Metrics (RSSI, RSRP and Noise+Interference): to assist the scheduling and automated logging functions.
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5G FAPI: P19 RF and digital frontend control API
This P19 interface specification serves as a companion to the 5G FAPI P5/P7 specification.
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5G FAPI: Network monitor mode API
The functional application platform interface (FAPI) is an initiative within the small cell industry released by the Small Cell Forum, which establishes interoperability and innovation among suppliers of platform hardware, platform software and application software by providing a common API around which suppliers can create a competitive ecosystem. In doing this, we support a long and distinguished engineering tradition of providing an ‘interchangeability of parts’ to ensure that the systems vendors can take advantage of the latest innovations in silicon and software with minimum barriers to entry, and the least amount of custom re-engineering. Hence the specification helps support an innovative and competitive ecosystem for vendors of 5G small cell hardware, software and equipment.
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