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xApps vs. rApps: Network automation fundamentals

Specialized software apps for network automation, xApps and rApps are part of a RIC — a Radio Access Network (RAN) Intelligent Controller.

The RIC software functions interact with Radio Unit (RU) hardware to maintain maximum RAN optimization and efficiency. The RIC is an essential software component of the Open RAN architecture specified by the O-RAN Alliance. It controls and optimizes radio functions. The RIC separately controls non-real time (non-RT) events — from 10 milliseconds to 1 second — and near-real time (near-RT) events — more than 1 second. 

The RIC is a key element in the management of advanced 5G network functions, like network slicing, high-bandwidth, low-latency applications, prioritized communications and more. Its architecture includes a Distributed Unit (DU) software function, multi-RAT CU protocol stack, a near-real time RIC and orchestration/NMS layer with Non-Real Time RIC. 

xApps and rApps are network automation tools. They maximize the radio network’s operational efficiency. rApps are specialized microservices operating on the non-RT RIC. xApps and rApps provide essential control and management features and functionality. xApps are hosted on the near RT RIC and optimize radio spectrum efficiency.

The features and functionality of the RIC — and RAN disaggregation in general — are spelled out in 3GPP’s Release 15. The O-RAN Alliance operates several technical workgroups responsible for shaping different elements of the Open RAN specification.

Guidance for the RIC specification falls under the aegis of O-RAN Workgroups 2 and 3. Those are the Non-real-time RAN Intelligent Controller and A1 Interface Workgroup and the Near-real-time RIC and E2 Interface Workgroup, respectively.

rApps: Non-real time network automation

The non-RT RIC operates from within the RIC’s Service Management and Orchestration (SMO) framework. This software functions centrally on the operator’s network. The non-RT RIC communicates with the near-RT RIC’s counterpart applications, called xApps, to provide policy-based guidance.

The SMO supports open software interfaces to facilitate rApp communications. This open design keeps RAN software vendors from locking down network features. Operators can and should update and optimize the network automation software continuously as part of a DevOps process.

Ericsson’s Intelligent Automation Platform is an implementation of an Open RAN SMO. Using Artificial Intelligence (AI) and Machine Learning (ML), the network automation software constantly adjusts RAN operations to manage and optimize network conditions. It provides key automation tools operators need to effectively scale digitized RAN operations in a cloud-native environment.

xApps work in near-real time

The near-RT RIC handles those events requiring action from 10 milliseconds (ms) to 1 second. The near-RT RC operates as a cloud-based process on the network edge. It provides policy guidance back to the non-RT RIC through xApps. xApps exist to continuously enhance the RAN’s spectrum efficiency.

Within the structure of the near-RT RIC itself, xApps communicate via defined interface channels. There’s an internal messaging infrastructure. It provides the framework to handle conflict mitigation, subscription management, app lifecycle management functions and security. Data flows via the RIC’s E2 interface for other network automation policy functions.

Nokia and AT&T successfully tested a RIC configuration on the carrier’s mmWave 5G network in early 2020. Measurement and optimization xApps collected live network data during the trial.

VMware’s RAN Intelligent Controller incorporates both non-RT and near-RT functions. The software uses Intel’s FlexRAN reference architecture and is based on a specifications developed by the O-RAN Alliance. VMware anticipates releasing it early in 2022.

ABOUT AUTHOR

Peter Cohen
Peter is a Technology Editor for RCR Wireless News whose coverage areas include hyperscalers, telco cloud, edge computing, and data centers. Before joining RCR, Peter was a freelance writer with a background in tech journalism. He worked as a senior editor for Macworld magazine, editor at iMore.com and has contributed to many other tech publications. He and his family live in Massachusetts.

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