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High Level Architecture Of ORAN

As per WG1 ORAN alliance spec, figure shown below, the radio side includes Near-RT RIC, O-CU-CP, 17 O-CU-UP, O-DU, and O-RU functions. The E2 interface connects O-eNB to Near-RT RIC. O-eNB does support O-DU and O-RU functions with an Open Fronthaul interface between them.

Figure: High Level Architecture ORAN

Service Management and Orchestration (SMO): The SMO is a consolidation of a wide variety of management services and provides many network management like functionalities. In a Service Provider’s Network, the SMO may provide management services that go well beyond RAN management and can include things such as: Core Management, Transport Management, End to End Slice Management etc. The key capabilities of the SMO that provide RAN support in O-RAN are:

• FCAPS (Fault, Configuration, Accounting, Performance, Security) interface to O-RAN Network Functions

• Non-RT RIC for RAN optimization

• O-Cloud Management, Orchestration and Workflow Management.

The SMO performs these services through four key interfaces to the O-RAN Elements.

• A1 Interface between the Non-RT RIC in the SMO and the Near-RT RIC for RAN Optimization

• O1 Interface between the SMO and the O-RAN Network Functions for FCAPS support

• Optionally, and only in the hybrid model, Open Fronthaul M-plane interface between SMO and O-RU for FCAPS support

• O2 Interface between the SMO and the O-Cloud to provide platform resources and workload management.

FCAPS: It is Fault, Configuration, Accounting, Performance, Security which includes following operations:

  • “Start-up” installation
  • SW management
  • Configuration management
  • Performance management
  • Fault Management
  • File Management


Non-Real Time RAN Intelligent Controller (Non-RT RIC) is the functionality internal to the SMO in O-RAN architecture that provides the A1 interface to the Near-Real Time RIC.The primary goal of Non-RT RIC is to support intelligent RAN optimization by providing policy-based guidance, ML model management and enrichment information to the near-RT RIC function so that the RAN can optimize, e.g., RRM under certain conditions. It can also perform intelligent radio resource management function in non-real-time interval (i.e., greater than 1 second).Non-RT RIC can use data analytics and AI/ML training/inference to determine the RAN optimization actions for which it can leverage SMO services such as data collection and provisioning services of the O-RAN nodes.

O-Cloud Management, Orchestration and Workflow Management :

The SMO provides the capability of managing the O-Clouds as well as providing support for the orchestration of platform and application elements and workflow management. The SMO utilizes the O2 interface to the O-Cloud to provide these capabilities. The O2 interface supports the management of the cloud infrastructure and the use of the cloud resources allocated to the RAN. The example functionalities should be supported but are not limited to the following:

•Discovery and administration of O-Cloud Resources

• Scale-In, Scale-Out for O-Cloud

• FCAPS (PM, CM, FM, Communication Surveillance) of O-Cloud

• Software Management of Cloud Platform

• Create, Delete Deployments and Associated Allocated O-Cloud Resources.

Near-RT RIC:

It is a logical function that enables near real-time control and optimization of E2 nodes functions and resources via fine grained data collection and actions over the E2 interface with control loops in the order of 10 ms-1s. The Near-RT RIC hosts one or more xApps that use E2 interface to collect near real-time information (e.g. on a UE basis or a Cell basis) and provide value added services. The Near-RT RIC control over the E2 nodes is steered via the policies and the enrichment data provided via A1 from the Non-RT RIC.

O-CU-CP: The O-CU-CP terminates the NG-c, X2-c, Xn-c, F1-c and E1 interfaces as well as the RRC and PDCP (for SRB) protocols towards the UE.

O-CU-UP: The O-CU-UP terminates the NG-u, X2-u, S1-u, Xn-u, F1-u and E1 interfaces as well as the PDCP and SDAP protocols towards the UE.

O-eNB :O eNB is the eNB which is capable to work with ORAN architecture.The O-eNB terminates the S1, X2 and E2 interfaces as well as the RRC, PDCP, RLC, MAC and PHY layers of the LTE-Uu radio interface towards the UE in case O-eNB is an eNB.

O-Cloud: O-Cloud is a cloud computing platform comprising a collection of physical infrastructure nodes that meet O-RAN requirements to host the relevant O-RAN functions (i.e., Near-RT RIC, O-CU-CP, O-CU-UP, and O-DU), the supporting software components (such as Operating System, Virtual Machine Monitor, Container Runtime, etc.) and the appropriate management and orchestration functions

Interfaces in O-RAN Architecture:

A1 Interface: A1 interface is between Non-RT-RIC and the Near-RT RIC functions. A1 is the interface between the Non-RT RIC function in SMO and the Near-RT RIC function. A1 interface supports three types of services as given below:

• Policy Management Service

• Enrichment Information Service

• ML Model Management Service.

O1 Interface: The O1 interface is between O-RAN Managed Element and the management entity,for operation and  management, by which FCAPS management, PNF (Physical Network Function) software management, File management shall be achieved.

O2: Interface between management entities and the O-Cloud for supporting O-RAN virtual network functions.