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2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. NOTE: While any hyperlinks i...
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3 Definition of terms, symbols and abbreviations
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3.1 Terms
For the purposes of the present document, the terms given in ETSI TR 121 905 [i.2], the O-RAN specifications Non-RT RIC & A1/R1 Interface: Use Cases and Requirements [2], Non-RT RIC: Architecture [i.3], O-RAN Architecture Description [3] and the following apply: A1 enrichment information: enrichment information that is...
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3.2 Symbols
Void.
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3.3 Abbreviations
For the purposes of the present document, the abbreviations given in ETSI TR 121 905 [i.2], the O-RAN specifications Non-RT RIC & A1/R1 Interface: Use Cases and Requirements [2], Non-RT RIC: Architecture [i.3], O-RAN Architecture Description [3] and the following apply: A1-EI A1 Enrichment Information service A1-ML A1 ...
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4 General Aspects
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4.1 A1 architecture
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4.1.1 General
O-RAN Architecture Description [3] includes a Non-RT RIC and a Near-RT RIC which are connected through the A1 interface as shown in figure 4.1.1-1. Near-RT RIC Non-RT RIC A1 Figure 4.1.1-1: A1 is the interface between the Non-RT RIC and the Near-RT RIC ETSI ETSI TS 103 983 V4.0.0 (2025-05) 9
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4.1.2 Role of A1 in the O-RAN architecture
The Non-RT RIC function resides in the SMO layer as described in O-RAN Architecture Description [3]. that also handles deployment, configuration, and data collection from RAN nodes. In the SMO layer there also resides functions that handle AI/ML workflow, e.g. training and update of ML models, as well as functions for ...
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4.1.3 A1 service architecture
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4.1.3.1 A1 policy management service (A1-P)
Based on high level goals for the system expressed in RAN intent, and on observables (events and counters) provided over O1, the Non-RT RIC can define policies that are provided to the Near-RT RIC over the A1 interface. The purpose of the A1 policies is to guide the RAN performance towards the overall goal expressed in...
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4.1.3.2 A1 enrichment information service (A1-EI)
Enrichment information is generically defined as information provided to an entity, in addition to the information that is generally available to it, in order to enhance the performance of its tasks. It can be produced based on information from one or more sources, e.g. by relaying, combining, refining or analysing inf...
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4.1.3.3 A1 ML model management service (A1-ML)
The A1 ML model management service (A1-ML service) supports AI/ML workflows between SMO/Non-RT RIC and Near-RT RIC. SMO/Non-RT RIC and Near-RT RIC can exchange AI/ML model training related messages via A1 interface.
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4.2 A1 interface general principles
The general principles for the specification of the A1 interface are as follows: • the A1 interface is an open logical interface within O-RAN architecture between the Non-RT RIC functionality in the SMO and the Near-RT RIC functionality in the RAN; • the A1 interface enables a multi-vendor environment and is independen...
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4.3 A1 interface specification objectives
The A1 interface specification facilitates the following: • inter-connection of Non-RT RIC functionality in the SMO with Near-RT RIC functionality in the Radio Access Network supplied by different manufacturers; • provision of policies for individual UEs or groups of UEs, or for individual cells or group of cells; • pr...
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4.4 A1 interface capabilities
As described in Non-RT RIC & A1/R1 Interface: Use Cases and Requirements [2], the A1 interface supports: • transfer of policy management information from Non-RT RIC to Near-RT RIC; • policy status and feedback information from Near-RT RIC to Non-RT RIC; • discovery and request of A1 enrichment information from Near-RT ...
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5 Functions of the A1 interface
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5.1 Policy management
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5.1.1 Introduction
The purpose of A1 policies is to enable the Non-RT RIC function in the SMO to guide the Near-RT RIC function, and hence the RAN, towards a better fulfilment of the RAN intent. NOTE 1: RAN intent represents e.g. the SLA from the BSS (Business Support System) that the RAN is to fulfil for all users or for a subset of use...
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5.1.2 The policy management function
The policy management function is used by the Non-RT RIC to provision and manage A1 policies in the Near-RT RIC. The Non-RT RIC is responsible for definition and administration of A1 policies. The function is used to query the available A1 policies in the Near-RT RIC. The function is used to create, update, and delete ...
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5.1.3 Lifecycle aspects of A1 policies
Per default, the Near-RT RIC controls the RAN based on the persistent configuration. The RAN operation can be optimized using A1 policies that, compared to the persistent configuration: • are not critical to traffic; • have temporary validity; • handle individual UE or dynamically defined groups of UEs; • express goals...
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5.1.4 Identification and scope of A1 policies
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5.1.4.0 General
An A1 policy type is identified by the policy type identifier (PolicyTypeId). Different policy types have different PolicyTypeIds. Based on the PolicyTypeId, schemas are identified and used for creation, validation, and formulation, and for query of the status, of A1 policies of that type. ETSI ETSI TS 103 983 V4.0.0 (...
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5.1.4.1 Identification of UEs
In the scope of A1 policies, a UE is identified by a UE identifier. The UE identifier identifies a logical UE entity that is known to the RAN and measurements related to it. It does not identify any hardware equipment or user subscription. The UE identifier is used for correlating O1-PM data with service targets and en...
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5.1.4.2 Identification of groups of UEs
In the scope of A1 policies, a group of UEs can be identified based on a group identifier. When the Near-RT RIC receives a group identifier in an A1 policy, it may resolve it into a set of UEs that are present in the nodes controlled by the Near-RT RIC and applies the policy statements to each one of the UEs.
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5.1.4.3 Identification of slices
When the Near-RT RIC receives a slice identifier in an A1 policy, it may resolve it into a set of UEs and a set of QoS flows that are present in the nodes controlled by the Near-RT RIC and applies the policy statements to each one of the UEs or the QoS flows. ETSI ETSI TS 103 983 V4.0.0 (2025-05) 15
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5.1.4.4 Identification of QoS flows
When the Near-RT RIC receives a QoS identifier in an A1 policy, it may resolve it into a set of QoS flows (that are related to the applications that the Non-RT RIC is intending to optimize) and the set of UEs (that are present in the nodes controlled by the Near-RT RIC) for which they apply. Then it applies the policy ...
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5.1.4.5 Identification of cells
In the scope of A1 policies, a part of the radio network can be identified based on a cell identifier or a set of cell identifiers. When the scope identifier in an A1 policy contains one or more cell identifiers, the policy statement may contain policy resources and the policy may implicitly impact on multiple UEs hand...
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5.1.5 A1 policy content
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5.1.5.1 General
In addition to a scope identifier, an A1 policy contains policy statements. There are several kinds of policy statements that cover policy objectives and policy resources. NOTE: The detailed rules for how to formulate policy statements, and which combinations of identifiers and statements that are allowed, are specifie...
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5.1.5.2 Policy objectives
A statement for policy objectives expresses the goal for the policy. It can be related to e.g. QoS or QoE targets, or KPI or KQI targets. For detailed definitions of statements for policy objectives, see clause 6.3.3 of A1TD [4]. There is normally only one statement for policy objectives in an A1 policy.
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5.1.5.3 Policy resources
A statement for policy resources expresses the conditions for resource usage for the policy. It can be related to e.g. cell preferences. For detailed definitions of statements for policy resources, see clause 6.3.4 of A1TD [4]. Statements for policy resources can be combined with a statement for policy objectives in an...
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5.2 A1 enrichment information
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5.2.1 Introduction
The purpose of A1 enrichment information is to enable the Near-RT RIC to improve its RAN optimization performance by utilizing information that is not available within the RAN. The information sources can be O-RAN internal and O-RAN external, and the derived A1 enrichment information can be provided by the Non-RT RIC o...
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5.2.2 The enrichment information function
The enrichment information function is used by the Non-RT RIC to produce and make A1 enrichment information available to the Near-RT RIC. The Non-RT RIC is responsible for exposure and secure delivery of A1 enrichment information. The function is used to publish available EiTypeIds over A1. The function is used to deli...
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5.2.3 Lifecycle aspects of A1 enrichment information
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5.2.3.1 Registration of enrichment information source
Before the Non-RT RIC can provide a certain EiTypeId over A1, the SMO needs to set-up the collection of input information from O-RAN internal and/or external sources and the Non-RT RIC needs to set-up the functions that produce the enrichment information based on the input information and deliver it. When onboarding an...
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5.2.3.2 Discovery of enrichment information
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5.2.3.2.0 General
Before a Near-RT RIC can use A1 enrichment information it needs to identify that the needed EiTypeId is available and how to access it. The Near-RT RIC can discover available EiTypeIds using A1-EI. The Non-RT RIC controls which EiTypeIds are discoverable and accessible by a specific Near-RT RIC. For a specific EiTypeId...
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5.2.3.2.1 Lifecycle aspects of EI types
The Non-RT RIC is responsible for ensuring that the EI types that are discoverable over A1 can be used for EI jobs and delivery of EI job results. An EiTypeId shall not be made available until EI jobs can be created, and EI job results delivered for that EI type. In case Non-RT RIC detects that it is no longer able to ...
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5.2.3.3 Request and Delivery of enrichment information
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5.2.3.3.0 General
A1 enrichment information can be delivered to the Near-RT RIC in different ways depending on the type of the A1 enrichment information or on the needs from the using internal function or application. ETSI ETSI TS 103 983 V4.0.0 (2025-05) 17 A1 enrichment information can be delivered on an as per needed basis, due to an...
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5.2.3.3.1 Lifecycle aspects of EI jobs
The Near-RT RIC can initiate creation, update, and deletion of EI jobs. The EI job is created when the Near-RT RIC needs A1 enrichment information of a specific EI type and the EI job is deleted when the Near-RT RIC no longer needs the information. In case the Near-RT RIC temporarily cannot use delivered EI, it can dis...
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5.2.3.3.2 Lifecycle aspects of EI job results
The Non-RT RIC is responsible for the set-up of connections to the Near-RT RIC for the delivery of EI job results according to the agreed EI job. The delivery of the EI job results is started when the EI job is created and stopped when the EI job is deleted. In case delivery connections cannot be set-up to the Near-RT ...
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5.2.4 Identification of A1 enrichment information
A1 enrichment information is identified by the A1 enrichment information identifier (EiTypeId). Different types of A1 enrichment information have different EiTypeIds. The Near-RT RIC can request delivery of A1 enrichment information from the Non-RT RIC by creating an EI job for an EiTypeId. The EI job and the EI job re...
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5.2.5 A1 enrichment information format and delivery
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5.2.5.1 Push based delivery
When A1 enrichment information has been produced during an EI job, it is pushed from the Non-RT RIC to the Near-RT RIC. This can be done once, regularly or event based depending on the conditions set for the EI job. ETSI ETSI TS 103 983 V4.0.0 (2025-05) 18
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6 Signalling procedures of the A1 interface
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6.1 General
The usage of the procedures listed in this clause are described in A1UCR [5] and defined in detail in A1AP [6].
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6.2 Policy related procedures
Policy related procedures include: • Query policy type identifiers procedure; • Query policy type procedure; • Query policy type status procedure; • Notify policy type status procedure; • Create policy procedure; • Query policy identifiers procedure; • Query policy procedure; • Update policy procedure; • Delete policy ...
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6.3 Enrichment information transfer procedures
A1 enrichment information related procedures include: For EI discovery: • Query EI type identifiers; • Query EI type; • Query EI type status, and • Notify EI type status. For EI job control: • Query EI job identifiers; • Create EI job; • Query EI job; • Update EI job; • Delete EI job; • Query EI job status; and • Notif...
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6.4 ML model related procedures
No ML model related procedures are listed in the present document.
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7 A1 interface protocol structure
The protocol stack of the A1 interface is shown in figure 7-1. The transport network layer is built on IP transport. For the secure and reliable transport of messages, HTTP/TLS is added on top of TCP/IP. The application layer protocol is based on a RESTful approach with transfer of JSON formatted policy statements. The...
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8 Other A1 interface specifications
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8.1 A1 TS-family overview
The present document is part of a TS-family covering the A1 interface. The other specifications cover Use Cases and Requirements, Transport Protocol, Application Protocol, Type Definitions, and Test cases. The relations between the A1 specifications and their relations to other O-RAN specifications for architecture and...
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8.2 A1 interface: Use Cases and Requirements
A1UCR [5] describes the use cases for the A1 procedures and the related requirements.
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8.3 A1 interface: Transport Protocol
A1TP [7] defines how the A1 protocol stack is based on TCP/IP, HTTP/1.1 over TLS and JSON as data interchange format.
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8.4 A1 interface: Application Protocol
A1AP [6] defines the service framework, the service operations and the service APIs for the A1 services including the URIs for HTTP based procedures.
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8.5 A1 interface: Type Definitions
A1TD [4] defines attributes, data types and objects for HTTP based procedures and JSON examples of objects are provided.
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8.6 A1 interface: Test Specification
A1TS [8] defines test cases for • A1 conformance testing of Non-RT RIC; • A1 conformance testing of Near-RT RIC; and • A1 interoperability testing between Non-RT RIC and Near-RT RIC; based on the procedures defined in A1AP [6]. ETSI ETSI TS 103 983 V4.0.0 (2025-05) 21 Annex A (informative): Change history Date Revision...
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1 Scope
The present document: • specifies the overall architecture of O-RAN; • describes the O-RAN architecture elements and relevant interfaces that connect them.
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2 References
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2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. Referenced documents which a...
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2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. NOTE: While any hyperlinks i...
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3 Definition of terms, symbols and abbreviations
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3.1 Terms
For the purposes of the present document, the terms given in ETSI TR 121 905 [i.1] and the following apply: E2 Node: logical node terminating E2 interface Managed Element: The definition of a Managed Element (ME) is given in ETSI TS 128 622 [2], clause 4.3.3. Managed Function: The definition of a Managed Function (MF) ...
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3.2 Symbols
Void.
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3.3 Abbreviations
For the purposes of the present document, the abbreviations given in ETSI TR 121 905 [i.1] and the following apply: 3GPP 3rd Generation Partnership Project 4G 4th Generation of mobile communications 5G 5th Generation of mobile communications 5GC 5G Core AAL Accelerator Abstraction Layer AI Artificial Intelligence AMF A...
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4 General O-RAN architecture principles
This clause contains the general O-RAN architecture principles as described below: • The O-RAN architecture, interface specifications, and terminology shall be consistent with 3GPP architecture, interface specifications, and terminology with additions to accommodate O-RAN specific features. • The present document repre...
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5 O-RAN Architecture
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5.1 Overall architecture of O-RAN
Figure 5.1-1 below provides a high-level view of the O-RAN architecture. It shows that the interfaces - A1, O1, Open Fronthaul M-plane and O2 - connecting SMO (Service Management and Orchestration) framework to O-RAN Network Functions and to O-Cloud. As depicted in this figure, the O-Cloud includes the O-Cloud Notifica...
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5.2 O-RAN control loops
The O-RAN architecture supports at least the following control loops involving different O-RAN functionalities: • Non-RT (Non-Real Time) control loops ETSI ETSI TS 103 982 V14.0.0 (2026-03) 16 • Near-RT (Near-Real Time) control loops • RT (Real Time) control loops Figure 5.2-1: O-RAN Control Loops As shown in Figure 5....
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5.3 Description of O-RAN Functions
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5.3.1 Service Management and Orchestration (SMO)
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5.3.1.1 SMO architecture principles
Service Based Architecture (SBA) introduces the roles of service producer and service consumer together with standardized service-based interfaces. These standardized service-based interfaces enable interoperability within the SMO. SBA is not concerned with the implementation, but it defines logical functions in their ...
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5.3.1.2 SMO Services (SMOSs)
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5.3.1.2.1 Introduction to SMO Services
In the O-RAN architecture, SMO is responsible for RAN domain management. The SMO description in this architecture document is focused on the SMO services that support the RAN. Following the SBA principles above, the SMO Services produced by the SMO are defined. A SMOF implementation can produce and/or consume any combi...
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5.3.1.2.2 SMO in the O-RAN architecture
All the SMO Service producers represented in Figure 5.3.1.2.1-1 can also be SMOS consumers. The SMO consumes services offered by other O-RAN architecture elements through four key southbound interfaces: • A1 Interface between the Non-RT RIC in the SMO and the Near-RT RIC for RAN Optimization. • O1 Interface provides SM...
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5.3.1.2.3 Non-RT RIC
Non-RT RIC is the functionality internal to the SMO that supports intelligent RAN optimization by: • enabling an A1-related SMOS to provide policy-based guidance over the A1 interface; • enabling an A1-related SMOS to provide enrichment information over the A1 interface; • enabling an A1-related SMOS to provide ML mode...
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5.3.1.2.4 SMO capabilities extensions
As a flexible extension mechanism, the SMO allows delivery of aspects of RAN management and orchestration functionality via rApps.
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5.3.1.2.5 External exposure of SMO capabilities and data
The exposure of SMO capabilities and data to external SMO consumers is done via SME and DME respectively, as represented in an SBA approach depicted in Figure 5.3.1.2.5-1. Figure 5.3.1.2.5-1: SMO external terminations
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5.3.2 Near-RT RIC
Near-RT RIC is an O-RAN NF that enables near real-time control and optimization of services and resources of E2 Nodes via fine-grained data collection and actions over the E2 interface with control loops in the order of 10 ms - 1 s. The Near-RT RIC hosts one or more xApps that use E2 interface to collect near real-time...
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5.3.3 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 as specified in ETSI TS 138 401 [10]. The O-CU-CP terminates E2 interface to Near-RT RIC as specified in E2GAP [22]. The O-CU-CP is managed via O1 interface by the SMO as specified in OAM ...
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5.3.4 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 as specified in ETSI TS 138 401 [10]. The O-CU-UP terminates E2 interface to Near-RT RIC as specified in E2GAP [22]. The O-CU-UP is managed via O1 interface by the SMO as specified in OAM Arc...
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5.3.5 O-DU
The O-DU is an O-RAN NF in the O-RAN Architecture. An O-DU, combined with one or more O-RU(s) connected to it, supports and is fully compatible with the functions of a gNB-DU as defined by ETSI TS 138 401 [10]. The O-DU may be implemented either by virtualized or non-virtualized methods. ETSI ETSI TS 103 982 V14.0.0 (2...
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5.3.6 O-RU
The O-RU terminates the Open Fronthaul interface (also known as LLS interface as specified in Open FH CUS-Plane [19]) as well as Low-PHY functions of the radio interface towards the UE. This is deployed as a PNF. The O-RU terminates the Open Fronthaul M-Plane interface towards the O-DU and SMO as specified in Open FH M...
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5.3.7 O-eNB
In case O-eNB is an O-RAN O-eNB, O-eNB terminates the S1, X2, O1 and E2 interfaces as well as the RRC, PDCP, RLC, MAC, and PHY layers of the LTE-Uu radio interface towards the UE as specified in ETSI TS 136 401 [4]. In case O-eNB is an O-RAN ng-eNB, O-eNB terminates the NG, Xn, O1, and E2 interfaces as well as the RRC,...
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5.3.8 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 NFs (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 ...
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5.4 Relevant interfaces in O-RAN architecture
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5.4.1 Introduction to relevant interfaces in O-RAN architecture
The following interfaces are defined and maintained by O-RAN: • A1 interface • O1 interface • O2 interface • E2 interface • Y1 interface • O-Cloud Notification interface • Open Fronthaul interface • R1 interface • Near-RT RIC APIs • D2 interface The following interfaces are defined and maintained by 3GPP, but seen also...
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5.4.2 A1 interface
A1 interface is between Non-RT-RIC and the Near-RT RIC as specified in A1GAP [18]. A1 is the interface between the Non-RT RIC in SMO and the Near-RT RIC function O-RAN NF. A1 interface supports three types of services as defined in A1GAP [18]: • Policy Management Service • Enrichment Information Service • ML Model Mana...
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5.4.3 O1 interface
The O1 interface is used by SMO for the management of the O-RAN NFs as defined in OAM Architecture [34] and OAM Interface [31].
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5.4.4 O2 interface
The O2 interface is between the SMO and O-Cloud as introduced in O2GAP [33]. The O2 interface provides two categories of services - O2 deployment management services (O2dms) and O2 infrastructure management services (O2ims).
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5.4.5 E2 interface
E2 is a logical interface connecting the Near-RT RIC with an E2 Node as defined in E2GAP [22]: • An E2 Node is connected to only one Near-RT RIC. • A Near-RT RIC can be connected to multiple E2 Nodes. The E2 interface is a control plane interface that provides support for Near-RT RIC Services using E2 Application Proto...
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5.4.6 O-Cloud Notification interface
The O-Cloud Notification interface allows event consumer such as an O-DU deployed on O-Cloud to subscribe to events/status from the O-Cloud. The cloud infrastructure will provide event producer to enable cloud workloads to receive events/status that might be known only to the infrastructure. ETSI ETSI TS 103 982 V14.0....
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5.4.7 Open Fronthaul interface
The Open FH (Fronthaul) interface is between O-DU and O-RU logical nodes as specified in Open FH CUS-Plane [19] and Open FH M-Plane [24]. The Open FH interface includes the CUS (Control User Synchronization) Plane and M (Management) Plane. In hybrid mode, the Open FH M-Plane interface connects the O-RU to the SMO for F...
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5.4.8 E1 interface
The E1 interface, as defined by 3GPP, is between the gNB-CU-CP and gNB-CU-UP logical nodes as specified in ETSI TS 138 401 [10] and ETSI TS 138 460 [14]. In O-RAN, it reuses the principles and protocol stack defined by 3GPP but is adopted between the O-CU-CP and the O-CU-UP logical nodes.
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5.4.9 F1-c interface
The F1-c interface, as defined by 3GPP, is between the gNB-CU-CP and gNB-DU logical nodes as specified in ETSI TS 138 401 [10] and ETSI TS 138 470 [16]. In O-RAN, it reuses the principles and protocol stack defined by 3GPP but is adopted between the O-CU-CP and the O-DU logical nodes, as well as for the definition of i...
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5.4.10 F1-u interface
The F1-u interface, as defined by 3GPP, is between the gNB-CU-UP and gNB-DU logical nodes as specified in ETSI TS 138 401 [10] and ETSI TS 138 470 [16]. In O-RAN, it reuses the principles and protocol stack defined by 3GPP but is adopted between the O-CU-UP and the O-DU logical nodes, as well as for the definition of i...
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5.4.11 NG-c interface
The NG-c interface, as defined by 3GPP, is between the gNB-CU-CP and the AMF in the 5GC as specified in ETSI TS 138 300 [8]. It is also referred as N2 in ETSI TS 138 300 [8]. In O-RAN, it reuses the principles and protocol stack defined by 3GPP but is adopted between the O-CU-CP and the 5GC.