# Summary O-RAN Working Group 3

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### Definition of terms
- Near-RT RIC: A logical function that enables near-real-time control and optimization of RAN elements and resources via fine-grained data collection and actions over E2 interface.
- Non-RT RIC: A logical function within SMO that drives the content carried across the A1 interface. It is comprised of the Non-RT RIC Framework and the Non-RT RIC Applications.
- xAPP: An application designed to run on Near-RT RIC. It may consist of one or more microservices and at the point of on-boarding it identifies which data it consumes and which data it provides. It is independent of Near-RT RIC and may be provided by any third party. The E2 interface enables a direct association between xApp and RAN functionalities.

### Near-RT RIC Functions Description
1. **Database, and related SDL** **(Shared Data Layer) services:** allows reading and writing of RAN/UE information and other information required to support specific use cases;
* UE-NIB
* R-NIB
* SDL: used by xApps to subscribe to database notification services and to read, write, and modify information stored on the database.
2. **xApp subscription management**: merges subscriptions from different xApps and provides unified data distribution to xApps
3. **Conflict mitigation**: resolves potentially overlapping or conflicting requests from multiple xApps. The conflicts of control:
* Direct conflicts, mitidated by pre-action coordination
* Indirect conflicts, resolved by post-action verification
* Implicit conflicts, hard to mitigate. It may be possible to ensuring that use cases (xApps) target different parameters
4. **Messaging infrastructure**: provides low-latency message delivery service between Near-RT RIC internal endpoints
5. **Security**: provides the security scheme for xApps (ex: prevent malicious xApps from abusing radio network information)
6. **Management Function**/**OAM (Operations, Administrations, and Management) Management**:
- Fault management, configuration management, and performance management as a service producer to SMO
- Logging, tracing and metrics collection, which capture, monitor and collect the status of Near-RT RIC internals and can be transferred to external system for further evaluation.
7. **Interface Termination**:
- E2 termination, which terminates E2 interface from an E2 Node;
- A1 termination, which terminates A1 interface from Non-RT RIC;
- O1 termination, which terminates O1 interface from SMO.
8. **Functions hosted by xApps**: allow services to be executed at Near-RT RIC and outcomes to be sent to E2 Nodes via E2 interface
9. **API Enablement** function supporting capabilities related to Near-RT RIC API operations (API repository/registry, authentication, discovery, generic event subscription, etc.)
10. **AI/ML support**:
- Data pipelining, Training, and Performance monitoring for xApps.
11. **xApp Repository Function**:
- Selection of xApps for A1 message routing based on A1 policy types and operator policies
- Access control of A1-EI types for xApps based on operator policies
12. **xApps**: collaborate with the Near-RT RIC platform functions to support various specialized use cases. Upon registration to the Near-RT RIC platform, an xApp informs the Near-RT RIC platform of its OAM and control information to enable relevant functionalities.

### Near-RT RIC APIs
* The Near-RT RIC APIs are a collection of well-defined interfaces providing Near-RT RIC platform services.
* The Near-RT RIC APIs are essential to host 3rd party xApps in an inter-operable way on different Near-RT RIC platforms.
* Overview of Near-RT RIC APIs:
* Near-RT RIC APIs may be implemented using two approaches:
* **Network API approach**: Each relevant Near-RT RIC endpoint exposes a network endpoint and specifies a particular data encoding protocol and a network transport protocol that should be used to communicate with it.

* **SDK approach**: The Near-RT RIC vendor provides an SDK (software development kit). This SDK is a software library which handles all connection management and exposes a simple API for the xApp to interact with the Near-RT RIC.

These two approaches to Near-RT RIC APIs are not necessarily mutually exclusive.

- **A1 related APIs**: The xApps in Near-RT RIC provide value added services based on the policies or enrichment information or both which are transferred through A1 interface by Non-RT RIC.
- **E2 related APIs**: The xApps in Near-RT RIC provide value added services using RIC functional mechanisms and related procedures via E2 interface towards E2 Nodes. The E2 related APIs allow access to E2 related functionality and the associated xApp Subscription Management and Conflict Mitigation functionality.
- **Management APIS**: Including the xApp’s ML Model related APIs and the FCAPS related APIs
- **SDL APIs**: The SDL APIs provide a simple yet flexible way to store and retrieve data while hiding details such as type and location of database, management operations of database layer such as high availability, scaling, load-balancing. SDL APIs support defined data structures used to provide E2 Node related information.
- **Enablement APIs**: The Enablement APIs support exchange of API enablement related information between xApps and the API enablement functionality.

### Near-RT RIC API Procedures
#### **1. A1 Related API Procedures**
A1 Policy Procedures:
- Setup
- Update
- Delete
- Query
- Status update

A1-EI (Enrichment Information) Procedures:
- Query
- Subscription setup
- Subscription update
- Subscription delete
- Delivery

#### **2. E2 Related API Procedures**
RIC Functional Procedures:
- E2 Subscription API
- E2 Subscription Delete (initiated by an xApp)
- E2 Subscription Delete Query and E2 Subscription Notification Procedures
- E2 Indication
- E2 Control

E2 Guidance Related Procedures (to allow authorized xApp to obtain guidance from the Conflict Mitigation platform function prior to initiating an action.)
- xApp initiated E2 guidance request/response procedure
- Modification API: xApp Subscription Management initiated
- Modification API: Message monitoring initiated
- Modification API: Conflict Mitigation initiated

#### **3. Management API Procedures**
- xApp registration
- xApp deregistration
- xApp configuration

#### **4. SDL API Procedures**
- SDL Client Registration
- SDL Client Deregistration
- Fetch Data
- Subscribe/Notify
- Store Data
- Modify Data
- Subscribe/Push

**Use cases of SDL APIs:**
- Subscribe/Notify for E2NodeInfo and E2NodeList
- Subscribe/Push for for E2NodeInfo and E2NodeList

#### **5. API Enablement Procedures**
- Near-RT RIC API Discovery procedure
- API Event Subscription and Notification