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O-RAN Stack

In the figure above, there are two type of interface:

  1. 3GPP interfaces (e.g., F1, E1, X2 and NG) and
  2. O-RAN interfaces:
  • E2 is an interface between Near-Real-Time RIC (NearRT-RIC) and E2-Nodes (e.g., DU, CU-UP, CU-CP and eNB), and it allows NearRT-RIC to control and monitor the selected RAN functions in the E2-Nodes, facilitating dynamic optimization and management. Reference
  • Open Fronthaul is an interface between DU and RU with a lower layer functional split 7.2x Reference
  • O1 is an interface between SMO and network elements (e.g., NearRT-RIC, DU, CU-UP, etc.), responsible for deploying and configuring the network elements. Reference
  • A1 is an interface between NearRT-RIC and Non-Real-Time RIC (NonRT-RIC), enabling the exchange of policy management and enrichment information between NearRT-RIC and NonRT-RIC. Reference
  • The other interfaces, such as O2 and Y1 are out of scope for the current version of the ORS.

Lab Architecture​

Lab Architecture

For our lab, the network deployment is as shown in the figure above, which uses FlexRIC as NearRT-RIC, ODIN as NonRT-RIC and Athena as Service Management and Orchestration (SMO). E2-Nodes, including CU and DU provided by OpenAirInterface, will setup E2 connections (SCTP mechanism) with NearRT-RIC.

xApp Principles​

xApp Architecture
  • xApp is an application running on top of NearRT-RIC to control and monitor specific RAN functions in connected E2-Nodes via the RIC report and control service. It is independent of NearRT-RIC and can be provided by any third party.
  • RAN functions are the internal functions within an E2-Node responsible for managing UEs and Cells (e.g., MAC scheduler, stats of RLC, PDCP and RRC layers)
  • Service Model (SM) serves as a framework for storing collected data and control information, and it is used to communicate between xApp and RAN functions.

There are several SMs existing:

  1. Standardized SMs from O-RAN: Key Performance Measurement (KPM), Radio Control(RC), and Cell Configuration and Control (CCC)
  2. Customized SMs from FlexRIC: MAC, RLC, PDCP, GTP, Slice Control (SC), and Traffic Control (TC)
Last updated on by Alireza Mohammadi