*********************
O-DU High Architecture
-======================
+-----------------------
O-DU implements the functional blocks of L2 layer of a 5G NR protocol stack in SA(StandAlone) mode.
These layers primarily include NR MAC, NR Scheduler and NR RLC layers.
Figure 1 - O-DU High Architecture Diagram
O-DU High Thread Architecture
--------------------------------
+==============================
As shown in Figure 1, there are multiple entities within O-DU High. Modules sharing a
given color belong to one thread. O-DU architecture can be defined at a thread
- Thread 8: O1
O-DU High Modules
---------------------------
+=================
DU APP
^^^^^^^^^^^^^^^^^^
O-DU Utility and Common Functions
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
These modules contain platform specific files and support O-DU High functionality and message exchanges.
O-DU-High Interfaces
-======================
-
+--------------------
This section describes the other modules that O-DU High interfaces with, as shown in below diagram.
- F1 Reset
+ - PAGING
+
- UE Context Management
- UE Context Setup
- RRC Delivery Report
- Near RT RIC: O-DU High communicates with Near RT RIC on the E2 interface. The below E2AP messages are
- implemented, as per ORAN WG3.E2AP v01.00:
+ implemented, as per ORAN WG3.E2AP v02.00:
- Global Procedures
- E2 Setup
+ - E2 Node Configuration Update
+
- Near RT RIC Functional Procedures
- RIC Subscription
O-DU High functionality
-========================
+-----------------------
Cell Up and Broadcast Procedure
---------------------------------
+================================
This section describes the cell-up procedure within O-DU High.
UE Related Procedure
------------------------
+====================
The O-DU High supports
- RRC Release
Closed Loop Automation Procedure
------------------------------------
+================================
This section describes the closed loop automation procedure within O-DU High.
O1 Netconf get-alarm list procedure
------------------------------------
+===================================
This section describes the *Health Status Retrieval* scenario of O-DU High health-check. It enables a northbound client(SMO) to retrieve the health of the O-DU High based on the last self-check performed. The alarm-list is provided as the response to the request via O1 Netconf interface.
Network Slicing procedure
---------------------------
+=========================
This section describes the Network Slicing feature within O-DU High.
- Scheduler updates the received Slice Configuration in its DB and sends back the Slice Reconfiguration Response to MAC and further MAC forwards it to DU APP. Scheduler applies the optimized RRM policies for the dedicated slice.
+Idle Mode Paging procedure
+===========================
+
+This section describes the Idle Mode Paging procedure within O-DU High.
+
+
+.. figure:: IDLE_mode_Paging.jpg
+ :width: 869
+ :alt: Idle Mode Paging flow
+
+ Figure 9 - Idle Mode Paging flow
+
+As seen in the Figure 9,
+
+- When a Paging is received from O-CU and the Cell to be Paged is UP then DU APP will calculate Paging Frame(PF) and i_s(Index of Paging Ocassion/Slot) and groups the Paging of UEs falling on same PF/SFN together and stores in its Cell's Databse.
+
+- When a Slot Indication for SFN is received then DU APP extracts the Paging of all UEs whose PF is ahead by PAGING_DELTA and builds Paging RRC PDU. DU APP sends the same via DL PCCH Indication to MAC.
+
+- MAC forwards to SCH as PAGING INDICATION.
+
+- SCH stores the Page Message in its DB and when the SLOT_INDICATION for that SFN arrives, SCH performs scheduling and resource allocation for PDCCH (alongwith DCI 1_0 format) and PDSCH channels and sends to MAC through DL PAGING ALLOCATION message.
+
+- MAC forwards the PAGE to PHY in TX_Data.Request.
+
+Inter-DU Handover within O-CU
+=============================
+
+This section describes the handling of inter-DU handover of a UE within O-DU High.
+
+.. figure:: Inter_DU_Handover_Within_OCU.png
+ :width: 600
+ :alt: Inter-DU Handover withing O-CU
+
+ Figure 9 - Inter_DU Handover call flow
+
+Assumption: UE is RRC connected with DU and PDU data session is active.
+
+- The UE sends Measurement Report message to the source O-DU. This message is sent from O-DU to O-CU in the UL RRC MESSAGE TRANSFER message over F1AP interface.
+
+- Based on UE Measurement Report, O-CU makes a handover decision to another cell belonging to the target O-DU.
+
+- The O-CU sends a UE CONTEXT MODIFICATION REQUEST message to source O-DU to query the latest configuration.
+
+- The DU APP in source O-DU responds with a UE CONTEXT MODIFICATION RESPONSE message that includes latest full configuration information.
+
+- The O-CU sends a UE CONTEXT SETUP REQUEST message to the target O-DU to create an UE context and setup one or more data bearers. The UE CONTEXT SETUP REQUEST message includes Hand-overPreparationInformation. At target O-DU, DU APP sends UE Create Request to MAC and RLC layers to create the UE context with radio resources and receives UE Create Response from the respective protocol layers.
+
+- The target O-DU responds with a UE CONTEXT SETUP RESPONSE message if the target O-DU can admit resources for the handover.
+
+- The O-CU sends a UE CONTEXT MODIFICATION REQUEST message to the source O-DU, which includes RRCReconfiguration message towards the UE. The O-CU also indicates the source O-DU to stop the data transmission for the UE.
+
+- The source O-DU forwards the received RRCReconfiguration message to the UE and then sends the UE Reconfiguration Request to MAC/Scheduler and RLC layer and get the UE Reconfiguration Response from the respective protocol layers.
+
+- The source O-DU responds to the O-CU with UE CONTEXT MODIFICATION RESPONSE message.
+
+- UE triggers Random Access procedure at the target O-DU. This is a contention free random access if UE was informed about its dedicated RACH resources in RRC Reconfiguration message.
+
+- Once Random Access procedure with target O-DU is complete, the UE responds to the target O-DU with a RRCReconfigurationComplete message.
+
+- The target O-DU sends UL RRC MESSAGE TRANSFER message to O-CU to convey the received RRCReconfigurationComplete message.
+
+- The downlink and uplink data packets are sent to/from the UE through the target O-DU.
+
+- The O-CU sends UE CONTEXT RELEASE COMMAND message to the source O-DU.
+
+- The source O-DU sends UE DELETE REQUEST to MAC/RLC layers to release the UE context and receives UE DELETE RESPONSE message.
+
+- The source O-DU responds to O-CU with UE CONTEXT RELEASE COMPLETE message.
+
+
OSC Testcases Supported
-=========================
+-----------------------
The O-DU High partially supports below use-cases:
Code Review / o-du / l2.git / blobdiff