.. SPDX-License-Identifier: CC-BY-4.0
-O-DU-L2 Architecture
-======================
+O-DU High Overview
+*********************
+O-DU High Architecture
+======================
-O-DU implements the functional blocks of L2 layer of a 5G NR protocol stacks.
-These layers primarily include NR MAC NR Scheduler and NR RLC layers.
+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.
O-DU modules are developed as shown in the below diagram.
-.. image:: ODUArch.jpg
- :width: 400
- :alt: ODU Arch diagram
+.. figure:: ODUArch.jpg
+ :width: 600
+ :alt: Figure 1 O-DU High Architecture Diagram
-O-DU Thread Architecture
---------------------------
+ Figure 1 - O-DU High Architecture Diagram
+
+O-DU High Thread Architecture
+-------------------------------
-As shown in Figure 1, there are multiple entities within O-DU. Modules sharing a
+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
level as follows:
-- Thread 1: O-DU thread
+- Thread 1: O-DU thread
-- Thread 2: DU APP inclusive of Config Handler, DU Manager, UE Manager, EGTP Handler and ASN.1 Codecs
+- Thread 2: DU APP inclusive of Config Handler, DU Manager, UE Manager, EGTP Handler and ASN.1 Codecs
-- Thread 3: 5G NR RLC DL and MAC (inclusive of 5G NR SCH and Lower MAC)
+- Thread 3: 5G NR RLC DL and MAC (inclusive of 5G NR SCH and Lower MAC)
-- Thread 4: 5G NR RLC UL
+- Thread 4: 5G NR RLC UL
-- Thread 5: SCTP Handler
+- Thread 5: SCTP Handler
-- Thread 6: Lower MAC Handler
+- Thread 6: Lower MAC Handler
-O-DU Modules
+O-DU High Modules
--------------------------
DU APP
This module configures and manages all the operations of O-DU.
It interfaces with external entities as follows:
-- OAM: DU APP interacts with OAM on the O1 interface for configuration, alarms and performance management.
+- OAM: DU APP interacts with OAM on the O1 interface for configuration, alarms and performance management.
-- O-CU: DU APP interacts with O-CU for RAN functionalities over the F1 interface which is built on SCTP. Control messages are exchanged on the F1-C interface and data messages on the F1-U interface.
+- O-CU: DU APP interacts with O-CU for RAN functionalities over the F1 interface which is built on SCTP. Control messages are exchanged on the F1-C interface and data messages on the F1-U interface.
-- RIC: DU APP interacts with RIC on E2 interface over SCTP.
+- RIC: DU APP interacts with RIC on E2 interface over SCTP.
DU App submodules are as follows:
-- Config Handler manages the configurations received on O1 interfaces andstores them within DU APP context.
+- Config Handler manages the configurations received on O1 interfaces and stores them within DU APP context.
-- DU Manager handles all cell operations at the DU APP.
+- DU Manager handles all cell operations at the DU APP.
-- UE Manager handles UE contexts at the DU APP.
+- UE Manager handles UE contexts at the DU APP.
-- SCTP handler is responsible for establishing SCTP connections with O-CU, RIC.
+- SCTP handler is responsible for establishing SCTP connections with O-CU, RIC on the F1AP and E2AP interfaces
+ respectively.
-- EGTP handler is responsible for establishing EGTP connection with O-CU for data message exchange.
+- EGTP handler is responsible for establishing EGTP connection with O-CU for data message exchange on the F1-U
+ interface.
-- ASN.1 Codecs contain ASN.1 encode/decode functions which are used for System information, F1AP and E2AP messages.
+- ASN.1 Codecs contain ASN.1 encode/decode functions which are used for System information, F1AP and E2AP messages.
5G NR RLC
^^^^^^^^^^^^^^^^^^
on the various logical channels.
Functions of the 5G NR MAC module are as follows:
-- 5G NR MAC is responsible for multiplexing and de-multiplexing of the data on various logical channels.
+- 5G NR MAC is responsible for multiplexing and de-multiplexing of the data on various logical channels.
-- 5G NR SCH schedules resources on UL and DL for cell and UE based procedures.
+- 5G NR SCH schedules resources in UL and DL for cell and UE based procedures.
+ 5G NR SCH is completely encapsulated within the 5G NR MAC i.e., all interactions of the 5G NR SCH is via the 5G NR MAC.
+
+- Lower MAC interfaces between the MAC and the O-DU Low. It implements all the messages of FAPI
+ specification. It has a receiver thread to handle messages from L1.
-- Lower MAC interfaces between the MAC and the lower layers of the O-DU and implements all the messages of FAPI
- specification. It has a receiver thread to handle messages from L1.
O-DU Utility and Common Functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-These modules help in the working of O-DU and message exchanges between
-the O-DU modules.
+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.
+
+.. figure:: O-DUHighInterfaces.jpg
+ :width: 600
+ :alt: O-DU High Interfaces
+
+ Figure 2 - O-DU High Interfaces
+
+
+As shown in Figure 2, O-DU High interfaces with the following modules:
+
+- O-CU: O-DU High communicates with O-CU on the F1AP interface. The control message exchanges are on F1-C while
+ data message exchanges are on F1-U interfaces. The below F1AP messages on F1-C are implemented, as per
+ 3GPP 38.473-f60 v15.3:
+
+ - Interface Management
+
+ - F1 Setup
+
+ - gNB-DU Configuration Update
+
+ - F1 Reset
+
+ - UE Context Management
+
+ - UE Context Setup
+
+ - RRC Message Transfer
+
+ - Initial UL RRC Message Transfer
+
+ - DL RRC Message Transfer
+
+ - UL RRC Message Transfer
+
+ - 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:
+
+ - Global Procedures
+
+ - E2 Setup
+
+ - Near RT RIC Functional Procedures
+
+ - RIC Subscription
+
+ - RIC Indication
+
+- O-DU Low: O-DU High communicates with O-DU Low on the FAPI interface. The below FAPI messages are supported,
+ as per FAPI interface files shared by Intel:
+
+ - P5 messages - PHY mode control interface
+
+ - PARAM.request/PARAM.response
+
+ - CONFIG.request/CONFIG.response
+
+ - START.request
+
+ - STOP.request
+
+ - STOP.indication
+
+ - P7 messages - Main data path interface
+
+ - DL_TTI.request
+
+ - UL_TTI.request
+
+ - SLOT.indication
+
+ - UL_DCI.request
+
+ - TX_Data.request
+
+ - RX_Data.indication
+
+ - CRC.indication
+
+ - UCI.indication
+
+ - RACH.indication
+
+- OAM: O-DU High communicates with OAM on the O1 interface.
+
+
+
+O-DU High functionality
+========================
+
+
+Cell Up and Broadcast Procedure
+--------------------------------
+
+This section describes the cell-up procedure within O-DU High.
+
+.. figure:: CellUpAndBroadcast.png
+ :width: 720
+ :alt: Cell Up and Broadcast Procedure
+
+ Figure 3 - O-DU High Cell Up and Broadcast Procedure
+
+
+As seen in the Figure 3,
+- The DU APP module of O-DU High sends F1 Setup Request to O-CU. This message contains a list of cells that the O-DU High has been configured with.
+
+- The O-CU responds with F1 Setup Response. This message contains a list of cells which must be activated.
+
+- The O-DU High scans the list of cells received and sends corresponding cell configurations to 5G NR MAC.
+
+- 5G NR MAC, in-turn configures the 5G NR SCH. It also configures the O-DU Low via the Lower MAC module.
+
+- On receiving the cell config response, DU APP sends a gNB DU Config Update towards the O-CU. The O-CU responds with
+ gNB DU Config Update ACK towards the O-DU High.
+
+- The DU APP now exchanges F1 Reset message with the O-CU to initialize the UE contexts.
+
+- DU APP sends Cell Start Req towards 5G NR MAC. This message is translated by the Lower MAC into the FAPI message START.request towards the O-DU
+ Low.
+
+- On receiving START.request, O-DU Low begins to send slot indications towards 5G NR MAC via the lower MAC.
+ The frequency of these slot indications is determined by the numerology(Mu) supported.
+ 5G NR MAC forwards these slot indications to the 5G NR SCH and DU APP modules.
+
+- When the first slot indication reaches the DU APP, cell is marked as up.
+
+- The 5G NR SCH, keeps tracking the SSB and SIB1 ocassions on receiving regular slot indications.
+ On detecting the relevant ocassion, 5G NR SCH schedules SSB/SIB1 and forwards the DL Scheduling Information to 5G NR MAC.
+
+- The 5G NR MAC mutiplexes the PDU and sends SSB/SIB1 packets towards the O-DU Low through the Lower MAC.
+
+
+
+UE Related Procedure
+-----------------------
+
+
+The O-DU High supports
+
+- All physical channels - PBCH, PRACH, PDCCH, PDSCH, PUSCH, PUCCH
+
+- All control logical channels - UL CCCH, DL CCCH, UL DCCH, DL DCCH
+
+- All control transport channels - BCH, UL-SCH, DL-SCH, RACH
+
+The above channels are used to achieve the below messages:
+
+- Cell broadcast of System Information which includes SSB and SIB1.
+
+- RACH Procedure
+
+ - RACH Indication
+
+ - Random Access Response
+
+ - RRC Setup Request
+
+ - RRC Setup
+
+- UE attach signalling flow
+
+ - RRC Setup Complete
+
+ - Registraton Request
+
+ - Security Mode Command
+
+ - Security Mode Complete
+
+ - Registraton Accept
+
+ - Registraton Complete
+
+ - Several NAS Message Exchanges
+
+ - RRC Reconfiguration
+
+ - RRC Reconfiguration Complete
+
+Figure 4 below depicts the above call flow, inclusive of all interfaces:
+
+.. figure:: UeAttach.png
+ :width: 800
+ :alt: O-DU High UE Attach Flow
+
+ Figure 4 - UE Attach Flow
+
+
+
+OSC Testcases Supported
+=========================
+
+The O-DU High partially supports below use-cases:
+
+- Traffic Steering
+
+- Health Check
Code Review / o-du / l2.git / blobdiff