.. 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
-As shown in Figure 1, there are multiple entities within O-DU. Modules sharing a
+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
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, 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
+- Thread 7: EGTP Handler
+- Thread 8: O1
-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 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.
-- 5G NR SCH schedules resources on UL and DL for cell and UE based procedures.
+- 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.
+
+
+O1 Module
+^^^^^^^^^^
+
+.. figure:: ODU-O1-Arch.jpg
+ :width: 554
+ :alt: Figure 2 O1 Architecture
+
+ Figure 2 - O1 Architecture
+
+As shown in figure 2 the O1 module runs as a thread in O-DU High. Alarm communication happens over a Unix socket between the O1 and O-DU threads. O1 module uses API calls for interacting with the Netconf server(Netopeer) and datastore(sysrepo) for providing the Netconf interface.
+
+O1 architecture has following components:
+
+- Netconf Session Handler: Subscribe to Netconf YANG modules and events. Register callback handler methods.
+
+- VES Agent : Sends the VES events to SMO
+
+- Alarm Manager: Stores and manages(add/updated/delete) alarms.
+
+- Alarm Interface : Provides an interface to O-DU High threads for sending the alarm messages to O1 module over Unix socket.
+
+- Config Interface : Interface to handle the configurations sent from SMO to the stack
+
+- Netopeer server: Serves the northbound SMO/OAM Netconf requests.
+
+
+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 3 - O-DU High Interfaces
+
+
+As shown in Figure 3, 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
+
+ - PAGING
+
+ - UE Context Management
+
+ - UE Context Setup
+
+ - UE Context Modification
+
+ - UE Context Release
+
+ - 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 v02.00:
+
+ - Global Procedures
+
+ - E2 Setup
+
+ - E2 Node Configuration Update
+
+ - 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 4 - O-DU High Cell Up and Broadcast Procedure
+
+
+As seen in the Figure 4,
+- If O1 interface is enabled, SMO sends cell configuration to DU APP. DU APP stores the configurations in its local database.
+
+- If O1 interface is disabled, DU APP module uses static configuration.
+
+- 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. If O1 is enabled, DU APP triggers an alarm to SMO to indicate the CELL is 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 5 below depicts the above call flow, inclusive of all interfaces:
+
+.. figure:: UeAttach.png
+ :width: 800
+ :alt: O-DU High UE Attach Flow
+
+ Figure 5 - UE Attach Flow
+
+- UE Release Signalling flow
+
+ - RRC Release
+
+Closed Loop Automation Procedure
+-----------------------------------
+
+This section describes the closed loop automation procedure within O-DU High.
+
+.. figure:: CLA_call_flow.png
+ :width: 720
+ :alt: Closed Loop Automation Procedure
+
+ Figure 6 - O-DU High Closed Loop Automation Procedure
+
+
+1. SMO commands ODU-High to bring the cell down via O1 interface.
+
+2. DU-APP module of ODU-High sends GNB-DU configuration update message to O-CU. It contains the details of cell to be deleted. O-CU acknowledges this message by sending GNB-DU configuration update acknowledgment.
+
+3. For each UE, DU APP sends UE Context Release Request to O-CU with information about the to be released. O-CU responds with UE Context Release request. It contains the RRC release message. O-DU high sends this RRC Release message to UE.
+
+4. DU APP then sends UE delete request to MAC and RLC. Once a confirmation is received from both MAC and RLC, DU APP deletes UE from its own database as well.
+
+5. Once all UEs are released, O-DU High sends STOP.Request to L1. L1 responds with stop indication.
+
+6. Once cell has stopped, DU APP sends cell delete request to MAC. On receiving confimation from MAC, DU APP deletes cell information from its own database as well and sends UE Context Release Complete.
+
+7. On receiving cell bring up command from SMO, the complete Cell bring up and UE attach procedure will be repeated (as explained in above sections)
+
+
+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.
+
+
+.. figure:: ODU-O1-GetAlarmListFlow.jpg
+ :width: 869
+ :alt: Figure 6 O1 get alarm-list flow
+
+ Figure 7 - O1 get alarm-list flow
+
+As seen in the Figure 7,
+
+- On the cell state change from de-active to activate, DU APP module raises a cell up alarm message and sends it over the Unix socket using the Alarm Interface API.
+
+- On other side a Unix socket server, running as a thread, in O1 module receives the cell up alarm message and it passes on the alarm information to the Alarm Manager.
+
+- Alarm Manager stores the alarm data in a list.
+
+- Whenever SMO/OAM requires the current alarm list, it sends a Netconf get request. The request is received by the Netopeer Server and a callback method, registered with the Session Handler, is invoked.
+
+- The callback function fetches the alarm list from Alarm Manager and sends it back to the client (SMO/OAM) via Netconf interface.
+
+
+Network Slicing procedure
+--------------------------
+
+This section describes the Network Slicing feature within O-DU High.
+
+
+.. figure:: Network_Slicing.png
+ :width: 869
+ :alt: Network Slicing flow
+
+ Figure 8 - Network Slicing flow
+
+As seen in the Figure 8,
+
+- Once the Cell is UP, Slice Configuration received from O1 to O-DU is processed. DU APP forwards the Slice Configuration Request towards MAC which is further forwarded to Scheduler.
+
+- Scheduler stores the Slice Configuration in DB and sends the Slice Configuration Response for each Slice to MAC and further towards DU APP. Slice Configuration Procedure completes.
+
+- Once a UE attaches and PDU session is established then RLC will periodically calculate the Slice Performance Metrics(UL and DL Throughput) for slices configured during UE Context Setup/Modification procedure.
+
+- RLC sends the Consolidated Slice Metrics to DU APP at every 60 sec duration. This is further forwarded towards SMO/Non-RT RIC.
+
+- SMO/Non-RT RIC analyses these metrics and may optimize the slice configuration(RRM Policies) for dedicated slice. This is received at MAC and Scheduler as Slice Reconfiguration Request from DU APP.
+
+- 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 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.
+
+OSC Testcases Supported
+=========================
+
+The O-DU High partially supports below use-cases:
+
+- Traffic Steering
+
+- Health Check
Code Review / o-du / l2.git / blobdiff