X-Git-Url: https://gerrit.o-ran-sc.org/r/gitweb?a=blobdiff_plain;f=docs%2Foverview.rst;h=caeffa65655657292b9cefb9129a6c238324326e;hb=bd13ba3b2661a413492608b9cb16c699b3831d5e;hp=2de67068bb15b509a5cf5f94cc0370437b1fa1d5;hpb=2e947aab8340b0f2cced69217f2378badeb716f2;p=o-du%2Fl2.git diff --git a/docs/overview.rst b/docs/overview.rst index 2de67068b..caeffa656 100644 --- a/docs/overview.rst +++ b/docs/overview.rst @@ -2,14 +2,304 @@ .. SPDX-License-Identifier: CC-BY-4.0 -o-du-l2 Overview +O-DU High Overview +********************* + +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. + +O-DU modules are developed as shown in the below diagram. + +.. figure:: ODUArch.jpg + :width: 600 + :alt: Figure 1 O-DU High Architecture Diagram + + 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 +level as follows: + +- Thread 1: O-DU thread + +- 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 4: 5G NR RLC UL + +- Thread 5: SCTP Handler + +- Thread 6: Lower MAC Handler + + +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. + +- 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. + + +DU App submodules are as follows: + +- 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. + +- UE Manager handles UE contexts at the DU APP. + +- 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 on the F1-U + interface. + +- ASN.1 Codecs contain ASN.1 encode/decode functions which are used for System information, F1AP and E2AP messages. + +5G NR RLC +^^^^^^^^^^^^^^^^^^ +This module provides services for transferring the control and data messages +between MAC layer and O-CU (via DU App). + +5G NR RLC UL and 5G NR RLC DL are the sub modules of this module that implement +uplink and downlink functionality respectively. + +5G NR MAC +^^^^^^^^^^^^^^^^^^ +This module uses the services of the NR physical layer to send and receive data +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 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. + + +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. + +.. 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 -O-DU implements the functional blocks of L2 layer of a 5G NR protocol stacks. -These layers primarily include NR MAC and NR RLC layers. -In order to manage these layers, DU_APP submodule has been introduced which can be comsidered as the -master module of O-DU. +- Health Check