ORAN概览

ORAN Architecture

ORAN-high-level-arch

上图显示了SMO通过4个关键接口：O2, A1, O1, Open fronthaul M-Plane 连向Oran network functions和O-Cloud。

ORAN network functions可以是建立在O-Cloud内部VMs/Container中的VNF(Virtualized Network Functions)，也可以是基于传统硬件的PNF(Physical Network Functions)。

SMO和ORU之间的Open Fronthaul M-plane interface，用于支持hybrid mode下的ORU management。

ORAN Logical arch

从上图中可知，ORAN架构的radio side包括了Near-RT RIC, O-CU-CP, O-CU-UP, O-DU, O-RU functions。虽然图中没有画出，但是O-eNB通过Open Fronthaul interface是可以与ODU, ORU相连的。
ORAN架构的management side包括了SMO和Non-RT-RIC function。

• non-RT RIC: O-RAN non-real-time RAN Intelligent Controller
  It is comprised of the Non-RT RIC Framework and the Non-RT RIC Applications (rApps).
  The rApp functionality enables non-real-time control and optimization of RAN elements and resources and policy-based guidance to the applications/features in near-RT RIC.
  Non-RT RIC focus on feature functionality of A1-interface (consumer and provider). The Non-RT RIC project will also work together with the OAM project to align activities on a case-by-case base for O1 interfaces.
• near-RT RIC: O-RAN near-real-time RAN Intelligent Controller
  A logical function that enables near-real-time control and optimization of O-RAN elements and resources via fine-grained data collection and actions over E2 interface.
• NMS: A Network Management System for the O-RU to support legacy Open Fronthaul M-Plane deployments. (它与SMO应该是同一个东西)
• O1: Interface between management entities in Service Management and Orchestration(SMO) Framework and O-RAN managed elements, for operation and management, by which FCAPS(fault/config/account/perf/secure) management, Software management, File management shall be achieved.
  The O1 interface supports the NETCONF protocol to configure and manage the network elements in the O-RAN solution. These network elements include Near RT-RIC, O-CU, O-DU and O-RU. The SMO uses data models to drive the configuration and management of the network elements.
• O1*（已更名为O2）: Interface between Service Management and Orchestration(SMO) Framework and Infrastructure Management Framework supporting O-RAN virtual network functions.
• OAM: Operations and Maintenance
  The O-RAN-SC-OAM project provides reference implementation according to the O-RAN OAM (Working Group1) documents, provides administrative and operator functions for O-RAN components, such as Near-Realtime-RAN-Intelligent-Controller, O-RAN Centralized Unit, O-RAN Distributed Unit and O-RAN Radio Unit.
• O-CU: O-RAN Central Unit
  A logical node hosting RRC, SDAP and PDCP protocols
• O-CU-CP: O-RAN Central Unit – Control Plane
  A logical node hosting the RRC and the control plane part of the PDCP protocol
• O-CU-UP: O-RAN Central Unit – User Plane
  A logical node hosting the user plane part of the PDCP protocol and the SDAP protocol
• O-DU: O-RAN Distributed Unit: a logical node hosting RLC/MAC/High-PHY layers based on a lower layer functional split.
• O-RU: O-RAN Radio Unit: a logical node hosting Low-PHY layer and RF processing based on a lower layer functional split. This is similar to 3GPP’s “TRP” or “RRH” but more specific in including the Low-PHY layer (FFT/iFFT, PRACH extraction).
• xAPP: Independent software plug-in to the Near-RT RIC platform to provide functional extensibility to the RAN by third parties.

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M-Plane

In ORAN, the O-RU management functions are done over the NETCONF/YANG based M-Plane.

There are two configuration model for O-RU management:

• Hierarchical model : In this configuration, an O-RU is managed by O-DUs.
  If existing NMS does not support NETCONF, this model has the advantage of enabling network construction without affecting the existing system since O-DU supports NETCONF in this M-Plane.
  O-DU works as NETCONF client and O-RUs as NETCONF server.
• Hybrid model: In this configuration, an O-RU is managed by one or more NMSs in addition to O-DUs. An advantage of this model is that NMSs can monitor/control other network devices in addition to O-RUs.
  O-DU and NMS works as NETCONF client and O-RUs as NETCONF server.

在以上任意一个model中，NETCONF client的功能都可以进行切割。比如分出一个专门用于SW management的NETCONF client，以及一个专门用于fault management的NETCONF client。

ORAN M-Plane Functions:

• O-RU startup procedure
  specifies the establishment of M-Plane between O- RU and NETCONF clients.
• O-RU Software management
  The O-RU software can be managed via NETCONF client.
  It's common that NETCONF client and ORU are made by different vendors, so SW management mechanism be independent of ORU implementation is important.
  There are mainly 4 procedures : Software Inventory、Software Download、Software Installation/Upgrade、Software Activation.
• O-RU parameter set/get (Configuration Management)
  NETCONF client sets O-RU parameters required on the C/U-Plane and S-Plane, and gets equipment status information, by sending <edit-config> and <get-config> messages.
  The setting of required parameters is specified in the form of YANG modules.
  In NETCONF, establishing a session is accompanied by an exchange of <hello> messages. Each of these messages contains the NETCONF functions supported by that equipment and what YANG modules it support.
• O-RU measurement (Performance Management)
• O-RU fault management (Fault Management)
  An NETCONF client manages O-RU faults via the M-Plane.
  O-RU sends <notification> to the NETCONF client, about the infomation of the fault.
• O-RU data file send/receive management (File Management)

总的来说，ORAN架构中，ORU的management，走的是M-Plane这条通道，用的手段是NETCONF。其中ODU和NMS扮演NETCONF client，ORU扮演NETCONF server。NETCONF client调用事先定义的NETCONF functions，实现不同的管理功能。