# <center> **Daily Report 8** </center>
###### tags: `O-RAN` `IVC` `5G O-RAN` `ITB NTUST 5G course`
> Date: 28/07
## <center> **O-DU and O-CU** </center>

### **Important Aspects**
#### **1. O-CU**
#### **2. O-DU**
#### **3. 5G NR Radio Protocol Stack**

### **Summary**
CU is the centralized unit software that runs the Radio Resource Control (RRC) and Packet Data Convergence Protocol (PDCP) layers. The gNB consists of a CU and one DU connected to the CU via Fs-C and Fs-U interfaces for CP and UP respectively. A CU with multiple DUs will support multiple gNBs. The separate architecture enables the 5G network to use different protocol stack distributions between the CU and DU according to the mid-transmission availability and network design. The CU controls the operation of several DUs over the midhaul interface. CU software can be co-located with DU software on the same server on site. Radio Resource Control (RRC) is a layer within the 5G NR protocol stack. It exists only in the control plane, in the UE and in the gNB. The behaviour and functions of RRC are governed by the current state of RRC. In 5G NR, RRC has three distinct states: RRC_IDLE, RRC_CONNECTED and RRC_INACTIVE. O-CU APIs are:
* RRC-SDAP
* RRC-PDCP
* SDAP-PDCP

DU is the distributed unit software that is deployed on site on a COTS server. DU software is normally deployed close to the RU on site and it runs the RLC, MAC, and parts of the PHY layer. This logical node includes a subset of the eNodeB (eNB)/gNodeB (gNB) functions, depending on the functional split option, and its operation is controlled by the CU. The modules in O-DU are DU APP to configures and manages all the opreations of O-DU, 5G NR RLC to provides services for transferring the control and data messages between MAC layer and OCU (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 uses the services of the NR physical layer to send and receive data on the various logical channels, O-DU Utility and Common Functions these modules help in the working of O-DU and message exchanges between the O-DU modules. 3GPP considered the split concept (DU and CU) for 5G from the beginning of writing its specifications. The DU is responsible for real time layer 1 (L1, physical layer) and lower layer 2 (L2) which contains the data link layer and scheduling functions. The CU is responsible for non-real time, higher L2 and L3 (network layer) functions.

### Comment
Between CU and DU will distribute the functionality of the RAN, this software can be placed together with the aggregator.

## <center> **Discussion with team** </center>
:::info
### 1. Confirm final presentation and sub-topic for each other
### 2. Practice out report before final presentation
:::