---
# System prepended metadata

title: 0-DU & O-CU
tags: [5G O-RAN, PNJ, ITB NTUST 5G course]

---

# 0-DU & O-CU 
Day 8: July 28th, 2021

###### tags: `PNJ` `5G O-RAN` `ITB NTUST 5G course`

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### 3 Most Important Aspects
1.	O-DU
2.	O-CU
3.	O-DU and O-CU Interface
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### Summary
1.	O-DU
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 is divided into two parts: O-DU High and O-DU Low. O-DU High communicates with O-DU Low on the FAPI interface. O-DU High handles the L2 function there are of RLC and MAC and also DU APP. DU APP is the module that configures and manages all the operations of O-DU. Meanwhile, O-DU Low consist of High PHY. O-DU High modules not only consists of RLC and MAC, but also DU APP. DU APP interfaces with external entities as below:
	- 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.

    RLC 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. RLC can do error correction, segmentation, reassembly, re-segmentation, and re-ordering. MAC 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 multiplexing/demultiplexing, scheduling information reporting, handling UE priority, error correction (HARQ), and logical channel prioritization.

2.	O-CU
O-DU High communicates O-CU on the F1AP interface. O-CU is divided into two parts: C-plane and U-Plane functional blocks. C-plane consist RRC, meanwhile U-plane consist PDCP and SDAP. PDCP (Packet Data Convergence Protocol) is used for the user plane to sequence numbering, header compression and decompression, transfer of user data, and etc. The main services and function of SDAP (Service Data Adaptation Protocol) is mapping between a QoS flow and a data radio bearer ans also marking QoS flow ID (QFI) in both DL and UL packets.   O-CU have several interface there are E2, O1, F1, nad XnAP.

3.	O-DU and O-CU Interface
a.	E2 Interface : The near real-time RIC in the open RAN architecture connects to the O-CU, O-DU, and O-eNB.
b.	O1 interface : connects the SMO to the RAN managed elements. These include the near real-time RIC, O-CU, O-DU, O-RU, and the open evolved NodeB (O-eNB). 
c.	F1 interface : connect CU to DU. The control message exchanges are on F1-C while data message exchanges are on F1-U interfaces. 
d.	XnAP interface : connects Control Plane to other Control Plane
e.	FAPI interface : connects O-DU high and O-DU low.
f.	Open Fronthaul Interface : connects O-DU and O-RU.
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### Comment
Separates between O-DU, O-CU and also O-RU is application of functional split. The functional split concept was introduced for 5G, though it can be applied to 2G, 3G 4G as well. These previous generations, with their lower data rates than 5G, can still benefit from Open RAN, though not to the extent of 5G. When the RAN is opened up horizontally, it could bring in a new range of low-cost radio players, and it gives mobile operators a choice to optimize deployment options for specific performance requirements at much better cost. 
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### Discussion Team
1. Discuss about our main theme for final project
2. send notes on each other's subtopics in the group chat
3. Each task: find the main topic to discuss tomorrow
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