OAI F1AP CU/DU Split Mode Deployment Guide

This guide explains how to deploy and run the OAI gNB Central Unit (CU) and Distributed Unit (DU) in F1 split mode.

You can run the CU/DU setup in two ways:

1. On the same server
2. On different servers

For a complete end-to-end (E2E) test, you will need:

• UE (OAI nrUE)
• gNB DU
• gNB CU
• OAI 5G Core (CN5G)

Before starting, ensure the OAI 5G Core is installed and configured:

OAI CN5G Setup Follow: https://gitlab.eurecom.fr/oai/openairinterface5g/-/blob/develop/doc/NR_SA_Tutorial_OAI_CN5G.md

Once the core is running, proceed to deploying the CU and DU.

For more details on F1 interface configuration, refer to: https://gitlab.eurecom.fr/oai/openairinterface5g/-/blob/develop/doc/F1AP/F1-design.md#how-to-run

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1. Running CU and DU on the Same Server

Expand steps

Prerequisites: Build UHD from Source (Optional – only for real SDR testing)

If you want to test with real radios (SDRs) instead of RFsim, build UHD:

# https://files.ettus.com/manual/page_build_guide.html
sudo apt install -y autoconf automake build-essential ccache cmake cpufrequtils doxygen ethtool g++ git inetutils-tools libboost-all-dev libncurses-dev libusb-1.0-0 libusb-1.0-0-dev libusb-dev python3-dev python3-mako python3-numpy python3-requests python3-scipy python3-setuptools python3-ruamel.yaml

git clone https://github.com/EttusResearch/uhd.git ~/uhd
cd ~/uhd
git checkout v4.8.0.0
cd host
mkdir build
cd build
cmake ../
make -j $(nproc)
make test # optional
sudo make install
sudo ldconfig
sudo uhd_images_downloader

Build OAI gNB and nrUE

git clone https://gitlab.eurecom.fr/oai/openairinterface5g.git ~/openairinterface5g
cd ~/openairinterface5g
git checkout develop

cd ~/openairinterface5g/cmake_targets
./build_oai -I

sudo apt install -y libforms-dev libforms-bin

cd ~/openairinterface5g/cmake_targets
./build_oai -w SIMU --ninja --nrUE --gNB --build-lib "nrscope" -C

Note: Use -w USRP instead of -w SIMU if building for real SDR testing.

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Configure CU and DU

Patch files (Same server): https://github.com/ngkore/OAI_CU_DU_Split/tree/main/patch_files/same-server

cd ~/openairinterface5g
wget https://raw.githubusercontent.com/ngkore/OAI_CU_DU_Split/refs/heads/main/patch_files/same-server/cu.patch
wget https://raw.githubusercontent.com/ngkore/OAI_CU_DU_Split/refs/heads/main/patch_files/same-server/du.patch
git apply cu.patch
git apply du.patch

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Run CU and DU

Run CU

cd ~/openairinterface5g
sudo cmake_targets/ran_build/build/nr-softmodem -O ci-scripts/conf_files/gnb-cu.sa.band78.106prb.conf

Run DU

cd ~/openairinterface5g
sudo cmake_targets/ran_build/build/nr-softmodem -O ci-scripts/conf_files/gnb-du.sa.band78.106prb.rfsim.conf --rfsim

Remove --rfsim if running with USRP.

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Run OAI nrUE

With USRP B210

cd ~/openairinterface5g/cmake_targets/ran_build/build
sudo ./nr-uesoftmodem -r 106 --numerology 1 --band 78 -C 3619200000 --ue-fo-compensation -E --uicc0.imsi 001010000000001

With RFsim

cd ~/openairinterface5g/cmake_targets/ran_build/build
sudo ./nr-uesoftmodem -r 106 --numerology 1 --band 78 -C 3619200000 --uicc0.imsi 001010000000001 --rfsim

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E2E Connectivity Test (RFsim Mode)

UE → CN5G

ping 192.168.70.135 -I oaitun_ue1

UE → Internet

ping 8.8.8.8 -I oaitun_ue1

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2. Running CU and DU on Different Servers

Expand steps

Topology

• Server 1: CN5G + gNB CU
• Server 2: gNB DU + UE

Build UHD (Optional, only on DU server)

Same instructions as above. Only required for real SDR testing.

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Build OAI gNB and nrUE on both servers

git clone https://gitlab.eurecom.fr/oai/openairinterface5g.git ~/openairinterface5g
cd ~/openairinterface5g
git checkout develop

cd ~/openairinterface5g/cmake_targets
./build_oai -I
sudo apt install -y libforms-dev libforms-bin

cd ~/openairinterface5g/cmake_targets
./build_oai -w SIMU --ninja --nrUE --gNB --build-lib "nrscope" -C

Use -w USRP on DU server if using SDR.

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Configure CU and DU

Patch files: https://github.com/ngkore/OAI_CU_DU_Split/tree/main/patch_files/different-servers

cd ~/openairinterface5g

# On CU server
wget https://raw.githubusercontent.com/ngkore/OAI_CU_DU_Split/refs/heads/main/patch_files/different-servers/cu.patch
git apply cu.patch

# On DU server
wget https://raw.githubusercontent.com/ngkore/OAI_CU_DU_Split/refs/heads/main/patch_files/different-servers/du.patch
git apply du.patch

Update IPs as shown in the patch:

CU config

local_s_address = "CU_Server_IP";
remote_s_address = "DU_Server_IP";

DU config

local_n_address = "DU_Server_IP";
remote_n_address = "CU_Server_IP";

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Run CU and DU

CU server

cd ~/openairinterface5g
sudo cmake_targets/ran_build/build/nr-softmodem -O ci-scripts/conf_files/gnb-cu.sa.band78.106prb.conf

DU server

cd ~/openairinterface5g
sudo cmake_targets/ran_build/build/nr-softmodem -O ci-scripts/conf_files/gnb-du.sa.band78.106prb.rfsim.conf --rfsim

Remove --rfsim if running with USRP.

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Run OAI nrUE (on DU server)

With USRP B210

cd ~/openairinterface5g/cmake_targets/ran_build/build
sudo ./nr-uesoftmodem -r 106 --numerology 1 --band 78 -C 3619200000 --ue-fo-compensation -E --uicc0.imsi 001010000000001

With RFsim

cd ~/openairinterface5g/cmake_targets/ran_build/build
sudo ./nr-uesoftmodem -r 106 --numerology 1 --band 78 -C 3619200000 --uicc0.imsi 001010000000001 --rfsim

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E2E Connectivity Test (RFsim Mode)

UE → CN5G

ping 192.168.70.135 -I oaitun_ue1

UE → Internet

ping 8.8.8.8 -I oaitun_ue1

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Logs

Sample logs for CU and DU are available here