srsRAN F1AP CU–DU Split

End-to-End 5G Deployment using Open5GS + srsRAN (CU/DU Split) + srsUE

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Overview

This repository documents a complete srsRAN F1AP CU–DU split deployment using a virtual RF setup (ZeroMQ). The deployment follows a 3GPP-aligned CU/DU architecture and is suitable for learning, experimentation, and research.

Key Components

• Open5GS – 5G Core Network (Docker-based)

• srsRAN Project – 5G gNB split into:

  • CU (CU-CP + CU-UP)
  • DU

• srsRAN 4G (srsUE) – UE implementation

• ZeroMQ – Virtual RF interface (no SDR required)

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High-Level Architecture

                 +-----------------------------+
                 |           VM 1              |
                 |                             |
                 |  Open5GS 5GC (Docker)       |
                 |            +                |
                 |  srsRAN CU (CU-CP + CU-UP)  |
                 +-------------+---------------+
                               |
                           F1AP / F1U
                               |
                 +-------------v---------------+
                 |           VM 2              |
                 |                             |
                 |  srsRAN DU                  |
                 |        +                    |
                 |  srsUE (ZMQ, netns)         |
                 +-----------------------------+

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Reference Documentation

• srsRAN CU–DU Split (Official Docs) https://docs.srsran.com/projects/project/en/latest/tutorials/source/cu_du_split/source/index.html#o-ran-cu-du-split

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System Requirements

Hardware

Resource	Recommendation
CPU	8 cores
RAM	12 GB
Disk	40+ GB

Operating System

• Ubuntu 22.04.1 LTS

Deployment Model

• VM 1 → Open5GS Core + srsCU
• VM 2 → srsDU + srsUE

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Software Components

• Open5GS (Docker-based)
• srsRAN Project (latest)
• srsRAN 4G v23.11 or later
• ZeroMQ

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Prerequisites (VM1 & VM2)

Install the following packages on both VMs:

sudo apt update
sudo apt install -y \
  git net-tools build-essential cmake \
  libfftw3-dev libmbedtls-dev \
  libboost-program-options-dev \
  libconfig++-dev libsctp-dev \
  libyaml-cpp-dev libgtest-dev \
  libzmq3-dev

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Build srsRAN Project (CU & DU)

Perform this step on both VM1 and VM2

cd ~
git clone https://github.com/srsran/srsRAN_Project.git
cd srsRAN_Project
mkdir build && cd build

cmake ../ -DENABLE_EXPORT=ON -DENABLE_ZEROMQ=ON
make -j$(nproc)

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VM 1 — Open5GS Core + srsCU

Install Docker (VM1 only)

sudo apt install -y ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg \
  -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc

echo "deb [arch=$(dpkg --print-architecture) \
signed-by=/etc/apt/keyrings/docker.asc] \
https://download.docker.com/linux/ubuntu \
$(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

sudo apt update
sudo apt install -y docker-ce docker-ce-cli \
  containerd.io docker-buildx-plugin docker-compose-plugin

Add your user to Docker group:

sudo usermod -aG docker $(whoami)
newgrp docker

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Deploy Open5GS 5G Core

cd ~/srsRAN_Project/docker
docker compose up --build 5gc -d

Verify:

docker ps

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Configure srsCU (VM1)

CU Configuration (cu.yml)

Minimum required configuration:

cu_cp:
  amf:
    addr: 10.53.1.2
    port: 38412
    bind_addr: 10.53.1.1
    supported_tracking_areas:
      - tac: 7
        plmn_list:
          - plmn: "00101"
            tai_slice_support_list:
              - sst: 1

  f1ap:
    bind_addr: 127.0.10.1   # CU IP

cu_up:
  f1u:
    socket:
      - bind_addr: 127.0.10.1

The amf parameters are specific to the docker configuration of the core. If you are running Open5GS via the local setup, your configuration will be different. For local Open5GS, use:

amf:
  addr: 127.0.1.100
  bind_addr: 127.0.1.1

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Run srsCU

cd ~/
wget https://raw.githubusercontent.com/ngkore/srsRAN_F1AP_Split/refs/heads/main/config/cu.yml
cd ~/srsRAN_Project/build/apps/cu
sudo ./srscu -c ~/cu.yml

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VM 2 — srsDU + srsUE

Build srsRAN 4G (srsUE)

cd ~
git clone https://github.com/srsRAN/srsRAN_4G.git
cd srsRAN_4G
mkdir build && cd build

cmake ../ -DENABLE_EXPORT=ON -DENABLE_ZEROMQ=ON
make -j$(nproc)

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Configure srsDU (VM2)

DU Configuration (du.yml)

f1ap:
  cu_cp_addr: 127.0.10.1
  bind_addr: 127.0.10.2

f1u:
  socket:
    - bind_addr: 127.0.10.2

ru_sdr:
  device_driver: zmq
  device_args: tx_port=tcp://127.0.0.1:2000,rx_port=tcp://127.0.0.1:2001,base_srate=23.04e6
  srate: 23.04
  tx_gain: 75
  rx_gain: 75

cell_cfg:
  dl_arfcn: 368500
  band: 3
  channel_bandwidth_MHz: 20
  common_scs: 15
  plmn: "00101"
  tac: 7

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Run srsDU

cd ~/
wget https://raw.githubusercontent.com/ngkore/srsRAN_F1AP_Split/refs/heads/main/config/du.yml
cd ~/srsRAN_Project/build/apps/du
sudo ./srsdu -c ~/du.yml

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Run srsUE (VM2)

Create network namespace:

sudo ip netns add ue1

Run srsUE:

cd ~/
wget https://docs.srsran.com/projects/project/en/latest/_downloads/fbb79b4ff222d1829649143ca4cf1446/ue_zmq.conf
cd ~/srsRAN_4G/build/srsue/src
sudo ./srsue ~/ue_zmq.conf

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Routing Configuration

# Host Routing
sudo ip route add 10.45.0.0/16 via 10.53.1.2
# UE Namespace Routing
sudo ip netns exec ue1 ip route add default via 10.45.1.1 dev tun_srsue

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Connectivity Test

Uplink (UE → Core)

sudo ip netns exec ue1 ping 10.45.1.1

Downlink (Core → UE)

ping 10.45.1.2

Successful ping confirms end-to-end CU–DU split connectivity.