This part of the tutorial requires a working version of Docker for hosting the RIC on your localhost.

We first start by cloning and setup the Colosseum’s near-RT RIC with the following commands:

git clone -b ns-o-ran <https://github.com/wineslab/colosseum-near-rt-ric>
cd colosseum-near-rt-ric/setup-scripts

Then we first import all the images we need in Docker, we tag them properly and we build and launch them:

./import-wines-images.sh  # import and tag
./setup-ric-bronze.sh  # setup and launch

After the last step, the main entities of the RIC should be up and running in different Docker containers (this can be easily checked with the docker ps command). To understand what is going on in the RIC and to have a feedback once we start ns-O-RAN, we can open two terminal for the RIC, one for logging the values on the E2Term and check the E2AP messages exchange, the other for the xApp.

# Terminal 1 logs the E2Term
docker logs e2term -f --since=1s 2>&1 
# you can add "| grep gnb:" if you want to show only when a gnb is interacting 
./start-xapp-ns-o-ran.sh

This last command will build and run a Docker container for the x-app and will also create a shell inside the container, and log you inside the container. Finally, we can move to the /home/sample-xapp directory inside the Docker container, and run the xApp logic:

cd /home/sample-xapp
./run_xapp.sh

To properly install ns-3 and ns-O-RAN, several options are available, including the use of the Dockerfile provided in the root of the near-RT RIC repository. In this part of the tutorial, we will setup and install the ns-O-RAN framework. As described in the related paper and in the Figure above, ns-O-RAN is composed by three main parts:

• The e2sim software, which was originally developed by the OSC community.
• The ns3-mmWave version, which was originally developed by the University of Padova and NYU.
• The ns-O-RAN module, developed by Northeastern University and Mavenir, which is basically an external module that can be plugged in ns-3 and uses the e2sim to create a SCTP connection with the RIC.

We adapted the first two software to enable the end-to-end communication with the near-RT RIC and the digestion of the E2AP and E2SM messages. We first start with the installation of the prerequisites. In Ubuntu 20.04 LTS, these can be installed with:

sudo apt-get update
# Requirements for e2sim
sudo apt-get install -y build-essential git cmake libsctp-dev autoconf automake libtool bison flex libboost-all-dev 
# Requirements for ns-3
sudo apt-get install g++ python3

Then we can clone and install the e2Sim software. To see the E2 ASN messages on the e2sim, we build it with LOG_LEVEL equal to 3 (DEBUG). This is useful to debug the exchange of the messages between the ns-3 and the RIC, but we also provide different debug levels that can be setup. These levels are summarized in the table below.

git clone <https://github.com/wineslab/ns-o-ran-e2-sim> oran-e2sim # this will create a folder called oran-e2simcd oran-e2sim/e2sim/
mkdir build
./build_e2sim.sh 3

This last command shall configure the cmake project and install the e2sim on the system. Its main actions are also in the aforementioned Dockerfile that we report here to clarify the operations conducted by the script:

**RUN** mkdir /workspace/e2sim/e2sim/build
**WORKDIR** /workspace/e2sim/e2sim/build # Creation and cd on the build directory
**RUN** cmake .. -DDEV_PKG=1 -DLOG_LEVEL=**${**log_level_e2sim**}** # build of the project with the LOG_LEVEL desired**RUN** make package # Creation of the package**RUN** echo "Going to install e2sim-dev"
**RUN** dpkg --install ./e2sim-dev_1.0.0_amd64.deb # Installation of the generated package on the system**RUN** ldconfig  # library update to make the package linkable from ns-3 without rebooting the machine

It is now time to clone and install the ns3-mmWave project:

git clone <https://github.com/wineslab/ns-o-ran-ns3-mmwave> ns-3-mmwave-oran
cd ns-3-mmwave-oran

At the time of writing this tutorial, this project supports the 3.36 version of ns-3, thus we still use the old waf toolchain to configure, build and run ns-3. We plan to upgrade our version of ns-3 in the near future and, as a consequence of this, we will also update the guide. After this step, we can clone the ns-O-RAN module and insert it in the ns3-mmWave project in the contrib directory:

cd ns-3-mmwave-oran/contrib
git clone -b master <https://github.com/o-ran-sc/sim-ns3-o-ran-e2> oran-interface
cd ..  # go back to the ns-3-mmwave-oran folder
nano ns-o-ran-ns3-mmwave/src/core/helper/csv-reader.cc

Include the following additional headers in the csv-reader.cc

#include <stddef.h>
#include <limits>

We now have all the software in place to configure and build ns-3:

./waf configure --enable-examples --enable-tests
./waf build

Finally, we can run an example ns-3 scenario called “Scenario Zero”. This scenario features a Non Stand Alone (NSA) 5G setup in which we have one LTE eNB positioned in the center of the scenario and four gNBs around it with an inter site distance of 1000 between the eNB and each gNB. We can run the scenario with the command:

./waf --run scratch/scenario-zero.cc

And if everything goes as intended we should be able to see in order the following messages flowing between the ns-3 and the RIC:

• E2 Setup Request (ns-O-RAN to E2 Term on RIC);
• E2 Setup Response (E2 Term on RIC to ns-O-RAN);
• E2 Subscription Request (xApp to ns-O-RAN through E2 Term on RIC);
• E2 Subscription Response (ns-O-RAN to xApp through E2 Term on RIC);
• E2SM RIC Indication Message (ns-O-RAN to xApp through E2 Term on RIC);

• xApp terminal

• logs terminal