Networking

The Twizy uses a Teltonika RUT950 industrial 4G/LTE router as its onboard network gateway, combined with a NetBird mesh VPN to enable secure remote access to all ROS2 nodes from anywhere with internet connectivity.

Architecture

graph LR
    subgraph vehicle["Twizy (on-board)"]
        rut950["RUT950\n(4G/LTE router)"]
        pc["On-board PC\n(Ubuntu 22.04)"]
        ds["FastDDS\nDiscovery Server\n:11811"]
        pc --- ds
        rut950 --- pc
    end

    subgraph remote["Remote Operator"]
        laptop["Laptop\n+ Xbox Controller"]
        teleop["teleop_joy_xbox\n(ROS2 node)"]
        laptop --- teleop
    end

    rut950 -->|"4G/LTE"| internet["Internet"]
    internet -->|"NetBird VPN\n(mesh P2P)"| laptop
    teleop <-->|"ROS2 Topics\nvia Discovery Server"| ds

RUT950 Router

The Teltonika RUT950 provides mobile connectivity to the vehicle.

Spec	Value
Technology	4G LTE Cat 4 (up to 150 Mbps download), 3G, 2G
SIM	Dual SIM with automatic failover
WiFi	IEEE 802.11b/g/n (AP + STA)
Ethernet	4 ports × 10/100 Mbps (1 WAN + 3 LAN)
CPU	Atheros Wasp, MIPS 74Kc, 550 MHz
RAM	128 MB DDR2
Storage	16 MB Flash
Power	9–30 VDC (4-pin industrial connector)
OS	RutOS (OpenWrt-based Linux)
Housing	Aluminium with plastic panels

Physical installation

The router's WiFi/config credentials are on a label on the back of the device. A 3D-printed bracket is needed to mount it in the rear of the vehicle.

SIM card

Connectivity was validated with a test SIM. A dedicated SIM plan must be purchased for production use.

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NetBird VPN

NetBird creates an encrypted mesh VPN between all team devices. Each machine gets a stable hostname and IP on the NetBird network regardless of its physical network or NAT.

Why NetBird

• No static IP needed on the vehicle — the RUT950 has a dynamic 4G IP
• Peer-to-peer when possible (low latency), relay fallback when NAT blocks direct connection
• Works over 4G, WiFi, and any internet connection
• Free tier available for small teams (self-hosted or cloud)

Installation (all machines)

curl -fsSL https://pkgs.netbird.io/install.sh | sh

Authentication and connection

# Generate an authentication token in the NetBird dashboard (cloud or self-hosted)
sudo netbird up --setup-key <generated_token>

Verification

netbird status
# Both the vehicle and the operator machine should appear as "Connected"

ping twizy

Network considerations for ROS2

The ROS2 Docker containers must use network_mode: host so that ROS2 traffic is routed through the NetBird interface (wt0) rather than being isolated inside Docker's bridge network.

services:
  carro:
    network_mode: host   # required — routes ROS2 over NetBird wt0

Camera GigE interface conflict

The FastDDS Discovery Server must be configured to listen only on the NetBird interface (wt0), not on the GigE camera interface (169.254.x.x). Running the server on all interfaces caused a conflict that prevented the camera from connecting.

ip addr show wt0
# Should show a 100.x.x.x address assigned by NetBird

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FastDDS Discovery Server

Standard ROS2 relies on multicast for node discovery, which does not work across VPN tunnels or between machines on different networks. The solution is a centralized FastDDS Discovery Server running on the vehicle, which all nodes (local and remote) register with via unicast.

How it works

sequenceDiagram
    participant V as Vehicle PC
    participant DS as Discovery Server (port 11811)
    participant O as Remote Operator

    V->>DS: register nodes (local, via 127.0.0.1 or wt0)
    O->>DS: register nodes (via NetBird IP)
    DS-->>V: peer list
    DS-->>O: peer list
    V<-->>O: ROS2 topic exchange (unicast)

Setup on the vehicle

FROM ros:humble-ros-core
RUN apt-get update && apt-get install -y \
    ros-humble-rmw-fastrtps-cpp \
    fastdds-tools \
    && rm -rf /var/lib/apt/lists/*
ENTRYPOINT ["fastdds", "discovery"]

services:
  discovery-server:
    build:
      context: .
      dockerfile: Dockerfile.server
    container_name: fastdds_server
    network_mode: "host"        # must use host to reach NetBird wt0 interface
    command: -i 0               # discovery server ID 0
    restart: unless-stopped

docker compose up -d discovery-server

# Or without Docker:
source /opt/ros/humble/setup.bash
fastdds discovery -i 0

GigE camera conflict

Running the Discovery Server without binding it to a specific interface caused it to advertise on the camera's GigE interface (169.254.x.x), blocking camera connections. Using network_mode: host combined with the NetBird-only FastDDS profile resolves this.

Environment variables

Vehicle side:

ROS_DOMAIN_ID=0
RMW_IMPLEMENTATION=rmw_fastrtps_cpp

Operator side:

export ROS_DISCOVERY_SERVER=twizy:11811   # NetBird hostname of the vehicle
export ROS_SUPER_CLIENT=true              # disables multicast, forces Discovery Server usage
export ROS_DOMAIN_ID=0
export RMW_IMPLEMENTATION=rmw_fastrtps_cpp

Variable	Value	Description
ROS_DISCOVERY_SERVER	twizy:11811	NetBird hostname (or IP) of the vehicle running the server
ROS_DOMAIN_ID	0	Must be identical on all machines in the network
ROS_SUPER_CLIENT	true	Disables multicast, forces exclusive use of Discovery Server
RMW_IMPLEMENTATION	rmw_fastrtps_cpp	Sets FastDDS as the ROS2 middleware

Verification

ros2 topic list
# Should show topics from the vehicle