SITL (Software-In-The-Loop) runs the real autopilot firmware against a simulated physics engine. The MAVLink endpoints are the same as hardware — only the transport differs.

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Common SITL connection strings
────────────────────────────────────────────────────────────
Autopilot   Transport   Connection string         Notes
──────────  ──────────  ────────────────────────  ──────────────
PX4 SITL    UDP         udpin:0.0.0.0:14550       Default GCS port
PX4 SITL    UDP         udp:127.0.0.1:14540       API port (MAVSDK)
ArduPilot   TCP         tcp:127.0.0.1:5760        Default SITL TCP
ArduPilot   UDP         udpin:0.0.0.0:14550       After mavproxy
Any         Serial      /dev/ttyUSB0,57600        USB telemetry radio

bash

# PX4 SITL with Gazebo (launches MAVLink on :14550 and :14540)
cd PX4-Autopilot
make px4_sitl gz_x500

# ArduPilot SITL
cd ardupilot
sim_vehicle.py -v ArduCopter --map --console

Multiple connections

PX4 SITL exposes port 14550 for GCS and 14540 for offboard APIs. If you need a second connection (e.g. GCS + your app), use mavproxy to multiplex: `mavproxy.py --master=udp:127.0.0.1:14550 --out=udp:127.0.0.1:14551`.

SITL connection examples

Multiple connections