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An adoption of NMEA0183 (National Marine electronics Association) at RS-232 voltage levels is used for the data link between level 1 and level 2. The standard was chosen on the following basis: It has a low power consumption, the bandwidth requirements are low, it is human readable, and the signal can be tapped for easy debugging. Level 1 will once per second transmit a request for rudder and commands to the Level 2, in the form of a NMEA message.

There are three kind of NMEA-like messages involved for different communications: - Level 2 - Level 1 communication; - Level 1 - Operator bilateral communication.

Level 2 sends messages to Level 1 containing the desired rudder angle and thruster intensity. These come as a result of high-level control (PIDs) implemented in DUNE. The format of this message is:
;#; MSG = BBB01 , RUD , THR , PWR_SETT , FALLB_MODE ;#; Where:
- BBB01 is the msg ID; - RUD is the rudder angle [-450,450]; - THR is the thruster intensity [-100,100]; - PWR_SETT are the power settings: 6-bits string where 1 disables and 0 enables; - FALLB_MODE selects the fallback mode: 0 for rudder 0, 1 for circle, 2 for autopilot.