When a control message is determined and sent from a master system to a slave system, the control message is accompanied with a time stamp, indicative of the master model version of the environment which was applied when the control data was determined by the master system. When data, triggered by data provided from the environment to the slave system in the form of updated sensor data is provided from the slave system to the master system, also that data, indicative of an updated slave model version of the environment made by the slave system, is provided to the master system, together with a time stamp, indicative of when the update of the slave model version was made. By applying the suggested time stamp, a coordination of model versions can be obtained between the master system and the slave system.