DSRC (Dedicated Short Range Communications) is a well known widespread technology. One of the main applications of DSRC is RTTT (Road Transport and Traffic Telematics), especially EFC (Electronic Fee Collection) on tolled roads, bridges or tunnels. Other vehicle-related applications had been envisaged, such as car parking or fuel refilling automatic payment. These applications were successfully developed, deployed and are in current use in Portugal. Especially for EFC, medium access control is of utmost importance. In this paper we present a possible implementation scheme for the MAC-layer, suitable for low-cost microcontrollers, to operate between the two equipments (as in fig.1), the RSE (Road Side Equipment) and the OBE (On Board Equipment). The result is interface software that controls the referred communication, embracing hardware and software into a join solution.