UIC Leaflet 917-3 provides a technical specification for a standardized interface and defines the mechanism for the information exchange over a Cellular Network (CN) between Mobile Unit (MU) and Communication Server (CS) for railway freight wagon telematics applications. The exchanged information defines the behaviour of MU and/or informs the CS about status and events of the MU. This document specifies the structure of the information that has to be exchanged and the dependant architecture ("how"). A complete optiSMS application specification document defines all the content of the information that has to be exchanged ("what"). The objectives of these international previsions are to promote interoperability, improve operating conditions and enhance the quality of service in international rail freight traffic.