In the VDL Mode 2 environment where the protocol and infrastructure is a real challenge in terms of interoperability, it is important to provide guidancesrecommendations about how the ground systems are expected to behave and what is the expected avionics answer. This document aims at defining a coordinated understanding of the ground behaviors in addition to the MOPS which are more related to avionics systems. In particular some out of sync cases have been identified in operations, showing a need for interoperability improvement. This document supplements DO-224 applicable to ground systems, and the requirements in MASPS still apply. For airworthiness and TSO/E-TSO approval the MASPS have precedence over this document and avionics requirements are defined in the MASPS.