This document covers the specification of the communication between the on-board subsystems and the ground subsystems. The communication system, interfaces and protocols are specified as a Mobile Communication function, using any available wireless technology. This document provides requirements in order to: 1. select the wireless network on the basis of QoS parameters requested by the application; 2. allow TCMS and/or OMTS applications, installed on-board and communicating on the on-board communication network, to have a remote access to applications running on ground installations; 3. allow applications running on ground installations to have a remote access to the TCMS and/or OMTS applications installed on-board. This document specifies further requirements which allow the applications running on-board and the applications running on ground to connect each other applying the virtual/functional addressing mechanism specified by IEC 61375-2-3 and exchanging application data sets produced or consumed by the on-board functions implemented in the devices attached to the TCN network. Furthermore this document covers the security requirements in order to grant the access only to authenticated and authorised applications and to allow encryption of exchanged data. The communication of safety related data between onboard applications and ground applications are out of the scope of this standard as well as Internet connectivity service for passengers.