This part of IEC 61375 establishes the specification for 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: a) select the wireless network on the basis of QoS parameters requested by the application; b) 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; c) allow applications running on ground installations to have a remote access to the TCMS and/or OMTS applications installed on-board.