This International Standard provides defnitions and procedures for the establishment, maintenance and termination of an ITS (intelligent transport systems) communications session within a CALM (communication access for land mobiles) system environment using bi-directional satellite communications.It defnes the operation of the medium management adaptation entity (MMAE), which provides the management interface between a proprietary satellite communications medium and the “ITS station management”. This enables the “ITS station management” to know the status of the communications medium and control the interface without the need for applications at the ITS station to have any knowledge of the satellite communications interface. The procedures that the “ITS station management” expects to use are also explained.NOTE 1 CALM links are required for quasi-continuous, prolonged and short-duration communications between vehicles and the roadside, between vehicles, and between mobile equipment and fxed infrastructure points, over medium and long ranges.This International Standard defnes how to connect and disconnect a communication session using satellite communication systems in the context of an application operated within the environment defned in ISO 21217. It supports peer-to-peer modes of communication. Support for broadcast satellite systems is defned in ISO 13183, which provides a common approach for all broadcast media. It supports satellite communications networks that are interconnected with the public network, as well as those which connect via the internet and those which provide a stand-alone capability.NOTE 2 As there are multiple instantiations of satellite systems, most of which are not interoperable, there is the possibility of several simultaneous satellite sessions, each forming a separate CALM medium (although the differences may only be in software within the on-board equipment).