"The present document is written as a ""Read-me-first"" manual or ""Getting started with TETRA Air-Ground-Air"". It is not intended to be a guide to the TETRA Air-Ground-Air standard nor an authoritative interpretation of the standard. If any conflict is found between the present document and the corresponding sections in the TETRA standard then the standard takes precedence. The reader of the present document is assumed to have a working knowledge TETRA technology. The guidance provided in the present document is prepared with the experience of implementing an Air-Ground-Air to an existing national network. The aims of the present document are: ? to introduce and detail the different aspects of Air-to-Ground communication in a TETRA network; ? to show the reader that Air-Ground-Air is an integral part of a TETRA network when required; ? to provide the reader with sufficient knowledge to engage in qualified discussions with the equipment and service suppliers; ? to expose the reader to the specific language and technical terminology used in the present document; ? to enable the reader to understand the flexibility in system design@ system network topography@ system availability@ various modes of operation and security features; ? to provide basic guidance on optimising a TETRA network when including an Air-Ground-Air element. The present document provides guidance on the requirements for an Air-Ground-Air service and how best to implement an AGA service."