**3. Managing train-to-earth wireless communications**

This section describes a general purpose wireless communications architecture to address the needs for high bandwidth and wide coverage. This solution is based on the management of a wireless communications channel at the application layer. The architecture proposed is currently being deployed in some railway companies from Spain (Euskotren and ETS from Basque Country, and Renfe from Spain), will be presented (Gutiérrez et al., 2010). It is an innovative general purpose wireless communication channel which allows the train to communicate with the railway control centres in such a way that the applications or services are unaware of communication issues such as: establishment and closure of the communication, management of the state of connectivity, prioritization of information and so on.

This new wireless communication architecture has to respond to the demand for communication and transmission of information from any application, so it will have to take into account the nature of the information to be sent. The information exchanged between two applications (one on earth and the other on a train) may have different urgency degrees depending on their purpose or treatment with respect to the exchanged information. In fact, there is information that needs to be transmitted at the time that it is generated, for example in case of positioning information or alarms in some critical train operation elements. On the other hand, there may be less urgent information whose transmission can be postponed, such as train CCTV images, or audio files used by the background music. In addition, the urgent or priority information is usually smaller than the non-priority information.
