**4.1.2 Selection of the physical communication network link**

The communication platform is based on different physical communication link existence so that the combination of these independent links offers a continuous train-to-earth connectivity in order to respond to the final applications communications demand in realtime. Thus, depending on the status of each of these media and their characteristics and restrictions, the platform must be designed to utilize the link that offers better performance in order to provide a high availability.

The system is designed to select at every moment the physical link that is most favorable for communications. Therefore, taking into account the availability of enabled different physical links, the system selects always as active link one that offers the best bandwidth (based on the features and coverage of the physical link).

At this point it should be emphasized that the basis is that the system always defines a single train-to-earth network link as active for communications (most favorable). So, all communications will always be generated by the channel set as active (WiFi, GSM / GPRS, Tetra, etc.) regardless of the availability of other physical channels simultaneously.
