**4.2 Design of the Real-time broadband communications platform**

This platform defines two main entities (Fig. 5): Terrestrial Communications Manager (TCM) and On-board Communications Manager (OCM). The former manages terrestrial aspects of the architecture and the latter train-side issues.

Therefore, this platform proposes a set of communication requests prioritization criteria in order to respond final applications communication demand (both on ground and onboard train). So, these criteria are applied to establish the order of the communication requests in

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

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

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,

The main feature of the system is to manage the transmission of real-time broadband train-

 Real-time bidirectional communication between train and terrestrial applications allowing generating new digital services with quality of service (QoS) guarantees. Thus, different kind of information exchange between final applications (multimedia, text,

 Train-to-earth communication management without requiring the participation of the final applications. However, transmission retries are delegated to the application logic. When an application information transmission is cut by the platform (because there is another higher priority request), and then it is re-established, it is responsibility of this application to decide if it continues transmitting from the point where it had left, or if

 Changing the requests bandwidth allocation in cases where the data traffic on the physical environment allows platform to assign applications' communications a greater

This platform defines two main entities (Fig. 5): Terrestrial Communications Manager (TCM) and On-board Communications Manager (OCM). The former manages terrestrial

Tetra, etc.) regardless of the availability of other physical channels simultaneously.

train-to-earth communication prioritization queues.

in order to provide a high availability.

the features and coverage of the physical link).

**4.1.3 Train-to-earth Information exchange management** 

to-earth information. Therefore, the platform has to offer:

the transmission is restarted from the beginning.

bandwidth than initially requested from them.

aspects of the architecture and the latter train-side issues.

**4.2 Design of the Real-time broadband communications platform** 

bytes, etc.) has to be supported.

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

TCM interact with the OCM installed on each train in order to (1) select the best network link available at each time and then (2) manage applications communication requests serving those that are considered most priority first.

Fig. 5. Train and ground side components which conform the architecture of the real-time broadband communications platform.
