Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Ad hoc content upload via GPRS (GPRS connectivity of the light train's infotainment system)

The biggest amount of content is transmitted over night. As content containing graphic or video files is of a large size, a high-performance technology is needed. We choose the WLAN-technology for the main updates on a regular basis, which should take, place overnight when the light train is parked in the depot.

But during the day there are maybe some small updates necessary, when e.g. some remaining tickets for a theatre at the evening should be presented for a special price or the latest news have to be displayed. Also current special offers and changes in the train schedule which cannot be planned in advance should be shown as quick as possible in the trains. To avoid delays (mostly it is not at all possible to wait a whole day and to upload new content overnight only), a solution for content upload during the day was found in the GPRS technology.

Because of the much lower bandwith of GPRS compared to WLAN, only small updates should be performed through a GPRS network. The train polled each 15 minutes for content. The upload was realized with FTP. The content was stored in a special folder for small updates. This folder also contained an updated schedule.
How was the connection realized?

A GPRS cellular phone was attached to the serial port of the Linux based On Board
Computer, which was part of the Infotainment System in the train.

The phone we used worked as a simple modem, the connectivity to the GPRS bearer was established via internal commands (modem AT commands). The internal commands were processed by Linux shell scripts.

These shell scripts called the internal PPPD (Point-Point-Protocol-Daemon) program to establish the GPRS connection.

Most Linux OS versions have such a kind of PPPD program. It is a standard network feature of the operating system.

All scripts were started automatically, so there was a possiblity to get the data during the night as well. No manual intrusion was necessary.

If the scripts were successfully started, the GPRS connection was available. If the scripts were not started successfully an error message occured (eg. No Carrier!).
Important to know is that the GPRS environment does not allow to hold the line if the driving speed is too high. So in this case the data transfer will be corrupt or not possible at all.

The GPRS application (e.g. the download application) should provide an interface (piece of code) which guarantees an excellent data transfer (e.g. packet error detection). The error detection is necessary to get a data transfer with good quality in e.g. tunnels or after a cell hand-over.

Reported by

Vodafone Terenci GmbH
D2-Park 5
40878 Ratingen
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