Nowadays GNSS technologies are used for a large variety of precise positioning applications. The accuracy can reach the mm level depending on the data analysis methods. GNSS technologies thus offer a high potential to support tsunami early warning systems, e.g., by detection of ground motions due to earthquakes. Although GPS-based precise ground motion monitoring is a standard method, it is not yet common to apply this technique under tight time constraints and, hence, in the absence of precise satellite orbits and clocks. The most challenging task in this context might be the direct detection of tsunami waves with GPS. A proper instrumental setup implies GPS-equipped buoy systems and tide gauge sensors. At the latter GPS can help to distinguish between real tsunami waves and apparent sea height changes due to co-seismic landmass movements. In our presentation we will show the sensor network and data communication layout chosen for the German Indonesian Tsunami Early Warning System (GITEWS). We will describe how data are collected, transferred and processed. This includes a view on the sensor system design, the communication system layout with real-time data streaming, the precise data processing strategy and the final products that are delivered to support the tsunami alert decision process.