NTT ’ s Ultra High - speed Net - work Experiment and Realtime VLBI Trials

In 1995, NTT Laboratories have started a joint research project on ultra high-speed communications with public research organizations using a large scale network testbed having the maximum speed of 2.4 Gb/s. Among many applications tried in the first phase of the project, the realtime VLBI (very long baseline interferometry) has proved to be benefited greatly from the high performance communications technologies. With the realtime data transmission using high-speed communications network, the bottleneck regarding the data transfer in the conventional VLBI system can be removed. Furthermore, as the bandwidths of the network become larger, the performance of the observation system will become better. In the second phase of the project started in 1998, therefore, the focus is placed on the advancement of this real-time VLBI technology. Extensive research items regarding the realtime VLBI technology are being conducted, together with the scientific observations using the testbed. So far, through the experiments using the developed realtime VLBI system, great improvement in observation performance has been achieved. This paper explains the outline of this research project from the viewpoint of communications technologies which play a major role in the realtime VLBI system.