From Gineipaedia, the Legend of Galactic Heroes wiki
Solivision was a form of media popularized during the Galactic Federation's golden age. It was capable of projecting either 2D or 3D video and audio.
Solivision was developed some time prior to the foundation of the Galactic Federation. It was still the primary form of interstellar communication during the waning years of the Galactic Empire and Free Planets Alliance. Using the FTL Network, solovision could be used to facilitate real-time communication across thousands of light years, and was necessary for the day-to-day function of every interplanetary state. (Legend of Galactic Heroes Volume 1: Dawn)