SATNET, also known as the Atlantic Packet Satellite Network, was an early satellite network that formed an initial segment of the Internet. It was implemented by BBN Technologies under the direction of the Advanced Research Projects Agency. The first heterogeneous computer network was implemented in 1973, connecting the ARPANET to University College London. This evolved into SATNET. The first Transmission Control Program demonstration, linking SATNET, the ARPANET, and PRNET took place on November 22, 1977.