Also known as: Satellites.
Before and after the Catastrophe, the Habitats were connected to the satellites that orbited the planet. Each habitat had several satellite dishes that could communicate with the outside world and the other habitats.
Communications with satellite systems were considered asynchronous, meaning information could be exchanged simultaneously without delay. Until it eventually failed, the satellite network was used for entertainment, news, communication, and data exchange.
These satellites were launched initially by surface-side entities years before the Catastrophe. Once situated above our atmosphere, they could not be damaged by nuclear war or winter on the surface. They were even active during the nuclear event itself. The constant dark cloud cover during the nuclear winter denied satellite access. Once the nuclear winter dissipated, satellite connections between the habitats and real-time interactions were restored.