NO ACTIVE ATC - that's the CPDLC, or to put it the long way
Controller Pilot Datalink Communication. Basically, you can log onto an air traffic unit via satcomm, and use a keypad to transmit written messages, and ATC reply via written messages back. Very advanced texting!!
It's a beauty of a system to use when you're over the middle of the Indian Ocean, means that you don't have to use HF comms
All the other laymans guesses are pretty spot on..