Controller-Pilot Datalink Communication (CPDLC) is a part of FANS (Future Air Navigation System). It's basically a datalink system using VHF and SATCOM to transmit position reports and many other things to ground controllers without having to make voice position reports using HF radio. It's a nice system and will become more and more popular as time goes on. Automatic Dependant Surveillance (ADS) is another part of it.