It depends on the avionics suite and network you plan to use for your CPDLC. If you are going to use FANS 1/A, which allows datacom directly with the Oceanic Controller (instead of via a Radio operator), then you are using the ACARS "network" (SATCOM when outside of VHF coverage) for CPDLC. FANS CPDLC can also be used over continental airspace, such as Canada and Europe. However, in Europe the current plan remains to use VDL Mode 2 which uses ATN network. It is costly to carry both FANS and ATN CPDLC avionics. For this reason a lot of people are doing their best to avoid this "dual stack."
FANS is the initial version of the Future Air Navigation System, which includes CPDLC and ADS-C.
• “FANS-1” is a Boeing derived system.
• “FANS-A” is an Airbus derived system.
• “FANS 1/A” refers to both Boeing and Airbus FANS.
• “FANS 1/A+” means that the aircraft completely complies with Revision A of the initial standard, which includes a message latency monitor.
• “FANS 2” and “FANS B” are the second generation of FANS and will not use the ACARS network, but rather the ATN network.
CPDLC in Europe is not yet performing as required. Some aircraft within limited areas are utilizing CPDLC, and hopefully they have "best in class" avionics in order to avoid "Provider Aborts." However, if you read the ELSA report you will learn that multi-frequency, separate frequency (terminal vs. enroute ops), and improved use of VHF Ground Stations are just two of the items that need to be addressed in order to move European CPDLC forward.